Electrochemical reactions

Abstract

A process, a device and / or a system for flow based electrocatalytic chemical reactions, particularly hydrogenation reactions in a pH neutral or pH alkaline, and preferably, a high pH electrolyte, that is, an aqueous solution including a reactant, where electrolyte is either a water-in-oil emulsion or an oil- in-water emulsion.

Description

Electrochemical ReactionsTechnical field

[0001] The invention relates to chemical reactions, particularly electro(catalytic) chemical reactions, such as electro(catalytic) hydrogenation reactions.Background to the Invention

[0002] Catalysis of chemical reactions is an important part of synthetic chemistry techniques which involve conversion of one or more reactants or starting materials into one or more products. The process of catalysis accelerates or otherwise facilitates a chemical reaction. New and improved catalytic methods in chemical synthesis are always desirable.

[0003] Hydrogenation and dehydrogenation reactions are well known in chemical synthesis and many catalysts have been developed for accelerating the rate of specific transformations. Heterogeneous, or surface mediated (de)hydrogenation is preferred because separation of the catalyst from the product is not required after the reaction has been completed. Electrocatalytic hydrogenation is a useful process in applications such as chemical synthesis. The electrocatalytic hydrogenation may involve reactants and products in which hydrogenation, that is, addition of H across one or more unsaturated or conjugated bonds is irreversible (under reasonable energy conditions) and results in stable product formation. Alternatively, the electrocatalytic hydrogenation may involve reactants and products in which hydrogenation, that is, addition of H across one or more unsaturated or conjugated bonds is reversible (under reasonable energy conditions) and results in a hydrogenated product in which the hydrogen can be readily recovered or extracted from the hydrogenated product when required. The latter embodiment would be desirable in reversible hydrogen storage applications, for example, where a reversible reactant / product couple is used to chemically store hydrogen in the product compound, e.g., in grid energy storage, whereby an application of a subsequent dehydrogenation reaction, the stored hydrogen can be released for use, e.g., to generate electricity. The dehydrogenation reaction is ideally one that that readily occurs under the most energy efficient conditions possible. For example, the dehydrogenation could involve thermal dehydrogenation or electro(catalytic) dehydrogenation. Thermal systems typically involve multiphase reactions using methylcyclohexene (MCH) or dibenzyltoluene (DBT) as reversible H carrier, where the MCH I DBT is catalytically hydrogenated by gaseous H2 as source of hydrogen at high pressure and moderate temperature in an exothermic reaction as there is a significant activation barrier to creation of the reactive adsorbed atomic H species on the catalyst, which is typically the rate limiting step. The hydrogenated product perhydro-dibenzyltoluene is catalytically dehydrogenated at a temperature between 250-320°C at moderate pressure in an endothermic reaction to extract gaseous H2 from perhydro-dibenzyltoluene.

[0004] Chemically stored hydrogen, that is hydrogen that is chemically locked within a compound, has significantly higher energy density and is much safer than compressed pure hydrogen. Materials and method for reversibly storing hydrogen are therefore of great interest, particularly those involving reversible hydrogenation and dehydrogenation reactions (‘(de)hydrogenation)’). Solid hydridesgenerally have good hydrogen uptake capacities, but they also suffer from issues around ease of reversibility (dehydrogenation reactions are difficult if even possible), slow kinetics and they can be difficult to handle. By comparison, reactants known as liquid organic hydrogen carriers (LOHCs) tend to be more reversible in terms of ease of dehydrogenation, are easier to handle and importantly, are compatible with existing infrastructure for liquid fuels. Mechanistically the LOHC forms part of a reversible reactant / product couple, where the reactant comprises hydrogenatable unsaturated bonds across which hydrogen is added to form the unsaturated hydrogenated product.

[0005] Liquid organic hydrogen carriers, ‘LOHCs’ (a type of liquid aromatic organic) such as toluene / methylcyclohexane, benzene / cyclohexane and biphenyl I bicyclohexyl have hydrogen capacities of between 6 and 7 wt% and can be reversibly hydrogenated via thermal cycling. However, thermal cycling requires a significant amount of energy, and although hydrogenation of the LOHC is exothermic, it nevertheless requires high pressure hydrogen over a noble metal catalyst, a process that requires rigorous safety controls. Dehydrogenation conditions use lower pressures but higher temperatures meaning the hydrogen produced can be contaminated by residual LOHC and its degradation products. These must be removed from the hydrogen if the gas is to be used in fuel cells. Therefore these (de)hydrogenation methods are not ideal.

[0006] To date, two LOHCs have been commercialised (i) toluene I methylcyclohexane by Chiyoda Corporation in Japan and (ii) dibenzyltoluene I perhydro-dibenzyltoluene by Hydrogenious LOHC Technologies GmbH in Germany. However, the processes used in both rely on high pressures and temperatures to (de)hydrogenate the LOHCs, which is energy and materials intensive. Again these (de)hydrogenation methods are not ideal.

[0007] Among the various candidates of LOHCs, the toluene (TOL) I methylcyclohexane (MCH) couple stands out for large-scale hydrogen storage due to easy handling, high volumetric mass density, utilization of existing infrastructure, and abundance of TOL from petroleum resources. Storage and transportation of hydrogen to a site of demand as liquid MCH offer notable advantages in terms of safety and cost-effectiveness as both toluene and MCH remain in a liquid state under ambient temperatures and pressures. At the hydrogen consumption site, gaseous hydrogen is extracted from MCH through a catalytic dehydrogenation process. The by-product of this extraction process, toluene, is continuously recycled as a raw material for MCH production. Given the exothermic nature of the TOL hydrogenation reaction, most of the documented studies so far have been conducted under elevated pressures (around 30-50 bar) and temperatures (approximately 150-200°C). These conditions are employed alongside a catalyst, utilizing gaseous H2 as the source of hydrogen for the hydrogenation reaction.

[0008] Electrochemical hydrogenation of LOHCs is an alternative approach to thermal methods. Electroreductive electrolysis of a suitable proton source generates hydrogen in-situ, avoiding the need for an external source of gaseous hydrogen for the hydrogenation reactions. The reaction rate is instantaneously measurable and controllable. Water is an obvious candidate for a proton source and for the commercial scale storage and transportation of hydrogen, compounds such asmethylcyclohexane (from toluene), cyclohexane (from benzene), dimethylcyclohexane (from xylene) and decalin (from naphthalene) are promising candidates as the LOHC.

[0009] Electrohydrogenation based on water decomposition in acidic solutions is typically undertaken in a two-compartment reactor / cell in which hydrogen from the water electrolysis step is transferred to a second compartment of the cell is and passed over a hydrogenation catalyst that is also in contact with the LOHC. The two-compartment electrohydrogenation of TOL to MCH with the electro-oxidation of water in acidic media is typically carried out using a proton exchange membrane (PEM) electrolysis cell. In this system, water is electrochemically oxidized on the anode in the anode chamber, resulting in the production of oxygen, protons, and electrons in an OER reaction. The protons formed then diffuse through the membrane to the cathodic compartment, where TOL in contact with the electrode is reduced to MCH through the participation of the arriving protons reduced to adsorbed atomic hydrogen Hads on the catalyst by electrons from the electrical circuit. Typical catalysts for this system are Pt / C, PtRu / C or Ru / KB for the catalytic hydrogenation of the organic aromatic on the cathode (WE) and a thermally decomposed lrO2-Ta2Os / Ti cathode for the DSE anode for the OER reaction. A competing reaction to hydrogenation however is the re-association of adsorbed atomic hydrogen to form diatomic hydrogen gas (H2). Therefore, electrochemical generation of H2 competes with the formation of MCH, and so to enhance the efficiency of MCH formation, suppression of H2 production is necessary but has found to be challenging. Furthermore, existing PEM electrolysis systems require expensive and environmentally hazardous PEMs and incorporating a catalyst layer, and gas diffusion layers to form a Membrane Electrode Assembly (MEA), performance and stability of which can be unreliable. There are also challenges with electrode corrosion / dissolution which occur in low pH media which means a dimensionally stable anode (DSA) is required in practice, adding to the overall cost of existing methods of electrochemical hydrogenation of LOHCs. As an example, Mitsushimas 2016 (Electrocatalysis (2016) 7:127-131 ) describes a membrane electrolyser for TOL hydrogenation involving acidic water splitting for energy carrier synthesis. Notably, different catalyst materials are used at different locations in this process. Electrolysis of acidic water occurs at a thermally decomposed lrO2-Ta2Os / Ti of DSE anode to generate H+from OER at the anode. The H+then diffuses across a PFSA membrane from the anode side to a Pt / C or PtRu / C coated porous carbon cathode which the H+is used in the electrohydrogenation of TOL present at the cathode. Separate catalytic electrodes will add to the cost and complexity.

[0010] In a variation of the second compartment process, a more direct in-situ electrocatalytic hydrogenation of TOL to form MCH in a stable acidic microemulsion with a Faradaic efficiency of 80% for the conversation using Pt black has been reported by Wakisaka 2016 (Electrochemistry Communications 64 (2016) 5-8). The method involves a fixed volume of a stable acidic microemulsion of a surfactant, LOHC (TOL), t-butyl alcohol and an acidic proton source (H2SO4 solution) is created inside the electrolyser in the presence of an active Pt or Pt black catalyst. Pt or Pt / C catalysed electrolysis of a proton source (a water phase) compartmentalised near the stable emulsion phase generates reactive hydrogen adjacent to LOHC droplets through OER at the anode which are then hydrogenated directly in the stable emulsion phase by a Pt or Pt catalyst working electrode. This direct, but batch style, electrochemical hydrogenation of TOL using an acidic stable microemulsion electrolyteis only possible due to formation of a stablised surfactant phase in coexistence with an oil / organic phase and water phase which results on settling after completion of initial electrolyte / media mixing. Notably, two separate catalytic electrodes are required, one for OER (CE) and one for hydrogenation of the organic aromatic (WE). While the reactions occur in the same compartment of a physical electrochemical cell, on media settling, the electrolyte is effectively compartmentalised into three distinct phases as follows: (i) oil / organic phase (toluene / methylcyclohexane), (ii) thermodynamically stable surfactant phase (water and toluene / methylcyclohexane) (functionally the cathode I working electrode compartment), and (iii) water phase (functionally the anode compartment, where OER occurs at a counter electrode). In the cathode compartment / surfactant phase, electrohydrogenation of toluene (TOL) to methylcyclohexane (MCH) occurs at the working electrode (cathode) by reduction in the aqueous phase (anode compartment) of H+to atomic hydrogen (H) which then reacts with TOL in the oil / organic phase to form MCH. In the anode compartment (in the water phase), water electrolysis occurs at a counter electrode and H+is produced at the anode through OER and is also readily available from H2SO4. The H+diffuses from the anode compartment (aqueous phase) to the stable surfactant phase cathode compartment as a source of atomic hydrogen (H) for the hydrogenation reaction. Conveniently, the MCH formed in this reaction is immiscible with water, so it accumulates in the oil / toluene phase, from which it is easily recovered. Notably, commercial scale up of such a system would be challenging not least because electrochemistry in mixed fluid phase systems in which one of the phases is non-conducting is complex. There are problems of lower solution conductivity, and occlusion of the electrode by the non-conducting fluid, as occurs with gas evolution, but also adsorption effects by the non-conducting phase and any surfactants added to stabilise the emulsion. Separate catalytic electrodes also add to cost and complexity.

[0011] To the best of the inventors’ knowledge, electrocatalytic hydrogenation reactions in alkaline media has not been demonstrated, and certainly not with high efficiency. Compared to acidic conditions, obtaining H under alkaline conditions would experience a slower kinetic rate for H generation and thus hydrogenation. Furthermore, expensive catalysts would be expected to counter the issues for the alkaline processes, and even then, the sluggish nature of H generation in alkaline media means alkaline hydrogenation is expected to occur with prohibitively low efficiency compared to the acidic system where OER generates H+. Like the acidic electrolysis, suppression of competing H2 production would also be a requirement in the alkaline system. These are thought to be the main reasons why existing literature studies on electro(catalytic) hydrogenation focus on acidic media. Nonetheless, if these problems could be addressed, alkaline systems would be preferred because construction materials for the reactor are less costly, as Pt catalysts, PEMs and dimensionally stable anodes (DSAs), etc., are not required moving away from the acidic system. In particular, the electrocatalytic hydrogenation of LOHCs such as TOL / MCH in alkaline media (e.g., using concentrated KOH solution as electrolyte) is of interest due to the significant challenges associated with the poor catalyst and device stability and corrosion in the more commonly studied acidic conditions.

[0012] The process of LOHC hydrogenation in alkaline media is expected to begin with the catalyst surface adsorption of LOHC, followed by the electrochemical reduction of H2O in alkaline conditions.This process leads to the generation of atomic hydrogen species (H) from water electrolysis through the Volmer step (H2O + e" -> H + OH"), which in turn reacts with adsorbed TOL on the catalyst surface. However, as foreshadowed above, H generation in alkaline solutions is prohibitively slower than in acidic solutions because the rate of diffusion of water (the reactant in alkaline solutions) is much slower than H+present in abundance in acidic solutions. This would result in a slower kinetic rate for hydrogen generation and, consequently, LOHC hydrogenation.

[0013] Adsorption plays a role in electrohydrogenation and both atomic hydrogen (H) and the LOHC must be adsorbed onto the catalyst surface for electrohydrogenation to proceed. Furthermore, the LOHC must be adsorbed long enough for electron transfer to take place. Where these conditions are met, hydrogen transfer may occur at the surface. The speed, duration and strength of adsorption onto the catalyst surface is complex function of surface and solution properties, but two primary driving forces are the surface excess charge and the solution pH, which are interrelated. Further the LOHC may not be the only compound in solution that can be adsorbed (e.g. water, Na+and K+) and competition for surface adsorption sites can affect the results. Due to surface charge, a significant challenge is that adsorption of neutral aromatic molecules at metal surfaces is suppressed in alkaline pH solutions. It is therefore no trivial matter to develop a system that overcomes the many problems associated with electrocatalytic hydrogenation in alkaline solutions in a way that would support efficient electrocatalytic hydrogenations reactions in alkaline I high pH solutions in which water is used as a proton source.

[0014] Efficient chemical reactions including electrocatalytic hydrogenation processes and reversible electrocatalytic hydrogenation processes in alkaline I high pH media are therefore much desired.

[0015] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0016] Where any or all of the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components.Summary of the Invention

[0017] In a first aspect, the invention provides a flow based electrocatalytic hydrogenation process comprising: contacting a pH neutral or pH alkaline flow of a liquid proton source and at least one liquid H- uptake reactant compound (R) which is immiscible with the liquid proton source with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell, thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the liquid proton source and at least one liquid H-uptake reactant compound (R),whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert under the same set of operating conditions, adsorbed reactive species on catalytic active sites of electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the proton source in the emulsion, and• H-uptake compound reactant species (Rads) generated from the reactant in the emulsion, chemically storing the electrochemically generated atomic hydrogen species in a hydrogenated product (R-H) of the H-uptake reactant compound, (R), through transfer of adsorbed reactive atomic hydrogen species (Hads) on a catalyst active site of the electrocatalyst to a reactive H-uptake compound reactant species, (Rads), adsorbed on an adjacent catalyst active site to form the hydrogenated product (R-H).

[0018] Suitably, in additional to catalysing formation of the above adsorbed species, simultaneously the catalyst (i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and (ii) promotion of reaction of the adsorbed species to form a hydrogenated product of the nonpolar H- uptake reactant compound (R-H). Generally speaking, as the competing reaction is increasingly suppressed, the desired product is generated with associated higher Faradaic efficiency (selectivity)) and I or high current density (rate I intensity of reaction). In preferred embodiments, the process is operated under conditions that are balance for any desired outcome, e.g., higher Faradaic efficiency at expense of current density. Thus, optimisation of the process conditions can strike a balance where maximum Faradaic efficiency can be associated with a maximum current density.

[0019] Suitably, for reactions involving water as proton source, an applied current density which corresponds to the onset potential for water reduction to form reactive hydrogen species under any set of operation conditions I system set up is particularly preferred.

[0020] If desired the pH neutral or pH alkaline flow may be provided to the electrochemical flow cell as a single solution in a pre-dispersed form or distinct component flows may be provided as distinct solutions to the electrochemical flow cell where they are mixed for the first time on contacting the static mixer. Desirably, the catholyte is formed adjacent to surfaces of the static mixer elements.

[0021] Desirably, the reactant (R) is a hydrogen uptake compound, such as an organic aromatic compound, e.g., an LOHC, such as toluene (TOL). Preferred hydrogen uptake compounds, such as TOL, are those whose hydrogenation product, e.g., MCH, may be dehydrogenated efficiently to release the stored hydrogen and reform the reactant (R) is a hydrogen uptake compound under energetically favourable conditions, e.g., that allow commercial I industrial use of the process in energy storage applications.

[0022] In a related aspect the invention provides a flow based electrocatalytic chemical hydrogen generation and storage process, comprising:contacting water and liquid toluene reactant which is immiscible with the water with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the water and the toluene reactant, wherein the toluene reactant forms a one part of a reversible (de)hydrogenation reactant / product couple, wherein another part of the couple is methylcyclohexane as a hydrogenated product; whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert, under the same set of operating conditions, adsorbed reactive species on catalytic active sites of an electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the water in the emulsion, and• toluene reactant species (Rads) generated from the toluene reactant compound (R) in the emulsion, while simultaneously• suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and• promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H), wherein the electrocatalyst is ruthenium or a ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel; and chemically storing the electrochemically generated atomic hydrogen species (Hads) in the methylcyclohexane product, by allowing transfer of adsorbed reactive atomic hydrogen species (HadS) on a catalyst active site of the electrocatalyst to the toluene reactive reactant species (Rads) adsorbed on an adjacent catalyst active site, thereby storing the electrochemically generated atomic hydrogen species chemically in the methylcyclohexane product.

[0023] Desirably, wherein the proton source is water, and the H-uptake reactant compound, (R), is a liquid organic hydrogen carrier (LOHC) such as toluene (TOL), preferably in an amount of 20:80 v / v% TOL: 1 M KOH.

[0024] Desirably, for the process involving hydrogenation of TOL to product MCH using Ru black, wherein the operating temperature is about 55 to about 85 °C, and the current density is about -3 to about -32 mA I cm-2, for an emulsion comprising 20:80 v / v% toluene in 1 M KOH (v / v), and a flow rate equivalent to of about 500 to about 700 mL min-1for a reaction volume of 2.5 mL. Desirably, the Faradaic efficiency of hydrogenation of TOL to product MCH is > 70%, > 75%, > 80%, > 85%, > 90%, > 95%, or > 99%.

[0025] Desirably, The process of any one of the preceding claims, involving hydrogenation of TOL to product MCH using Ru black, wherein the operating temperature is room temperature, and the current density is about -3 to about -5 mA I cm-2, preferably - 4 mA I cm-2, for an emulsion comprising 20:80 v / v% toluene in 1 M KOH (v / v), and a flow rate equivalent to of about 550 to about 650 mL min-1,preferably 600 mL min-1for a reaction volume of 2.5 mL. Desirably, the Faradaic efficiency is > 90%, > 95%, or > 99%, most preferably 100%.

