Transition metal carbonitride catalysts for the reduction of carbon monoxide and carbon dioxide

Abstract

Disclosed is a method for the catalytic reduction of CO2 and / or CO, the method comprising steps of (i) providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one transition metal carbonitride; (ii) providing CO2 and / or CO in the electrolytic cell; and (iii) applying electrical potential to the electrolytic cell so that the CO2 and / or CO undergoes a reduction reaction at the cathode. Also disclosed are electrolytic cells and chemical reactors containing the disclosed transition metal carbonitride catalysts.

Description

FIELD

[0001] The disclosure relates to the reduction of carbon dioxide and carbon monoxide by electrolysis and new transition metal catalysts therefor.INTRODUCTION

[0002] Since the start of the 20 th< century the world climate has been changing more noticeably. The balance in nature is lost due to dramatic increasing CO 2 emissions by burning of carbonaceous fuels which results in global warming. An urgent effort is needed to overcome this problem to reduce the ratio of CO 2 and turn it into fuel and other useful chemical products. On the other hand, the large-scale use of unsustainable fossil fuels for energy has led to an energy crisis in the world and an increasing amount of CO 2 in the atmosphere. Due to this, the world climate is changing day by day and scientific effort is needed to overcome the emission of CO 2 in the air by converting the already present CO 2 into green energy fuels. Previous experimental and theoretical research concluded that conversion of CO 2 into valuable products can be achievable, but not yet efficient for commercialization. In the whole process of CO 2 reduction reaction (CO 2 RR), the catalyst plays a key role in capturing CO 2 and converting it into valuable chemical products and fuels. CO 2 is a chemically stable molecule and this makes its electrolytic reduction challenging with high reduction overpotential, poor product selectivity and low current efficiency. To address this challenge, researchers and scientists have been exploring novel catalysts which can overcome these issues and speed up the electrolytic process (Ebbesen & Mogesen, J. Power Sources 2009, 193:349; Fu et al, Energy & Environmental Sci 2010, 3:1382).

[0003] In CO 2 RR the catalysts play a key role in the conversion of CO 2 into valuable products. In previous decades many experimental studies have been done for electrolytic CO 2 RR on different metal catalysts. For example, pure Cu, Ag, Au, and Pt catalysts have been studied as catalysts for the CO 2 reduction reaction. However, their application for the commercial purposes is not enough due to poor product selectivity, low faradic efficiency and high overpotential that is needed. It is well known that the Cu is a widely used catalyst for the reduction of CO 2 to CH 4 but its overpotential is high (~0.9 V) and moreover it produces 15 different carbon containing products which require large amount of energy for their separation. In addition to pure Cu, polycrystalline Cu was also used for the application of CO 2 RR and it produces amounts of C 2 and C 3 aldehydes as well as ethylene.

[0004] In addition to pure metal electrocatalysts, metal oxide catalysts i.e. TiO 2 have been studied by DFT methods and considered impressive and more efficient catalysts for CO 2 conversion to CH 3 OH and CH 4 products (Ramesha, ACS Catalysis, 2014, 4:3249). In another study RhO 2 is predicted to be a novel candidate for the formation of formic acid at -0.20 V onset potential. However, stability and electron conductivity of oxides as cathode materials are a challenge that limits the application of oxides for CO 2 RR. There are numerous research studies that have been conducted to explore novel catalyst materials for the CO 2 RR. Materials studied by DFT (density functional theory) include graphene-based materials, metals, metal oxides, zeolites, sulfides, and metal organic frameworks. The utilization of catalysts for large scale production is however still a challenge and improved methods are required to overcome this problem.SUMMARY

[0005] The present disclosure provides methods to overcome the above deficiencies of the prior art. The need to explore alternative materials for catalysis of CO 2 RR and CORR arises from the imperative to develop efficient and sustainable methods for converting carbon dioxide and carbon monoxide into valuable products. Traditional catalysts may have limitations in terms of activity, selectivity, efficiency, or cost. By searching for other materials, the aim is to identify catalysts that can enhance the performance of CO 2 RR and CORR processes, making them more economically viable and environmentally friendly.

[0006] In particular, in light of the challenge of finding good electrocatalysts for CO 2 and CO reduction, the disclosure provides certain transition metal carbonitrides that are useful catalysts for CO 2 RR and CORR.

[0007] An aspect of the disclosure relates to a method for catalytic electrolytic reduction of CO 2 and / or CO, the method comprising (a) providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one carbonitride of one or more transition metal; (b) providing CO 2 and / or CO in the electrolytic cell; and (c) applying electrical potential to the electrolytic cell; whereby the CO 2 and / or CO undergoes at least one reduction reaction at the cathode.

[0008] Another aspect of the disclosure relates to an electrolytic cell for the reduction of carbon dioxide and / or carbon monoxide, comprising: an anode; a cathode, the cathode comprising a catalyst comprising at least one transition metal carbonitride, and a power supply connected to the anode and the cathode.

[0009] The disclosure further relates to a chemical reactor comprising at least one electrolytic cell as described herein; and a power supply connected to the electrolytic cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows adsorption of different species on distinctive sides of TMCNs. FIG. 2 shows HER analysis of catalyst surfaces in CO2RR. FIG. 3 shows an illustration of the most favourable pathway to create the CH 4(g) via the MvK mechanism of CO2RR for (a) MoCN and (b) VCN. FIG. 4 shows the required onset potential for methane production via MvK mechanism for CO2RR. FIG. 5 shows reaction pathways with possible products during the conventional mechanism for CO2RR. FIG. 6 shows the onset potential for different products via conventional mechanism for CO2RR. FIG. 7 shows the formation of methanol, formic acid, and methane via a conventional mechanism for CO2RR, the most promising pathways with low onset potentials (a) TiCN and (b) VCN. FIG. 8 shows a comparison between the current results and previously published catalysts for CO2RR. FIG. 9 shows an illustration of TMCNs's efficiency in CORR: CO adsorption and surface poisoning resistance. FIG. 10 shows a demonstration of the best possible route for producing CH 4(g) through the MvK mechanism for (a) MoCN, (b) CrCN and (c) VCN for the CORR. FIG. 11 shows the required potential for CH 4(g) formation through MvK mechanism for CORR. FIG. 12 shows a visual representation of CORR via the conventional mechanism. FIG. 13 shows onset potential for CH 4(g) and CH 3 OH (aq) formation via conventional mechanism for CORR. FIG. 14 shows the formation of methanol and methane via the conventional mechanism for (a) TiCN (b) MoCN and (c) HfCN. DESCRIPTION

[0011] In the following, exemplary embodiments of the invention will be described, referring to the figures. These examples are provided to provide further understanding of the invention, without limiting its scope.

[0012] In the following description, a series of steps are described. The skilled person will appreciate that unless required by the context, the order of steps is not critical for the resulting configuration and its effect. Further, it will be apparent to the skilled person that irrespective of the order of steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

[0013] As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0014] Throughout the description and claims, the terms "comprise", "including", "having", and "contain" and their variations should be understood as meaning "including but not limited to" and are not intended to exclude other components.

[0015] The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., "about 3" shall also cover exactly or "substantially constant" shall also cover exactly constant).

[0016] The term "at least one" should be understood as meaning "one or more", and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with "at least one" have the same meaning, both when the feature is referred to as "the" and "the at least one".

[0017] The present disclosure is based on the surprising finding that transition metal carbonitrides, when used as a catalyst in the electrolytic reduction of CO 2 and CO, allow for efficient reduction to produce valuable small compounds at low temperatures and pressure and using low applied potential. Given the ever-increasing levels of CO 2 in the global atmosphere and concomitant need to find ways to achieve a carbon neutral energy technology, these catalysts can be used to facilitate the conversion of CO 2 and CO into valuable carbon-containing fuels.

[0018] In general, the catalysts can be used to reduce CO 2 and / or CO to produce hydrocarbons or oxygenates having from 1 to 3 carbon atoms. Exemplary products include methane, methanol, methanediol, formaldehyde, formic acid, ethanol, ethylene glycol, ethanediol, propane and propanol.

[0019] Accordingly, the disclosure provides means in the form of methods and systems for electrolytic conversion of CO 2 and / or CO at low temperature and pressure. Compounds such as short-chain alkanes and oxygenates (e.g. alcohols and acids) having from 1 to 3 carbon atoms can be produced using the disclosed transition metal carbonitrides. Through selection of appropriate catalysts, catalyst surface and appropriate applied voltage, the reduction reaction can be geared to produce compounds of particular interest.

[0020] In an aspect, the present disclosure is based on the investigation of the capability of transition metal carbonitrides (TMCNs) to catalyze the conversion of CO 2 and CO into valuable organic compounds that can for example be used as valuable fuel. The results are based on studies that delve into the electronic intricacies of TMCNs, unraveling their potential to drive the transformation of CO 2 and CO .

[0021] One distinct advantage of the transition metal carbonitride catalysts described herein is their unique usefulness to drive the CO 2 and CO reduction reactions via the Mars van Krevelen (MvK) reaction mechanism. This is not possible on most other catalysts surfaces and explains in part the unique chemistry possible by using these catalysts.CO 2 Reduction Reaction (CO 2 RR)

[0022] Density Functional Theory (DFT) to explore the reactivity of the reduction of CO 2 in the presence of 11 different transition metal carbonitride surfaces. The goal was to get an understanding of the performance and competence of these materials for CO 2 RR.

[0023] DFT is a quantum mechanical methodology that accounts for the interaction between electrons and the nucleus. The input is the atomic structure of the molecular system of interest and the output is the ground state energy of the system. The reaction mechanism of CO 2 reduction to CH 4 on a stepped Cu(211) surface was first proposed by Peterson et al (Energy Environ Sci 2010, 3:1311). The free energy of adsorbed intermediates on the catalyst surface were calculated using a thermochemical model (TCM). The same approach has been successfully applied on several other electrolytic systems, including water oxidation on transition metal oxides, N 2 electroreduction on transition metal surfaces, transition metal nitrides and transition metal oxides, hydrogen evolution reaction (HER) on transition metal nitrides and CO 2 RR on transition metals and transition metal oxides.

[0024] The need to explore alternative materials for the CO 2 RR arises from the imperative to develop efficient and sustainable methods for converting carbon dioxide into valuable products. Traditional catalysts may have limitations in terms of activity, selectivity, efficiency, or cost. By searching for other materials, researchers aim to identify catalysts that can enhance the performance of CO 2 RR processes, making them more economically viable and environmentally friendly. The surface chemistry of TMCNs is comparable to precious Pt-group metals which was already described by Levy and Boudart (Science 1973, 181:185). In previous studies these TMCNs have been used for wide range of reactions such as CO oxidation, hydrogenation, methane dry reforming, desulfurization, conversation of methane to gas and water gas shift reaction. Hence these materials have received great attention for application in catalysis.

[0025] Utilizing advanced quantum mechanical simulations and computational models, the present disclosure is based on an exploration of the binding energies and reaction pathways of TMCNs (CrCN, HfCN, MoCN, YcCN, ScCN, NbCN, ZrCN, TaCN, TiCN, WCN, and VCN), with a focus on their suitability for catalyzing CO 2 reduction. In this research a complete and comprehensive analysis for above mentioned TMCNs on the (100) facets was conducted.

[0026] In the following Example 1 it is described how DFT calculations can be used to describe the interaction of CO 2 with TMCN surfaces and predict the reaction pathway for CO 2 RR on TMCN. Two mechanisms were considered, the Mars-van Krevelen mechanism (MvK) and conventional surface mechanism, to study the CO 2 RR towards methane and methanol production on TMCNs surfaces, The analysis reveals that several TMCNs exhibit remarkable catalytic activity for CO 2 reduction, surpassing the performance of conventional catalysts. The electronic structure of these TMCNs plays a pivotal role in facilitating the conversion of CO 2 into valuable chemical products.

[0027] According to our investigation, it seems that HfCN, NbCN, TiCN, TaCN and WCN are highly active to convert the CO 2 into formic acid, HCOOH (aq) , at 0V via CO 2 RR (conventional mechanism), following eq.1 below.         Clean → COOH* → HCOOH (aq)      (1)

[0028] Similarly, VCN, YCN and ZrCN also produced HCOOH (aq) at 0V by following eq. 2 below:         Clean → OCHO* → HCOOH (aq)      (2)

[0029] Thus, we are able to assert that at least these eight catalytic surfaces exhibit a high level of activity for the conversion of CO 2 RR to HCOOH (aq) via conventional procedure. However, TaCN, YCN and ZrCN are most promising due to single product formation at lowest onset potential, being only formic acid.

[0030] On the other hand, TiCN is very active for CH 3 OH (aq) formation with only -0.22 V by following the eq.3 below:         Clean → COOH* → HCOOH* → CHO* → CH2O* → CH30* → CH3OH (aq)      (3)

[0031] By contrast, VCN is most promising catalyst to produce methane at small onset potential of -0.57 V by following the eq. 4 below:         Clean→ COOH*→ C(OH*) 2 → COH*→ CHOH*→ CH2OH*→ CH3*+OH*→ CH3→ CH 4(g)      (4) CO reduction reaction (CORR)

[0032] The disclosure also shows that transition metal carbonitrides (TMCNs) are capable of catalyzing the conversion of CO into valuable organic compounds via CORR.

[0033] Protonation along the reaction pathway from CO to CH 4 and CH 3 OH on 11 transition metal carbonitrides have been calculated, including CrCN, HfCN, MoCN, NbCN, TaCN, ScCN, TiCN, VCN, WCN, YCN and ZrCN with the (100) facets. These facets of TMCNs are considered the most stable structure with the 1:1 TM:C:N ratio and cubic crystallography.

[0034] Two mechanisms were considered, the Mars-van Krevelen mechanism (MvK) and conventional surface mechanism, to study the CORR towards methane and methanol production on TMCNs surfaces. In MvK mechanism, carbon vacancy is generated with the formation of methane and then vacancy is filled with the Carbon of CO and release of Oxygen of CO in form of water molecule. The stability of the vacancy (as an indication of material stability against decomposition) is crucial to investigate here and thus Climbing Image Nudged Elastic Band (CI-NEB) has been done to estimate the activation energy of migration of carbon atom from second layer to first layer to fill the carbon vacancy. In conventional surface mechanism the interaction of CO gas molecule on the surface of TMCNs with different sites is studied. All aspects of each mechanism are calculated explicitly, and free energy diagrams are drawn for each adsorbed species on the surface of catalyst. Thermochemical model was implemented to obtain the trends of CORR on each TMCNs surface.