[0026] In a third aspect, the invention provides a flow based electrocatalytic hydrogenation system comprising: an electrochemical flow cell having a cathodic chamber configured as part of a continuous electrochemical flow cell and provided with an electrocatalytically active static mixer cathode for forming in situ a catholyte which is a liquid-liquid phase emulsion comprising a liquid proton source and a liquid H-uptake reactant compound (R); wherein the static mixer cathode comprises an electrocatalyst that is suitable for, in situ and in concert, electroreductively generating under the same operating conditions: adsorbed reactive atomic hydrogen species (Hads) from electroreduction of the polar proton source in the emulsion onto catalyst active sites, and adsorbed reactive reactant compound (Rads) species from electroreduction of the nonpolar Fluptake reactant compound in the emulsion onto catalytic active sites of the electrocatalyst associated with the static mixer, while simultaneously(i) suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and(ii) promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).

[0027] In a fourth aspect, the invention provides a use of a flow based electrocatalytic hydrogenation system as defined in the third aspect in an energy storage application, or a grid energy storage application.

[0028] In a fifth aspect, the invention provides a use of pH neutral or pH alkaline catholyte in the form of an emulsion comprising a liquid proton source and at least one liquid H-uptake compound (R) which is immiscible with the liquid proton source, in an electrocatalytic hydrogenation process in an electrochemical flow cell comprising an electrocatalytically active static mixer cathode that generates the emulsion in situ in the electrochemical cell.

[0029] Desirably, the catholyte is surfactant free and / or is substantially free of sulfuric acid. Suitably, the catholyte has a pH of > 7, preferably a pH of >10, preferably a pH > 14.

[0030] Desirably, the catholyte is used in combination with an electrocatalyst operated under a single set of conditions that, in situ and in concert, electroreductively generates under the same set of operating conditions: adsorbed reactive atomic hydrogen species (Hads) from electroreduction of a polar proton source in the emulsion onto catalyst active sites, andadsorbed reactive reactant compound (Rads) species from electroreduction of a nonpolar Fluptake reactant compound in the emulsion onto catalytic active sites of the electrocatalyst associated with the static mixer, while simultaneously the electrocatalyst(i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and(ii) promotes reaction of the adsorbed species together to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).

[0031] Desirably, the electrocatalyst is a ruthenium electrocatalyst or ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel. These electrocatalysts are particularly useful where the reactant is toluene and the desired product is methylcyclohexane.Brief Description of Drawings

[0032] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings, in which:

[0033] Figure 1 is a schematic showing typical conditions of high temperatures and high pressures for hydrogenation and dehydrogenation, which are used in conventional process for the storage and release of hydrogen in the LOHC, dibenzyl toluene (DBT) (credit: Wunsch et al. 2020);

[0034] Figure 2 compares volumetric and gravimetric energy densities of different materials for chemically storing hydrogen (credit: He et al. 2015);

[0035] Figure 3 is a schematic comparing the reactions involved in water electrolysis carried out in alkaline electrolyte solutions and provides an illustration of the concurrent and selective catalytic reactions that must occur in situ at the same catalyst surface to result in simultaneous and concurrent electrocatalytic H generation from the first step of water splitting (while stopping the water splitting reaction at this first step) and the electrocatalytic hydrogenation of an LOHC, while at the same time, suppressing the competing reaction of hydrogen gas production. These aims are achieved only through appropriate selection of a bifunctional catalytic which is used under appropriate operating conditions required to drive the desired behaviour;

[0036] Figure 4 is a schematic of the direct electrocatalytic hydrogenation of an LOHC oil-in-water emulsion which occurs at the Ru based electrocatalyst as described in Example 1 below. The lighter coloured circles represent LOHC oil droplets in the water main phase which comprises the reactant to be hydrogenated (LOHC-Ho), while the darker circles represent oil droplets that have picked up the hydrogenated LOHC product (LOHC-H1);

[0037] Figure 5 illustrates two static mixer shapes, the Kenics KMS (left) and Sulzer SMV (right), that are useful for forming oil-in-water or water-in-oil emulsions (depending on the concentration of component phases used); and

[0038] Figure 6a is a schematic of one example of an electrochemical flow cell of the invention; Figure 6b is a schematic of one example of an electrochemical flow cell of the invention in (a) cross-sectional view;

[0039] Figure 7 illustrates1H NMR spectra (CDCh) of 20 v / v% TOL in 1 M KOH after 4 h of electrolysis at four different applied current densities (-4, -8, -12 and -20 mA / cm2) in the electrochemical flow cell at ambient conditions;

[0040] Figure 8 illustrates1H NMR spectra (CDCI3) of 20 v / v% TOL in 1 M KOH after 24 h of electrolysis at applied current density of -4 mA / cm2in the electrochemical flow cell at ambient conditions. Samples were withdrawn at the start of the experiment and at 2, 4 and 24 h thereafter;

[0041] Figure 9 illustrates GC-MS data recorded for the organic phase of 20 v / v% TOL in 1 M KOH after 24 h of electrolysis in the electrochemical flow cell at ambient conditions. The applied current density was -4 mA / cm2;

[0042] Figure 10 illustrates1H NMR spectra (CDCI3) of 20 v / v% TOL in 1 M KOH after 4 h of electrolysis using the electrochemical flow cell at ambient conditions. The applied current density was -4 mA / cm2and the liquid flow rate was varied from 200 to 800 mL min-1;

[0043] Figure 11 illustrates cyclic voltammograms (3rd cycle) recorded in 20 v / v% TOL in 1 M KOH (pH ~14) in the CSIRO electrochemical flow cell at different temperatures and scan rate of 20 mV s-1;

[0044] Figure 12 illustrates1H NMR spectra (CDCI3) of 20 v / v% TOL in 1 M KOH after 4 h of electrolysis at different temperatures (at -8 mA / cm2) in the electrochemical flow cell at ambient conditions;

[0045] Figure 13 illustrates1H NMR spectra (CDCI3) of 20 v / v% TOL in 1 M KOH after 4 h of electrolysis at different applied current densities at 80 °C in the electrochemical flow cell at ambient conditions;

[0046] Figure 14 is a schematic diagram of HER mechanism in alkaline media;

[0047] Figure 15 illustrates1H NMR spectra (CDCI3) of 20 v / v% benzyl alcohol (BA) in 1 .5 M mixture of K2HPO4 and KH2PO4 (pH ~7) after 4 h of electrolysis at -4 mA / cm2and -1 mA / cm2applied current density in the electrochemical flow cell at ambient conditions;

[0048] Figure 16A illustrates cyclic voltammograms (3rdcycle) recorded in 20 v / v% BA in 1 .5 M mixture of K2HPO4 and KH2PO4 (pH ~7) in the flow electrochemical cell at ambient conditions and scan rate of 20 mV s-1. Figure 16B illustrates cyclic voltammograms (3rd cycle) recorded in 20 v / v% BA in 1 M KOH (pH ~14) in the CSIRO electrochemical flow cell at ambient conditions and scan rate of 20 mV s-1;

[0049] Figure 17 illustrates1H NMR spectra (CDCI3) of 20 v / v% BA in 1 M KOH (pH ~14) after 4 h of electrolysis at -4 mA / cm2applied current density in the electrochemical flow cell at ambient conditions;

[0050] Figure 18 shows (a) Traditional volcano plot for HER in acidic solutions, (b) and updated “volcano plot” for HER in alkaline media based on DFT calculations of hydrogen adsorption energies. Adapted from Quaino et al. (2014), Beilstein Journal of Nanotechnology 5, 846-854.(doi:10.3762 / bjnano.5.96) and reproduced under the under the terms of the Creative Commons Attribution License (httD: / / creativecommons.org / licenses / bv / 2.0); and

[0051] Figure 19A illustrates development of emulsion formation at different regions along the static mixer (a) Entry, (b) Middle and (c) Exit using an oikwater ratio of 1 :1 by pumping both oil and water at the same flow rate of 100 mL min-1; Figure 19B illustrates development of emulsion formation at different regions along the static mixer (a) Entry, (b) Middle and (c) Exit using an oikwater ratio of 1 :2 by pumping oil at a flow rate of 100 mL min-1and water at a flow rate of 200 mL min-1; Figure 19B illustrates development of emulsion formation at different regions along the static mixer (a) Entry, (b) Middle and (c) Exit using an oikwater ratio of 1 :5 by pumping oil at a flow rate of 100 mL min-1and water at a flow rate of 500 mL min-1.

[0052] In Figures 7 to 13, and 15 to 17, the cathode was a Ru black coated stainless steel static mixer, the anode was a stainless-steel tube with a diameter of 12 mm and the electrodes were separated by a porous ceramic tube of outer diameter 10mm, inner diameter of 8mm, and wall thickness of 1 mm. The reactor working volume for the experiments described herein is 2.5 mL, the static mixer section length of the cathode is 110 mm, and the electrode length including end tubes are 215 mm. The geometric surface area of the used static mixer in this work is 25.3 cm2. The reported current density values have been rounded for consistency.Detailed Description of the Invention

[0053] The invention provides a process, a device and / or a system for flow based electrocatalytic chemical reactions, in any electrolyte solution, but particularly, reduction I hydrogenation reactions in a pH neutral, alkaline, and preferably, a high pH electrolyte, that is, an aqueous solution that is either a water-in-oil emulsion or an oil-in-water emulsion. The invention is based on the ability of the electrochemical flow cell to accelerate the rates of diffusion limited reactions when operated under flow conditions by intensifying the mixing in the cell and surface activity to the degree that overcomes the many challenges associated with HER (hydrogen evolution reaction) in neutral or alkaline media, including difficultly I suppression of adsorption of neutral aromatic molecules at metal surfaces in alkaline pH solutions. It does this by simultaneously presenting all the reactants in the electrolyte (e.g. water and LOHC precursor) to a single electrocatalytically active electrode in the form of an emulsion of droplets of the reactant and a proton source provided in the electrolyte. The mixing of the reactants and contact with the electrode is enhanced as the electrolyte flows along the length of the static mixer whereby the mixer elements generate an emulsion of different phases (liquid-liquid emulsion). As the component pass along the mixer the size of the droplets in the emulsion reduces and contact with the electrode is continuously improved, particularly where the electrolyte is recirculated through the cell. In the case of a reduction I hydrogenation reaction in water, success of the process is also dependent on selection of an appropriate catalyst and operating conditions for any reaction under study. Both concepts are discussed further below in terms of how the parameters and catalyst for any given reaction I system can be determined such that the examples provided herein are demonstrated as a general principle of application that can be applied to a large range of electro(catalytic) chemical reactions. Itshould be appreciated that the proton generation reaction (i.e. selective first step of HER) and the hydrogenation of the LOHC precursor reactant occur on the same catalyst surface at the same time in the cathode chamber.

[0054] Preferably the process and device support electrocatalytic chemical reactions in a pH neutral, or more preferably a pH alkaline I high pH media (electrolyte) which produces one or more desired chemical product. In some examples, the yield for the desired compound is very high, e.g., >75%, more preferably >90% target product formation, and in some cases 100%, which is due to the high Faradaic efficiency that this invention supports. Faradaic efficiency which is a measure of the overall selectivity of an electrochemical process and is defined as the amount (moles) of collected product relative to the amount that could be produced from the total charge passed, expressed as a fraction or a percent. While application specific, preferred reactions are associated with good to excellent Faradaic efficiency in the context of any given commercial application. What is considered as good to excellent Faradaic efficiency will vary. In certain embodiments, the Faradaic efficiency of a preferred process may be about > 55%, > 60%, > 65%, > 70%, > 75%, > 80%, > 85%, > 90%, > 95%, or > 99% (about means ±5%). In the case the reaction is bulk hydrogen production, a very high Faradaic efficiency is desirable, e.g., >90%. In contrast, a high-value product such as a pharmaceutical, a far lower Faradaic efficiency may be acceptable (e.g., 5%) and the result being quite satisfactory. In this case, the current density and FE may be sacrificed to ensure product purity or yield.

[0055] In general, the process requires low energy input for the formation of atomic hydrogen distinguishing it from existing hydrogenation technologies, particularly hydrogenation of neutral organic aromatics, such as TOL hydrogenation. The process and system of the invention avoid addition of H2 gas as an external proton source (as the hydrogen is generated in situ), avoid the thermal barrier for splitting H2 molecules and overcoming mass transport limitation arising from H2 gas solubility. Further advantageously, expensive DSA anodes are not required. As the process and system is not carried out in strong acid solutions, it results in minimal if any corrosion free or experiences only ultra-low degree of corrosion, particularly where a stainless-steel anode and catalyst coated cathode are used in the cell. In the LOHC hydrogenation, advantageously the only byproduct of the hydrogenation reaction is oxygen.

[0056] While much discussion here focuses on hydrogenation, the invention is not limited by any means to hydrogenation or other reduction reactions. The principles taught herein can be applied to a wide variety of reactions that have poor electrochemical outcomes, e.g., through adverse surface charge effect or slow kinetics or issue with completing reactions. This is due to the ease of which the present invention can be tailored to any given reaction and the plurality of operating parameters that can be adjusted with a particular synthesis goal in mind. In general terms the chemical reaction may involve reduction of a reactant or oxidation of a reactant to form a corresponding product of the chemical reaction of interest. For example, the chemical reaction may involve a reduction reaction at the cathode as working electrode such as a hydrogenation, an oxidation reaction or a dehydrogenation reaction at the anode as working electrode.

[0057] As an exemplary system, the proof-of-concept studies described herein are hydrogenation reactions, particularly, involving reactants which are reversible LOHC reactant / product couples, which are particularly interesting and preferred due to their ability to reversibly carry hydrogen, an application which is desirable for energy storage applications, particularly grid storage applications. As hydrogen gas has low energy density, it requires large volumes of space for storage, and must therefore be liquefied at -253°C. The present invention avoids these issues by directly generating and storing in situ hydrogen from water in an LOHC which is liquid under ambient conditions, which is easier to handle and transport than liquified hydrogen gas. The process of the invention removes the need for a separate I distinct hydrogen compression I liquification step in a hydrogen generation and transport, which supports more effective use of electricity from renewable sources such as photovoltaics and wind power, underlined by a more efficient conversion through direct electrochemical hydrogenation of LOHC precursor to LOHC. The invention is a significant improvement on conventional multistep reaction process consisting of distinct steps of water electrolysis and gas-solid catalytic LOHC precursor hydrogenation with the produced hydrogen.

[0058] In some examples, operation of the process involves providing or forming a pH neutral or alkaline, but preferably high pH electrolyte flow comprising liquid-liquid phase emulsion droplets comprising a liquid proton source and at least one reactant (e.g., a liquid H-uptake compound (R)) which is immiscible with the liquid proton source and thus capable of forming an emulsion of the liquid components in the cell on contacting a suitable static mixer electrode in the cell. On formation by the static mixer, the emulsion travels through the cell along the mixer length, enabling droplets of the emulsion to contact and interact with charged surfaces of an electrocatalytically active static mixer electrode provided in a continuous electrochemical flow cell. On travelling along the length of the mixer, and even more so, over time where the electrolyte is recirculated through the cell, the droplets of the emulsion become increasingly smaller in size and thus more efficiently contact surfaces of the electrode. During the contacting step, under appropriate operating conditions, e.g., when the correct current density and / or potential conditions are applied, the electrocatalytically active static mixer electrode in situ and in concert, under the same operating conditions, generates adsorbed reactive species (e.g., Hads and Rads) on catalytic active sites of electrocatalyst associated with the static mixer, which then react together to form a chemical product of the desired reaction (e.g., a H -storage compound, R-H in the case of a hydrogenation reaction). The catalyst and current density and / or potential conditions are selected to ensure that otherwise typically favoured but competing H2 formation reaction is supressed, whole the desired hydrogenation reaction is promoted such that the desired product is formed with high Faradaic efficiency. As demonstrated herein, other operating conditions including temperature, pressure, flow rate, ratio of reactant(s) to proton sources, reaction time, electrolyte additives, etc, may be adjusted to optimise formation of a product at one or more desired yields / desired Faradaic efficiency.

[0059] The liquid proton source for many reactions, particularly reduction reactions, and those including a hydrogenation reaction, is water, although other proton sources may be used for other types of reactions, as long as they are liquid under the operating conditions. For example, for oxidation reactionsmay involve proton sources such as alcohols, e.g., methanol, ethanol, etc. Water is a preferred proton source, certainly for hydrogenation reactions, as water is readily available and inexpensive making it an ideal source of the atomic hydrogen (H) needed for reduction reactions such as hydrogenation.Electrolyte & Emulsion Formation

[0060] The electrolyte for a chemical reaction includes ions that conduct current through the electrolyte via ion transport. A catholyte is electrolyte solution that is on the cathode side of an electrochemical cell and serves as proton source (e.g., aqueous phase and reactant I LOHC in the hydrogenation examples described herein), while an anolyte is electrolyte solution on the anode side of the electrochemical cell (e.g., aqueous phase only in the hydrogenation examples described herein), isolated from each other via the separator. The electrolyte for the reaction and its component and concentration varies depending on the reaction of interest.

[0061] As explained herein for a reduction I hydrogenation reaction, the electrolyte solution which is the catholyte comprises one or more reactants in the presence of a proton source, where both reactant and proton source are liquid at the process operating conditions. The liquid reactants and liquid proton source must be immiscible such that an emulsion of both components can be formed under the operating conditions by contacting the components with elements of the static mixer electrode. The anolyte is the electrolyte solution without the reactant I LOHC, typically, aqueous phase only.

[0062] The ratio of reactant(s) to proton source (and other components if present) in the electrolyte may vary. For example, the liquid reactant to liquid proton source ratio is not particularly limited once an emulsion may be formed from the mixture as it passes over the mixer elements. In principle, the ratio may range from 5:95% v / v% to 95:5 v / v%. In the case of reduction I hydrogenation reactions involving water as proton source (such as hydrogenation of a LOHC), the reactant to proton source ratio may range from 10:90 v / v% to 50:50 v / v%. In some examples, higher ratios are preferred as at higher ratio of aqueous phase compared to organic phase, smaller droplets are formed going through the static mixer element in a larger volume, specifically in mid and exit section of the mixer. Recirculation of the liquid-liquid emulsion may further improve the quality of the emulsion formed in terms of increasingly smaller droplet size resulting in higher surface area contact with the electrocatalytic surfaces of the electrode. In some examples, the liquid reactant is present in a greater amount than the liquid proton source, where a preferred example involves between 10-40 v / v% liquid reactant with the balance of liquid proton source. In one example, involving TOL in 1 M KOH, the ratio may range from 10:90 v / v% to 50:50 v / v%. Preferably, the ratio is from 10-40 v / v% TOL with the balance of liquid proton source. In some particularly preferred embodiments, a ratio of 20:80 v / v% TOL in 1 M KOH is particularly preferred. As an example, a typical electrolyte for hydrogenation of toluene in water is 20 v / v% LOHC in aqueous 1 M KOH, while a typical electrolyte for hydrogenation of benzyl alcohol in water is 20 v / v% in 1 .5 M mixture of K2HPO4 and KH2PO4 (pH ~7). As explained above, generally speaking, smaller droplets are formed in the emulsion as the solution passes over the static mixer elements, specifically in the mid and exit section. It will be understood that the LOHC precursor is not provided to the mixer part of the electrode as a pure stream, there is always a quality of water present as protonsource. The proton source and the LOHC precursor can be premixed before entering the electrode chamber or maybe suppled separately to the entrance of the electrode chamber, with the former being the preferred option.

[0063] Preferably, the electrolyte solution is free of acid, particularly strong acid free, such as H2SO4. For hydrogenation reactions, acid is not required, as the protons required for the reaction do not come from OER in the anode chamber as is the case for conventional acidic water splitting processes, but instead are formed directly in the cathode in accordance with the Volmer step of water dissociation under alkaline conditions. Thus, a significant difference between the invention and conventional acidic water splitting processes is that all the reactions (i.e., H generation from water splitting as well as hydrogenation of the LOHC precursor) occur concurrently at the cathode through catalysis by the same electrocatalyst provided on the static mixer. The catalyst is one which, under the same set of operating conditions, simultaneously (i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and (ii) promotes reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound. It should be appreciated that the acidic solution hydrogenation prior art discussed above differ from the present invention in that two distinct catalysts are needed on each electrode for those systems - one to specifically catalyse OER at the anode to generate the proton supply needed for the hydrogenation reaction which occurs in the cathode through action of a different catalyst for hydrogenation. This is no trivial difference to the present invention, where a single (individual) catalytic material on the cathode selectively drives the Volmer step of water splitting and concurrently drives the hydrogenation reaction at the same electrode under the same operating conditions in neutral or alkaline electrolyte. That is, one type of catalyst is only required for both reactions, and it is provided on the static mixer cathode exclusively. In typical examples, the anode is a stainless-steel electrode which does not require its own catalyst as the reactions occurring in at the anode are not of particular interest at least for a hydrogenation process.

[0064] Preferred electrolyte solutions have a pH which is not acidic, i.e., the pH is > 7. In some embodiments, a pH neutral, alkaline, or high pH electrolyte is preferred. By pH neutral, it is meant a pH of about ?, while an alkaline pH is >7, a high pH electrolyte is one with a pH of > 10. In some examples, the electrolyte pH is between pH 7 and 15. In some examples the pH is selected from pH 7, 8, 9, 10, 11 , 12, 13, 14 or 15. In some embodiments, a pH of > 10 is particularly preferred (high pH electrolyte). In some examples, the pH is preferably pH of > 14. The pH of the catholyte may depend on the proton source and the liquid reactant (e.g. H-uptake compound) used. For example, the inventors have successfully hydrogenated benzyl alcohol in water at pH 7 and at pH 14. Likewise, toluene has been successfully hydrogenated in water at pH 14.

[0065] A preferred catholyte may comprise a concentration of hydroxide ions [OH ] of from 0.1 M to 7 M. Thus, the catholyte may be an aqueous solution of KOH or NaOH. In some embodiment, KOH is preferred. In the case of toluene hydrogenation in water, a preferred alkaline catholyte may be 1 M KOH. It is particularly preferred for processes involving water splitting as the source of in situ generated H+, that the electrolyte is free of strong inorganic acids, particularly H2SO4. The benefits are described elsewhere herein.

[0066] The liquid proton source or the liquid reactant may be in excess, depending on the reaction of interest. Where the proton source is water, the emulsion can for example involve an oil-in-water, or a water-in-oil emulsion. In some embodiments, an oil-in-water emulsion is preferred, for example, for a hydrogenation process, particularly the LOHC hydrogenation process, e.g., the TOL hydrogenation process described herein, where water is used as proton source and the LOHC is immiscible with the water phase. Suitable mixing of this system results in formation of an oil-in-water emulsion. An oil-in water emulsion is desirable in many cases as this ensures that the conductivity of the catholyte is high. However, notably, a water-in-oil emulsion may be used if an oil soluble supporting electrolyte is used. Many examples of oil soluble supporting electrolytes are known to the skilled person.

[0067] The liquid proton source and the liquid reactant, e.g., H uptake compound, is liquid under the operating conditions which is required to form a liquid-liquid phase emulsion at the electrolyte surface as the electrolyte flows past the elements of the static mixer cathode. A room temperature solid proton source and / or H update compound can be heated to a suitable temperature as necessary to ensure thy are both in the liquid state under the operating conditions. An adjustment of operating pressure may also be utilised if necessary. Indeed, control of the operating pressure can be used to supress the formation of H2 gas under undesirable competing reactions, as well as to minimise the vaporisation of volatile organic components, if necessary.

[0068] In some embodiments, surfactant is not required to aid in emulsion formation. In some embodiments, including surfactant in the electrolyte may be undesirable due to the enhanced difficulty of separating the product from the electrolyte as phase separation does not readily occur because the surfactant stabilises the emulsion. Further, presence of surfactant can overly complicate the electrochemistry. Thus, in preferred embodiments, the electrolyte is surfactant free which means the emulsion is an unstable emulsion. There are advantages to using an unstable emulsion as the individual components separate readily on cessation of the mixing conditions. Further the electrochemistry is likely to be less complex and the reactions are simplified. Thus, preferred liquid-liquid phase emulsions formed are unstable emulsions, i.e., once the mixing conditions are eliminated, the emulsion readily separates into distinct, more easily separated phases. It will be understood that where the hydrogenation product in portioned in one of the distinct phases, as both phases can be readily separated from each other, the hydrogenated product can be conveniently recovered from its phase, e.g., by conventionally known methods. However, if desired, a surfactant can be included in the catholyte. However, typically, a surfactant or other emulsion stabilising additives are not needed and thus are not included.

[0069] Forming an emulsion requires energy because more surface area between the phases is created and the surface free energy increases as a result. This energy is supplied by mixing, and the droplet size distribution in the emulsion is a function of the mixing intensity. In the present invention, component mixing occurs as the liquids flow past the elements of the static mixer. The efficiency of emulsion creation depends on the shape and orientation of these elements, as well as the length of the mixer electrode. Modelling studies, such as Computational Fluid Dynamics (CFD) can be used to design, manufacture and / or screen suitable static mixer electrodes (SME) for use as the workingelectrode with any particular electrolyte composition. However, typical reactor working volumes may range from about 1 mL to about 20 L. Typical static mixer lengths may range from about 5 mm to about 5 m. Typical static mixer diameters may range from about 1 mm to about 2 m. The reactor working volume for the experiments described herein is 2.5 mL, and the static mixer section length of the cathode is 110 mm. Based on the working examples, the inventors believe that emulsions mixing starts from first couple of centimetres of the static mixer section, continues in mid-section and at the exit point, the droplets are smaller than at the start, whereby the reduction in droplet size increased surface area exposure and thus contact with the electrode, as well as increases mass transport and efficiency. A minimum length for the mixer elements would be about 4 cm with no particular limitation on the maximum length, but pressure drop and current distribution for longer static mixer electrodes should be considered and could be modelled by CFD modelling. In preferred examples of LOHC hydrogenation, the aspect ratio for the mixer elements (the ratio of length to diameter of a single element) may be about 15 to 20, for example, about 17 in the currently exemplified study. The parameters may be adjusted to maintain this preferred aspect ratio. Other aspect ratios may be used for different reactions, conditions and cell set up.

[0070] It will be understood that reactant mixing and emulsion formation occurs as the electrolyte solution I fluid feedstock (comprising liquid proton source and liquid reactants, e.g., H uptake compound) flows past the elements of the static mixer which are configured to mix in a way that results in emulsion droplet formation, whereby the emulsion formation efficiency is determined by the shape and orientation of the static mixer elements. If desired the electrolyte may be recirculated through the cell as required. A key feature of a preferred hydrogenation aspect of the invention is the in-situ generation of a reactant- in -water emulsion (preferably an unstable emulsion) as the reactant is delivered to the charged electrode on contact of droplets of the emulsion with the electrode. Further, the formed hydrogenation product is conveniently provided back to the emulsion, e.g., droplets or main phase depending on the polarity) as they pass over the mixer surfaces. Due to the unstable nature of the preferred surfactant free emulsion, the product may be easily separated from the aqueous phase in a quiescent separator tank, for example, after leaving the cell and phase settling.

[0071] The droplet size in the emulsion may vary as the fluid mixture traverses the flow cell because of droplet interactions with the static mixer. The distribution may be macroscopic at the inlet to the flow cell, centred around several millimeters but may diminish to a fraction of a millimeter, or micron or nanometer at the exit. Therefore, the length of the electrode mixer and / or recirculation time can be adjusted accordingly to account for emulsion formation efficiency for any given feedstock of components. In addition, at least for the water case, the droplet size is dependent on the ratio of organic to aqueous phase. In some examples, at higher ratio of aqueous phase compared to organic phase, smaller droplets are formed going through the static mixer element in larger volume specifically in mid and exit section. This has been observed for at least the TOL / water system exemplified herein.

[0072] The flow conditions also affect emulsion formation and hence reaction efficiency. The flow conditions of one or more of the anode and cathode solutions into the electrochemical flow cell may vary depending on the specific feedstocks used and the volume of the particular cell used. Exemplaryflow rates for 2.5 mL reactor volume used in the reported examples herein may range from 50 mL min-1to 1500 mL min-1. In some examples, for a 2.5 mL reactor volume, flow rates are greater than 100 and less than 800 mL min-1, preferably 200 min-1to 600 mL min-1may be used. Moreover, it is preferable to use flow conditions that are as high as possible without generating turbulence. Typically, this means choosing conditions where the Reynolds number is <2000 which represents laminar flow as opposed to turbulent flow. The optimal flow conditions for any reaction of interest for any flow cell used as described herein can be optimised for a particular desired outcome in terms of target product, yield, isomer, stereochemistry, etc. Highly volume cells can tolerate higher flow rates.

[0073] Generally, increasing the flow rate enhances mixing of the reactant and the aqueous phases which reduces the droplet size in the liquid dispersion. Furthermore, it improves the mass transfer by thinning diffusion layers and hence, increases reaction rates. As a general rule, increasing the flow rate generally increases the hydrogenation yield. For the TOL to MCH process described herein, under the conditions and cell size I reactor volume (2.5 mL) described herein, the Faradaic efficiency was 100% for all three lower liquid flow rates: 200, 400 and 600 mL min-1. However, at 800 mL min-1, the Faradaic efficiency decreases to 85%, possibly because the contact time between Hads and TOL becomes shorter than is required for complete reaction. The viscosity of the dispersion can also affect the Faradaic efficiency (FE).Process Efficiency

[0074] The synergistic combination of catalyst activity for proton generation, hydrogenation, and simultaneous suppression of hydrogen gas formation and LOCH precursor hydrogenation at the same catalyst surface under the same set of operating conditions, in combination with the continuous delivery of reactants and removal of products from the cathode surface via the flow of emulsion past the mixer element means the reaction proceeds at relatively low energy demand, with incredibly high yields (selectivity) and / or efficiency. The results are impressive for the alkaline electrochemical hydrogenation reactions described herein, given the well understood challenges with alkaline water splitting I hydrogenation systems. The efficiency of the process can be measured in terms of the Faradaic efficiency which describes the overall selectivity of an electrochemical process and is defined as the amount (moles) of collected product relative to the amount that could be produced from the total charge passed, expressed as a fraction or a percent. The specific intensity of the process is measured by the current density (total current / working electrode geometric surface area). The combination of these two parameters defines the effectiveness of the overall technology for undertaking the reaction of interest: a high current density with a high Faradaic efficiency is desirable, as this means a fast rate of reaction with a high selectively towards the desired product of the electrochemical reaction.

[0075] Depending on the reaction off interest and system set up used, the Faradaic efficiency in some cases can be associated with current densities of about: > 1 mA / cm2, > 2 mA / cm2, > 3 mA / cm2, > 4 mA / cm2, > 8 mA / cm2, > 12 mA / cm2, > 16 mA / cm2, > 20 mA / cm2, > 24 mA / cm2, > 28 mA / cm2, > 32 mA / cm2, > 36 mA / cm2, > 40 mA / cm2, > 44 mA / cm2, > 48 mA / cm2, > 52 mA / cm2, > 56 mA / cm2, > 60 mA / cm2, > 64 mA / cm2, > 70 mA / cm2, > 74 mA / cm2, > 79 mA / cm2, > 83 mA / cm2. About means ±2%. Forparticularly preferred reduction I hydrogenation processes, as reported herein, the product (e.g., hydrogenation product) may be generated in pH > 7 electrolyte with an associated Faradaic efficiency of > 50 %, even at current densities of > 4 mA / cm2. This has been demonstrated at least for the TOL to MCH process described herein. In certain embodiments, the Faradaic efficiency of a preferred process may be about > 55%, > 60%, > 65%, > 70%, > 75%, > 80%, > 85%, > 90%, > 95%, or > 99% About means ±5%. This has been demonstrated at least for the TOL to MCH process described herein. In some preferred cases, the Faradaic efficiency (FE) is > 80%, e.g., at a current density of about 20 mA / cm2. About means ±2%. These results have been demonstrated for at least the TOL to MCH hydrogenation example reported herein, the Faradaic efficiency (FE) is about 80% (about means ±5%) at a current density of about 20 mA / cm2(about means ±2%).

[0076] Such high Faradaic efficiencies (indicating the degree of selectivity of the reaction) at high current densities (indicating the rate I intensity of reaction) were completely unexpected for an alkaline electrocatalytic hydrogenation process for the reasons discussed above. Generating H+at the cathode decreases the pH at the catalyst surface, which has an opposing effect on the charge at the surface which would be expected to decrease the reaction rate and reaction efficiency, and makes it approach of neutral organic aromatic molecules to the electrode surface very difficult. The inventors believe that while conventional agitation mixing does not overcome these effects sufficiently well so that the reaction efficiency in conventional agitation systems is poor due to sluggish reactions and poor mass transport to and from the catalyst surface. However, in the present invention, where the emulsion formed by the static mixer, and resultant efficient mixing and emulsion formation occurs directly at the bifunctional selective catalyst surface, the flow nature of the system and process ensures that the mass transport issues are addressed as reactants and products are quickly delivered and removed to, or from, the catalyst active sites where the reactions occur, such that the pH lowering observed for conventional systems is mitigated. There is also a dramatic increase in active surface area due to the favourably small droplet sizes that occur on mixing.

[0077] In the experiments described herein the cathode is a stainless-steel mixer electrode coated with catalyst with a geometric surface area of 25.3 cm2(rounded to 25 cm2). A 12 mm diameter stainless steel tube is used as anode. It will be appreciated that the dimensions may be scaled up as desired.

[0078] The applied current density also affects the process and reaction efficiency and Faradaic efficiency. For example, the applied current density for the hydrogenation reaction ranges using the cell of the invention in the experiments below ranges from -2 mA / cm2to -60 mA / cm2, preferably -4 mA / cm2to -20 mA / cm2, more preferably -4 mA / cm2to -12 mA / cm2. These values may be particularly relevant to the TOL to MCH example described herein. Other reactions may involve different applied current density. In one example, applied current density of -4 mA / cm2was preferred for TOL to MCH system, particularly in the flow cell described in the examples, as in some cases it supports around 100% (± 5%) Faradaic efficiency for the conversion. For the TOL system, the Faradaic efficiency was found to decrease with excess increase in the applied current density which shifted the cell potential to less desirable conditions, where an increasing amount of H2 gas was produced as the applied current density increased. Increased activity in the competing reaction reduced the overall yield of MCHproduced, as the Faradaic efficiency I reaction selectivity was reduced due to increasing preference for the competing hydrogen gas generation reactions. Thus, for reactions involving water as proton source, the inventors have found that an applied current density which corresponds to the onset potential for water reduction to form reactive hydrogen species under any set of operation conditions I system set up is particularly preferred. Under such conditions the competing H2 generation reaction is suppressed and the selectivity for the hydrogenation reaction (Faradaic efficiency) has been found to be higher. Similarly, for the benzyl alcohol hydrogenation system, at an electrolyte pH of 14, a current density of 4 mA / cm2was preferred, while for the pH 7 system, an applied current density of 1 mA / cm2was preferred, in terms of providing the highest the selectivity for the hydrogenation reaction (Faradaic efficiency).

[0079] The Faradaic efficiency can be calculated by any suitable analytical technique that determine the amount of product relative to the amount of reactant and the charge passed. For example, the concentrations of reactants and products can be determined via1H NMR analysis. As an example, the estimated Faradaic efficiency (F.E.) of electrocatalytic hydrogenation of toluene can be calculated using:F.E. = (experimental hydrogenation yield / theoretical hydrogenation yield) x 100 wherein the maximum theoretical yield of methylcyclohexane in mole percent can be calculated from the total charge passed using the equation below. It assumes the hydrogenation reaction was the only electrochemical process taking place.Theoretical hydrogenation yield= ( (current x time) I (mole of TOL used x Faraday's constant x number of electrons required to convert TOL to MCH which is 6) ) x 100.

[0080] The cell potential required for the hydrogenation reactions can varies with the cell design, electrolyte nature, catalyst identity an applied current density. Generally speaking, it may range from - 1.5 V to -2.0 V for the LOHC type hydrogenation reactions described herein. In the exemplary setup described herein, the cell potential generally ranges from -1 .53 V to -1 .72 V. It will be understood that these values may be particularly relevant to the TOL to MCH example described herein. For at least the TOL to MHC example described herein, application of larger current density of at least -20 mA / cm2was associated with more negative potentials and thus resulted in conditions that favour the generation of H2 gas over reactive hydrogen radical formation (-1 .89 V), and thus it is preferable to use conditions that suppress H2 generation where high Faradaic efficiency is desirable. It will be understood that H2 gas generation at this voltage / current density is particular to the set up I operating conditions described in the example section below. The skilled person will appreciate that appropriate conditions can be determined via carrying out a screening set of experiments that elucidate the optimised conditions for any given cell and set of reactants, for example, as described herein.

[0081] The process may be operated for any desired amount of e.g., up to 24 hours or more. In some example, 1 hr, 2hrs, 3hrs, 4hrs, 5hrs, 6hrs, 7hrs, 8hrs, 9hrs, or 10hrs may be a sufficient reaction time. The electrolyte is recirculated through the cell for the required time. The operating parameters can be adjusted to speed up or slow down the reaction time as desired.

[0082] In the TOL to MCH system, desirably the process is operated under conditions that do not produce any substantial amounts of H2 gas and / or cyclohexane. In some examples, only oxygen is formed at the cathode.Electrochemical Flow Cell, Static Mixer & Emulsion Formulation

[0083] Another aspect of the invention provides a flow based electrocatalytic hydrogenation system. The system comprises an electrochemical flow cell having one or more of a cathodic chamber and an anodic chamber configured as part of a continuous electrochemical flow cell. One or more of the cathodic chamber and the anodic chamber may be provided with an electrocatalytically active static mixer electrode having an arrangement of a multitude of elements of a shape and / or configuration to form liquid-liquid phase emulsion in an electrolyte solution provided to flow by the elements of the static mixer.