[0035] Employing Density Functional Theory (DFT) the 11 TMCNs were thus explored for the conversion of CO to methane and methanol via both MvK and conventional surface mechanism.

[0036] Results of the study are presented in the following Example 2. In the study, TiCN, MoCN and HfCN were found to be particularly good candidates to produce methanol during the CORR according to the following equations (1) - (3), and equation 4 shows vacancy regeneration with CO:         CO*→CHO*→ CH2O* → CH3O*→ CH3OH (aq)      (1)         CO* → CHO*→ CHO*+CH* → CH2O*+CH*→CH3O*+CH* → CH3QH (aq) +CH*     (2)         CO*→ CHO*→ CH2O*→ CH2OH*→ CH 3 OH (aq)      (3)         Uac+ CO (g) + H 2(g) → Clean + H 2 O (l)      (4)

[0037] Moreover, TiCN was found particularly promising due to its high activity to produce only CH 3 OH (aq) at a very small applied potential of -0.19 V.

[0038] Via MvK mechanism, MoCN, CrCN, VCN, TiCN, TaCN, NbCN, ZrCN are surfaces that produce methane via the mechanism of eq. (4). However, MoCN, CrCN and VCN are most active for CORR to CH 4(g) due to smaller values of onset potential.

[0039] All of these surfaces having the most promising catalyst activity were found to require a potential less than -0.7V to produce any product.

[0040] Overall, the findings indicate due to CO spontaneously adsorption, less poisoning, less over potential and high product selectivity TMCNs are excellent choice for CORR to produce valuable products such as methane and methanol.Electrolytic cells

[0041] In general, an electrolytic cell is a chemical reactor where chemical reactions take place, driven by an applied electric potential. An electrolytic cell in the present context is therefore an electrolytic cell that undergoes a redox reaction when electrical potential is applied to the cell.

[0042] Design of electrolytic cells is known in the art. Examples of suitable electrolytic cells include H-type cells, polymer electrolyte membrane (PEM) flow cells, microfluidic flow cells, solid oxide electrolytic cells and DEMS cells. It should be appreciated that the transition metal carbonitrides disclosed herein can be adapted for use in any type of electrolytic cell. Examples of suitable electrolytic cells are described in Liang et al. (Journal of CO2 Utilization, 2020, 35:90-105).

[0043] In an H-type cell, the cathodic and anodic compartments are typically separated by an ion-exchange membrane that allows ions to flow across while preventing reaction products from being reoxidized at the anode. There can be a reference electrode present in the cathodic compartment. In these cells, there is a liquid electrolyte solution at the cathode and anode, and CO 2 gas is typically streamed into the cathodic compartment.

[0044] In PEM flow cells, CO and / or CO 2 can be streamed directly at the cathode or it can be provided by dissolved bicarbonate. There can be either a liquid phase at both electrodes, a gas phase at the cathode and liquid at the anode or a humified gas phase at both electrodes. Typically, there is a gas diffusion electrode at the cathode and possibly also at the anode.

[0045] In microfluidic flow cells, an electrolyte channel is provided between a cathode and an anode, with a stream of CO and / or CO 2 gas delivered at the cathode. Instead of utilizing a membrane, the cathode and anode are separated by the diffusion of products.

[0046] Solid state electrolysis cells can improve the kinetics of reactions and achieve high efficiency. In these cells, there is a solid electrolyte to facilitate transfer of ions, with a membrane separating the cathode and anode. The cells can operate at high temperatures if needed, e.g. at or above 600°C, such as high as 700°C, 800°C or 900°C, even as high as 1000°C.

[0047] The transition metal carbonitride catalysts disclosed herein can be provided in any suitable form in the electrolytic cell of interest, depending on its design and intended use. Thus, the catalysts can be provided as a coating, film, as a powder, dopant etc., and in forms such as microparticles, nanoparticles such as zero- dimensional (0D), one-dimensional (1 D), two-dimensional (2D) and three- dimensional (3D) nanoparticles, nanotubes, nanosheets, heterostructures, a single atom catalyst, a dual-atom catalyst and a triple-atom catalyst.

[0048] Transition metal carbonitrides can have the general 2:1:1 (TM:C:N) stoichiometry, e.g. VCN, MoCN, WCN, TiCN etc. Other stoichiometries are however also possible.

[0049] Thus, the skilled person will appreciate that the carbonitrides may have an alternative stoichiometry and such alternative stoichiometries are also within scope of the present disclosure. Further, chemical compounds as described herein are provided by their chemical formula irrespective of their phase or state. In particular, compounds that are present in their gaseous state when present in a pure and isolated form at room temperature (such as CO or CO 2 ) are herein described by their chemical formula. For example, carbon monoxide and carbon dioxide is herein described as CO and CO 2 , whether present as a gas, as individual molecules, in clusters, bound to surfaces or present as a solute, and the same applies to other molecular species described herein.

[0050] A mixture of CO and CO 2 can be provided in the electrolytic cell. During such operation of the cell, both CORR and CO2RR reactions will take place with products formed depending on the type of catalyst used (i.e., which TMCN) and the applied voltage.

[0051] Alternatively, only CO or only CO 2 can be provided in the cell. This may be preferable, as it will be easier to control the respective reaction (CORR or CO2RR) for the type of TMCN being used in the cell.

[0052] The proton donor in the electrolytic reactions can be any suitable substance that is capable of donating protons in the electrolytic cell. The proton donor can for example be water or it can be in the form of an acid, such as any suitable organic or inorganic acid. The proton donor can be provided in an acidic, neutral or alkaline aqueous solutions. The proton donor can also, or alternatively, be provided by H 2 oxidation at the anode. In other words, hydrogen can be considered as a source of protons: H 2 <=> 2(H +< + e -< )

[0053] The electrolytic cell can in general comprises at least three general parts or components, a cathode electrode, an anode electrode and an electrolyte.

[0054] The electrolytic reduction of carbon dioxide is the conversion of carbon dioxide to more reduced chemical species using electrical energy.

[0055] The different parts or components can be provided in separate containers, or they can be provided in a single container. The electrolyte can be a solid or an aqueous solution in which ions are provided, for example in a dissolved form in an aqueous solution when present. When provided as an aqueous solution, the aqueous solution can be a neutral, an alkaline or an acidic solution.Sources of CO 2 and CO

[0056] Carbon dioxide (CO 2 ) can be provided by a source such as any one of bicarbonate (HCO 3 -< ), carbonate (CO 3 -2< ) and / or carbonic acid (H 2 CO 3 ). For example, bicarbonate and carbonate can be provided as bicarbonate or carbonate salts, either in pure form as a solid or in solution, or in a mixture into a solution, that can preferably be an aqueous solution. A mixture of bicarbonate, carbonate and carbonic acid will reach equilibrium in solution. Therefore, the relative concentration of these species will depend on pH of an aqueous solution.

[0057] An alternate source of CO and CO 2 is the gaseous form of the compounds, CO(g) and CO 2 (g). Gaseous CO and CO 2 can be provided as a sole source of CO and / or CO 2 , or it can be provided as a supplement to other sources of CO or CO 2 in the cell. In the case of CO 2 , this includes the previously mentioned bicarbonate, carbonate and carbonic acid.

[0058] Other or additional sources of CO and CO 2 are possible. For example, direct injection of CO 2 gas is possible by bubbling CO 2 directly into an electrolyte solution.

[0059] Alternatively, dissolved carbonate salts (e.g., sodium carbonate, Na 2 CO 3 ) in water can be used to provide a source of CO 2 .

[0060] An alternative source can be provided from industrial CO 2 Emissions. Capturing CO 2 from industrial processes such as cement production, steel manufacturing, or chemical production can also form a source of CO 2 . Further, chemical reactions that release CO 2 can be a source of CO 2 .

[0061] Certain microbial processes, such as fermentation, produce CO 2 as a byproduct and can serve as a source of CO 2 . The CO 2 can also be provided through photocatalytic production.

[0062] Another source is represented by CO 2 captured from fossil fuel-based power plants (coal, natural gas, oil) which produce large amounts of CO 2 .

[0063] Yet another source can be CO 2 generated from burning biomass such as agricultural waste, forestry residues, or bioenergy crops. Further, CO 2 emitted from the incineration of municipal solid waste can be captured as a source of CO 2 .

[0064] Through advanced capture technologies, CO 2 can be captured directly from the ambient air.

[0065] Carbon monoxide can be provided e.g. from microbial production, decomposition of metal carbonyls, thermal decomposition of formic acid, reforming reactions, water-gas shift reaction or gasification of biomass or coal.Catalysts

[0066] In general terms, the catalyst on the electrode surface should ideally have the following characteristics: It should (a) be chemically stable, it should (b) not become reduced or otherwise consumed during the electrolytic process, it should facilitate the formation of carbon-containing products, and (d) use of the catalyst should lead to the production of minimal amount of hydrogen gas. The catalysts disclosed herein fulfil these characteristics.

[0067] A catalyst can comprise one or more stabiliser that serves the role of preventing degradation of the catalyst. Suitable stabilisers should be more stable to degradation than the metal carbonitride(s) being employed, but otherwise are inert with respect to the catalytic reactions taking place on the electrode surface. Exemplary stabilisers include, but is not limited to, metal oxycarbonitrides, metal oxynitrides, bimetallic oxides and the like.

[0068] The transition metal carbonitrides can be provided as a film, i.e. as a thin layer (e.g., as few layers or as a monolayer) on a stable and conductive surface.

[0069] The catalysts disclosed herein are transition metal carbonitride catalysts. The catalysts can generally contain one or more transition metal carbonitride, or any mixture of transition metal carbonitrides.

[0070] The transition metal carbonitride can preferably be selected from the group consisting of carbonitrides of Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. The preferable catalyst composition can be varied depending on the intended use, i.e. the reactant being provided (CO or CO 2 ) and the desired product(s) formed in the electrolytic cell.

[0071] For the catalytic reduction of CO 2 , the suitable catalyst can comprise one or more carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr, more preferably selected from Ta, Y, Zr, V and Ti.

[0072] For the catalytic reduction of CO, the suitable catalyst can comprise one or more carbonitride of a transition metal selected from Mo, Hf, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Ti, Cr and V.

[0073] For formation of methane from CO 2 , the suitable catalyst(s) can comprise one or more of Vanadium, Chromium, Niobium, Molybdenum, Tantalum, Titanium or Zirconium carbonitrides.

[0074] For formation of formic acid from CO 2 , the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr.

[0075] For formation of methanol from CO 2 , the suitable catalyst can comprise titanium and / or Wolfram carbonitrides.

[0076] For formation of methane from CO, the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Cr and V.

[0077] For formation of methanol from CO, the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Ti, Mo and Hf.

[0078] An advantage of the present invention is that the process can be suitably operated using suitable electrolytes in solid or liquid form. An electrolyte solution can be non-aqueous or aqueous. For example, an electrolyte solution can comprise, or consist of an aqueous solutions containing dissolved electrolytes (salts). Thus, in certain embodiments of the process and system, the electrolytic cell comprises one or more aqueous electrolytic solutions, in one or more cell compartments. Individual cell compartments can be separated by suitable barriers, such as membranes that allow electrolytes to pass through.

[0079] Solid and liquid electrolytes may comprise any of various typical inorganic or organic salts such as but limited to soluble salts of e.g. chloride, nitrate, chlorate bromide, etc. e.g. sodium chloride, potassium chloride, calcium chloride, ammonium chloride, and other suitable salts. The electrolyte may also comprise any one or a combination of, alkali or alkaline earth metal oxides, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, rubidium hydroxide and cesium hydroxide.

[0080] An aqueous electrolyte solution can preferably comprise carbonate, bicarbonate or carbonic acid as a source of CO 2 . Such an aqueous electrolyte solution can also further comprise one or more organic or inorganic acids. Inorganic acids can include mineral acids that include but are not limited to, hydrochloric acid, nitric acid, phosphoric acid, sulphuric acid, boric acid, hydrofluoric acid, hydrobromic acid, and perchloric acid. The electrolyte can alternatively be provided as a protic or aprotic, non-aqueous solution. For example, the electrolyte can be provided as an ionic liquid, i.e. as a molten salt, for example a sodium chloride salt.

[0081] Depending on the substance composition of the catalyst, a suitable surface crystal structure may be preferred. Various different crystal structures exist for transition metal carbonitrides and different structures can be obtained at different growth conditions. It is within scope of the skilled person to select appropriate surface crystal structures.

[0082] Further, it is possible that a catalyst contains more than transition metal carbonitride, such as two or more or three or more transition metals. For example, a transition metal carbonitride can be doped by a small amount of a second (or more) transition metal. Alternatively, a catalyst can contain one or more layer of a transition metal carbonitride that is provided over one or more layers of another transition metal carbonitride.

[0083] In certain embodiments of the invention, the catalyst surface is provided as a pure transition metal carbonitride, i.e. the catalyst comprises a single transition metal carbonitride, i.e. the catalyst for example does not contain a mixture of transition metal carbonitrides or one transition metal carbonitride that is coated by one or several layers of a second (or more) transition metal carbonitrides.

[0084] Thus, as will be apparent to the skilled person, the catalyst according to the invention can comprise a single transition metal carbonitride. The catalyst can alternatively comprise, or consist of, a mixture of two or more transition metal carbonitrides. Such mixed transition metal carbonitrides can comprise a single crystal structure or polycrystalline structures, for example a rocksalt structure. The mixed transition metal carbonitrides can also comprise a mixture of transition metal carbonitrides that are of different crystal structures and / or carbonitride with different catalytic facets. Accordingly, such mixed transition metal carbonitrides can further comprise a single, or a mixture of, facets. Mixed transition metal carbonitride catalysts can be grown or manufactured separately and then assembled into mixed catalysts comprising the different metal carbonitrides, wherein the carbonitrides in the mixture have the same or different crystal structures.

[0085] As described in more detail herein, running a current through the electrolytic cell leads to a chemical reaction in which carbon monoxide (CO) and / or carbon dioxide (CO 2 ) is reduced in a series of steps to ultimately form one or more valuable short chain organic products, including for example methane, methanol and formic acid. The running of current is achieved by applying a voltage to the cell. An advantage of the disclosed transition metal carbonitride catalysts is the possibility of performing electrolytic production of these valuable products at a low electrode potential under conditions of low temperature and / or gas pressure, which is beneficial in terms of energy efficiency and required equipment.