[0084] In a preferred example involving LOHC hydrogenations, e.g., TOL to MCH hydrogenation, the electrolyte may be a pH neutral or a pH alkaline electrolyte, wherein the catholyte form of the electrolyte may be a two-phase liquid solution that comprises a liquid proton source and at least one liquid reactant compound (e.g., aqueous phase and reactant I LOHC), which is immiscible with the liquid proton source. The anolyte form of the electrolyte may be the liquid proton source only without reactant (e.g., aqueous phase only). Preferably, the liquid reactant compound is a H-uptake compound, (R) such as a LOHC, and particularly toluene or benzyl alcohol. Toluene is particularly preferred as it can be fully hydrogenated to methylcyclohexane, which is a considered a reversible product-reactant couple that can be used in H-storage and H release applications, such as energy storage. In preferred hydrogenation reactions, the electrocatalytically active static mixer cathode comprises an electrocatalyst selected from one or more metals selected from ruthenium, platinum, palladium, rhodium, iridium, or cocatalyst compound of one or more thereof, or noble or non-noble metals or metal salts. Preferred examples use an Ru or supported Ru catalyst including Ru with co-catalysts, supported or unsupported. Desirably, the electrocatalyst is a monomeric Ru catalyst such as ruthenium black or a Ru catalyst provided with one of more additional metals and / or metal salt as co-catalysts. For example, co-catalyst metals can include d-block metals including Ni, Pt and Ir, and / or salts thereof, particularly Ni and Pt. As explained elsewhere herein the catalyst may be provided on a support which increases the active surface area. In some preferred embodiments the catalyst is not Pt on its own, that is, elemental Pt, in supported or unsupported form. These catalysts are believed to have good bifunctionality for H generation and hydrogenation as described elsewhere herein.

[0085] It will be appreciated that the cell may be part of an electrolyser system. Two or more cells can be provided as part of an electrolyser system.

[0086] The features and parameters described above for the process, equally apply to the system and electrochemical cell thereof. The cell does not include a membrane electrode assembly. The cell preferably does not include a catalyst coating on the anode of the cell. Advantageously, there is no need to employ DSA as anode in alkaline medium.

[0087] In some examples, the system further comprising downstream of the cell, a settling chamber for allowing the emulsion to phase separate thereby facilitating product recovery. The system may comprise means for loading the hydrogenated product (R-H) for storage and / or transportation.

[0088] The reactor or electrochemical cell is provided in the form of an electrochemical flow cell, preferably an axial flow cell. An exemplary cell is show in Figure 6 below.

[0089] Preferably, the flow based electrocatalytic cell comprises a cathodic chamber and / or an anodic chamber configured as part of an electrochemical flow cell. One or both cathode and anode chambers is provided with an electrocatalytically active static mixer cathode having an arrangement of a multitude of elements of a shape and / or configuration suitable for forming liquid-liquid phase emulsion droplets as electrolyte flows past the elements of the mixer. The static mixer cathode may be of any desired length that may be required to ensure a suitable emulsion is formed. This because it has been found that depending on the electrolyte physical properties, the best mixing and best emulsion droplet sizes are generated further along on the length of the static mixer cathode remote from the cell entry point.

[0090] The cathodic and anodic chamber of the flow cell are isolated from each other by a porous separator. The separator prevents mixing of species formed at the anode with the species formed in the cathode. An ideal separator should provide ionic conduction pathways between these two chambers via a network of numerous, fine, tortuous pores, or by ionic conductivity through a solid-state matrix. The separator should be chemically inert. Many materials are used as separators but in alkaline solutions, an organic component that is chemically inert under basic conditions should be used. In one example, a porous ceramic tube may be used. Separators that include a pore size distribution of < 2 pm, more preferably < 1 pm in diameter are desirable.

[0091] In some examples, the anodic chamber may be defined by a stainless-steel tube (diameter is 12 mm in the experimental cell described herein), which may serve as the anode as counter electrode, whereas the cathode where the reduction occurs is the working electrode. It will be understood that for oxidation reactions the static mixer will be included in the anodic compartment. In some examples, it is possible that a static mixer is included in both the cathode and anode compartments. For the proof-of- concept studies reported herein, the static mixer electrode need only be provided in the cathodic compartment where it operates as the working cathode in the hydrogenation of a reactant of interest. However, in reactions where the main byproduct is oxygen in the anolyte, inclusion of a suitable alcohol reactant in the anolyte stream may support reactions that generate useful products for the chemical and pharmaceutical industries (https : / / doi.org / 10.1021 / acsaem.1c01932; the contents of which are incorporated by reference herein). In some examples, alcohols can be electrooxidized and evolve hydrogen at the same time. The inventors therefore envisage that hydrogen could be evolved at both electrodes, along with other useful chemicals at the anode. Thus, inclusion of certain other reactant compounds may also be useful in the anolyte, which may be transformed into valuable chemicals. The reactant compounds may be organic compounds with smaller positive onset potential than water oxidation. For example, electro-oxidation reactions of alcohols, amines, urea, hydrazine, andcarbohydrates could be used in oxidation half-reactions (from https : / / doi.org / 10.1021 / acsaem.1 cO1932; the contents of which are incorporated by reference herein).

[0092] The working electrode should fit snugly within a tubular separator creating working compartment. In some examples, a tubular counter electrode surrounds the working compartment at a small distance from the separator, creating a low volume counter compartment and forms the outside casing of the cell. The whole assembly may then be sealed using two end caps. The fully assembled and cross section of the flow cell showing all the components is shown in Figure 6.

[0093] Desirably, the electrocatalytically active static mixer electrode comprises an electrocatalyst that catalyses the reaction I reactions of interest. In the case of reduction I hydrogenation in water, on contacting emulsion droplets of the electrolyte, the electrocatalyst, in situ and in concert, electroreductively generates (under the same operating conditions) adsorbed reactive species on catalytic active sites of the electrocatalyst associated with the static mixer: (i) reactive atomic hydrogen species from electroreduction of the polar proton source in the electrolyte, and (ii) reactive reactant (e.g., reactive H-uptake compound) species from electroreduction of the reactant compound in the electrolyte. Simultaneously, the electrocatalyst suppresses recombination of the reactive atomic hydrogen species to form H2 gas and promotes reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound. In the provided hydrogenation examples, the electrocatalyst supports generation and transfer of adsorbed reactive atomic hydrogen species (Hads) to adsorbed reactive reactant (Rads) species (adsorbed toluene or adsorbed benzyl alcohol) on an adjacent catalyst active site to chemically stores the electrochemically generated reactive atomic hydrogen species in a hydrogenated product (R-H) of the reactant compound (R), while suppressing the competing reaction involving recombination of the adsorbed hydrogen species to form hydrogen gas. It will be understood that adsorption means the accumulation or adherence of molecules or particles onto the surface of another substance without penetrating the bulk of the other substance. This is a different process to absorption where one material incorporates or penetrates into the bulk of another substance.

[0094] Preferably, the electrocatalyst is drop cast onto the electrode, at least on to the static mixer elements. Other application techniques such as electrodeposition may be used as long as the catalyst conformally coats the static mixer elements in a way that preserves the mixer element shape and configuration.

[0095] The electrolyte may be circulated through the cell continuously during a reactant for any period of time, if desired. The electrolyte circuit may include a stirred reservoir to provide the flow cell with a partially dispersed feed of reactants if desired. Alternative, a separate flow of individual component steams can be provided at the entrance to the electrode chamber, though the former case is preferred. Thus, in some examples, upstream of the reactor / electrochemical cells, a pre-mixer or a stirred reservoir of inputs may be used to provide a premixed flow (partially dispersed feed) of the electrolyte, e.g., from separate flows of the components in the electrolyte. Suitable pumps with controllable flow rates can be used to adjust the flow rate and mix ratio of the components into the pre-mixer and ultimately the reactorelectrochemical cells. A desalination unit may be provided upstream of the cell if required to remove ions such as Na+, K+and Ch, etc. Suitably, flow cell is part of an electrocatalytic reactor system comprising downstream of the cell, a settling chamber for allowing the emulsion to phase separate. In some embodiments, the electrocatalytic reactor system is an electrocatalytic hydrogenation system which further comprises means for loading the hydrogenated product (R-H) for storage and / or transportation.

[0096] Suitably, the flow cell involved in the process is absent a proton exchange membrane (PEM) as in the present invention, the required H is generated and stored in the same chamber / catholyte. The flow cell may also be absent a means for introducing externally generated hydrogen into the cell. There is no need for such a means, as the cell and process described herein produce the required hydrogen in situ in the working electrode chamber from the water proton source. As such, acidic electrolytes, e.g., those comprises strong acids, for example, strong inorganic acids such as H2SO4 etc. are not required. The present alkaline system therefore avoids the significant corrosion issues that are observed in many conventional acidic systems.

[0097] Thus far, the inventors have used a static mixer of a type that is suitable to form an emulsion involving two or more phases. For example, a Kenics KMS mixer and a Sulzer SMV mixer are two examples of commercially available mixers that can form liquid-liquid phase emulsions at the mixer surface. Static mixer design relies on a knowledge of fluid flow around solid shapes and an understanding of the science of mixing. For example, a Kenics KMS mixer or Sulzer SMV mixer shown in Figure 5 may be used. The mixer shape generates a reactant I aqueous phase emulsion in situ in the electrode chamber as described elsewhere herein. The unstable nature of the preferred generated in situ emulsion aid later phase separation making the product separation and subsequent transport steps low energy and energy efficiency. The mixer also ensures improved mixing and dispersion of emulsion in the electrode chamber so that more reactant contacts the electrode surface thereby supported enhanced mass transport.Reduction / Hydrogenation Reactions

[0098] In a preferred proof-of-concept embodiment, the invention provides a process, a device and / or a system for flow based electrocatalytic reduction I hydrogenation in an alkaline I high pH media (electrolyte) with hydrogenated product generation. Preferably the process and device support electrocatalytic hydrogenation in an alkaline I high pH media (electrolyte) producing a desired hydrogenation product associated with excellent Faradaic efficiency. It will be understood that Faradaic efficiency which is a measure of the overall selectivity of an electrochemical process and is defined as the amount (moles) of collected product relative to the amount that could be produced from the total charge passed, expressed as a fraction or a percent. The inventors believe that flow based electrocatalytic hydrogenation in alkaline I high pH media as described herein is an entirely new process I device I system. In preferred embodiments, the electrocatalytic reaction involves electrohydrogenation. Hydrogenation by heterogeneous catalysis is ubiquitous in synthetic chemistry. It is used to add hydrogen across many different atom-atom bonds, most commonly multiple bonds ofthe type Ri= R2, Ri= R2 where R1 and. R2 may be C, N, O, B, Si, P, S, or a metallic element or any combinations of these. Chemical classes that are commonly hydrogenated in this way include but are not limited to alkenes, alkynes, aldehydes, ketones, nitriles, nitro compounds, aromatics and heteroaromatics, imines, etc.

[0099] In this work, the electrochemical flow cell technology is used in the one-pot electrocatalytic hydrogenation of LOHCs under flow conditions in selected aqueous electrolyte (i.e. neutral and alkaline media).

[0100] The process involves providing or forming a pH neutral or alkaline catholyte flow comprising liquid-liquid phase emulsion droplets comprising a liquid proton source and at least one reactant which is a liquid H-uptake compound (R) immiscible with the liquid proton source. The emulsion quality is improved as the mixture passes over the mixer elements. Contacting the emulsion with charged surfaces of an electrocatalytically active static mixer cathode provided in a continuous electrochemical flow cell is allowed to occur. During the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert, the following adsorbed reactive species on catalytic active sites of electrocatalyst associated with the static mixer: (i) atomic hydrogen species (Hads) generated from the proton source in the emulsion droplets, and (ii) H-uptake compound species (Rads) generated from the H-uptake compound in the emulsion droplets. Adjacent adsorbed atomic hydrogen species (Hads) and adsorbed H-uptake compound species (Rads) then react together on the catalyst surface to form a hydrogenated product, e.g., H-stored compound. The electrocatalyst suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and promotes reaction of the adsorbed species together to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H). It will be understood that the process therefore involves the step of chemically storing the electrochemically generated atomic hydrogen species in a hydrogenated product (R-H) of the H-uptake compound (R) (the reactant) by allowing transfer of adsorbed reactive atomic hydrogen species (HadS) on a catalyst active site of the electrocatalyst to a reactive H-uptake compound species (Rads) adsorbed on an adjacent catalyst active site.

[0101] It will be understood that the atomic hydrogen species (H) required for reduction I hydrogenation is not sourced from an associated anodic system or from outside the continuous electrochemical flow cell. A key point to note is that the H+leading to the HadSdoes not originate through an OER reaction at the anode nor from inorganic acids, such as H2SO4, present in acidic reaction media. As a result, no special conditions or catalysts are required at the anode side of the cell for this application. Further, a PEM is not required for the same reason, there is no requirement for H+to be sourced from anode from elsewhere in the cell. Further, as acidic corrosion of the electrodes is not a concern, dimensionally stable anodes are not required.Reduction / Hydrogenation Operating Conditions

[0102] In some examples, the operating conditions may be optimised such that no partially hydrogenated products are formed. Where possible, at least for water-based reduction I hydrogenation processes, the operating conditions should be adjusted to correspond to potentials slightly negativethat of the onset potential for water reduction to ensure the preferential creation of hydrogen radicals over H2 gas.

[0103] Preferably, the reduction I hydrogenation process occurs under conditions that do not involve particularly elevated pressures (e.g., above 30 bar) and / or elevated temperatures (e.g., temperatures of 150 °C or higher) which are typically required for convention LOHC hydrogenation reactions. However, higher pressures suppress the formation of gaseous hydrogen, thereby increasing the number of reactive adsorbed hydrogen radicals, Hads on the catalyst surface. Therefore, most preferably, the process occurs at temperatures of 20 °C or higher, and / or at pressures of about 3-5 atm or greater. In some embodiments, process occurs at temperatures of up to 100 °C in the case involving water as proton source. For example, for hydrogenation of LOHCs, increased Faradaic efficiency is possible at temperatures of between 50 and 90°C. Particularly good results for TOL hydrogenation have been achieved at a temperature of 80°C. Generally, the inventors have found that increasing temperature impacts the hydrogenation yield. For the examples described herein, increasing the temperature led to a slight reduction in the onset potential while increasing the current density. Increasing the temperature thus desirably shifted the operational current density to higher values. In simpler terms, raising the temperature lowered the onset potential, which facilitated the production of a higher quantity of hydrogenated product at a higher operational current density. Consequently, this reduction in operational time allows for the conversion of LOHC, (e.g., TOL) into its fully hydrogenated product (e.g., MCH), more efficiently. In the case where the proton source is water, the reaction temperature may be up to 100 °C, up to 95 °C, up to 90 °C, up to 85 °C, up to 80 °C, up to 75 °C, up to 70 °C, up to 65 °C, etc. It will be appreciated that temperature around the boiling point of the components in the electrolyte solution should be avoided.Preferred Reduction / Hydrogenation Reactants

[0104] Preferably, the process involves electrocatalytically hydrogenating a reactant (e.g., a H-uptake compound (R) such as a LOHC precursor reactant, particularly toluene) in which hydrogen is stored chemically in the form of a hydrogenated product (e.g., a hydrogenated H-uptake compound (R-H)).

[0105] The invention enables flow based electrochemical hydrogenation reactions in an alkaline I high pH media (electrolyte) that irreversibly hydrogenate a reactant to provide a hydrogenated product, such as a hydride compound. The term “irreversibly hydrogenate” means that the product of the reaction is one which cannot be dehydrogenated under reasonable energy conditions, for example, by applying, e.g., conventional catalytic dehydrogenation conditions such as elevated pressures (around 30-50 bar) and temperatures (approximately 150-200°C).

[0106] The invention further enables flow based electrochemical reactions in an alkaline I high pH media (electrolyte) that reversibly hydrogenate a reactant to provide a hydrogenated product, such as a hydride compound, which can be readily dehydrogenated efficiently, e.g., with known dehydrogenation methods, at reasonable energy efficiency. In some case, electrocatalytic dehydrogenation methods may preferably be used. The term “reversibly hydrogenate” means that the product of the reaction is one which can be readily dehydrogenated under reasonable energyconditions, for example, by applying, e.g., conventional catalytic dehydrogenation conditions such as elevated pressures (around 30-50 bar) and temperatures (approximately 150-200°C).

[0107] In some embodiments, suitable reactant / product couples for a hydrogenation reaction include: a) toluene / methylcyclohexane; g) 2-phenyl-pyridine / 2-cyclohexyl- b) benzene / cyclohexane; piperidine; c) xylene / dimethylcyclohexane; h) 2-benzylpyridine / 2-(cyclohexyl- d) napthalene / decalin; methyl)pyridine; and e) dibenzyltoluene / perhydro- i) N-ethylcarbazole / dodecahydro-n- dibenzyltoluene; ethylcarbazole. f) benzyl alcohol / cyclohexylmethanol;

[0108] Reactant / product couples f) to h) are believed to give rise to irreversible hydrogen productsReactant I product couples a) to e) are believed to give rise to reversible hydrogen products and may be suitable for H-storage and H-release applications, such as grid energy applications.

[0109] In a preferred embodiment, the invention provides a one pot I flow based electrocatalytically driven hydrogen generation and hydrogen storage process in an alkaline / high pH media (electrolyte), which may use, e.g., the reactant product couples described above, particularly those that are readily reversible under reasonable energy conditions.

[0110] It will be understood that for H-generation and H-storage applications, it is preferred that the compounds of the couple may be continuously reused or recycled. For other products, where reversibly is not possible, this feature is not applicable.

[0111] The hydrogen may be generated from a suitable proton source such as water, preferably pH neutral, alkaline or high pH water, and the hydrogen formed in situ is concurrently chemically stored in a suitable H-uptake compound. For example, a reactant which is a H-uptake compound, e.g., LOHCs such as toluene (TOL), can be efficiently hydrogenated to a hydrogenated product, such as methylcyclohexane (MCH), by hydrogen generated in the same cell compartment in a single flow through electrolyte media which is an emulsion of the LOHC and the proton source, e.g. water. Depending on the choice of H-uptake compound, the hydrogenated product maybe dehydrogenated subsequently to release H when there is demand, for example, in a grid energy application. It will be understood that this embodiment relies on selection of a reversible (at reasonable energy) H-uptake I H-storage reactant I product couple, such as TOL / MCH. The H-uptake I H-storage reactant I product couple is not particularly limited, however, H-uptake compound reactant and corresponding hydrogenated product (H-storage product) should ideally be liquid at standard (e.g., STP) conditions as they are easily transported at ambient conditions from source to another site where energy generation may be required.

[0112] The preferred flow based electrocatalytic hydrogenation process of the invention involves a pH neutral, a H alkaline or most preferably a high pH alkaline electrolyte solution comprising liquidliquid phase emulsion comprising a liquid proton source and at least one reactant, e.g., liquid H-uptakecompound (R), which is immiscible with the liquid proton source. Desirably, the liquid-liquid phase emulsion is an oil-in-water emulsion.

[0113] The electrolyte solution is provided as an electrolyte flow in the electrochemical flow cell. When provided as to a cathode chamber, the emulsion droplets contact charged surfaces of an electrocatalytically active static mixer cathode provided in a continuous electrochemical flow cell. During the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert, under the same set of operating conditions, adsorbed reactive species on catalytic active sites of electrocatalyst associated with the static mixer. The adsorbed reactive species are (i) atomic hydrogen species (Hads) generated from the proton source in the emulsion droplets, and (ii) H-uptake compound species (Rads) generated from the H-uptake compound in the emulsion droplets. Simultaneously, the catalysts under the applied operating conditions, suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and promotes reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H). The process involves chemically storing the electrochemically generated atomic hydrogen species (H) in a hydrogenated product of the reactant, e.g., H-uptake compound by allowing transfer of adsorbed reactive atomic hydrogen species (Hads) on a catalyst active site of the electrocatalyst to the reactant, e.g., a reactive H-uptake compound species (Rads) adsorbed on an adjacent catalyst active site. In the case of electrocatalytic hydrogenation of a LOHC in alkaline I high pH water, the hydrogen species (HadS) is generated directed from water electrolysis at the catalyst surface, while the H-uptake compound species (Rads) is formed from LOHC adsorption at the catalyst surface. In a specific example, the H-uptake compound species (Rads) can be reactive adsorbed toluene (TOLadS) onto catalytic sites on the static mixer, which is converted to methyl cyclohexane, on transfer of hydrogen species (HadS) to the TOLadS. The term “chemically storing” means the hydrogen generated from HER at the cathode is taken up into the product compound through chemical combination of the hydrogen with the reactant, by additional across unsaturated bonds in the reactant molecule.

[0114] In some embodiments, the flow based electrocatalytic hydrogenation of the invention is an electrochemical hydrogen generation and hydrogen storage process. In this process, the liquid proton source is water, and the H-uptake compound (R) forms a first part of a reversible (de)hydrogenation reactant / product couple, wherein a second part of the couple is a hydrogenated derivative (R-H) of the H-uptake compound (R). In this embodiment, the nature of the couple is that the process involves chemically storing the electrochemically generated atomic hydrogen species in the hydrogenated product (R-H) of the reversible (de)hydrogenation reactant / product couple. Notably, the hydrogen generation and hydrogen storage occur in the same catholyte solution whereby both steps are catalysed by the same electrocatalyst associated with the static mixer cathode.

[0115] It is believed that reversible reactant I product couples may include a) to e) above may be suitable for reversible H-storage applications as LOHCs, while irreversible reactant I product couples may include f) to i) above and may be particularly useful in electrosynthesis applications, where the reversibility / ease of dehydrogenation is not a concern.

[0116] The electrocatalytic hydrogenation may produce a hydrogenated product (R-H) of the Fluptake compound (R), in which the H cannot be easily recovered from the hydrogenated product (R- H), designed as ‘irreversible hydrogenation’. However, in preferred embodiments, the hydrogenated product (R-H) of the H-uptake compound (R) is one in which the H is readily recovered from the hydrogenated product (R-H) though application of reasonable energy expenditure dehydrogenation processes, for example, thermal catalytic dehydrogenation process, or electrodehydrogenation. This is designated herein as ‘reversible hydrogenation’.

[0117] For example, in one embodiment, the flow based electrocatalytic hydrogenation process of the invention may be an electrochemical hydrogen generation and storage process, in which case, the liquid proton source may be water, and the H-uptake compound (R) may form a first part of a reversible (de)hydrogenation reactant / product couple, wherein a second part of the couple is a hydrogenated derivative (R-H) of the H-uptake compound (R). Since the couple involves reversibly generatable compounds, the process may be used to chemically store electrochemically generated atomic hydrogen species chemically in the hydrogenated product (R-H) of the reversible (de)hydrogenation reactant / product couple.

[0118] The H-uptake (reactant) compound may comprise one or more saturated bonds (double or triple bonds conjugated bonds, e.g., aromatic bonds) and the reactant stores the hydrogen from water splitting formed in the cathode chemically in the hydrogenation product after the reactant undergoes a catalytic hydrogenation reaction in which the hydrogen is added across at least one of the unsaturated bonds (and preferably all of the unsaturated bonds) of the reactant to form a saturated, preferably fully saturated H carrier product compound. The saturated H carrier product compound releases stored hydrogen on undergoing a suitable catalytic dehydrogenation reaction in which hydrogen is extracted from at least one saturated bond of the product to form the reactant compound (reversible hydrogenation).

[0119] In some embodiments, the reactant (e.g., H-uptake compound (R)) is a compound having unsaturated, conjugated and / or aromatic bonds which can be reduced by additional of hydrogen across the bonds. Suitably, the reactant (e.g., H-uptake compound (R)) comprises one or more of the following functional groups: alkene, alkyne, aldehyde, ketone, ester, carboxylic acid, and nitro. In embodiments involving electrocatalytic hydrogenation, it will be understood that these functional groups are reduced as a result of the hydrogenation reaction. A fully saturated or fully hydrogenated product compound is preferred for reversible H storage application as the maximum capacity for chemical H storage is availed of.

[0120] During the hydrogenation process using water as the proton source, the sole by-product formed in the anode chamber is oxygen (O2) which is generated at the anode by the OER (oxygen evolution reaction). Oxygen generated by electrolysis can be a valuable by-product as it has use in several industrial processes including wastewater treatment, aquaculture, steel making, medical applications and enhanced combustion processes (see https : / / doi.org / 10.1016 / i.biortech.2020.123595: https: / / doi.Org / 10.1016 / i.ces.2O21 .117008:https : / / DOI:10.1016 / i. energy.2004.07.004; the contents of which are incorporated herein by reference).

[0121] In some embodiments, the process, cell or system may be used for asymmetric electrocatalytic synthesis, for example, electrohydrogenation to make stereoselective products by the use of immobilised molecular catalysts or chirally modified metallic catalysts. (See, https: / / doi.Org / 10.1016 / i.checat.2023.100631 ; the contents of which are incorporated herein by reference).Hydrogenation Electrocatalyst & Selection

[0122] The electrocatalyst may be coated on the entire surface of the static mixer cathode, or it may be confined to certain surfaces of the static mixer, e.g., surfaces of elements of the static mixer. In preferred embodiments, a catalyst is not included on the anode, particular one for catalysing OER. It is important that the catalyst is provided on at least the mixer elements if the static mixer in a conformal manner where the shape and orientation of the mixer elements is preserved. Known conformal coating methods may be used, however, the inventors have successfully used dip coating and electrodeposition methods in the present invention.

[0123] In water splitting, H radical formation is first step of HER (i.e., the Volmer step-water dissociation), while the second step of HER (i.e., the Tafel or the Heyrovsky step) involves H radicals reacting together to form H2 gas. Where water is used as proton source, the electrocatalyst must be suitable for simultaneously catalysing the Volmer step of HER (hydrogen evolution reaction) selectively (without catalysing the further water splitting steps) as well as the catalytic reduction I hydrogenation of the reactant compound. That is, the catalyst must generate atomic hydrogen species (Hads) and the reactive reactant species (Rads) concurrently on catalytic active sites of the cathode, while suppressing recombination of the atomic hydrogen species (Hads) to generated H2 gas.

[0124] As H2 gas generation is a competing reaction in the case of hydrogenation, the catalyst must favour H radical formation (that is the first step of HER - the Volmer step-water dissociation) while suppressing the second step of HER (i.e., the Tafel or the Heyrovsky step), as H2 gas formation is not desired in hydrogenation process of the invention. H2 gas formation reduced the Faradaic efficiency of the process towards hydrogenation product, e.g., LOHC formation.

[0125] Preferably, the electrocatalyst is dual functioning, that is, bifunctional, and selectively and simultaneously reduces the proton source (e.g., water) to form Hads and generates the uptake compound Rads at the same time on the catalytic surface. The electrocatalyst must be selective towards these reactions, over the H2 generation, e.g., the second step of the conventional HER reaction that occurs at the cathode in alkaline media, which should be suppressed under the ideal operating conditions. It will be understood that this behaviour may be preferential observed under certain operation conditions the determination of which will be apparent from the disclosure provided herein.

[0126] It is the dual I bifunctional nature of the catalyst that allows both reaction steps to be carried out in the same chamber or more specifically in a single body of electrolyte media. Unlike the hydrogenations that use PEMs, the reactions occurring in the anolyte are not important, as the Hads is generated in situ in the catholyte chamber through initiation of the Volmer step of alkaline water hydrolysis but avoidance of the second step of alkaline water hydrolysis (the Tafel or the Heyrovsky step). Catalysts must accelerate the rate of production of reactive hydrogen radicals (Hads), while minimising the rate of H2 gas formation while also providing a high number of active sites for reactant adsorption and hydrogenation. The composition and morphology of the catalysts may both affect their catalytic efficiencies. The ideal catalyst is one that supports generation and adsorption of reactive atomic hydrogen from water with an affinity that is suitable to allow release of the adsorbed reactive atomic hydrogen making it available for transfer to adsorbed reactive H-update compound, e.g., toluene. The ideal catalyst does not hold the adsorbed H too tightly. Further the ideal catalyst should generate and adsorb reactive TOL. In other words, the adsorption of the reactants on the catalyst surface should neither be too strong or nor too weak to achieve high activity.

[0127] The catalyst cannot be any water splitting catalyst, e.g., any catalyst suitable for OER in acidic media, instead it must be one that supports water dissociation as the first step of HER but it must also support pausing the reaction prior to the second step in which H radicals form H2 gas. The inventors have identified that through correct selection of catalysts and application of suitable operating current / potential, that aim can be achieved.

[0128] The catalyst for any particular reactant and particularly reduction reaction (e.g. hydrogenation) can be identified by carrying out hydrogen evolution pre-study, that considers (based on the inventors’ realisation) catalysts that adsorb reactive atomic hydrogen with sufficient strength that it stays at the catalytic surface, but not so strongly that it cannot combine with the dehydrogenated reactant. Furthermore, this adsorption behaviour helps to avoid self-reaction of the atomic hydrogen, a completing process discussed above that is not desirable because it forms hydrogen gas. Thus, a catalyst may fail if it adsorbs atomic hydrogen too weakly or too strongly. A secondary function of the catalyst may be to adsorb atomic hydrogen into its bulk structure such that it is prevented from recombining to for hydrogen gas but be available for reaction with the dehydrogenated reactant when both are at the surface of the catalyst. The inventors have found that the catalytic activity of a material can be determined by first testing how efficiently it evolves hydrogen when it is held at different negative potentials in solution, then second, to measure the rate of hydrogenation of a dehydrogenated reactant at different negative potentials.

[0129] Thus in some examples, the hydrogenation electrocatalyst in reactions using water as proton source selectively catalyses the generation of reactive atomic hydrogen species (H) (which is adsorbed onto the catalyst surface as HadS) from the proton source and the reactive reactant (e.g., H- uptake compound species (Rads)) in preference to hydrogen gas (H2) formation. Both reactive species are generated and adsorbed onto the catalyst surface. Preferred electrocatalysts are those that show minimal activity for the completing hydrogen gas (H2) formation reaction. Preferred electrocatalysts are simultaneously active for the generation of adsorbed reactive atomic hydrogen species (HadS) andadsorbed reactants (e.g., H-uptake compound (Rads), preferably reduced LOHCads- Further, this dual or bifunctionality must be preferred over catalysing the competing H2 generation reaction which can occur via combination of Hads which is the second step of the HER reaction that occurs in alkaline aqueous media.

[0130] The dual or bifunctional electrocatalyst may be composed of a single (that is one homogeneous type of) electrocatalytic material. It should be appreciated that the process of the invention uses an electrode (e.g., cathode) coated with just one catalyst material. Further the single catalyst material is provided in just one location in the cell, i.e., in the cathodic chamber, where the catalyst is used to catalytically drive two different reactions at the same time at cathode: (i) the HER reaction that is needed generate Hads on the catalyst surface, and (ii) the generation of reduced H uptake compound Rads on surfaces of the same catalyst. When the catalyst has a balanced ability to generate both Hads and Rads in substantial preference to H2 gas evolution at the catalyst surface, by providing the reactants for these species (proton source and H uptake compound) continuously to the catalyst surface in the form of a continuous flow of emulsion droplets has been found to overcome the problems discussed elsewhere herein which have hindered electrocatalytic hydrogenation in alkaline media.

[0131] Thus, the selection of a balanced electrocatalyst which is conformally associated with emulsion generating elements of a static mixer electrode provides a unique system involving a cleverly configured catalyst surface whereby reactants for the reaction are continuously provided to the catalytic surface in the form of emulsion droplets containing the reactants where the emulsion droplets are continuously generated in situ at the catalytic cathode surface via action of the electrolyte flow past the mixer elements. The combination of the catalytic activity together with the continuous delivery of reactants provided at the cathode surface as emulsion droplets overcomes the challenges associated with electrocatalytic reactions in alkaline media.

[0132] A preferred electrocatalyst may be composed of, or may comprise, one or more metals selected from ruthenium, platinum, palladium, rhodium, iridium, or compounds comprises one or more of these metals, or other noble or non-noble metals or metal salts. The catalyst may be a binary metal catalyst or may be a mixture of two or more metals (e.g., Ru-lr, Ru-Ni). The catalyst may be supported on another material to increase the surface area of the catalyst thereby increasing the availability of active sites. A suitable support includes carbonaceous materials, such as activated carbon, Ketjenblack and activated charcoal or alumina I aluminium oxide. In particularly preferred embodiments, e.g., where water is used as proton source and the reactant is a LOHC, the catalyst may be Ru black, Ru / C, Ru-lr / C or Ru-Ni / C. In some embodiments, typical water splitting catalysts such as ruthenium dioxide are not used. In some examples, expensive catalysts such as Ir, Pt or Pd on its own are not required nor used.

[0133] For hydrogen production from water splitting, the electrolysis catalysts are used in a way where they aid in the recombination of hydrogen radicals to form H2 gas, but they are not required to form a particularly strong bond between the catalyst and the H radicals which would hold the H radicals in away that suppresses hydrogen radical recombination. Instead, they are used to facilitate the opposite reaction thereby promoting H2 generation by providing an environment that promotes the combination of H radicals to form H2 molecules. Electrocatalytic hydrogen production from water splitting does not contemplate formation of strong bond of H radicals to the catalysts which is an important feature of the present invention. In fact, they teach away from this requirement, as promotion of the reaction (that is to be suppressed for this invention) is required for hydrogen production from water splitting, and the catalysts are operated accordingly. Thus, the inventors have found that catalysts including Ir, Pt and Pd, often used in hydrogen production from acidic water splitting applications, are not preferred for the LOHC precursor hydrogenation reactions described herein, certainly for the TOL to MCH reaction described herein. This is because, while they may be suitable for HER under appropriate operating conditions, they are not suitable for simultaneous adsorption of both H radicals and the organic aromatic compound, which is required for hydrogenation. In other words, they do not have the bifunctional activity required for hydrogenation of at least TOL to MCH. The inventors believe that they are likely to have useful activities in catalysing other chemical reactions using the process and system of the invention. The method screening such activity for any reaction for any particular system will be understood by the skilled person based on the teachings provided herein.

[0134] Ruthenium is one metal that has been found to be very effective at meeting this balance under alkaline operating conditions, and particularly for the system involving water as proton source and reactants such as H-uptake compounds, e.g., LOHCs, such as TOL to MCH. In some examples, the catalyst is ruthenium black, which is a finely divided ruthenium powder having a medium specific surface area catalyst. Other supported ruthenium catalysts include ruthenium on carbon or Ketjen black which are good supports for increasing the catalyst surface area. All of these materials show good ability for the bifunctional ability described herein with respect to LOHC hydrogenation, particularly TOL to MCH hydrogenation. However, single ruthenium metal has given the best results for the LOHC hydrogenations, particularly TOL to MCH hydrogenation as described herein. It is believed that using a higher specific surface area form of ruthenium and / or a higher ruthenium loading on the carbon supports or would further improve the Faradaic efficiency.

[0135] The effectiveness of ruthenium in terms of the balance between reactive hydrogen formation, hydrogenation of an organic aromatic molecule and suppression of molecular hydrogen formation required by the invention was a surprising result. This is because previous research in acidic HER systems has suggested that monometallic Ru catalysts are inefficient at generating Hads because they exhibit slow reduction kinetics of protons to yield Hads and hence, have undesirably high HER overpotentials and iridium as co-catalyst was needed to promote reactive hydrogen radical formation. In the present invention, catalysts including metals having certain hydrogen formation and hydrogen adsorption, and high organic aromatic adsorption behaviour are required (balanced bifunctional activity). An indicator of possible catalyst performance for HER in the process of the invention is the “volcano” plot, where the exchange current density (proportional to reaction rate) is plotted against the metal-hydrogen (M-H) bond strength, as shown in Figure 7a. The traditional volcano plot is only relevant for HER in acidic media but updated “volcano” plots for HER in alkaline media have beendeveloped using computational methods rather than experimental data and given useful insight (and notably Ru is not included on either plot due to lack of experimentally established positions). The inventors have found that under optimum operating conditions a suitable HER catalyst for the present applications, should be capable of displaying a moderate M-H bond strength to allow for atomic hydrogen to be adsorbed on the catalyst’s surface but not too strongly for it to react and be released from the surface. This is in addition concurrent organic aromatic adsorption ability under the same operating conditions. While the theoretical alkaline media plots form a starting point for HER activity, behaviour can be different outside the tested conditions (e.g., different reaction, pH, flow rate, etc). The Volcano plots do not give the skilled person any hint as to ability to (i) pause the water splitting after the Volmer step, and simultaneously (ii) ability to catalyse hydrogenation of organic molecule in present of reactive hydrogen species. Further, it is important to appreciate that it is the synergistic effects derived from implementation of the flow cell described herein and the emulsion formation I improved mass transport aspect of the invention, together with the right catalyst being used under the correct operating conditions that allow the catalyst to operate in a balanced bifunctional manner that underlies the invention, that is suppresses H2 generation and promotion of hydrogenation. In summary, a catalyst (i.e. single metal, bi-metal or metals on carbon type materials as support) must have an ability to (1 ) dissociate water electrochemically to generate H radicals, (2) adsorb H radicals and organic molecules, (3) catalyse hydrogenation reaction of organic molecules, all under the same operating condition and thus this is not a trivial choice. Similar requirements apply to co-catalysts for Ru-based materials. Likewise, d-metals, particularly nickel (Ni) and platinum (Pt), exhibit high exchange current densities (see Figure 17b) corresponding to appropriate hydrogen adsorption energies (Figure 7b) and are expected to behave well in electrocatalysis synthesis under optimised conditions, alone and when used as co-catalyst for ruthenium. The inventors have found that the most effective catalyst for electrocatalytic hydrogenation of TOL to MCH with high Faradaic efficiency and low cell potential (i.e. power consumption) is monometallic ruthenium I monometallic ruthenium black (Ru black).Applications

[0136] The invention provides for a use of a flow based electrosynthetic flow cell as described above in an electrosynthetic process for chemical synthesis. For example, the flow based electrosynthetic flow cell can be used as an electrocatalytic hydrogenation system, which may be used in an energy storage application, or a grid energy storage application.

[0137] The invention provides for a use of a catholyte in the form of an emulsion comprising a liquid proton source and at least one liquid reactant (e.g., a H-uptake compound (R)) which is immiscible with the liquid proton source in a flow based electrocatalytic hydrogenation process.