[0086] An electrolytic cell can be operated at an ambient gas pressure of about 1 atmosphere. The electrolytic cell can also be operated at higher pressure, i.e. pressure that is greater than ambient pressure. For example, the cell can be operated at a pressure of up to 50 atmospheres (atm), up to 40 atmospheres, up to 30 atmospheres, up to 20 atmospheres or up to 10 atmospheres. In some embodiments, the electrolytic cell is operated at a pressure that is in the range of 1 to 30 atmospheres, in the range of 1 to 20 atmospheres, in the range of 1 to 10 atmospheres, in the range of 1 to 5 atmospheres or in the range of 1 to 3 atmospheres. The electrolytic cell can also be operated at a pressure that is in the range of 2 to 20 atmospheres, in the range of 3 to 20 atmospheres, in the range of 4 to 20 atmospheres, or in the range of 5 to 20 atmospheres, such as at about atmospheres, about 6 atmospheres, about 7 atmospheres, about 8 atmospheres, about 9 atmospheres, about 10 atmospheres, about 11 atmospheres, about 12 atmospheres, about 13 atmospheres, about 14 atmospheres, about 15 atmospheres, about 16 atmospheres, about 17 atmospheres, about 18 atmospheres, about 19 atmospheres or about 20 atmospheres.

[0087] The electric potential can be applied as a constant or variable electric potential. Pulsed electric fields generated by pulsed potentials can be varied by adjusting a number of parameters such as electric field intensity, rise time of voltage pulses, number of pulses, frequency of pulses, pulse wave shape, treatment time (i.e. the length of time the pulse sequence is applied, resulting in from a product of the number of pulses and the duration of each pulse).

[0088] In certain useful embodiments, the cell is operated at an electric potential that results in formation of the desired product(s). The electric potential can in different applications be less than (i.e., less negative) than about -2.0V, less than about -1.5V, less than about -1.0 V, less than about -0.9 V, less than about -0.8V, less than about - 0.7 V, less than about -0.6 V, less than about 0.5 V, less than about -0.4 V, less than about -0.3 V or less than about -0.2 V. In some embodiments, the cell is operated at electrode potential in the range of about -1.5 V to about 0.0V or in the range of about -1.0 V to about 0.0 V, such as in the range of about -0.9 V to about 0.0V, such as in the range of about -0.8 V to about 0.0 V, such as in the range of about -0.7V to about 0.0V, about -0.6 V to about 0.0 V, about -0.5 V to about 0.0 V, or in the range of about -0.3 V to about 0.0 V or in the range of about -0.2 V to about 0.0 V. The upper limit (i.e., more negative potential limit) of the range can be about -0.3 V, about -0.4 V, about -0.5 V, about -0.6 V, about -0.7 V, about -1.0V, about -1.5V or about -2.0V. The lower limit (i.e. less negative potential limit) of the range can be as high as about +1.0V, about +0.5V, about 0.0 V, about -0.1 V, about -0.2 V, or about -0.3 V. Any of these electric potentials and ranges of electric potentials are contemplated for the electrolytic methods and electrolytic cells disclosed herein.

[0089] A high (more positive) or low (more negative) potential may be applied to the electrolytic cell before and / or after operation of the cell to produce products from CO / CO 2 . For example, it may be beneficial to increase voltage to a more positive potential (e.g., a voltage greater than 0.0V) to free the surface of the catalyst / electrode from adsorbents that may have an adverse effect on its operation. After such cleaning, the electrolytic cell can be operated under normal production potential.

[0090] During operation of the cell, the composition of products obtained in the reduction of CO and / or CO 2 can be altered / controlled by selective adjustment of applied potential for any given catalyst surface. Thus, the data provided herein shows that depending on the relative binding energies of adsorbed intermediates the selectivity of the electrolytic cell changes depending on the applied voltage.

[0091] The temperature of the cell may be varied as needed. One advantage of the present catalysts is that the CO 2 RR and CORR reactions can be carried out at low temperature, such as at or near ambient room temperature. However, it will be appreciated that the temperature may be adapted and / or adjusted as needed.

[0092] For example, solid state electrolytic cells can operate at high temperatures of up to or close to 1000°C, and the catalysts described can be used at such high temperatures.

[0093] In general therefore, the temperature of the electrolytic cell, and in particular the temperature at the cathode of the cell, can be in the range of 0°C to 1000°C, in the range of 0°C to 900°C, 0°C to 800°C, 0°C to 700°C, 0°C to 600°C, 0°C to 500°C, 0°C to 400°C, 0°C to 300°C, 0°C to 200°C, 0°C to 100°C or 0°C to 50°C. In some embodiments, the temperature is in the range of 0°C to 50°C, 5°C to 45°C, 10°C to 40°C, 15°C to 35°C, or 20°C to 30°C.

[0094] An advantage of the present invention is the specificity and efficiency of product formation over side-product (such as H 2 ) formation, which is a challenge due to the competing binding energies of hydrogen and oxygen on the catalyst surface. In certain embodiments, less than about 50% moles H 2 are formed compared to moles of the desired product formed, and preferably less than about 40% moles H 2 , less than about 30% moles H 2 , less than about 20% moles H 2 , less than about 10% moles H 2 , less than about 5% moles H 2 , less than about 2% moles H 2 , or less than about 1 % moles H 2 .

[0095] Further, reaction conditions (choice of catalyst, applied potential in particular) can be set so that one reaction product is selectively formed over other reaction products. This means that the reaction predominantly or even completely leads to the formation of one particular reaction product (e.g., methane, methanol, formic acid, methanediol).

[0096] The reaction pathway of CO and CO 2 reduction depends on the relative energies of reaction intermediates. Thus, the pathway can depend on the system within which the reaction takes place, including the chemical composition of the catalysis and the catalytic surface being used in the reaction.

[0097] The active part of an industrial heterogeneous catalyst is most commonly a solid surface, e.g. a transition metal or transition metal carbonitride or mixture of transition metal carbonitrides. The surface offers a favourable energy path from reactants to products, by binding reactants and reaction intermediates. The binding energy of reactants to the surface must be strong enough to produce reaction intermediates, but weak enough to allow products to leave the surface, allowing more reactions to take place on the surface. The consequence is that for a reaction, there will be an optimum binding energy for an intermediate, such that both stronger and weaker binding leads to lower activity. A result of this phenomenon is a reaction relationship called the volcano-shaped relationship, or commonly referred to as a Volcano plot.

[0098] Catalyst activity can in general be modified by altering the local electronic structure by strain, ligand, substitution and / or alloying. These alterations can result in changes in binding energies of reaction intermediates, and thereby a change in the thermodynamics of the overall reaction profile. Thereby it may be possible to adapt the reaction profile to specifically obtain desired reaction products.

[0099] Exemplary embodiments in accordance with the present disclosure include the following: 1. A method for catalytic electrolytic reduction of CO 2 and / or CO, the method comprising: a. providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one transition metal carbonitride; b. providing CO 2 and / or CO in the electrolytic cell; and c. applying electrical potential to the electrolytic cell; whereby the CO 2 and / or CO undergoes at least one reduction reaction at the cathode. 2. The method of clause 1, wherein the catalyst is provided as a surface coating, a film, a microparticle, nanotubes, nanosheets, heterostructure, dopant and / or a nanoparticle. 3. The method of any one of the previous clauses, wherein the temperature at the at least one cathode is in the range of 0°C to 300°C, 0°C to 200°C, 0°C to 100°C, 0°C to 50°C 5°C to 45°C, 10°C to 40°C, 15°C to 35°C, or 20°C to 30°C. 4. The method of any one of the previous clauses, wherein the electrolytic cell comprises gas diffusion electrodes at the anode and / or the cathode. 5. The method of any one of the previous clauses, wherein the electrolytic cell further comprises at least one reference electrode. 6. The method of any one of the previous clauses, wherein the electrolytic reduction reaction results in formation of at least one alkane, lower alcohol or acid having from 1 to 3 carbon atoms. 7. The method of any one of the previous clauses, wherein the electrolytic reduction reaction results in formation of at least one product selected from methanol, methane, methanediol, formic acid, formaldehyde, ethanol, ethane, ethylene glycol, ethanediol, propane and propanol. 8. The method of any one of the previous clauses, wherein CO 2 and / or CO are provided in gaseous form into the electrolytic cell, and wherein the gas pressure at the at least one cathode is in the range of about 1 atm to 40 atm, 5 atm to 30 atm, or 10 atm to 20 atm. 9. The method of any one of the previous clauses 1 to 8, wherein the gas pressure at the at least one cathode is ambient pressure of about 1 atm. 10. The method of any one of the previous clauses, wherein the electrical potential applied to the electrolytic cell is in the range of -2.0 V to +1.0 V using a reversible hydrogen electrode (RHE) as a reference. 11. The method of any one of the previous clauses, wherein molar production of hydrogen (H 2 ) compared with CO 2 and / or CO reduction in the electrolytic cell is less than 50%. 12. The method of any one of the previous clauses, wherein the electrolyte solution comprises at least one source of CO 2 selected from carbonate (CO 3 2-< ), carbonate salts, bicarbonate (HCO 3 -< ) and carbonic acid (H 2 CO 3 ). 13. The method of any one of the previous clauses, wherein CO and / or CO 2 is provided in the solution by a stream of gas. 14. The method of any one of the previous clauses, wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 15. The method of any one of the previous clauses, wherein CO 2 only is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr, more preferably selected from Ta, Y, Zr, V and Ti. 16. The method of any one of the previous clauses, wherein CO only is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Mo, Hf, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Ti, Cr and V. 17. The method of any one of the previous clauses, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of vanadium (V), Chromium (Cr), Niobium (Nb), Molybdenum (Mo), Tantalum (Ta), Titanium (Ti) or Zirconium (Zr), the catalytic reduction resulting in formation of methane. 18. The method of any one of the previous clauses 1-13, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Hf, Nb, Ti, Ta, W, V, Y and Zr, the catalytic reduction resulting in the formation of formic acid. 19. The method of any one of the previous clauses 1-13, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of titanium (Ti), the catalytic reduction resulting in formation of methanol. 20. The method of any one of the previous clauses 1-13, wherein CO only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Mo, Cr, V, Ti, Ta, Nb and Zr, the catalytic reaction resulting in formation of methane. 21. The method of the previous clause, wherein the carbonitride is a carbonitride of a transition metal selected from Mo, Cr and V. 22. The method of any one of the previous clauses 1-13, wherein CO only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Ti, Mo and Hf, the catalytic reaction resulting in formation of methanol. 23. An electrolytic cell for the reduction of carbon dioxide and / or carbon monoxide, comprising: an anode; and a cathode, the cathode comprising a catalyst comprising at least one transition metal carbonitride. 24. The electrolytic cell of the previous clause, wherein the catalyst comprises at least one carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 25. The electrolytic cell of the previous clause, wherein the catalyst is provided as a surface coating, a film, a microparticle, nanotubes, nanosheets, nanoarrays, nanoribbons, heterostructure, dopant, a nanoparticle, zero- dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three- dimensional (3D), a single atom catalyst, a dual-atom catalyst and a triple-atom catalyst. 26. The electrolytic cell of any one of the previous two clauses, wherein the catalyst is provided as a pure carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 27. The electrolytic cell of any one of the previous four clauses, wherein the electrolytic cell comprises gas diffusion electrodes at the anode and / or the cathode. 28. The electrolytic cell of any one of the previous five clauses, wherein the electrolytic cell further comprises at least one reference electrode. 29. A chemical reactor comprising at least one electrolytic cell as set forth in any one of clauses 23-28; and a power supply connected to the electrolytic cell.

[0100] The invention will now be exemplified by the following non-limiting Examples.Example 1 CO2RR on transition metal carbonitride surfaces Computational method

[0101] The interaction of CO 2 with TMCN surfaces and formation of different intermediates were studied by DFT calculations with Generalized Gradient Approximation (GGA) using RPBE exchange correlation function. The tool used for these calculations was ab initio simulation package (VASP) and cutoff energy was 450 eV with the 4×4×1 Monkhorst-Pack K-point mesh until energy differences are converged within 10 -4< eV. The Projector augmented wave (PAW) method was implemented due to full wavefunction by utilizing computationally efficient pseudopotentials, significantly reducing computation time. The surface of TMCNs were considered in the rocksalt (RS) crystallographic structure with the texture orientation of (100). A slab was prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms. The boundary conditions were periodic with 20 Å vacuum along the z direction to avoid self-interaction of neighboring layers. The bottom two layers were fixed, and the top 3 layers were allowed to fully relax together with any adsorbates on the surface.

[0102] The binding energy of an adsorbate was calculated according to the equation 1: ΔE ads = E adsorbate / TMCN slab − E TMCN slab − E adsorbate

[0103] Here E (adsorbate / TMCN slab) is the total energy of the system with an adsorbate on the TMCN slab, E (TMCN slab) is the total energy of the pristine TMCN slab, and E(adsorbate) is the total energy of the adsorbate. The negative ΔE ads corresponds to the exothermic adsorption phenomenon.

[0104] The Computational hydrogen electrode model as proposed by Norskov et al was used to calculate the free energy diagram for CO 2 RR and / or CORR along different paths at certain applied potential. According to this method at room temperature kinetic barrier is negligible for the proton coupled electron step and the potential limiting step is the most positive energy difference between the two adjacent steps.