[0138] The cell or system described may be used in an energy storage application, or a grid energy storage application. In another aspect of the invention the flow cell of the invention may be integrated into a hydrogen storage and / or transport system, preferably a commercial hydrogen storage and / or transport system, particularly a LOHC hydrogen storage and / or transport system.

[0139] Further this technology may also be used in other applications including green hydrogen gas production through water electrolysis, iron ore electrolysis, metal electrowinning, water purification and disinfection and material electrosynthesis.

[0140] An advantage of the cell and process described herein, in the case of reversible hydrogenation of LOHCs, where the hydrogenation reaction is driven under a constant applied current or potential. As the cell typically involves a low operation potential and current for the flow cell means, an advantage of the system is that can integrate with solar and wind or other renewable energy sources - synergistic coupling enhances sustainability - cleaner and greener hydrogen production.

[0141] In another example, the invention involves use of a catholyte in the form of an emulsion comprising a liquid proton source and at least one liquid reactant compound, such as a H-uptake compound, (R), which is immiscible with the liquid proton source in a flow based electrocatalytic hydrogenation process.Description of Preferred Embodiments

[0142] The inventors have developed technology that involves an electrochemical flow cell adapted with a specific static mixer design having an efficient electrocatalyst coating which enables one-pot electrosynthetic reactions in alkaline media with high Faradaic Efficiency. The invention has been demonstrated for electrocatalytic hydrogenation of substrates toluene (TOL) (hydrogenated to methylcyclohexane (MCH) and benzyl alcohol (BA) (hydrogenated to cyclohexanemethanol (CHM)).

[0143] In proof-of-concept examples described herein, CSIRO’s electrochemical flow cell technology is used in a one-pot electrocatalytic hydrogenation of LOHCs under flow conditions in selected aqueous electrolyte (i.e. neutral and alkaline media).

[0144] The inventors have developed technology that involves an electrochemical flow cell adapted with a specific static mixer design having an efficient electrocatalyst coating which enables a one-pot electrocatalytic hydrogenation in alkaline media with high Faradaic Efficiency. The invention has been demonstrated for electrocatalytic hydrogenation of toluene to methylcyclohexane and further for electrocatalytic hydrogenation of benzyl alcohol to cyclohexanemethanol. However, the invention is not limited to these reactions.

[0145] The hydrogenation of the reactant in alkaline media has been achieved by employing an efficient catalyst in conjunction with a flow cell configured with a static mixer. In the case of the hydrogenation product MCH, it is known to be reversibly dehydrogenated, e.g., at least through known thermal dehydrogenation processes.

[0146] The proof-of-concept embodiment described herein involves generating an unstable liquidliquid reactant oil-in-water emulsion in situ at the catalytic surface of the mixer. An unstable emulsion is desirable as it aids phase separation of the electrocatalytically generated product. The static mixer improves mixing and dispersion of emulsions in the cathode compartment, so that significantly more reactants are in contact to the electrode surface which results in enhanced mass transport. Overall, generation of emulsion droplets at the catalytic surface of the cathode static mixer quickly andefficiently delivers reactants and removes product from the catalyst active sites whereby the reactants are replenished in a continuous matter due to the flow arrangement of the cell / process.

[0147] The electrocatalyst used in the preferred examples is a Ru-based electrocatalyst, preferably a Ru on black catalysts. In this example, the Ru-based electrocatalyst is applied to the static mixer through a dip-coating approach or an electrochemical deposition approach. Indeed, the inventors have found that at least for the examples described herein that the most effective catalyst for electrocatalytic hydrogenation of TOL to MCH with high Faradaic efficiency (high selectivity) and low cell potential (i.e. power consumption) is monometallic Ruthenium black (Ru black).

[0148] Cyclic voltammetry for 20 v / v% toluene (TOL) solution in 1 M KOH electrolyte, utilising Ru black coated stainless steel static mixer electrode indicate that the Ru black coated electrode displayed a distinct shoulder in the cyclic voltammetry (CV) curve (Figure 16). This observation suggests the formation and adsorption of reactive hydrogen radicals (Hads) at a larger potential range (i.e. 1 .5-2.0 V), allowing the surface to retain Hads in a larger potential range with less tendency to H2 gas formation. This characteristic is particularly advantageous for the electrochemical hydrogenation of TOL, as it facilitates the shift of the operational potential towards more negative values, thereby enhancing the rate of the electrochemical hydrogenation reaction. The CV experiments involve recording at the 3rdcycle in in 20 v / v% TOL in 1 M KOH in the electrochemical flow cell at ambient conditions and scan rate of 20 mV s-1. The cathode was Ru black coated on stainless steel static mixer, the anode was am uncoated stainless-steel tube with a diameter of 12 mm and these electrodes were separated by a porous ceramic tube. Overall, the process results in efficient reactant hydrogenation under suitable conditions, e.g., a constant applied current or a constant applied potential.

[0149] It is believed that the electrocatalytic hydrogenation of TOL in alkaline emulsion occurs through the adsorption of H on Ru domains via the electrochemical reduction of H2O (H2O + e" + Ru^ H-Ru + OH"). Then, the generated H atoms react with TOL also present on the Ru surface to form MCH (TOL-Ru + 6H-Ru — > MCH + Ru). Advantageously, there is no need to employ DSA as anode in alkaline medium. To improve the safety and efficiency of the cell, a porous ceramic tube was used to separate the anodic and cathodic compartments to prevent the mixing of the resulting O2 gas with the hydrogen species generated in the cathode. The hydrogenated product can easily be separated from the aqueous phase downstream due to the formation of unstable emulsion under the operating conditions.

[0150] The dynamic process within the cell results in remarkably efficient hydrogenation of TOL under alkaline conditions while minimising energy losses, resulting in notable and new types of electrocatalytic transformation. In this process, LOHC can be hydrogenated with H radicals generated electrochemically in-situ from a H-source (preferably H2O). This process requires low energy input for the formation of atomic hydrogen distinguishing it from existing TOL hydrogenation technologies. This includes avoiding addition of H2 gas as an external proton source, avoid the thermal barrier for splitting H2 molecules and overcoming mass transport limitation arising from H2 gas solubility. Furthermore,as mentioned above, generation of an unstable emulsion in-situ which aids downstream phase separation.

[0151] In addition, the ability to hydrogenate LOHCs, such as TOL into MCH, within an alkaline environment offers a practical solution to address long-term production cost concerns associated with corrosion of anode in low pH as well as employment of expensive proton exchange membranes (with negative impact to the environment). This aspect further enhances the viability and sustainability of the process with lower costs.

[0152] In the proof-of-concept examples described herein the hydrogenation of TOL in alkaline media occurs by employing a suitable catalyst in conjunction with the flow cell. An exemplary Ru-based electrocatalyst has been developed and effectively applied to the static mixer, for example, through a simple dip-coating approach (though electrodeposition could also be used), which results in efficient TOL hydrogenation under a constant applied current / potential. As explained above the catalyst must have balanced activity in that it must catalyse two different reactions: the hydrogen evolution reaction (HER) and the subsequent hydrogenation of the LOHC, in preference to hydrogenation gas formation.

[0153] It is apparent that the system is expandable beyond TOL and creates opportunities for hydrogenation of other compatible LOHCs.

[0154] Due to the relatively low operational potential and current requirements of the flow cell, it can easily be integrated with renewable energy sources like solar and wind power. This synergistic coupling would further enhance the system's environmental sustainability, ensuring a greener and more efficient hydrogen production process.

[0155] This technology can be also used in other applications including green hydrogen gas production through water electrolysis; iron ore electrolysis; metal electrowinning; water purification and disinfection; and material electrosynthesis.

[0156] The inventors believe that the work represents a significant milestone as it demonstrates the first successful electrocatalytic reactant hydrogenation in an aqueous alkaline environment using an in-situ water electrolysis approach within a continuous flow cell technology. This pioneering technology leverages the remarkable potential of water as a hydrogen source, resulting in the generation of oxygen as the sole by-product. The ground-breaking methodology showcased in this study not only emphasizes the efficiency and effectiveness of MCH production from TOL but also highlights its immense potential for seamless integration into commercial applications, particularly those related to LOHC-based hydrogen storage and transportation. By harnessing this approach, the industry can take advantage of enhanced processes that promote sustainability, while simultaneously facilitating the widespread adoption of hydrogen as a clean and renewable energy source.EmbodimentsEmbodiment 1 . A flow based electrocatalytic hydrogenation process comprising: contacting a pH neutral or pH alkaline flow of a liquid proton source and at least one liquid H-uptake reactant compound (R) which is immiscible with the liquid proton source with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell, thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the liquid proton source and at least one liquid H-uptake reactant compound (R), whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert under the same set of operating conditions, adsorbed reactive species on catalytic active sites of electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the proton source in the emulsion, and• H-uptake compound reactant species (Rads) generated from the reactant in the emulsion, chemically storing the electrochemically generated atomic hydrogen species in a hydrogenated product (R-H) of the H-uptake reactant compound, (R), through transfer of adsorbed reactive atomic hydrogen species (Hads) on a catalyst active site of the electrocatalyst to a reactive H-uptake compound reactant species, (Rads), adsorbed on an adjacent catalyst active site to form the hydrogenated product (R-H).Embodiment 2. The process of Embodiment 1 , whereby, in additional to catalysing formation of the above adsorbed species, the catalyst simultaneously (i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and (ii) promotion of reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H). Embodiment 3. The process of Embodiment 1 or Embodiment 2, wherein the proton source is water.Embodiment 4. The process of any one of Embodiments 1 to 3, wherein the H-uptake reactant compound (R) is any compound having unsaturated, conjugated and / or aromatic bonds which can be reduced by addition of hydrogen across the bonds.Embodiment 5. The process of any one of the preceding Embodiments, wherein the H- uptake reactant compound (R) comprises one or more of the following functional groups: alkene, alkyne, aldehyde, ketone, ester, carboxylic acid, and nitro, which can be reduced by addition of hydrogen across the bonds.Embodiment 6. The process of any one of the preceding Embodiments, wherein the H- uptake reactant compound (R) is selected from toluene (hydrogenation product is methylcyclohexane); benzene (hydrogenation product is cyclohexane); xylene (hydrogenation product is dimethylcyclohexane), naphthalene (hydrogenation product is decalin); dibenzyltoluene (hydrogenation product is perhydro-dibenzyltoluene); benzyl alcohol (hydrogenation product is cyclohexylmethanol); 2-phenyl-pyridine (hydrogenation product is 2-cyclohexyl-peperidine); 2- bezylpyridine (hydrogenation product is 2-(cyclohexyl-methyl)pyridine); N-ethylcarbazole (hydrogenation product is dodecahydro-n-ethylcarbazole).Embodiment 7. The process of any one of the preceding Embodiments, wherein the reactant (R) is toluene (hydrogenation product is methylcyclohexane) or benzyl alcohol (hydrogenation product is cyclohexylmethanol).Embodiment 8. The process of any one of the preceding Embodiments, in the form of an electrochemical hydrogen generation and storage process, wherein the liquid proton source is water, and the H-uptake reactant compound (R) forms a first part of a reversible (de)hydrogenation reactant / product couple, wherein a second part of the couple is a hydrogenated derivative (R-H) of the H-uptake reactant compound (R), wherein the process chemically stores the electrochemically generated atomic hydrogen species chemically in the hydrogenated product (R-H) of the reversible (de)hydrogenation reactant / product couple.Embodiment 9. The process of any one of the preceding Embodiments, wherein the adsorbed reactive atomic hydrogen species (Hads) and the reactive H-uptake compound reactant species, (Rads), are both simultaneously I concurrently generated in the cell’s cathode chamber. Embodiment 10. The process of any one of the preceding Embodiments, where the electrocatalyst selectively catalyses the generation of reactive atomic hydrogen species (Hads) and the reactive H-uptake compound reactant species, (Rads), in preference to a competing hydrogen gas (H2) formation reaction.Embodiment 11 . The process of any one of the preceding Embodiments, wherein the electrocatalyst is composed of a single (binary) electrocatalytic metal or material or a bimetallic (two metals) electrocatalytic material.Embodiment 12. The process of any one of the preceding Embodiments, wherein the electrocatalyst is composed of, or comprises, one or more metals selected from ruthenium, platinum, palladium, rhodium, iridium, or compound of one or more thereof, or noble or non-noble metals or metal salts, preferably ruthenium or a ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel.Embodiment 13. The process of any one of the preceding Embodiments, wherein the electrocatalyst is confined to surfaces of the static mixer.Embodiment 14. The process of any one of the preceding Embodiments, wherein the reactive atomic hydrogen species (Hads) is not sourced from an associated anodic system or from outside the continuous electrochemical flow cell.Embodiment 15. The process of any one of the preceding Embodiments, wherein the emulsion is an oil-in-water emulation or water-in-oil emulsion.Embodiment 16. The process of any one of the preceding Embodiments, wherein the pH of the catholyte is > 7, between pH 7 and 15, and may be selected from pH 7, 8, 9, 10, 11 , 12, 13, 14 or 15, preferably pH >14.Embodiment 17. The process of any one of the preceding Embodiments, wherein the catholyte comprises 0.1 M - 7 M [OH-], for example, wherein the [OH-] is from KOH or NaOH.Embodiment 18. The process of any one of the preceding Embodiments, wherein the static mixer is adapted to generate an emulsion in situ as electrolyte flows over elements of the static mixer, preferably wherein the static mixer is Kenics KMS, Sulzer SMV mixer, or an emulsion generating variant thereof.Embodiment 19. A flow based electrocatalytic chemical hydrogen generation and storage process, comprising: contacting water and liquid toluene reactant which is immiscible with the liquid proton source with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the water and the toluene reactant, wherein the toluene reactant forms a one part of a reversible (de)hydrogenation reactant / product couple, wherein another part of the couple is methylcyclohexane as a hydrogenated product; whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert, under the same set of operating conditions, adsorbed reactive species on catalytic active sites of an electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the water in the emulsion, and• toluene reactant species (Rads) generated from the toluene reactant compound (R) in the emulsion, while simultaneously• suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and• promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H), wherein the electrocatalyst is ruthenium or a ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel; and chemically storing the electrochemically generated atomic hydrogen species (Hads) in the methylcyclohexane product, by allowing transfer of adsorbed reactive atomic hydrogen species (Hads) on a catalyst active site of the electrocatalyst to the toluene reactive reactant species (Rads) adsorbed on an adjacent catalyst active site, thereby storing the electrochemically generated atomic hydrogen species chemically in the methylcyclohexane product.Embodiment 20. The process of Embodiment 19, whereby in additional to catalysing formation of the above adsorbed species, the catalyst simultaneously (i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and (ii) promotion of reaction of the adsorbed species to form methylcyclohexane.Embodiment 21 . The process of any one of the preceding Embodiments, wherein the proton source is water, and the H-uptake reactant compound, (R), is a liquid organic hydrogen carrier (LOHC) such as toluene (TOL), preferably in an amount of 20:80 v / v% TOL: 1 M KOH.Embodiment 22. The process of any one of the preceding Embodiments, involving hydrogenation of TOL to product MCH using Ru black, wherein the operating temperature is about 55 to about 85 °C, and the current density is about -3 to about -32 mA / cm-2, for an emulsioncomprising 20:80 v / v% toluene in 1 M KOH (v / v), and a flow rate equivalent to of about 500 to about 700 mL min-1 for a reaction volume of 2.5 mL.Embodiment 23. The process of Embodiment 22, wherein the Faradaic efficiency of hydrogenation of TOL to product MCH is > 70%, > 75%, > 80%, > 85%, > 90%, > 95%, or > 99%. Embodiment 24. The process of any one of the preceding Embodiments, involving hydrogenation of TOL to product MCH using Ru black, wherein the operating temperature is room temperature, and the current density is about -3 to about -5 mA I cm-2, preferably - 4 mA / cm-2, for an emulsion comprising 20:80 v / v% toluene in 1 M KOH (v / v), and a flow rate equivalent to of about 550 to about 650 mL min-1 , preferably 600 mL min-1 for a reaction volume of 2.5 mL.Embodiment 25. The process of Embodiment 24, wherein the Faradaic efficiency is > 90%, > 95%, or > 99%, most preferably 100%.Embodiment 26. A flow based electrocatalytic hydrogenation system comprising: an electrochemical flow cell having a cathodic chamber configured as part of a continuous electrochemical flow cell and provided with an electrocatalytically active static mixer cathode for forming in situ a catholyte which is a liquid-liquid phase emulsion comprising a liquid proton source and a liquid H-uptake reactant compound (R); wherein the static mixer cathode comprises an electrocatalyst that is suitable for, in situ and in concert, electroreductively generating under the same operating conditions: adsorbed reactive atomic hydrogen species (Hads) from electroreduction of the polar proton source in the emulsion onto catalyst active sites, and adsorbed reactive reactant compound (Rads) species from electroreduction of the nonpolar H-uptake reactant compound in the emulsion onto catalytic active sites of the electrocatalyst associated with the static mixer, while simultaneously(i) suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and(ii) promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).Embodiment 27. The flow based electrocatalytic hydrogenation system of Embodiment 26, wherein the electrocatalyst is a ruthenium electrocatalyst or ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel.Embodiment 28. The flow based electrocatalytic hydrogenation system of Embodiment 26 or Embodiment 27, further comprising downstream of the cell, a settling chamber for allowing the emulsion to phase separate.Embodiment 29. The flow based electrocatalytic hydrogenation system of any one of Embodiments 26 to 28, further comprising means for loading the hydrogenated product (R-H) for storage and / or transportation.Embodiment 30. Use of a flow based electrocatalytic hydrogenation system as defined in any one of Embodiments 26 to 29 in an energy storage application, particularly a grid energy storage application.Embodiment 31 . Use of a pH neutral or pH alkaline catholyte in the form of an emulsion comprising a liquid proton source and at least one liquid H-uptake compound, (R), which is immiscible with the liquid proton source in an electrocatalytic hydrogenation process in an electrochemical flow cell comprising an electrocatalytically active static mixer cathode that generates the emulsion in situ in the electrochemical cell.Embodiment 32. Use of Embodiment 31 , wherein the catholyte is used in combination with an electrocatalyst operated under a single set of conditions that, in situ and in concert, electroreductively generates under the same set of operating conditions: adsorbed reactive atomic hydrogen species (Hads) from electroreduction of a polar proton source in the emulsion onto catalyst active sites, and adsorbed reactive reactant compound (Rads) species from electroreduction of a nonpolar H- uptake reactant compound in the emulsion onto catalytic active sites of the electrocatalyst associated with the static mixer, while simultaneously the electrocatalyst(i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and(ii) promotes reaction of the adsorbed species together to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).Embodiment 33. Use of any one of Embodiments 30 to 32, wherein the electrocatalyst is a ruthenium electrocatalyst or ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel.EXAMPLES

[0157] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

[0158] Figure 6 illustrates an exemplary electrochemical flow cell 1 accordingly to one aspect of the invention. The flow cell 1 comprises cathode chamber the internal part of which is provided with a static mixer cathode 101 and anodic chamber defined by a stainless-steel tubular chamber 103 surrounds the cathodic chamber with a porous ceramic separator 105 separates the respective chambers. In this example, the inner anodic chamber walls serve as the anode surface. Each of the cathodic and anodic chambers has an inlet and outlet, through which electrolyte solution flows in and out of the chambers. The direction of electrolyte solution flowing into the cathodic inlet is designed Breactin Figure 6 while direction of flow out of the cathode outlet is designated Bprod. Likewise, the direction of flow into the anode chamber inlet is designated is designed Ainin Figure 6 and direction of flow out of the cathode outlet is designated Aout. Figure 6 also shows a blown-up schematic view 2 of the surface of the static mixer cathode 101 which is coated with a Ru black catalyst 107. The electrolyte in this schematic is in the form of an oil in water emulsion designed E. The LOHC droplets are show in the body of water which is the main phase of the electrolyte solution in this example. Further blown-up schematic 3 shows the reactions occurring at the catalyst surface. The water phase of the electrolyte is designed 109 and the LOHC oil phase droplet is designed 110. Concurrently, water and LOHC are reduced at the catalyst surface forming Hads* and Rads* at active sites. Thereactive Hads* remains bound on the catalyst surface long for it to be picked up by a nearby Rads*, thus before it can associate with another Hads* which would result in the formation of gaseous H2. The resultant hydrogenated product R-H is then released from the surface and taken up into the electrolyte droplets of LOHC.Example 1 - Electrocatalytic Hydrogenation of Toluene to Methylcvclohexane

[0159] In a first example, the cell and process of the invention were used to electrocatalytically hydrogenated toluene to methylcyclohexane using alkaline water as proton source. The inventors believe that the most effective catalyst for the electrocatalytic hydrogenation of TOL to MCH with high Faradaic efficiency and low cell potential (i.e. power consumption) is monometallic Ruthenium black (Ru black).Example 1 - Materials and Methods, Operating Conditions

[0160] Cyclic voltammetry (CV) and toluene electrolysis experiments were performed in the CSIRO electrochemical flow cell using a Ru coated stainless steel static mixer electrode with a geometric surface area of 25.3 cm2as the cathode and a 12 mm diameter stainless steel tube as an anode. The catalyst was deposited on the cathode by drop casting. These two electrodes were separated by a porous ceramic tube with pore size of 2 pm. The anolyte was 100 mL aqueous 1 M KOH without any toluene and catholyte was 100 mL aqueous 80 v / v% 1 M KOH with 20 v / v% toluene. These solutions were circulated through the cell continuously during an experiment and the catholyte circuit included a small, stirred reservoir to provide the flow cell with a partially dispersed feed of TOL in aqueous KOH. Aliquots (50 pL) of the organic phase were sampled during and after electrolysis to determine the presence of TOL, hydrogenated products, and also to track the progress of hydrogenation by1H NMR. Aliquots (10 pL) of the organic phase was dissolved in 0.9 mL of dichloromethane (CH2CI2) for GC-MS analysis to identify any partially hydrogenated products or organic by-products. Aliquots (30 pL) of aqueous phase was collected and dried at 105 °C on a polypropylene watch glass for ED-XRF analysis to determine whether metal corrosion, catalyst dissolution, or decomposition occurred during electrolysis.Example 1 - Cell Operating Conditions

[0161] Toluene electrolysis experiments were conducted using CSIRO electrochemical flow cell at applied current density of 24 mA / cm2for 4 hours at operating temperature of 80 °C and ambient pressure. Catholyte and anolyte were pumped to the electrochemical flow cell (reactor volume of 2.5 mL) with flow rate of 600 mL min-1.

[0162] The inventors found that the most effective catalyst for electrocatalytic hydrogenation of TOL to MCH with high Faradaic efficiency and low cell potential (i.e. power consumption) is monometallic Ruthenium black (Ru black).Example 1 - Results & Discussion

[0163] 1H NMR spectra of the products obtained from TOL electrolysis in 1 M KOH at 0.6 A for 4 hours at 80 °C and ambient pressure confirmed the formation of MCH by visible MCH peaks between ~0.8 - 1 .8 ppm. The Faradaic efficiency of TOL electrolysis was 97% with cell potential of 1 .65 V and low power consumption of 0.004 kWh.

[0164] GC-MS spectra confirmed the formation of fully hydrogenated products as the only product of electrolysis. The durability of the Ru black dip-coated stainless steel static mixer electrodes and the corrosion rate of the stainless-steel anode were characterised using XRF analyses of the aqueous solution. No sign of Ru was detected in these analyses after 24 h of continuous electrolysis. Trace amount Fe and Cr are detected suggesting a low rate of corrosion of the stainless steel in 1 M KOH, which is expected.

[0165] ED-XRF spectra showed no metal dissolution in KOH solution over electrolysis confirming the durability of catalyst and electrodes, demonstrating no corrosion issues comparable to those in acidic solutions.

[0166] The results indicate that this process requires low energy input for the formation of atomic hydrogen distinguishing it from existing TOL hydrogenation technologies. This includes avoiding addition of H2 gas as an external proton source, avoid the thermal barrier for splitting H2 molecules and overcoming mass transport limitation arising from H2 gas solubility.Effect of Applied Current Density

[0167] The effect of applied current on TOL hydrogenation in the electrochemical flow cell was investigated using a 20 v / v% TOL solution in 1 M KOH at ambient conditions. Notably, the Ru black coated electrode displayed a distinct capacitive current with broader shoulder. This observation suggests the formation and adsorption of reactive hydrogen radicals (Had) at a larger potential range (i.e. 1 .5-2.0 V), allowing the surface to retain Had in larger current range with less tendency to H2 gas formation. This characteristic is particularly advantageous for the electrochemical hydrogenation of TOL, as it facilitates the shift of the operational current / potential towards more negative values, thereby enhancing the faradaic efficiency of the electrochemical hydrogenation reaction at higher operating currents.

[0168] Four currents were selected from the broad shoulder region in the corresponding CV plot. The lower current density values (i.e. -4 mA / cm2to -12 mA / cm2) corresponds to the potentials that allows adsorption of Hads on the cathode. Corresponding potentials at these lower currents ranged from -1 .56 V to -1 .72 V. In contrast, the larger current density of -20 mA / cm2required more negative potentials and thus favour the generation of H2 gas over hydrogen radical formation (-1 .89 V).1H NMR spectra (Figure 7) of the products from TOL electrolysis in 1 M KOH solution at four distinct applied currents after 4 h show peaks for MCH between - 0.8 to 1 .8 ppm. A strong sharp peak observed in both spectra at 1 .56 ppm records the presence of small amounts of water and reflects the difficulty in sampling the organic phase. This also indicates well dispersed TOL droplets into aqueous phase which is reflective of improved mass transport using static mixer electrodes in the electrochemical flow cell. See Figure 7 which illustrates1H NMR spectra (CDCI3) of 20 v / v% TOL in 1 M KOH after 4 h ofelectrolysis at four different applied current densities (-4, -8, -12 and -20 mA / cm2) in the electrochemical flow cell at ambient conditions. In these tests, the cathode was a Ru black coated stainless steel static mixer, the anode was a stainless-steel tube with a diameter of 12 mm and the electrodes were separated by a porous ceramic tube. Table 2 summarises experimental parameters for electrocatalytic hydrogenation of 20 v / v% TOL in 1 M KOH solution at the four different applied currents and estimated Faradaic efficiencies based on the1H NMR spectra of the product. As expected, the Faradaic efficiency decreases with an increase in the applied current. The highest conversion of approximately 100% was achieved at the lowest applied current density of -4 mA / cm2, which closely corresponds to the onset potential for water reduction to form reactive hydrogen species. Increasing the applied current from -4 mA / cm2to -20 mA / cm2promotes the formation of H2 gas over the desired product, MCH, thus reducing the overall hydrogenation yield of TOL despite the faster reaction rate and higher hydrogenation yield at higher currents. However, Faradaic efficiencies at current of -8 mA / cm2and -12 mA / cm2was 89% and 81% respectively. A further rise in the applied current (-20 mA / cm2) resulted in a reduction of Faradaic efficiency to 58%. This led to the generation of more H2 bubbles, which was noted within the system.

[0169] The results show that the applied current and voltage impact the FE and yield of the reaction, but can be tuned to optimise any given process, whereby tuning involves avoiding conditions that favour the competing H2 production reactions. The inventors propose that conditions close to the onset potential for water reduction to form reactive hydrogen species are preferred.Table 2. Summary of experimental parameters for TOL electrolysis at four different applied current in the electrochemical flow cell at ambient conditions (room temperature and pressure). The hydrogenation convert Osion figures quoted are based on the1H NMR data.t This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.Effect of Electrolysis Time

[0170] The effect of electrolysis time on TOL hydrogenation in the electrochemical flow cell at ambient conditions was investigated using 20 v / v% TOL in 1 M KOH at an applied current density of -4 mA / cm2. The hydrogenation was performed for 24 h, and samples were collected for analysis before and during electrolysis. Figure 8 shows the1H NMR spectra for the products obtained from the electrolyses of the 20 v / v% TOL in 1 M KOH solution at applied current density of -4 mA / cm2. No MCH was observed at the start (blue trace), but relevant MCH peaks emerge between -0.8-1.8 ppm as the experiment proceeds. Table 3 summarises the experimental parameters for the electrocatalytic hydrogenation of20 v / v% TOL in 1 M KOH solution at an applied current of -4 mA / cm2. Samples of organic phase were recovered before starting the experiment and at 2, 4 and 24 h.Table 3. Summary of experimental parameters TOL electrolysis performed in the electrochemical flow cell over 24 h at ambient conditions. The hydrogenation conversion figures quoted are based on the1H NMR data.t This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.

[0171] The durability of the Ru black dip-coated stainless steel static mixer electrodes and the corrosion rate of the stainless-steel anode were characterised using XRF analyses of the aqueous solution. No sign of Ru was detected in these analyses after 24 h of continuous electrolysis. Trace amount Fe and Cr are detected suggesting a low rate of corrosion of the stainless steel in 1 M KOH, which is expected.

[0172] Notably, no partially hydrogenated products were detected after 24 h of electrolysis, confirming the stability of the fully hydrogenated products throughout the entire electrolysis.

[0173] To confirm the hydrogenation yields of TOL in the electrochemical flow cell and definitively identify the hydrogenation products, GC-MS analyses were also conducted on the sample collected after 24 h of electrolysis. The spectra recorded is presented in Figure 9. The results from the GC-MS analysis confirm that the main product is MCH, the fully hydrogenated product. Notably, no partially hydrogenated products were detected after 24 h of electrolysis, confirming the stability of the fully hydrogenated products throughout the entire electrolysis.Effect of Flow Rate

[0174] The effect of flow rate on TOL hydrogenation in the electrochemical flow cell was studied using 20 v / v% TOL in 1 M KOH and an applied current density of -4 mA / cm2at ambient conditions. The flow rates of the anolyte and catholyte in the electrochemical flow cell were gradually varied from 200 mL min-1to 800 mL min-1and the impact of this variation on the TOL hydrogenation rate was studied. Figure 10 shows the1H NMR spectra of the products recovered after 4 h. The peaks for MCH are visible between -0.8-1 .8 ppm. Table 4 summarises the experimental parameters for the electrocatalytic hydrogenation of 20 v / v% TOL in 1 M KOH at different flow rates varying from 200 to 800 mL min-1. The Faradaic efficiencies were estimated from the1H NMR spectra of the products. Increasing the flow rate enhances mixing of TOL and aqueous phases which reduces the droplet size in the liquid dispersion. Furthermore, it improves the mass transfer by thinning diffusion layers and hence, increases reaction rates. Therefore, increasing the flow rate generally increases the TOL hydrogenation yield. Most importantly, in the conditions used here the Faradaic efficiency was 100%for all three lower liquid flow rates: 200, 400 and 600 mL min-1. At 800 mL min-1the Faradaic efficiency decreases to 85%, possibly because the contact time between Hads and TOL becomes shorter than is required for complete reaction.Table 4. Summary of experimental parameters for TOL electrolysis performed at various liquid flow rates in the flow cell. The hydrogenation conversion figures quoted are based on the1H NMR data.This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.Effect of Operating Temperature

[0175] The effect of operating temperature on the hydrogenation of toluene (TOL) in an electrochemical flow cell was investigated. Emulsion in catholyte comprised 20 v / v% TOL in 80 v / v% 1 M KOH solution at varied applied currents. The selection of the applied current density was based on the distinct features in the cyclic voltammetry (CV) plots obtained at different temperatures (Figure 11).

[0176] The investigation confirmed that increasing temperature has a significant impact on the hydrogenation yield. Desirably, increasing the temperature led to a slight reduction in the onset potential while increasing the current density. This, in turn, shifted the operational current to higher values. In simple terms, raising the temperature lowered the onset potential, which facilitated the production of a higher quantity of hydrogenated product at a higher operational current (reaction rate). Consequently, this reduction in operational time allows for the conversion of TOL into its fully hydrogenated product (MCH), more efficiently. Figure 12 shows the1H NMR spectra of the products recovered after 4 h. The peaks for MCH are visible between -0.8-1 .8 ppm.

[0177] In the experiment conducted at 80°C with an applied current density of -24 mA / cm2, an impressively high Faradaic efficiency exceeding 96% (±5%) was achieved. This represents the highest Faradaic efficiency recorded for the maximum applied current in the study. Moreover, at the same temperature of 80°C, the Faradaic efficiency was more than 70% when using an applied current density of -40 mA / cm2. Figure 13 represents1HNMR spectra at 80 °C at applied current density of - 24 mA / cm2and -40 mA / cm2.

[0178] At higher temperatures, more H radicals are generated. However, at higher current densities, the H radicals combine and H2 gas bubbles are observed, which is not desirable for the present goal of hydrogenation with high Faradaic efficiency. However, at optimal temperature and applied current density, although more H radicals are generated, it is believed that further TOL is adsorbed on the catalysts surface, counterbalancing the adsorbed H radicals and overall resulting higher hydrogenation yield and a reduction of the gas formation. Also, at higher temperature, catalytic activity of Ru for hydrogenation reaction is improved as well as mass transport. This phenomenon could beattributed to the expanding broader shoulder observed in the respective CVs. However, an optimal temperature value can be achieved at a particular temperature using an applied current density where the adsorbed hydrogen on the surface is effectively counterbalanced by TOL near the catalyst surface, resulting in the most efficient hydrogenation of TOL with minimal energy dissipation. In addition, the operating temperature significantly enhance the catalyst's activity and mass transfer which favours the hydrogenation process. In the studies herein, the process at 60°C with an applied current density of -24 mA / cm2with Faradaic efficiency exceeding 96% used less energy than the process at 80°C with an applied current density of -40 mA / cm2with Faradaic efficiency of around 73%. Therefore, for any system, a similar study can be used to determine optimised conditions for any desired outcome.

[0179] Table 5 summarises the experimental parameters for the electrocatalytic hydrogenation of 20 v / v% TOL in 1 M KOH at different operating temperature varying from 20 to 80 °C and varied applied current.Table 5. Summary of experimental parameters for TOL electrolysis at different temperatures in the electrochemical flow cell at ambient conditions. The hydrogenation conversion figures quoted are based on the1H NMR data.t This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.Effect of Operating Pressure

[0180] The process should be more effective at higher operating pressure and should exhibit higher a hydrogenation rate. To explain how operating pressure would impact hydrogenation yields in the flow cell, the HER mechanisms must be considered. Hydrogen production from electrochemical water splitting involves two different reaction pathways including the reduction of protons in the solution via the Volmer step (first step) and generation of hydrogen molecules through electrochemical (the Heyrovsky step) or chemical (Tafel step) route (alternative second steps) (Figure 14). In the LOHC processes described herein an alkaline electrolyte (1 M KOH) is the aqueous phase. As explained above, the first step of HER is the Volmer reaction, wherein an electron (e-) transfers to the electrode reacts with the H2O on a void active site of the catalyst to produce the adsorbed hydrogen atoms (Hads) (1 ).t-W - e" - OH’ + H,;(Volmer Step) (1 )

[0181] Subsequently, the second step is associated with desorption and accumulation of the Hads for H2 formation which can proceed either via the Heyrovsky step (2) or the Tafel step (3). (Heyrovsky Step) (2)

[0182] The mechanism of hydrogenation of TOL is also involved in this step simultaneously, so a typical second step reaction of water splitting is considered as a competing reaction:

[0183] According to Le Chatelier’s Principle, an increase in pressure will cause the equilibrium to shift toward the side with fewer moles of gas. The suppression of competing reactions of hydrogen generation (2) and (3) should be achieved by introducing hydrogen gas or increasing pressure, thereby ensuring a higher Faradaic efficiency in the hydrogenation reaction of TOL (4) and guaranteeing a higher conversion rate of TOL to MCH. Thus, the inventors believe that at higher operating pressure, the competing reaction of H2 gas production will be suppressed which results in preferential reaction of adsorbed hydrogen radicals with adsorbed LOHC on the catalyst’s surface leading to favourable product formation.

[0184] In another example, the cell and process of the invention were used to electrocatalytically hydrogenate benzyl alcohol (BA) to the fully hydrogenated product cyclohexanemethanol (CHM) using alkaline water as proton source. This product is not as easily dehydrogenated to release hydrogen but it demonstrates the chemical synthesis potential of the process and system of the invention.Example 2 - Materials and Methods, Operating Conditions

[0185] Cyclic voltammograms (3rdcycle) were recorded in 20 v / v% BA in 1 .5 M mixture of K2HPO4 and KH2PO4 (pH ~7) in the electrochemical flow cell at ambient conditions and scan rate of 20 mV s-1. The cathode was Ru black coated on stainless steel static mixer, the anode was a stainless-steel tube with a diameter of 12 mm and these electrodes were separated by a porous ceramic tube. The ideal electrolysis current density (Figure 16A) corresponded to a potential slightly negative that of the onset potential for water reduction to ensure the preferential creation of hydrogen radicals. At this current it is important to note that both hydrogen radical formation and BA hydrogenation is expected, in preference to H2 gas formation, which is expected to occur at more negative potentials associated with more negative current densities in accordance with the CV study.