[0105] The reaction free energy of an adsorbate for CO 2 RR at any arbitrary potential U vs RHE and any arbitrary pH was calculated by equation: Δ G U RHE = Δ G U RHE = 0 + neU RHE eU RHE = eU RHE + 2 .3k b TpH where U RHE is the applied potential referred against the standard hydrogen electrode (SHE), n is number of electrons, e is the elementary charge , k b is the Boltzmann constant and T is the Temperature. By putting eq (2) into eq(3) we will get : Δ G U RHE = Δ G U RHE = 0 + n eU RHE = eU RHE + 2 .3k b TpH

[0106] Generally overpotential are independent of pH of electrolyte so in this study we will consider pH = 0. Hence for each elementary step ΔG (U = 0) is calculated by Δ G U = 0 = ΔE DFT + ΔE ZPE − T Δ S + ΔE 0K → T + ΔE sol

[0107] Where ΔG is the Gibbs free energy, ΔE DFT is the electronic energy calculated by DFT, ΔE ZPE is the zero-point energy correction and TΔS is entropy differences between the gas phase and adsorbed species calculated by vibrational frequencies for the adsorbed species, ΔE sol is the adsorbate stabilization term due to the solvent and we have not included in this study. ΔE OK → T is the change in internal energy because of temperature. The value of the gas phase is taken from the thermodynamic tables from textbooks.Results and discussion Screening of the active site

[0108] To initiate the CO 2 reduction reaction (CO2RR), the process begins with optimizing the structure, followed by a detailed screening of the active sites. This involves hydrogenating various sites on the surface. Additionally, we adsorb COOH, and OCHO on different regions of the surface to identify the most active sites for each species. The CO2RR process is often complicated by the production of H 2 as a byproduct, making it crucial to compare the efficiencies of CO2RR and the hydrogen evolution reaction (HER) before proceeding further. Moreover, the potential occupancy of active sites by oxygen (O), hydroxyl groups (OH), or water (H 2 O) necessitates additional scrutiny. To clarify whether the active sites are available for CO2RR or occupied by other species, we also investigate adsorption of these molecules. This comprehensive analysis ensures the true availability and activity of the active sites. All data is detailed in Fig. 1, where we can see that none of the catalyst surfaces perform well for the HER, which is needed for successful CO2RR. Additionally, the most active site is the carbon site, denoted as CH. Further, OCHO and COOH adsorption is found to be exothermic on these TMCNs.Compression of CO2RR and HER

[0109] To explain the CO2RR, we first need to examine the catalysts for the HER. This is because HER competes with CO2RR, and hydrogen (H 2 ) is often produced as a byproduct. Therefore, before delving into the details of CO2RR, the effectiveness of all catalysts for HER is summarized in Figure 2, which shows that most of these surfaces do not intend to bind proton and thus HER should be suppressed on these surfaces.Mars-van Krevelen (MvK) mechanism

[0110] In this mechanism, the carbon active site is repeatedly hydrogenated to produce methane in the gaseous phase. Sometimes, the surface requires more than four hydrogen atoms to produce CH 4(g) , but many surfaces can ideally produce CH 4(g) after four hydrogenation steps. Along with methane, a carbon vacancy is created where CO 2(g) adsorbing into the vacancy regenerates the catalyst by hydrogenation of the oxygen atoms of the adsorbed CO2 and releasing them into water, (Eq. 1). This process is cyclical: hydrogen in the electrochemical cell adsorbs onto the active site, creating a vacancy. The subsequent closure of the vacancy results in a clean structure. However, different catalytic surfaces require varying amounts of potential for this process to occur.         Vac+ CO 2(g) + 2H 2(g) → Clean + 2H 2 O (l)      (1)

[0111] During the current investigation, the eleven TMCNs were explored to evaluate their reactivity for methane formation at small potential. Consequently, free energy diagrams (FEDs) for the most promising catalysts via MvK mechanism have been constructed. According to Fig. 3 (a, b), the optimal pathway for methane formation via the MvK mechanism begins with the initial protonation step, leading to the formation of CH* and eventually methane, with a potential-determining step (PDS) value of 0.32 eV for MoCN. Similarly, for VCN, methane is formed with ΔG POS =0.41 eV, associated with the formation of CH 2 * during the second hydrogenation step.

[0112] However, different TMCNs require distinct onset potential values to produce methane, highlighting the variability in their efficiency. This is illustrated in Fig. 4, emphasizing the need to carefully select TMCNs based on their onset potential values for optimal methane production via the MvK mechanism.

[0113] Here, it is observed that MoCN, CrCN, and VCN exhibit higher activity towards methane formation at small onset potentials, whereas ScC, HfCN, and YCN are less active materials as they require higher potentials to produce CH 4(g) .Conventional mechanism

[0114] During this process, there are two approaches for reducing CO 2(g) . Combination of CO 2(g) and H 2(g) to form either COOH or OCHO. Through further hydrogenation / reduction, each of these intermediates leads to the formation of a different product. A comprehensive explanation of the products formed through different reaction pathways is shown in Fig. 5. These reaction pathways were followed for eleven TMCNs to obtain three main products: methane, formic acid, and methanol. The activity of TMCNs towards formation of these products is shown in Fig. 6. It can be seen that TiCN is more active for producing formic acid at 0 V and methanol at a very small potential of -0.22 V. Similarly, VCN is more active toward methane formation at a potential of -0.57 V, which is relatively low. The free energy diagrams of these two most promising catalysts are illustrated in Fig.7 (a, b).

[0115] To highlight the validity of the findings, the data was compared with Cu, RuO 2 , and transition metal oxides and shown in figure 8.

[0116] From Fig.8, it can be seen that TiCN is more promising than TiO 2 , Cu(211), Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 due to TiCN's smaller onset potential and higher activity for methanol and formic acid formation. Similarly, VCN is superior to V@VS 2 , Cu(211), Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 because VCN is more active toward methane formation. WCN is also better than Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 . Although WCN's onset potential for methane formation is higher than that of Cu 1 Ag 8 WC 0001 , WCN is active toward both formic acid and methanol formation. Likewise, NbCN is much better due to its higher activity for methane, methanol, and formic acid formation compared to NbO2, Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 , although it has a higher onset potential than Cu(211). In short, the identified promising catalysts are better than previously studied catalysts.References for FIG. 8

[0117] [1] Liu, S. P., Zhao, M., Gao, W., Jiang, Q., & Jacob, T. (2017). Theoretical Studies on the CO 2 Reduction to CH 3 OH on Cu (211). Electrocatalysis, 8, 647-656. [2] Liu, L., Su, X., Zhang, H., Gao, N., Xue, F., Ma, Y., ... & Fang, T. (2020). Zirconia-modified copper catalyst for CO2 conversion to methanol from DFT study. Applied Surface Science, 528, 146900. [3] Liu, L., Fan, F., Bai, M., Xue, F., Ma, X., Jiang, Z., & Fang, T. (2019). Mechanistic study of methanol synthesis from CO2 hydrogenation on Rh-doped Cu (111) surfaces. Molecular Catalysis, 466. [4] Tayyebi, E., Hussain, J., Abghoui, Y., & Skúlason, E. (2018). Trends of electrochemical CO2 reduction reaction on transition metal oxide catalysts. The Journal of Physical Chemistry C, 122(18), 10078-10087. [5] Chang, Q., Zhang, X., & Yang, Z. (2023). Improved performance of electrochemical reduction of CO2 to HCOOH by Cu incorporation into the supported Au monolayer on tungsten carbide: A DFT study. Results in Physics, 51, 106715. [6] Zhang, X. L., Wu, Z. J., Sun, F. L., Lin, C. B., Chen, W. X., Fang, L. C., & Zhuang, G. L. (2024). Crucial effect of surface oxygen species on CO2 electroreduction performance in Ti@ Cu single atom alloys. Molecular Catalysis, 555, 113894. Example 2 CORR on transition metal carbonitride surfaces

[0118] To study the reduction of CO, a slab is prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms.

[0119] Computational methods were as described above in Example 1.Screening of active site

[0120] To begin exploring the CO reduction reaction (CORR), the structure must first be optimized. Subsequently, the most active CO adsorption site on the surface needs to be evaluated. To determine the most active site, hydrogens are incorporated, the adsorption energy is calculated, and the favourable site for further reactions is identified based on the free energy diagram (FED) for each of the TMCNs. Furthermore, a supplementary test is necessary to analyze the surface's sensitivity to poisoning. This involves establishing if the site is only available for CO or if other species such as oxygen (O), hydroxyl groups (OH), or water (H 2 O) may also occupy it. Fig. 9 describes the performance of all TMCN surfaces towards CO / OH / O / H 2 O adsorption.

[0121] As can be seen in Fig. 9, it is evident that certain TMCN surfaces can potentially tie up the O 2-< and OH at zero potential. However, this is not a significant concern as these species can be experimentally removed by applying a negative potential, as the electrode surface will be negatively charged for the CORR and thus the surface repels off these negatively charged species (O 2-< and OH). Water adsorption on the catalyst surface is usually a problem but interesting. The CO adsorption is exergonic on all of these TMCNs which is beneficial to CO capture.Results and discussion

[0122] For the investigation of CORR, eleven TMCNs are evaluated, including CrCN, HfCN, MoCN, NbCN, ScCN, TaCN, TiCN, WCN, VCN, YCN, and ZrCN, to identify the most proficient catalyst for the conversion of CO into various carbon-based products such as methane and methanol, utilizing a promising reaction pathway characterized by a very low onset potential. During this comprehensive investigation, all catalysts are tested using two distinct reaction mechanisms: the Mars-van Krevelen (MvK) mechanism and the conventional mechanism. The objective is to ascertain which reaction process proves more feasible and efficient for CORR at low potential values.Mars-van Krevelen (MvK) mechanism

[0123] It was found that the carbon site is a highly active adsorption site for subsequent reactions and is frequently hydrogenated during the MvK. This mechanism involves the catalyst's continual hydrogenation, which produces methane (CH 4(g) ) while also creating carbon vacancy. However, certain catalytic surfaces produce CH 4(g) after the fourth protonation, while others require more protonation steps. Following CH 4(g) production and vacancy generation, the catalyst must be replenished for further reactions. In this cyclical process within the electrochemical cell, the catalyst speeds up the reaction, resulting in consecutive protonation, vacancy creation, and CH 4(g) generation. Subsequently, CO (g) binds the vacancy where the carbon atom of CO fills the carbon vacancy and the oxygen atom of CO gets reduced to water molecule and released, restoring the catalyst's clean structure for starting the next cycle (Eq.1). This dynamic cycle keeps the catalyst active and effective, constantly converting CO into useful carbon-based compounds.         Vac + CO (g) + H 2(g) → Clean + H 2 O (l)

[0124] As shown in Fig. 10 (a-c), the best pathway for CH 4(g) generation via the MvK mechanism starts with the second protonation step that yields CH 2 * and ultimately produces CH 4(g) , with a potential-determining step (PDS) value of 0.32 eV for MoCN.

[0125] Similarly, for CrCN and VCN, CH 4(g) is formed with ΔG PDS values of 0.36 eV and 0.41 eV, respectively, associated with the production of CH* and CH 2 * during the first and second hydrogenation steps.

[0126] The primary objective of this study is to determine an efficient pathway for creating methane with a limited onset potential using the MvK process. Thus, Fig. 11 is provided which shows the required onset potential for each catalyst investigated here to produce CH 4(g) via the MvK. This figure also shows the catalytic activity of these TMCNs.

[0127] According to Fig. 11, it is evident that MoCN, CrCN and VCN are highly active towards CH 4(g) production with very small onset potential of -0.32, -0.36 and -0.41 V, respectively. On the other hand, ScCN and YCN demand high potential and thus not interesting.Conventional mechanism

[0128] During this process, CO (g) is adsorbed onto the surface as CO*. Subsequent protonation divides the reaction into two paths: R1 from CHO* and R2 from COH*. The complete reaction pathways are shown in Fig. 12.

[0129] After screening eleven TMCNs for a suitable CO reduction, two primary products were observed: CH 4(g) and CH 3 OH (aq) . Notably, each catalyst demonstrates an entirely distinct pattern and selectivity for these products. This situation is described in Fig. 13 where on the y axis we have the onset potential (in V) as a function of activity.

[0130] From Fig. 13, it is clear that TiCN is the most promising TMCN due to its high activity and also selectivity for methanol formation at just -0.19 V. MoCN and HfCN, on the other hand, can be considered ideal due to their higher activity for methanol at -0.50 and -0.59 V. The potential window difference for formation of methane and methanol on MoCN and HfCN can be used to tune the selectivity as well. The free energy diagram (FED) of TiCN, MoCN, and HfCN is shown in Fig. 14 (a-c).

Examples

example 1

Example 1

CO2RR on transition metal carbonitride surfaces

Computational method

[0101]The interaction of CO 2 with TMCN surfaces and formation of different intermediates were studied by DFT calculations with Generalized Gradient Approximation (GGA) using RPBE exchange correlation function. The tool used for these calculations was ab initio simulation package (VASP) and cutoff energy was 450 eV with the 4×4×1 Monkhorst-Pack K-point mesh until energy differences are converged within 10 -4< eV. The Projector augmented wave (PAW) method was implemented due to full wavefunction by utilizing computationally efficient pseudopotentials, significantly reducing computation time. The surface of TMCNs were considered in the rocksalt (RS) crystallographic structure with the texture orientation of (100). A slab was prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition met...

example 2

Example 2

CORR on transition metal carbonitride surfaces

[0118]To study the reduction of CO, a slab is prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms.

[0119]Computational methods were as described above in Example 1.

Screening of active site

[0120]To begin exploring the CO reduction reaction (CORR), the structure must first be optimized. Subsequently, the most active CO adsorption site on the surface needs to be evaluated. To determine the most active site, hydrogens are incorporated, the adsorption energy is calculated, and the favourable site for further reactions is identified based on the free energy diagram (FED) for each of the TMCNs. Furthermore, a supplementary test is necessary to analyze the surface's sensitivity to poisoning. This involves establishing if the site is only available for CO or if oth...

FIELD

[0001] The disclosure relates to the reduction of carbon dioxide and carbon monoxide by electrolysis and new transition metal catalysts therefor.INTRODUCTION

[0002] Since the start of the 20 th< century the world climate has been changing more noticeably. The balance in nature is lost due to dramatic increasing CO 2 emissions by burning of carbonaceous fuels which results in global warming. An urgent effort is needed to overcome this problem to reduce the ratio of CO 2 and turn it into fuel and other useful chemical products. On the other hand, the large-scale use of unsustainable fossil fuels for energy has led to an energy crisis in the world and an increasing amount of CO 2 in the atmosphere. Due to this, the world climate is changing day by day and scientific effort is needed to overcome the emission of CO 2 in the air by converting the already present CO 2 into green energy fuels. Previous experimental and theoretical research concluded that conversion of CO 2 into valuable products can be achievable, but not yet efficient for commercialization. In the whole process of CO 2 reduction reaction (CO 2 RR), the catalyst plays a key role in capturing CO 2 and converting it into valuable chemical products and fuels. CO 2 is a chemically stable molecule and this makes its electrolytic reduction challenging with high reduction overpotential, poor product selectivity and low current efficiency. To address this challenge, researchers and scientists have been exploring novel catalysts which can overcome these issues and speed up the electrolytic process (Ebbesen & Mogesen, J. Power Sources 2009, 193:349; Fu et al, Energy & Environmental Sci 2010, 3:1382).

[0003] In CO 2 RR the catalysts play a key role in the conversion of CO 2 into valuable products. In previous decades many experimental studies have been done for electrolytic CO 2 RR on different metal catalysts. For example, pure Cu, Ag, Au, and Pt catalysts have been studied as catalysts for the CO 2 reduction reaction. However, their application for the commercial purposes is not enough due to poor product selectivity, low faradic efficiency and high overpotential that is needed. It is well known that the Cu is a widely used catalyst for the reduction of CO 2 to CH 4 but its overpotential is high (~0.9 V) and moreover it produces 15 different carbon containing products which require large amount of energy for their separation. In addition to pure Cu, polycrystalline Cu was also used for the application of CO 2 RR and it produces amounts of C 2 and C 3 aldehydes as well as ethylene.

[0004] In addition to pure metal electrocatalysts, metal oxide catalysts i.e. TiO 2 have been studied by DFT methods and considered impressive and more efficient catalysts for CO 2 conversion to CH 3 OH and CH 4 products (Ramesha, ACS Catalysis, 2014, 4:3249). In another study RhO 2 is predicted to be a novel candidate for the formation of formic acid at -0.20 V onset potential. However, stability and electron conductivity of oxides as cathode materials are a challenge that limits the application of oxides for CO 2 RR. There are numerous research studies that have been conducted to explore novel catalyst materials for the CO 2 RR. Materials studied by DFT (density functional theory) include graphene-based materials, metals, metal oxides, zeolites, sulfides, and metal organic frameworks. The utilization of catalysts for large scale production is however still a challenge and improved methods are required to overcome this problem.SUMMARY

[0005] The present disclosure provides methods to overcome the above deficiencies of the prior art. The need to explore alternative materials for catalysis of CO 2 RR and CORR arises from the imperative to develop efficient and sustainable methods for converting carbon dioxide and carbon monoxide into valuable products. Traditional catalysts may have limitations in terms of activity, selectivity, efficiency, or cost. By searching for other materials, the aim is to identify catalysts that can enhance the performance of CO 2 RR and CORR processes, making them more economically viable and environmentally friendly.

[0006] In particular, in light of the challenge of finding good electrocatalysts for CO 2 and CO reduction, the disclosure provides certain transition metal carbonitrides that are useful catalysts for CO 2 RR and CORR.

[0007] An aspect of the disclosure relates to a method for catalytic electrolytic reduction of CO 2 and / or CO, the method comprising (a) providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one carbonitride of one or more transition metal; (b) providing CO 2 and / or CO in the electrolytic cell; and (c) applying electrical potential to the electrolytic cell; whereby the CO 2 and / or CO undergoes at least one reduction reaction at the cathode.

[0008] Another aspect of the disclosure relates to an electrolytic cell for the reduction of carbon dioxide and / or carbon monoxide, comprising: an anode; a cathode, the cathode comprising a catalyst comprising at least one transition metal carbonitride, and a power supply connected to the anode and the cathode.

[0009] The disclosure further relates to a chemical reactor comprising at least one electrolytic cell as described herein; and a power supply connected to the electrolytic cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows adsorption of different species on distinctive sides of TMCNs. FIG. 2 shows HER analysis of catalyst surfaces in CO2RR. FIG. 3 shows an illustration of the most favourable pathway to create the CH 4(g) via the MvK mechanism of CO2RR for (a) MoCN and (b) VCN. FIG. 4 shows the required onset potential for methane production via MvK mechanism for CO2RR. FIG. 5 shows reaction pathways with possible products during the conventional mechanism for CO2RR. FIG. 6 shows the onset potential for different products via conventional mechanism for CO2RR. FIG. 7 shows the formation of methanol, formic acid, and methane via a conventional mechanism for CO2RR, the most promising pathways with low onset potentials (a) TiCN and (b) VCN. FIG. 8 shows a comparison between the current results and previously published catalysts for CO2RR. FIG. 9 shows an illustration of TMCNs's efficiency in CORR: CO adsorption and surface poisoning resistance. FIG. 10 shows a demonstration of the best possible route for producing CH 4(g) through the MvK mechanism for (a) MoCN, (b) CrCN and (c) VCN for the CORR. FIG. 11 shows the required potential for CH 4(g) formation through MvK mechanism for CORR. FIG. 12 shows a visual representation of CORR via the conventional mechanism. FIG. 13 shows onset potential for CH 4(g) and CH 3 OH (aq) formation via conventional mechanism for CORR. FIG. 14 shows the formation of methanol and methane via the conventional mechanism for (a) TiCN (b) MoCN and (c) HfCN. DESCRIPTION

[0011] In the following, exemplary embodiments of the invention will be described, referring to the figures. These examples are provided to provide further understanding of the invention, without limiting its scope.

[0012] In the following description, a series of steps are described. The skilled person will appreciate that unless required by the context, the order of steps is not critical for the resulting configuration and its effect. Further, it will be apparent to the skilled person that irrespective of the order of steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

[0013] As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0014] Throughout the description and claims, the terms "comprise", "including", "having", and "contain" and their variations should be understood as meaning "including but not limited to" and are not intended to exclude other components.

[0015] The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., "about 3" shall also cover exactly or "substantially constant" shall also cover exactly constant).

[0016] The term "at least one" should be understood as meaning "one or more", and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with "at least one" have the same meaning, both when the feature is referred to as "the" and "the at least one".

[0017] The present disclosure is based on the surprising finding that transition metal carbonitrides, when used as a catalyst in the electrolytic reduction of CO 2 and CO, allow for efficient reduction to produce valuable small compounds at low temperatures and pressure and using low applied potential. Given the ever-increasing levels of CO 2 in the global atmosphere and concomitant need to find ways to achieve a carbon neutral energy technology, these catalysts can be used to facilitate the conversion of CO 2 and CO into valuable carbon-containing fuels.

[0018] In general, the catalysts can be used to reduce CO 2 and / or CO to produce hydrocarbons or oxygenates having from 1 to 3 carbon atoms. Exemplary products include methane, methanol, methanediol, formaldehyde, formic acid, ethanol, ethylene glycol, ethanediol, propane and propanol.

[0019] Accordingly, the disclosure provides means in the form of methods and systems for electrolytic conversion of CO 2 and / or CO at low temperature and pressure. Compounds such as short-chain alkanes and oxygenates (e.g. alcohols and acids) having from 1 to 3 carbon atoms can be produced using the disclosed transition metal carbonitrides. Through selection of appropriate catalysts, catalyst surface and appropriate applied voltage, the reduction reaction can be geared to produce compounds of particular interest.

[0020] In an aspect, the present disclosure is based on the investigation of the capability of transition metal carbonitrides (TMCNs) to catalyze the conversion of CO 2 and CO into valuable organic compounds that can for example be used as valuable fuel. The results are based on studies that delve into the electronic intricacies of TMCNs, unraveling their potential to drive the transformation of CO 2 and CO .

[0021] One distinct advantage of the transition metal carbonitride catalysts described herein is their unique usefulness to drive the CO 2 and CO reduction reactions via the Mars van Krevelen (MvK) reaction mechanism. This is not possible on most other catalysts surfaces and explains in part the unique chemistry possible by using these catalysts.CO 2 Reduction Reaction (CO 2 RR)

[0022] Density Functional Theory (DFT) to explore the reactivity of the reduction of CO 2 in the presence of 11 different transition metal carbonitride surfaces. The goal was to get an understanding of the performance and competence of these materials for CO 2 RR.

[0023] DFT is a quantum mechanical methodology that accounts for the interaction between electrons and the nucleus. The input is the atomic structure of the molecular system of interest and the output is the ground state energy of the system. The reaction mechanism of CO 2 reduction to CH 4 on a stepped Cu(211) surface was first proposed by Peterson et al (Energy Environ Sci 2010, 3:1311). The free energy of adsorbed intermediates on the catalyst surface were calculated using a thermochemical model (TCM). The same approach has been successfully applied on several other electrolytic systems, including water oxidation on transition metal oxides, N 2 electroreduction on transition metal surfaces, transition metal nitrides and transition metal oxides, hydrogen evolution reaction (HER) on transition metal nitrides and CO 2 RR on transition metals and transition metal oxides.

[0024] The need to explore alternative materials for the CO 2 RR arises from the imperative to develop efficient and sustainable methods for converting carbon dioxide into valuable products. Traditional catalysts may have limitations in terms of activity, selectivity, efficiency, or cost. By searching for other materials, researchers aim to identify catalysts that can enhance the performance of CO 2 RR processes, making them more economically viable and environmentally friendly. The surface chemistry of TMCNs is comparable to precious Pt-group metals which was already described by Levy and Boudart (Science 1973, 181:185). In previous studies these TMCNs have been used for wide range of reactions such as CO oxidation, hydrogenation, methane dry reforming, desulfurization, conversation of methane to gas and water gas shift reaction. Hence these materials have received great attention for application in catalysis.

[0025] Utilizing advanced quantum mechanical simulations and computational models, the present disclosure is based on an exploration of the binding energies and reaction pathways of TMCNs (CrCN, HfCN, MoCN, YcCN, ScCN, NbCN, ZrCN, TaCN, TiCN, WCN, and VCN), with a focus on their suitability for catalyzing CO 2 reduction. In this research a complete and comprehensive analysis for above mentioned TMCNs on the (100) facets was conducted.

[0026] In the following Example 1 it is described how DFT calculations can be used to describe the interaction of CO 2 with TMCN surfaces and predict the reaction pathway for CO 2 RR on TMCN. Two mechanisms were considered, the Mars-van Krevelen mechanism (MvK) and conventional surface mechanism, to study the CO 2 RR towards methane and methanol production on TMCNs surfaces, The analysis reveals that several TMCNs exhibit remarkable catalytic activity for CO 2 reduction, surpassing the performance of conventional catalysts. The electronic structure of these TMCNs plays a pivotal role in facilitating the conversion of CO 2 into valuable chemical products.

[0027] According to our investigation, it seems that HfCN, NbCN, TiCN, TaCN and WCN are highly active to convert the CO 2 into formic acid, HCOOH (aq) , at 0V via CO 2 RR (conventional mechanism), following eq.1 below.         Clean → COOH* → HCOOH (aq)      (1)

[0028] Similarly, VCN, YCN and ZrCN also produced HCOOH (aq) at 0V by following eq. 2 below:         Clean → OCHO* → HCOOH (aq)      (2)

[0029] Thus, we are able to assert that at least these eight catalytic surfaces exhibit a high level of activity for the conversion of CO 2 RR to HCOOH (aq) via conventional procedure. However, TaCN, YCN and ZrCN are most promising due to single product formation at lowest onset potential, being only formic acid.

[0030] On the other hand, TiCN is very active for CH 3 OH (aq) formation with only -0.22 V by following the eq.3 below:         Clean → COOH* → HCOOH* → CHO* → CH2O* → CH30* → CH3OH (aq)      (3)

[0031] By contrast, VCN is most promising catalyst to produce methane at small onset potential of -0.57 V by following the eq. 4 below:         Clean→ COOH*→ C(OH*) 2 → COH*→ CHOH*→ CH2OH*→ CH3*+OH*→ CH3→ CH 4(g)      (4) CO reduction reaction (CORR)

[0032] The disclosure also shows that transition metal carbonitrides (TMCNs) are capable of catalyzing the conversion of CO into valuable organic compounds via CORR.

[0033] Protonation along the reaction pathway from CO to CH 4 and CH 3 OH on 11 transition metal carbonitrides have been calculated, including CrCN, HfCN, MoCN, NbCN, TaCN, ScCN, TiCN, VCN, WCN, YCN and ZrCN with the (100) facets. These facets of TMCNs are considered the most stable structure with the 1:1 TM:C:N ratio and cubic crystallography.

[0034] Two mechanisms were considered, the Mars-van Krevelen mechanism (MvK) and conventional surface mechanism, to study the CORR towards methane and methanol production on TMCNs surfaces. In MvK mechanism, carbon vacancy is generated with the formation of methane and then vacancy is filled with the Carbon of CO and release of Oxygen of CO in form of water molecule. The stability of the vacancy (as an indication of material stability against decomposition) is crucial to investigate here and thus Climbing Image Nudged Elastic Band (CI-NEB) has been done to estimate the activation energy of migration of carbon atom from second layer to first layer to fill the carbon vacancy. In conventional surface mechanism the interaction of CO gas molecule on the surface of TMCNs with different sites is studied. All aspects of each mechanism are calculated explicitly, and free energy diagrams are drawn for each adsorbed species on the surface of catalyst. Thermochemical model was implemented to obtain the trends of CORR on each TMCNs surface.

[0035] Employing Density Functional Theory (DFT) the 11 TMCNs were thus explored for the conversion of CO to methane and methanol via both MvK and conventional surface mechanism.

[0036] Results of the study are presented in the following Example 2. In the study, TiCN, MoCN and HfCN were found to be particularly good candidates to produce methanol during the CORR according to the following equations (1) - (3), and equation 4 shows vacancy regeneration with CO:         CO*→CHO*→ CH2O* → CH3O*→ CH3OH (aq)      (1)         CO* → CHO*→ CHO*+CH* → CH2O*+CH*→CH3O*+CH* → CH3QH (aq) +CH*     (2)         CO*→ CHO*→ CH2O*→ CH2OH*→ CH 3 OH (aq)      (3)         Uac+ CO (g) + H 2(g) → Clean + H 2 O (l)      (4)

[0037] Moreover, TiCN was found particularly promising due to its high activity to produce only CH 3 OH (aq) at a very small applied potential of -0.19 V.

[0038] Via MvK mechanism, MoCN, CrCN, VCN, TiCN, TaCN, NbCN, ZrCN are surfaces that produce methane via the mechanism of eq. (4). However, MoCN, CrCN and VCN are most active for CORR to CH 4(g) due to smaller values of onset potential.

[0039] All of these surfaces having the most promising catalyst activity were found to require a potential less than -0.7V to produce any product.

[0040] Overall, the findings indicate due to CO spontaneously adsorption, less poisoning, less over potential and high product selectivity TMCNs are excellent choice for CORR to produce valuable products such as methane and methanol.Electrolytic cells

[0041] In general, an electrolytic cell is a chemical reactor where chemical reactions take place, driven by an applied electric potential. An electrolytic cell in the present context is therefore an electrolytic cell that undergoes a redox reaction when electrical potential is applied to the cell.

[0042] Design of electrolytic cells is known in the art. Examples of suitable electrolytic cells include H-type cells, polymer electrolyte membrane (PEM) flow cells, microfluidic flow cells, solid oxide electrolytic cells and DEMS cells. It should be appreciated that the transition metal carbonitrides disclosed herein can be adapted for use in any type of electrolytic cell. Examples of suitable electrolytic cells are described in Liang et al. (Journal of CO2 Utilization, 2020, 35:90-105).