[0186] The experiments were performed in the electrochemical flow cell using Ru-coated stainless steel static mixer electrode with a geometric surface area of 25.3 cm2as the cathode and a 12 mm diameter stainless steel tube as an anode. The catalyst was deposited on the cathode by drop casting. These two electrodes were separated by a porous ceramic tube with pore size of 2 pm. The anolytewas 100 mL of aqueous 1 M KOH (pH ~14) or 1 .5 M mixture of K2HPO4 and KH2PO4 (pH -7) without any benzyl alcohol and catholyte was 100 mL of aqueous 80 v / v% 1 M KOH or 1.5 M mixture of K2HPO4 and KH2P with 20 v / v% benzyl alcohol. These solutions were circulated through the cell continuously during the experiment and the catholyte circuit included a small, stirred reservoir to provide the flow cell with a partially dispersed feed of BA in aqueous phase. Aliquots (50 pL) of the organic phase were sampled during and after electrolysis and dissolved in 1 mL d6-acetone to determine the presence of BA, hydrogenated products, and also track the progress of hydrogenation by1H NMR.Example 2 - Cell Operating Conditions

[0187] Benzyl alcohol electrolysis experiments were conducted using the electrochemical flow cell for 4 hours at ambient conditions and applied current density of 4 mA / cm2in pH 14 and 1 mA / cm2in pH 7 for comparison. Catholyte and anolyte were pumped to the electrochemical flow cell (reactor volume of 2.5 mL) with flow rate of 600 mL min-1.Example 2- Results & Discussion

[0188] 1H NMR spectra of the products obtained from BA electrolysis in 1 M KOH (pH ~14) at 4 mA / cm2for 4 hours at ambient conditions confirmed the formation of CHM by visible CHM peaks between -0.8-1.8 ppm. The Faradaic efficiency of BA electrolysis under these conditions was 70% with cell potential of 1 .5 V and low power consumption of 0.0006 kWh (Figure 17).1H NMR spectra of the products obtained from BA electrolysis in 1 .5 M mixture of K2HPO4 and KH2PO4 (pH -7) at 1 mA / cm2for 4 hours at ambient conditions confirmed the formation of CHM by visible CHM peaks between -0.8-1 .8 ppm. The Faradaic efficiency of BA electrolysis was 58% with cell potential of 1 .4 V and low power consumption of 0.0001 kWh (Figure 15 (top)).

[0189] Figure 15 (bottom) shows the1H NMR spectra recorded in d-chloroform of the products from the BA electrolysis at an applied current density of -4 mA / cm2for 4 h in 1 .5 M electrolyte mixture of K2HPO4 and KH2PO4 (pH -7) in the electrochemical flow cell. For the hydrogenated CHM product, a broad multiplet in the range 0.85-1 .85 ppm is observed due to the -CH2 protons of the cyclohexane ring which undergo spin-spin splitting and a doublet is observed at 3.46 ppm which is due to the -CH2 protons in the methoxy moiety and split by the adjacent CH group protons in the CHM cyclohexane ring. The hydroxyl proton in CHM is observed as a singlet at 4.8 ppm, which is merged with the BA peaks.

[0190] Table 6 summarises the experimental parameters for the electrocatalytic hydrogenation of 20 v / v% BA in 1 ,5M (K2HPO4 + KH2PO4) ((pH -7) at two selected current densities of 1 mA / cm2and 4 mA / cm2. The Faradaic efficiencies were estimated from the1H NMR spectra of the products.Table 6. Summary of experimental parameters for BA electrolysis performed in 20 v / v% BA in 1.5 M mixture of K2HPO4 and KH2PO4 (pH -7) in the CSIRO electrochemical flow cell at ambient conditions. The hydrogenation conversion figures quoted are based on the1H NMR data.t This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.

[0191] It is evident that selection of conditions associated with a slightly less negative voltage to that of the onset potential for water reduction results in promotion I preferential creation of hydrogen radicals over molecular hydrogen formation. At the more negative current density (-4 mA / cm2), the Faradaic efficiency was reduced to 37%, which was expected give the resulting more negative cell voltage would support hydrogen gas formation. At a neutral pH, while product is formed, it is formed at relatively poor Faradaic efficiency and low yield compared to the alkaline electrolyte conditions described below.Hydrogenation of Benzyl alcohol in pH ~14 aqueous electrolyte

[0192] Figure 16B shows the recorded CVs for 20 v / v% BA in 1 M KOH electrolyte (pH ~14) in the electrochemical flow cell. Figure 17 shows the1H NMR spectra recorded in d-chloroform of the products from the BA electrolysis at an applied current density of -4 mA / cm2for 4 h in 1 M KOH electrolyte (pH ~14) in the electrochemical flow cell.

[0193] Table 7 summarises the experimental parameters for the electrocatalytic hydrogenation of 20 v / v% BA in 1 M KOH at preferred applied current density of -4 mA / cm2(which result in a cell voltage which is slightly less negative voltage to that of the onset potential for water reduction and results in promotion of creation of hydrogen radicals). The Faradaic efficiency was estimated from the1H NMR spectra of the products.Table 7. Summary of experimental parameters for BA electrolysis performed in 20 v / v% BA in 1 M KOH (pH ~14) in the CSIRO electrochemical flow cell at ambient conditions. The hydrogenation conversion figures quoted are based on the1H NMR data.t This value is an estimated Faradaic efficiency and the errors associated with integration of the1H NMR data are expected to be about ± 5%.

[0194] Comparing the pH 7 and pH 14 systems under the same applied current density conditions shows that much better results for generation of the hydrogenation product (Faradaic efficiency is 70%) and the cell voltage is -1 .5 V versus a Faradaic efficiency of 37% at a cell voltage of -2.2 V.Example 4 - Determination of Operating Parameters.

[0195] The preferred operating parameters will be device, process and reaction specific. However, generally, operating parameters can be determined as follows for any particular cell and selected catalyst. Typically, cyclic voltammetry (CV) is recorded on electrolysis of the selected reactant (e.g. a LOHC candidate) and liquid proton source (e.g., aqueous phases such as TOL in KOH) in the electrochemical flow cell using the catalytic coated cathode in the cathode compartment and anode. From the capacitive region in CV spectra, an applied current (or voltage) is selected in the region / area where promotion of the formation and adsorption of reactive hydrogen radicals (Hads) takes place,thereby providing conditions allowing with less tendency to H2 gas formation. The conditions should be selected where that goal is obtained by the particular catalyst surface where it would retain Hads in largest current density range. This is typically under conditions which result in a cell voltage which is a slightly less negative voltage to the onset potential for water reduction and which instead of hydrogen gas formation, promotes the creation of hydrogen radicals which are adsorbed onto the catalyst surface. Where the catalyst is also useful for hydrogenation of the reactant at the same operating conditions, the desired product will be formed in desirable amounts, with a desirable level of Faradaic efficiency.

[0196] Other operating conditions including flow rate, temperature and pressure can be selected by a number of experimental works, noting the following general parameters. Increasing the flow rate enhances mixing of organic and aqueous phases which reduces the droplet size in the liquid dispersion and favours the desired reaction. However, too high a flow rate can lead to turbulent conditions and may disfavour the reaction of interest. Optimising the flow rate however generally improves the mass transfer by thinning diffusion layers and hence, increases reaction rates. As expected in the tested system, increasing the flow rate generally increases the TOL hydrogenation yield. However, at very high flow rates the hydrogenation yield drops possibly because the contact time between Hads and organic phase becomes shorter than is required for complete reaction.Example 3 - Other Operating Conditions for TOL to MCH

[0197] Electrocatalytic hydrogenation of a Liquid Organic Hydrogen Carriers (LOHCs) in CSIRO’s electrochemical flow cell begins with the in-situ generation of an unstable LOHC-in-water emulsion as the two liquid components flow past the static mixer (Figure 6B). Dispersion and mixing of component stream and generation of the emulsion within the cell ensure both liquid components contact the static mixer electrode simultaneously and close to each other. Operation conditions are used that cause water to be reduced on the catalytic static mixer surface to generate reactive hydrogen radical species, Hads which then react with the LOHC to hydrogenate it. The hydrogenated products are separated from the aqueous phase in a quiescent separator tank. The kinetics of the process requires careful control because the most likely side reaction is the self-reaction of two hydrogen radicals to form gaseous hydrogen. If this reaction is preferred the efficiency of the process will be negatively affected, and product yield and Faradaic efficiency will be undesirably low. Examples of how the process conditions can be optimised for any given reaction I system are described above.

[0198] Forming an emulsion requires energy because more interface is created between the phases and the surface free energy increases as a result. This energy is supplied by mixing and the resultant droplet size distribution is a function of the mixing intensity. Mixing in the electrochemical flow cell occurs as the fluid flows past the elements of the static mixer and the efficiency with which the emulsion is created depends very much on the shape and orientation of these elements, as well as the length of the mixer.

[0199] To investigate the effect of static mixer design and flow in emulsion formation, oil and water were separately pumped to the see-through cell at various pump speeds to obtain the desired oil water ratios (i.e. 1 :1 , 1 :2 and 1 :5). The oikwater ratio was adjusted by varying the flow rate of water whilekeeping the oil flow rate fixed at 100 mL min-1(Table 8). The emulsion formation was captured at three regions along the static mixer length (mixer element length is 110 mm), namely, entry, middle and exit regions. The results show that the oil droplets get smaller and are better mixed as they traverse the length of the static mixer (Figure 19). By increasing the water flow rate and consequently increasing the water in its ratio in the oil-water mixture, the oil droplets get smaller, and mixing is enhanced using the current static mixer design. This will help more oil droplets access the catalytic coated static mixer in hydrogenation experiments, producing higher mass transport and higher yields.Table 8. Oil and water flow rates used to achieve various oikwater ratiosOil: water ratio Oil flow rate (mL min1) Water flow rate (mL min1)1:1 100 1001:2 100 2001:5 100 500Example 4 - Catalyst Selection & Development

[0200] As explained above, the selection of a suitable catalyst is not trivial. Catalysts for water splitting and OER reactions have difference performance requirements to those required for the present invention and cannot be immediately transferred from conventional acidic process to the present process. The catalyst used need to be bifunctional, that is, capable of accelerating the rate of production of reactive hydrogen radicals (Hads), catalysing the hydrogenation part of the process, all the while simultaneously minimising the rate of H2 gas formation while also providing a high number of active sites for LOHC adsorption and hydrogenation. The preferred present catalysts, at least for the LOHC hydrogenation reactions exemplified herein, are Ru or Ru based. Ru cocatalysts may also be included with Ru for LOHC hydrogenation. The cocatalysts may be selected from d group metals having similar hydrogen formation and adsorption behaviour to that desired herein. Suitable other metals include one or more of Pt, Pt, Ni, Co and Ir, and salts thereof. Non-noble metals are preferred as they are more economical. One oftentimes useful guide to potential catalyst performance for HER is the “volcano” plot, where the exchange current density (joo) (proportional to reaction rate) for a particular metal is plotted against the metal-hydrogen (M-H) bond strength (EM-H), as shown in Figure 18a. The traditional volcano plot of Figure 18a is relevant for HER in acidic media, though recently “volcano” plots for HER in alkaline media have been developed using computational methods rather than experimental data (Quaino et al. 2014, Beilstein Journal of Nanotechnology 5, 846-854. doi:10.3762 / bjnano.5.96; Mahmood et al. 2018, Advanced Science 5, doi:10.1002 / advs.201700464); both of which are hereby incorporated by reference). The Volcano plot gives no information on the selectivity for the hydrogenation reaction, nor ability to supress H2 gas formation under the same operating conditions and where such reactions occur on the same catalyst surface. The inventors have identified that HER catalyst should in the first instance display a moderate M-H bond strength to allow for atomic hydrogen to be adsorbed on the catalyst’s surface but not too strongly for it to react and be released from the surface. Similar requirements apply to co-catalysts for Ru-based materials. Nickel (Ni) and Platinum (Pt) exhibiting high exchange current densities corresponding to appropriate hydrogen adsorption energies (Figure 18b).Flow & Emulsion Studies

[0201] To investigate the effect of static mixer design and flow in emulsion formation, oil and water were separately pumped to a see-through cell at various pump speeds to obtain the desired oikwater ratios (i.e. 1 :1 , 1 :2 and 1 :5). The oikwater ratio was adjusted by varying the flow rate of water while keeping the oil flow rate fixed at 100 mL min-1(Table 1). The emulsion formation was captured at three regions along the static mixer length, namely, entry, middle and exit regions. The results show that the oil droplets get smaller and are better mixed as they traverse the length of the static mixer. By increasing the water flow rate and consequently increasing its ratio in the oil-water mixture, the oil droplets get smaller, and mixing is enhanced using the current static mixer design. This will help more oil droplets access the catalytic coated static mixer in hydrogenation experiments, producing higher mass transport and higher yields.Table 9. Oil and water flow rates used to achieve various oikwater ratiosOil: water ratio Oil flow rate (mL min1) Water flow rate (mL min1)1:1 100 1001:2 100 2001:5 100 500

Claims

Claims1. A flow based electrocatalytic hydrogenation process comprising: contacting a pH neutral or pH alkaline flow of a liquid proton source and at least one liquid H-uptake reactant compound (R) which is immiscible with the liquid proton source with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell, thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the liquid proton source and at least one liquid H-uptake reactant compound (R), whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert under the same set of operating conditions, adsorbed reactive species on catalytic active sites of electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the proton source in the emulsion, and• H-uptake compound reactant species (Rads) generated from the reactant in the emulsion, chemically storing the electrochemically generated atomic hydrogen species in a hydrogenated product (R-H) of the H-uptake reactant compound, (R), through transfer of adsorbed reactive atomic hydrogen species (Hads) on a catalyst active site of the electrocatalyst to a reactive H-uptake compound reactant species, (Rads), adsorbed on an adjacent catalyst active site to form the hydrogenated product (R-H).

2. The process of claim 1 , whereby, in additional to catalysing formation of the above adsorbed species, the catalyst simultaneously (i) suppresses recombination of the reactive atomic hydrogen species to form H2 gas, and (ii) promotion of reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).

3. The process of claim 1 or claim 2, wherein the proton source is water.

4. The process of any one of claims 1 to 3, wherein the H-uptake reactant compound (R) is any compound having unsaturated, conjugated and / or aromatic bonds which can be reduced by addition of hydrogen across the bonds.

5. The process of any one of the preceding claims, wherein the H-uptake reactant compound (R) comprises one or more of the following functional groups: alkene, alkyne, aldehyde, ketone, ester, carboxylic acid, and nitro, which can be reduced by addition of hydrogen across the bonds.

6. The process of any one of the preceding claims, wherein the H-uptake reactant compound (R) is selected from toluene (hydrogenation product is methylcyclohexane); benzene (hydrogenation product is cyclohexane); xylene (hydrogenation product is dimethylcyclohexane), naphthalene (hydrogenation product is decalin); dibenzyltoluene (hydrogenation product is perhydrodibenzyltoluene); benzyl alcohol (hydrogenation product is cyclohexylmethanol); 2-phenyl-pyridine (hydrogenation product is 2-cyclohexyl-peperidine); 2-bezylpyridine (hydrogenation product is 2-(cyclohexyl-methyl)pyridine) ; N-ethylcarbazole (hydrogenation product is dodecahydro-n- ethylcarbazole).

7. The process of any one of the preceding claims, wherein the reactant (R) is toluene (hydrogenation product is methylcyclohexane) or benzyl alcohol (hydrogenation product is cyclohexylmethanol).

8. The process of any one of the preceding claims, in the form of an electrochemical hydrogen generation and storage process, wherein the liquid proton source is water, and the H-uptake reactant compound (R) forms a first part of a reversible (de)hydrogenation reactant / product couple, wherein a second part of the couple is a hydrogenated derivative (R-H) of the H-uptake reactant compound (R), wherein the process chemically stores the electrochemically generated atomic hydrogen species chemically in the hydrogenated product (R-H) of the reversible (de)hydrogenation reactant / product couple.

9. The process of any one of the preceding claims, wherein the adsorbed reactive atomic hydrogen species (Hads) and the reactive H-uptake compound reactant species, (Rads), are both simultaneously I concurrently generated in the cell’s cathode chamber.

10. The process of any one of the preceding claims, where the electrocatalyst selectively catalyses the generation of reactive atomic hydrogen species (Hads) and the reactive H-uptake compound reactant species, (Rads), in preference to a competing hydrogen gas (H2) formation reaction.

11. The process of any one of the preceding claims, wherein the electrocatalyst is composed of a single (binary) electrocatalytic metal or material or a bimetallic (two metals) electrocatalytic material.

12. The process of any one of the preceding claims, wherein the electrocatalyst is composed of, or comprises, one or more metals selected from ruthenium, platinum, palladium, rhodium, iridium, or compound of one or more thereof, or noble or non-noble metals or metal salts, preferably ruthenium or a ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel.

13. The process of any one of the preceding claims, wherein the electrocatalyst is confined to surfaces of the static mixer.

14. The process of any one of the preceding claims, wherein the reactive atomic hydrogen species (HadS) is not sourced from an associated anodic system or from outside the continuous electrochemical flow cell.

15. The process of any one of the preceding claims, wherein the emulsion is an oil-in-water emulation or water-in-oil emulsion.

16. The process of any one of the preceding claims, wherein the catholyte comprises 0.1 M - 7 M [OH ], for example, wherein the [OH ] is from KOH or NaOH.

17. The process of any one of the preceding claims, wherein the static mixer is adapted to generate an emulsion in situ as electrolyte flows over elements of the static mixer, preferably wherein the static mixer is Kenics KMS, Sulzer SMV mixer, or an emulsion generating variant thereof.

18. A flow based electrocatalytic chemical hydrogen generation and storage process, comprising: contacting water and liquid toluene reactant, which is immiscible with the water, with charged surfaces of an electrocatalytically active static mixer cathode provided in an electrochemical flow cell thereby generating in situ a catholyte which is a liquid-liquid phase emulsion of the water and the toluene reactant, wherein the toluene reactant forms a one part of a reversible (de)hydrogenation reactant / product couple, wherein another part of the couple is methylcyclohexane as a hydrogenated product; whereby during the contacting step, the electrocatalytically active static mixer cathode electroreductively generates selectively, in situ and in concert, under the same set of operating conditions, adsorbed reactive species on catalytic active sites of an electrocatalyst associated with the static mixer as follows:• atomic hydrogen species (Hads) generated from the water in the emulsion, and• toluene reactant species (Rads) generated from the toluene reactant compound (R) in the emulsion, while simultaneously• suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and• promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H), wherein the electrocatalyst is ruthenium or a ruthenium-metal cocatalyst, wherein the cocatalyst is one or more metals selected from platinum, palladium, rhodium, iridium and nickel; and chemically storing the electrochemically generated atomic hydrogen species (Hads) in the methylcyclohexane product, by allowing transfer of adsorbed reactive atomic hydrogen species (HadS) on a catalyst active site of the electrocatalyst to the toluene reactive reactant species (Rads) adsorbed on an adjacent catalyst active site, thereby storing the electrochemically generated atomic hydrogen species chemically in the methylcyclohexane product.

19. A flow based electrocatalytic hydrogenation system comprising: an electrochemical flow cell having a cathodic chamber configured as part of a continuous electrochemical flow cell and provided with an electrocatalytically active static mixer cathode for forming in situ a catholyte which is a liquid-liquid phase emulsion comprising a liquid proton source and a liquid H-uptake reactant compound (R);wherein the static mixer cathode comprises an electrocatalyst that is suitable for, in situ and in concert, electroreductively generating under the same operating conditions: adsorbed reactive atomic hydrogen species (Hads) from electroreduction of the polar proton source in the emulsion onto catalyst active sites, and adsorbed reactive reactant compound (Rads) species from electroreduction of the nonpolar H-uptake reactant compound in the emulsion onto catalytic active sites of the electrocatalyst associated with the static mixer, while simultaneously(i) suppressing recombination of the reactive atomic hydrogen species to form H2 gas, and(ii) promoting reaction of the adsorbed species to form a hydrogenated product of the nonpolar H-uptake reactant compound (R-H).

20. Use of a flow based electrocatalytic hydrogenation system as defined in claim 19 in an energy storage application, particularly a grid energy storage application.

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