[0043] In an H-type cell, the cathodic and anodic compartments are typically separated by an ion-exchange membrane that allows ions to flow across while preventing reaction products from being reoxidized at the anode. There can be a reference electrode present in the cathodic compartment. In these cells, there is a liquid electrolyte solution at the cathode and anode, and CO 2 gas is typically streamed into the cathodic compartment.

[0044] In PEM flow cells, CO and / or CO 2 can be streamed directly at the cathode or it can be provided by dissolved bicarbonate. There can be either a liquid phase at both electrodes, a gas phase at the cathode and liquid at the anode or a humified gas phase at both electrodes. Typically, there is a gas diffusion electrode at the cathode and possibly also at the anode.

[0045] In microfluidic flow cells, an electrolyte channel is provided between a cathode and an anode, with a stream of CO and / or CO 2 gas delivered at the cathode. Instead of utilizing a membrane, the cathode and anode are separated by the diffusion of products.

[0046] Solid state electrolysis cells can improve the kinetics of reactions and achieve high efficiency. In these cells, there is a solid electrolyte to facilitate transfer of ions, with a membrane separating the cathode and anode. The cells can operate at high temperatures if needed, e.g. at or above 600°C, such as high as 700°C, 800°C or 900°C, even as high as 1000°C.

[0047] The transition metal carbonitride catalysts disclosed herein can be provided in any suitable form in the electrolytic cell of interest, depending on its design and intended use. Thus, the catalysts can be provided as a coating, film, as a powder, dopant etc., and in forms such as microparticles, nanoparticles such as zero- dimensional (0D), one-dimensional (1 D), two-dimensional (2D) and three- dimensional (3D) nanoparticles, nanotubes, nanosheets, heterostructures, a single atom catalyst, a dual-atom catalyst and a triple-atom catalyst.

[0048] Transition metal carbonitrides can have the general 2:1:1 (TM:C:N) stoichiometry, e.g. VCN, MoCN, WCN, TiCN etc. Other stoichiometries are however also possible.

[0049] Thus, the skilled person will appreciate that the carbonitrides may have an alternative stoichiometry and such alternative stoichiometries are also within scope of the present disclosure. Further, chemical compounds as described herein are provided by their chemical formula irrespective of their phase or state. In particular, compounds that are present in their gaseous state when present in a pure and isolated form at room temperature (such as CO or CO 2 ) are herein described by their chemical formula. For example, carbon monoxide and carbon dioxide is herein described as CO and CO 2 , whether present as a gas, as individual molecules, in clusters, bound to surfaces or present as a solute, and the same applies to other molecular species described herein.

[0050] A mixture of CO and CO 2 can be provided in the electrolytic cell. During such operation of the cell, both CORR and CO2RR reactions will take place with products formed depending on the type of catalyst used (i.e., which TMCN) and the applied voltage.

[0051] Alternatively, only CO or only CO 2 can be provided in the cell. This may be preferable, as it will be easier to control the respective reaction (CORR or CO2RR) for the type of TMCN being used in the cell.

[0052] The proton donor in the electrolytic reactions can be any suitable substance that is capable of donating protons in the electrolytic cell. The proton donor can for example be water or it can be in the form of an acid, such as any suitable organic or inorganic acid. The proton donor can be provided in an acidic, neutral or alkaline aqueous solutions. The proton donor can also, or alternatively, be provided by H 2 oxidation at the anode. In other words, hydrogen can be considered as a source of protons: H 2 <=> 2(H +< + e -< )

[0053] The electrolytic cell can in general comprises at least three general parts or components, a cathode electrode, an anode electrode and an electrolyte.

[0054] The electrolytic reduction of carbon dioxide is the conversion of carbon dioxide to more reduced chemical species using electrical energy.

[0055] The different parts or components can be provided in separate containers, or they can be provided in a single container. The electrolyte can be a solid or an aqueous solution in which ions are provided, for example in a dissolved form in an aqueous solution when present. When provided as an aqueous solution, the aqueous solution can be a neutral, an alkaline or an acidic solution.Sources of CO 2 and CO

[0056] Carbon dioxide (CO 2 ) can be provided by a source such as any one of bicarbonate (HCO 3 -< ), carbonate (CO 3 -2< ) and / or carbonic acid (H 2 CO 3 ). For example, bicarbonate and carbonate can be provided as bicarbonate or carbonate salts, either in pure form as a solid or in solution, or in a mixture into a solution, that can preferably be an aqueous solution. A mixture of bicarbonate, carbonate and carbonic acid will reach equilibrium in solution. Therefore, the relative concentration of these species will depend on pH of an aqueous solution.

[0057] An alternate source of CO and CO 2 is the gaseous form of the compounds, CO(g) and CO 2 (g). Gaseous CO and CO 2 can be provided as a sole source of CO and / or CO 2 , or it can be provided as a supplement to other sources of CO or CO 2 in the cell. In the case of CO 2 , this includes the previously mentioned bicarbonate, carbonate and carbonic acid.

[0058] Other or additional sources of CO and CO 2 are possible. For example, direct injection of CO 2 gas is possible by bubbling CO 2 directly into an electrolyte solution.

[0059] Alternatively, dissolved carbonate salts (e.g., sodium carbonate, Na 2 CO 3 ) in water can be used to provide a source of CO 2 .

[0060] An alternative source can be provided from industrial CO 2 Emissions. Capturing CO 2 from industrial processes such as cement production, steel manufacturing, or chemical production can also form a source of CO 2 . Further, chemical reactions that release CO 2 can be a source of CO 2 .

[0061] Certain microbial processes, such as fermentation, produce CO 2 as a byproduct and can serve as a source of CO 2 . The CO 2 can also be provided through photocatalytic production.

[0062] Another source is represented by CO 2 captured from fossil fuel-based power plants (coal, natural gas, oil) which produce large amounts of CO 2 .

[0063] Yet another source can be CO 2 generated from burning biomass such as agricultural waste, forestry residues, or bioenergy crops. Further, CO 2 emitted from the incineration of municipal solid waste can be captured as a source of CO 2 .

[0064] Through advanced capture technologies, CO 2 can be captured directly from the ambient air.

[0065] Carbon monoxide can be provided e.g. from microbial production, decomposition of metal carbonyls, thermal decomposition of formic acid, reforming reactions, water-gas shift reaction or gasification of biomass or coal.Catalysts

[0066] In general terms, the catalyst on the electrode surface should ideally have the following characteristics: It should (a) be chemically stable, it should (b) not become reduced or otherwise consumed during the electrolytic process, it should facilitate the formation of carbon-containing products, and (d) use of the catalyst should lead to the production of minimal amount of hydrogen gas. The catalysts disclosed herein fulfil these characteristics.

[0067] A catalyst can comprise one or more stabiliser that serves the role of preventing degradation of the catalyst. Suitable stabilisers should be more stable to degradation than the metal carbonitride(s) being employed, but otherwise are inert with respect to the catalytic reactions taking place on the electrode surface. Exemplary stabilisers include, but is not limited to, metal oxycarbonitrides, metal oxynitrides, bimetallic oxides and the like.

[0068] The transition metal carbonitrides can be provided as a film, i.e. as a thin layer (e.g., as few layers or as a monolayer) on a stable and conductive surface.

[0069] The catalysts disclosed herein are transition metal carbonitride catalysts. The catalysts can generally contain one or more transition metal carbonitride, or any mixture of transition metal carbonitrides.

[0070] The transition metal carbonitride can preferably be selected from the group consisting of carbonitrides of Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. The preferable catalyst composition can be varied depending on the intended use, i.e. the reactant being provided (CO or CO 2 ) and the desired product(s) formed in the electrolytic cell.

[0071] For the catalytic reduction of CO 2 , the suitable catalyst can comprise one or more carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr, more preferably selected from Ta, Y, Zr, V and Ti.

[0072] For the catalytic reduction of CO, the suitable catalyst can comprise one or more carbonitride of a transition metal selected from Mo, Hf, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Ti, Cr and V.

[0073] For formation of methane from CO 2 , the suitable catalyst(s) can comprise one or more of Vanadium, Chromium, Niobium, Molybdenum, Tantalum, Titanium or Zirconium carbonitrides.

[0074] For formation of formic acid from CO 2 , the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr.

[0075] For formation of methanol from CO 2 , the suitable catalyst can comprise titanium and / or Wolfram carbonitrides.

[0076] For formation of methane from CO, the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Cr and V.

[0077] For formation of methanol from CO, the suitable catalyst can comprise one or more transition metal carbonitride of a transition metal selected from Ti, Mo and Hf.

[0078] An advantage of the present invention is that the process can be suitably operated using suitable electrolytes in solid or liquid form. An electrolyte solution can be non-aqueous or aqueous. For example, an electrolyte solution can comprise, or consist of an aqueous solutions containing dissolved electrolytes (salts). Thus, in certain embodiments of the process and system, the electrolytic cell comprises one or more aqueous electrolytic solutions, in one or more cell compartments. Individual cell compartments can be separated by suitable barriers, such as membranes that allow electrolytes to pass through.

[0079] Solid and liquid electrolytes may comprise any of various typical inorganic or organic salts such as but limited to soluble salts of e.g. chloride, nitrate, chlorate bromide, etc. e.g. sodium chloride, potassium chloride, calcium chloride, ammonium chloride, and other suitable salts. The electrolyte may also comprise any one or a combination of, alkali or alkaline earth metal oxides, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, rubidium hydroxide and cesium hydroxide.

[0080] An aqueous electrolyte solution can preferably comprise carbonate, bicarbonate or carbonic acid as a source of CO 2 . Such an aqueous electrolyte solution can also further comprise one or more organic or inorganic acids. Inorganic acids can include mineral acids that include but are not limited to, hydrochloric acid, nitric acid, phosphoric acid, sulphuric acid, boric acid, hydrofluoric acid, hydrobromic acid, and perchloric acid. The electrolyte can alternatively be provided as a protic or aprotic, non-aqueous solution. For example, the electrolyte can be provided as an ionic liquid, i.e. as a molten salt, for example a sodium chloride salt.

[0081] Depending on the substance composition of the catalyst, a suitable surface crystal structure may be preferred. Various different crystal structures exist for transition metal carbonitrides and different structures can be obtained at different growth conditions. It is within scope of the skilled person to select appropriate surface crystal structures.

[0082] Further, it is possible that a catalyst contains more than transition metal carbonitride, such as two or more or three or more transition metals. For example, a transition metal carbonitride can be doped by a small amount of a second (or more) transition metal. Alternatively, a catalyst can contain one or more layer of a transition metal carbonitride that is provided over one or more layers of another transition metal carbonitride.

[0083] In certain embodiments of the invention, the catalyst surface is provided as a pure transition metal carbonitride, i.e. the catalyst comprises a single transition metal carbonitride, i.e. the catalyst for example does not contain a mixture of transition metal carbonitrides or one transition metal carbonitride that is coated by one or several layers of a second (or more) transition metal carbonitrides.

[0084] Thus, as will be apparent to the skilled person, the catalyst according to the invention can comprise a single transition metal carbonitride. The catalyst can alternatively comprise, or consist of, a mixture of two or more transition metal carbonitrides. Such mixed transition metal carbonitrides can comprise a single crystal structure or polycrystalline structures, for example a rocksalt structure. The mixed transition metal carbonitrides can also comprise a mixture of transition metal carbonitrides that are of different crystal structures and / or carbonitride with different catalytic facets. Accordingly, such mixed transition metal carbonitrides can further comprise a single, or a mixture of, facets. Mixed transition metal carbonitride catalysts can be grown or manufactured separately and then assembled into mixed catalysts comprising the different metal carbonitrides, wherein the carbonitrides in the mixture have the same or different crystal structures.

[0085] As described in more detail herein, running a current through the electrolytic cell leads to a chemical reaction in which carbon monoxide (CO) and / or carbon dioxide (CO 2 ) is reduced in a series of steps to ultimately form one or more valuable short chain organic products, including for example methane, methanol and formic acid. The running of current is achieved by applying a voltage to the cell. An advantage of the disclosed transition metal carbonitride catalysts is the possibility of performing electrolytic production of these valuable products at a low electrode potential under conditions of low temperature and / or gas pressure, which is beneficial in terms of energy efficiency and required equipment.

[0086] An electrolytic cell can be operated at an ambient gas pressure of about 1 atmosphere. The electrolytic cell can also be operated at higher pressure, i.e. pressure that is greater than ambient pressure. For example, the cell can be operated at a pressure of up to 50 atmospheres (atm), up to 40 atmospheres, up to 30 atmospheres, up to 20 atmospheres or up to 10 atmospheres. In some embodiments, the electrolytic cell is operated at a pressure that is in the range of 1 to 30 atmospheres, in the range of 1 to 20 atmospheres, in the range of 1 to 10 atmospheres, in the range of 1 to 5 atmospheres or in the range of 1 to 3 atmospheres. The electrolytic cell can also be operated at a pressure that is in the range of 2 to 20 atmospheres, in the range of 3 to 20 atmospheres, in the range of 4 to 20 atmospheres, or in the range of 5 to 20 atmospheres, such as at about atmospheres, about 6 atmospheres, about 7 atmospheres, about 8 atmospheres, about 9 atmospheres, about 10 atmospheres, about 11 atmospheres, about 12 atmospheres, about 13 atmospheres, about 14 atmospheres, about 15 atmospheres, about 16 atmospheres, about 17 atmospheres, about 18 atmospheres, about 19 atmospheres or about 20 atmospheres.

[0087] The electric potential can be applied as a constant or variable electric potential. Pulsed electric fields generated by pulsed potentials can be varied by adjusting a number of parameters such as electric field intensity, rise time of voltage pulses, number of pulses, frequency of pulses, pulse wave shape, treatment time (i.e. the length of time the pulse sequence is applied, resulting in from a product of the number of pulses and the duration of each pulse).

[0088] In certain useful embodiments, the cell is operated at an electric potential that results in formation of the desired product(s). The electric potential can in different applications be less than (i.e., less negative) than about -2.0V, less than about -1.5V, less than about -1.0 V, less than about -0.9 V, less than about -0.8V, less than about - 0.7 V, less than about -0.6 V, less than about 0.5 V, less than about -0.4 V, less than about -0.3 V or less than about -0.2 V. In some embodiments, the cell is operated at electrode potential in the range of about -1.5 V to about 0.0V or in the range of about -1.0 V to about 0.0 V, such as in the range of about -0.9 V to about 0.0V, such as in the range of about -0.8 V to about 0.0 V, such as in the range of about -0.7V to about 0.0V, about -0.6 V to about 0.0 V, about -0.5 V to about 0.0 V, or in the range of about -0.3 V to about 0.0 V or in the range of about -0.2 V to about 0.0 V. The upper limit (i.e., more negative potential limit) of the range can be about -0.3 V, about -0.4 V, about -0.5 V, about -0.6 V, about -0.7 V, about -1.0V, about -1.5V or about -2.0V. The lower limit (i.e. less negative potential limit) of the range can be as high as about +1.0V, about +0.5V, about 0.0 V, about -0.1 V, about -0.2 V, or about -0.3 V. Any of these electric potentials and ranges of electric potentials are contemplated for the electrolytic methods and electrolytic cells disclosed herein.

[0089] A high (more positive) or low (more negative) potential may be applied to the electrolytic cell before and / or after operation of the cell to produce products from CO / CO 2 . For example, it may be beneficial to increase voltage to a more positive potential (e.g., a voltage greater than 0.0V) to free the surface of the catalyst / electrode from adsorbents that may have an adverse effect on its operation. After such cleaning, the electrolytic cell can be operated under normal production potential.

[0090] During operation of the cell, the composition of products obtained in the reduction of CO and / or CO 2 can be altered / controlled by selective adjustment of applied potential for any given catalyst surface. Thus, the data provided herein shows that depending on the relative binding energies of adsorbed intermediates the selectivity of the electrolytic cell changes depending on the applied voltage.

[0091] The temperature of the cell may be varied as needed. One advantage of the present catalysts is that the CO 2 RR and CORR reactions can be carried out at low temperature, such as at or near ambient room temperature. However, it will be appreciated that the temperature may be adapted and / or adjusted as needed.

[0092] For example, solid state electrolytic cells can operate at high temperatures of up to or close to 1000°C, and the catalysts described can be used at such high temperatures.

[0093] In general therefore, the temperature of the electrolytic cell, and in particular the temperature at the cathode of the cell, can be in the range of 0°C to 1000°C, in the range of 0°C to 900°C, 0°C to 800°C, 0°C to 700°C, 0°C to 600°C, 0°C to 500°C, 0°C to 400°C, 0°C to 300°C, 0°C to 200°C, 0°C to 100°C or 0°C to 50°C. In some embodiments, the temperature is in the range of 0°C to 50°C, 5°C to 45°C, 10°C to 40°C, 15°C to 35°C, or 20°C to 30°C.

[0094] An advantage of the present invention is the specificity and efficiency of product formation over side-product (such as H 2 ) formation, which is a challenge due to the competing binding energies of hydrogen and oxygen on the catalyst surface. In certain embodiments, less than about 50% moles H 2 are formed compared to moles of the desired product formed, and preferably less than about 40% moles H 2 , less than about 30% moles H 2 , less than about 20% moles H 2 , less than about 10% moles H 2 , less than about 5% moles H 2 , less than about 2% moles H 2 , or less than about 1 % moles H 2 .

[0095] Further, reaction conditions (choice of catalyst, applied potential in particular) can be set so that one reaction product is selectively formed over other reaction products. This means that the reaction predominantly or even completely leads to the formation of one particular reaction product (e.g., methane, methanol, formic acid, methanediol).

[0096] The reaction pathway of CO and CO 2 reduction depends on the relative energies of reaction intermediates. Thus, the pathway can depend on the system within which the reaction takes place, including the chemical composition of the catalysis and the catalytic surface being used in the reaction.

[0097] The active part of an industrial heterogeneous catalyst is most commonly a solid surface, e.g. a transition metal or transition metal carbonitride or mixture of transition metal carbonitrides. The surface offers a favourable energy path from reactants to products, by binding reactants and reaction intermediates. The binding energy of reactants to the surface must be strong enough to produce reaction intermediates, but weak enough to allow products to leave the surface, allowing more reactions to take place on the surface. The consequence is that for a reaction, there will be an optimum binding energy for an intermediate, such that both stronger and weaker binding leads to lower activity. A result of this phenomenon is a reaction relationship called the volcano-shaped relationship, or commonly referred to as a Volcano plot.

[0098] Catalyst activity can in general be modified by altering the local electronic structure by strain, ligand, substitution and / or alloying. These alterations can result in changes in binding energies of reaction intermediates, and thereby a change in the thermodynamics of the overall reaction profile. Thereby it may be possible to adapt the reaction profile to specifically obtain desired reaction products.

[0099] Exemplary embodiments in accordance with the present disclosure include the following: 1. A method for catalytic electrolytic reduction of CO 2 and / or CO, the method comprising: a. providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one transition metal carbonitride; b. providing CO 2 and / or CO in the electrolytic cell; and c. applying electrical potential to the electrolytic cell; whereby the CO 2 and / or CO undergoes at least one reduction reaction at the cathode. 2. The method of clause 1, wherein the catalyst is provided as a surface coating, a film, a microparticle, nanotubes, nanosheets, heterostructure, dopant and / or a nanoparticle. 3. The method of any one of the previous clauses, wherein the temperature at the at least one cathode is in the range of 0°C to 300°C, 0°C to 200°C, 0°C to 100°C, 0°C to 50°C 5°C to 45°C, 10°C to 40°C, 15°C to 35°C, or 20°C to 30°C. 4. The method of any one of the previous clauses, wherein the electrolytic cell comprises gas diffusion electrodes at the anode and / or the cathode. 5. The method of any one of the previous clauses, wherein the electrolytic cell further comprises at least one reference electrode. 6. The method of any one of the previous clauses, wherein the electrolytic reduction reaction results in formation of at least one alkane, lower alcohol or acid having from 1 to 3 carbon atoms. 7. The method of any one of the previous clauses, wherein the electrolytic reduction reaction results in formation of at least one product selected from methanol, methane, methanediol, formic acid, formaldehyde, ethanol, ethane, ethylene glycol, ethanediol, propane and propanol. 8. The method of any one of the previous clauses, wherein CO 2 and / or CO are provided in gaseous form into the electrolytic cell, and wherein the gas pressure at the at least one cathode is in the range of about 1 atm to 40 atm, 5 atm to 30 atm, or 10 atm to 20 atm. 9. The method of any one of the previous clauses 1 to 8, wherein the gas pressure at the at least one cathode is ambient pressure of about 1 atm. 10. The method of any one of the previous clauses, wherein the electrical potential applied to the electrolytic cell is in the range of -2.0 V to +1.0 V using a reversible hydrogen electrode (RHE) as a reference. 11. The method of any one of the previous clauses, wherein molar production of hydrogen (H 2 ) compared with CO 2 and / or CO reduction in the electrolytic cell is less than 50%. 12. The method of any one of the previous clauses, wherein the electrolyte solution comprises at least one source of CO 2 selected from carbonate (CO 3 2-< ), carbonate salts, bicarbonate (HCO 3 -< ) and carbonic acid (H 2 CO 3 ). 13. The method of any one of the previous clauses, wherein CO and / or CO 2 is provided in the solution by a stream of gas. 14. The method of any one of the previous clauses, wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 15. The method of any one of the previous clauses, wherein CO 2 only is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr, more preferably selected from Ta, Y, Zr, V and Ti. 16. The method of any one of the previous clauses, wherein CO only is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Mo, Hf, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Ti, Cr and V. 17. The method of any one of the previous clauses, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of vanadium (V), Chromium (Cr), Niobium (Nb), Molybdenum (Mo), Tantalum (Ta), Titanium (Ti) or Zirconium (Zr), the catalytic reduction resulting in formation of methane. 18. The method of any one of the previous clauses 1-13, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Hf, Nb, Ti, Ta, W, V, Y and Zr, the catalytic reduction resulting in the formation of formic acid. 19. The method of any one of the previous clauses 1-13, wherein CO 2 only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of titanium (Ti), the catalytic reduction resulting in formation of methanol. 20. The method of any one of the previous clauses 1-13, wherein CO only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Mo, Cr, V, Ti, Ta, Nb and Zr, the catalytic reaction resulting in formation of methane. 21. The method of the previous clause, wherein the carbonitride is a carbonitride of a transition metal selected from Mo, Cr and V. 22. The method of any one of the previous clauses 1-13, wherein CO only is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Ti, Mo and Hf, the catalytic reaction resulting in formation of methanol. 23. An electrolytic cell for the reduction of carbon dioxide and / or carbon monoxide, comprising: an anode; and a cathode, the cathode comprising a catalyst comprising at least one transition metal carbonitride. 24. The electrolytic cell of the previous clause, wherein the catalyst comprises at least one carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 25. The electrolytic cell of the previous clause, wherein the catalyst is provided as a surface coating, a film, a microparticle, nanotubes, nanosheets, nanoarrays, nanoribbons, heterostructure, dopant, a nanoparticle, zero- dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three- dimensional (3D), a single atom catalyst, a dual-atom catalyst and a triple-atom catalyst. 26. The electrolytic cell of any one of the previous two clauses, wherein the catalyst is provided as a pure carbonitride of a transition metal selected from Mo, Cr, V, Ti, Ta, Nb, Zr, Hf, W and Y. 27. The electrolytic cell of any one of the previous four clauses, wherein the electrolytic cell comprises gas diffusion electrodes at the anode and / or the cathode. 28. The electrolytic cell of any one of the previous five clauses, wherein the electrolytic cell further comprises at least one reference electrode. 29. A chemical reactor comprising at least one electrolytic cell as set forth in any one of clauses 23-28; and a power supply connected to the electrolytic cell.

[0100] The invention will now be exemplified by the following non-limiting Examples.Example 1 CO2RR on transition metal carbonitride surfaces Computational method

[0101] The interaction of CO 2 with TMCN surfaces and formation of different intermediates were studied by DFT calculations with Generalized Gradient Approximation (GGA) using RPBE exchange correlation function. The tool used for these calculations was ab initio simulation package (VASP) and cutoff energy was 450 eV with the 4×4×1 Monkhorst-Pack K-point mesh until energy differences are converged within 10 -4< eV. The Projector augmented wave (PAW) method was implemented due to full wavefunction by utilizing computationally efficient pseudopotentials, significantly reducing computation time. The surface of TMCNs were considered in the rocksalt (RS) crystallographic structure with the texture orientation of (100). A slab was prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms. The boundary conditions were periodic with 20 Å vacuum along the z direction to avoid self-interaction of neighboring layers. The bottom two layers were fixed, and the top 3 layers were allowed to fully relax together with any adsorbates on the surface.

[0102] The binding energy of an adsorbate was calculated according to the equation 1: ΔE ads = E adsorbate / TMCN slab − E TMCN slab − E adsorbate

[0103] Here E (adsorbate / TMCN slab) is the total energy of the system with an adsorbate on the TMCN slab, E (TMCN slab) is the total energy of the pristine TMCN slab, and E(adsorbate) is the total energy of the adsorbate. The negative ΔE ads corresponds to the exothermic adsorption phenomenon.

[0104] The Computational hydrogen electrode model as proposed by Norskov et al was used to calculate the free energy diagram for CO 2 RR and / or CORR along different paths at certain applied potential. According to this method at room temperature kinetic barrier is negligible for the proton coupled electron step and the potential limiting step is the most positive energy difference between the two adjacent steps.

[0105] The reaction free energy of an adsorbate for CO 2 RR at any arbitrary potential U vs RHE and any arbitrary pH was calculated by equation: Δ G U RHE = Δ G U RHE = 0 + neU RHE eU RHE = eU RHE + 2 .3k b TpH where U RHE is the applied potential referred against the standard hydrogen electrode (SHE), n is number of electrons, e is the elementary charge , k b is the Boltzmann constant and T is the Temperature. By putting eq (2) into eq(3) we will get : Δ G U RHE = Δ G U RHE = 0 + n eU RHE = eU RHE + 2 .3k b TpH

[0106] Generally overpotential are independent of pH of electrolyte so in this study we will consider pH = 0. Hence for each elementary step ΔG (U = 0) is calculated by Δ G U = 0 = ΔE DFT + ΔE ZPE − T Δ S + ΔE 0K → T + ΔE sol

[0107] Where ΔG is the Gibbs free energy, ΔE DFT is the electronic energy calculated by DFT, ΔE ZPE is the zero-point energy correction and TΔS is entropy differences between the gas phase and adsorbed species calculated by vibrational frequencies for the adsorbed species, ΔE sol is the adsorbate stabilization term due to the solvent and we have not included in this study. ΔE OK → T is the change in internal energy because of temperature. The value of the gas phase is taken from the thermodynamic tables from textbooks.Results and discussion Screening of the active site

[0108] To initiate the CO 2 reduction reaction (CO2RR), the process begins with optimizing the structure, followed by a detailed screening of the active sites. This involves hydrogenating various sites on the surface. Additionally, we adsorb COOH, and OCHO on different regions of the surface to identify the most active sites for each species. The CO2RR process is often complicated by the production of H 2 as a byproduct, making it crucial to compare the efficiencies of CO2RR and the hydrogen evolution reaction (HER) before proceeding further. Moreover, the potential occupancy of active sites by oxygen (O), hydroxyl groups (OH), or water (H 2 O) necessitates additional scrutiny. To clarify whether the active sites are available for CO2RR or occupied by other species, we also investigate adsorption of these molecules. This comprehensive analysis ensures the true availability and activity of the active sites. All data is detailed in Fig. 1, where we can see that none of the catalyst surfaces perform well for the HER, which is needed for successful CO2RR. Additionally, the most active site is the carbon site, denoted as CH. Further, OCHO and COOH adsorption is found to be exothermic on these TMCNs.Compression of CO2RR and HER

[0109] To explain the CO2RR, we first need to examine the catalysts for the HER. This is because HER competes with CO2RR, and hydrogen (H 2 ) is often produced as a byproduct. Therefore, before delving into the details of CO2RR, the effectiveness of all catalysts for HER is summarized in Figure 2, which shows that most of these surfaces do not intend to bind proton and thus HER should be suppressed on these surfaces.Mars-van Krevelen (MvK) mechanism

[0110] In this mechanism, the carbon active site is repeatedly hydrogenated to produce methane in the gaseous phase. Sometimes, the surface requires more than four hydrogen atoms to produce CH 4(g) , but many surfaces can ideally produce CH 4(g) after four hydrogenation steps. Along with methane, a carbon vacancy is created where CO 2(g) adsorbing into the vacancy regenerates the catalyst by hydrogenation of the oxygen atoms of the adsorbed CO2 and releasing them into water, (Eq. 1). This process is cyclical: hydrogen in the electrochemical cell adsorbs onto the active site, creating a vacancy. The subsequent closure of the vacancy results in a clean structure. However, different catalytic surfaces require varying amounts of potential for this process to occur.         Vac+ CO 2(g) + 2H 2(g) → Clean + 2H 2 O (l)      (1)

[0111] During the current investigation, the eleven TMCNs were explored to evaluate their reactivity for methane formation at small potential. Consequently, free energy diagrams (FEDs) for the most promising catalysts via MvK mechanism have been constructed. According to Fig. 3 (a, b), the optimal pathway for methane formation via the MvK mechanism begins with the initial protonation step, leading to the formation of CH* and eventually methane, with a potential-determining step (PDS) value of 0.32 eV for MoCN. Similarly, for VCN, methane is formed with ΔG POS =0.41 eV, associated with the formation of CH 2 * during the second hydrogenation step.

[0112] However, different TMCNs require distinct onset potential values to produce methane, highlighting the variability in their efficiency. This is illustrated in Fig. 4, emphasizing the need to carefully select TMCNs based on their onset potential values for optimal methane production via the MvK mechanism.

[0113] Here, it is observed that MoCN, CrCN, and VCN exhibit higher activity towards methane formation at small onset potentials, whereas ScC, HfCN, and YCN are less active materials as they require higher potentials to produce CH 4(g) .Conventional mechanism

[0114] During this process, there are two approaches for reducing CO 2(g) . Combination of CO 2(g) and H 2(g) to form either COOH or OCHO. Through further hydrogenation / reduction, each of these intermediates leads to the formation of a different product. A comprehensive explanation of the products formed through different reaction pathways is shown in Fig. 5. These reaction pathways were followed for eleven TMCNs to obtain three main products: methane, formic acid, and methanol. The activity of TMCNs towards formation of these products is shown in Fig. 6. It can be seen that TiCN is more active for producing formic acid at 0 V and methanol at a very small potential of -0.22 V. Similarly, VCN is more active toward methane formation at a potential of -0.57 V, which is relatively low. The free energy diagrams of these two most promising catalysts are illustrated in Fig.7 (a, b).

[0115] To highlight the validity of the findings, the data was compared with Cu, RuO 2 , and transition metal oxides and shown in figure 8.

[0116] From Fig.8, it can be seen that TiCN is more promising than TiO 2 , Cu(211), Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 due to TiCN's smaller onset potential and higher activity for methanol and formic acid formation. Similarly, VCN is superior to V@VS 2 , Cu(211), Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 because VCN is more active toward methane formation. WCN is also better than Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 . Although WCN's onset potential for methane formation is higher than that of Cu 1 Ag 8 WC 0001 , WCN is active toward both formic acid and methanol formation. Likewise, NbCN is much better due to its higher activity for methane, methanol, and formic acid formation compared to NbO2, Cu(ZrO 2 ) / Cu(100), Rh 6 Cu 3 (111), and RuO 2 , although it has a higher onset potential than Cu(211). In short, the identified promising catalysts are better than previously studied catalysts.References for FIG. 8

[0117] [1] Liu, S. P., Zhao, M., Gao, W., Jiang, Q., & Jacob, T. (2017). Theoretical Studies on the CO 2 Reduction to CH 3 OH on Cu (211). Electrocatalysis, 8, 647-656. [2] Liu, L., Su, X., Zhang, H., Gao, N., Xue, F., Ma, Y., ... & Fang, T. (2020). Zirconia-modified copper catalyst for CO2 conversion to methanol from DFT study. Applied Surface Science, 528, 146900. [3] Liu, L., Fan, F., Bai, M., Xue, F., Ma, X., Jiang, Z., & Fang, T. (2019). Mechanistic study of methanol synthesis from CO2 hydrogenation on Rh-doped Cu (111) surfaces. Molecular Catalysis, 466. [4] Tayyebi, E., Hussain, J., Abghoui, Y., & Skúlason, E. (2018). Trends of electrochemical CO2 reduction reaction on transition metal oxide catalysts. The Journal of Physical Chemistry C, 122(18), 10078-10087. [5] Chang, Q., Zhang, X., & Yang, Z. (2023). Improved performance of electrochemical reduction of CO2 to HCOOH by Cu incorporation into the supported Au monolayer on tungsten carbide: A DFT study. Results in Physics, 51, 106715. [6] Zhang, X. L., Wu, Z. J., Sun, F. L., Lin, C. B., Chen, W. X., Fang, L. C., & Zhuang, G. L. (2024). Crucial effect of surface oxygen species on CO2 electroreduction performance in Ti@ Cu single atom alloys. Molecular Catalysis, 555, 113894. Example 2 CORR on transition metal carbonitride surfaces

[0118] To study the reduction of CO, a slab is prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms.

[0119] Computational methods were as described above in Example 1.Screening of active site

[0120] To begin exploring the CO reduction reaction (CORR), the structure must first be optimized. Subsequently, the most active CO adsorption site on the surface needs to be evaluated. To determine the most active site, hydrogens are incorporated, the adsorption energy is calculated, and the favourable site for further reactions is identified based on the free energy diagram (FED) for each of the TMCNs. Furthermore, a supplementary test is necessary to analyze the surface's sensitivity to poisoning. This involves establishing if the site is only available for CO or if other species such as oxygen (O), hydroxyl groups (OH), or water (H 2 O) may also occupy it. Fig. 9 describes the performance of all TMCN surfaces towards CO / OH / O / H 2 O adsorption.

[0121] As can be seen in Fig. 9, it is evident that certain TMCN surfaces can potentially tie up the O 2-< and OH at zero potential. However, this is not a significant concern as these species can be experimentally removed by applying a negative potential, as the electrode surface will be negatively charged for the CORR and thus the surface repels off these negatively charged species (O 2-< and OH). Water adsorption on the catalyst surface is usually a problem but interesting. The CO adsorption is exergonic on all of these TMCNs which is beneficial to CO capture.Results and discussion

[0122] For the investigation of CORR, eleven TMCNs are evaluated, including CrCN, HfCN, MoCN, NbCN, ScCN, TaCN, TiCN, WCN, VCN, YCN, and ZrCN, to identify the most proficient catalyst for the conversion of CO into various carbon-based products such as methane and methanol, utilizing a promising reaction pathway characterized by a very low onset potential. During this comprehensive investigation, all catalysts are tested using two distinct reaction mechanisms: the Mars-van Krevelen (MvK) mechanism and the conventional mechanism. The objective is to ascertain which reaction process proves more feasible and efficient for CORR at low potential values.Mars-van Krevelen (MvK) mechanism

[0123] It was found that the carbon site is a highly active adsorption site for subsequent reactions and is frequently hydrogenated during the MvK. This mechanism involves the catalyst's continual hydrogenation, which produces methane (CH 4(g) ) while also creating carbon vacancy. However, certain catalytic surfaces produce CH 4(g) after the fourth protonation, while others require more protonation steps. Following CH 4(g) production and vacancy generation, the catalyst must be replenished for further reactions. In this cyclical process within the electrochemical cell, the catalyst speeds up the reaction, resulting in consecutive protonation, vacancy creation, and CH 4(g) generation. Subsequently, CO (g) binds the vacancy where the carbon atom of CO fills the carbon vacancy and the oxygen atom of CO gets reduced to water molecule and released, restoring the catalyst's clean structure for starting the next cycle (Eq.1). This dynamic cycle keeps the catalyst active and effective, constantly converting CO into useful carbon-based compounds.         Vac + CO (g) + H 2(g) → Clean + H 2 O (l)

[0124] As shown in Fig. 10 (a-c), the best pathway for CH 4(g) generation via the MvK mechanism starts with the second protonation step that yields CH 2 * and ultimately produces CH 4(g) , with a potential-determining step (PDS) value of 0.32 eV for MoCN.

[0125] Similarly, for CrCN and VCN, CH 4(g) is formed with ΔG PDS values of 0.36 eV and 0.41 eV, respectively, associated with the production of CH* and CH 2 * during the first and second hydrogenation steps.

[0126] The primary objective of this study is to determine an efficient pathway for creating methane with a limited onset potential using the MvK process. Thus, Fig. 11 is provided which shows the required onset potential for each catalyst investigated here to produce CH 4(g) via the MvK. This figure also shows the catalytic activity of these TMCNs.

[0127] According to Fig. 11, it is evident that MoCN, CrCN and VCN are highly active towards CH 4(g) production with very small onset potential of -0.32, -0.36 and -0.41 V, respectively. On the other hand, ScCN and YCN demand high potential and thus not interesting.Conventional mechanism

[0128] During this process, CO (g) is adsorbed onto the surface as CO*. Subsequent protonation divides the reaction into two paths: R1 from CHO* and R2 from COH*. The complete reaction pathways are shown in Fig. 12.

[0129] After screening eleven TMCNs for a suitable CO reduction, two primary products were observed: CH 4(g) and CH 3 OH (aq) . Notably, each catalyst demonstrates an entirely distinct pattern and selectivity for these products. This situation is described in Fig. 13 where on the y axis we have the onset potential (in V) as a function of activity.

[0130] From Fig. 13, it is clear that TiCN is the most promising TMCN due to its high activity and also selectivity for methanol formation at just -0.19 V. MoCN and HfCN, on the other hand, can be considered ideal due to their higher activity for methanol at -0.50 and -0.59 V. The potential window difference for formation of methane and methanol on MoCN and HfCN can be used to tune the selectivity as well. The free energy diagram (FED) of TiCN, MoCN, and HfCN is shown in Fig. 14 (a-c).

Examples

example 1

Example 1

CO2RR on transition metal carbonitride surfaces

Computational method

[0101]The interaction of CO 2 with TMCN surfaces and formation of different intermediates were studied by DFT calculations with Generalized Gradient Approximation (GGA) using RPBE exchange correlation function. The tool used for these calculations was ab initio simulation package (VASP) and cutoff energy was 450 eV with the 4×4×1 Monkhorst-Pack K-point mesh until energy differences are converged within 10 -4< eV. The Projector augmented wave (PAW) method was implemented due to full wavefunction by utilizing computationally efficient pseudopotentials, significantly reducing computation time. The surface of TMCNs were considered in the rocksalt (RS) crystallographic structure with the texture orientation of (100). A slab was prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition met...

example 2

Example 2

CORR on transition metal carbonitride surfaces

[0118]To study the reduction of CO, a slab is prepared from the bulk carbonitrides of 11 different materials. The composition of the slab follows a 2:1:1 ratio, meaning it consists of 40 atoms in total: 20 atoms of a transition metal, 10 carbon atoms, and 10 nitrogen atoms.

[0119]Computational methods were as described above in Example 1.

Screening of active site

[0120]To begin exploring the CO reduction reaction (CORR), the structure must first be optimized. Subsequently, the most active CO adsorption site on the surface needs to be evaluated. To determine the most active site, hydrogens are incorporated, the adsorption energy is calculated, and the favourable site for further reactions is identified based on the free energy diagram (FED) for each of the TMCNs. Furthermore, a supplementary test is necessary to analyze the surface's sensitivity to poisoning. This involves establishing if the site is only available for CO or if oth...

Claims

1. A method for catalytic electrolytic reduction of CO2 and / or CO, the method comprising: a. providing an electrolytic cell containing at least one reaction chamber that has at least one anode and at least one cathode and at least one electrolyte between the anode and the cathode, wherein the at least one cathode comprises at least one catalyst comprising at least one transition metal carbonitride; b. providing CO2 and / or CO in the electrolytic cell; and c. applying electrical potential to the electrolytic cell; whereby the CO2 and / or CO undergoes at least one reduction reaction at the cathode.

2. The method of claim 1, wherein the electrolytic reduction reaction results in formation of at least one product selected from methanol, methane, methanediol, formic acid, formaldehyde, ethanol, ethane, ethylene glycol, ethanediol, propane and propanol.

3. The method of any one of the previous claims 1, wherein the gas pressure at the at least one cathode is ambient pressure of about 1 atm.

4. The method of any one of the previous claims, wherein the electrical potential applied to the electrolytic cell is in the range of -2.0 V to +1.0 V using a reversible hydrogen electrode (RHE) as a reference.

5. The method of any one of the previous claims, wherein CO2 is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Hf, Nb, Ti, Ta, W, V, Y and Zr, more preferably selected from Ta, Y, Zr, V and Ti.

6. The method of any one of the previous claims 1 - 4, wherein CO is provided in the electrolytic cell, and wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Mo, Hf, Cr, V, Ti, Ta, Nb and Zr, more preferably selected from Mo, Ti, Cr and V.

7. The method of any one of the previous claims 1 - 5, wherein CO2 is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of vanadium (V), Molybdenum (Mo), Chromium (Cr), Niobium (Nb), or Titanium (Ti), the catalytic reduction resulting in formation of methane.

8. The method of any one of the previous claims 1 - 5, wherein CO2 is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Cr, Hf, Nb, Ti, Ta, W, V, Y and Zr, the catalytic reduction resulting in the formation of formic acid.

9. The method of any one of the previous claims 1 - 5, wherein CO2 is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of titanium (Ti), wolfram (W), niobium (Nb), molybdenum (Mo), or chromium (Cr), the catalytic reduction resulting in formation of methanol.

10. The method of any one of claims 1 - 4 or claim 6, wherein CO is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Mo, Cr, V, Ti, Ta, Nb, W and Zr, the catalytic reaction resulting in formation of methane.

11. The method of any one of claims 1 - 4 or claim 6, wherein the carbonitride is a carbonitride of a transition metal selected from Mo, Cr and V.

12. The method of any one of claims 1 - 4 or claim 6, wherein CO is provided in the electrolytic cell, and wherein the carbonitride is a carbonitride of a transition metal selected from the group consisting of Ti, Mo, W and Hf, the catalytic reaction resulting in formation of methanol.

13. An electrolytic cell for the reduction of carbon dioxide and / or carbon monoxide, comprising: an anode; and a cathode comprising a catalyst comprising at least one transition metal carbonitride.

14. The electrolytic cell of claim 13, wherein the transition metal carbonitride is a carbonitride of a transition metal selected from Ti, Mo, Hf, Cr, V, Ta, Y, Wand Zr.

15. A chemical reactor comprising at least one electrolytic cell as set forth in claim 14; and a power supply connected to the electrolytic cell.

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