electrocatalyst

Abstract

The present disclosure relates to a magnetic electrocatalyst, its synthesis and use. The magnetic electrocatalyst comprises a transition metal catalyst species coupled to a magnetic species. The magnetic electrocatalyst may be in particulate form.

Description

ElectrocatalystTechnical field

[0001] The present disclosure broadly relates to supported organometallic electrocatalysts.Background

[0002] Any discussion of the prior art throughout this specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] Certain electrocatalytic processes are known to be enhanced in the presence of a magnetic field. The magnetic field may be supplied by large magnetic blocks. The most investigated reaction using this method is the oxygen evolution reaction. However, this approach is not suitable for scaling up. The magnet-to-catalyst mass ratio usually needs to be above 1000 to provide the necessary magnetic field strength, which means 1 g of catalyst will require a magnet of at least 1 kg for enhancement in an electrolyzer of practical size. Such a heavy magnet is not only costly but also requires special care for handling to avoid potential safety risks.

[0004] A second method to provide a magnetic field for such reactions is by means of electric coils. In this setup, a conductive metal coil surrounds the electrochemical vessel, and the magnetic field is generated when a large current passes through the coil. This setup can generate either AC or DC magnetic field depending on the type of current. The coil size needs to expand to a diameter of a few meters to fit a practical electrolyzer, making scaling up difficult. Also, using a coil-generated magnetic field requires a high-current power source and additional electricity, introducing additional infrastructural and operation costs.

[0005] Oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) are important industrial catalytic processes. Catalytic activity in these reactions has been shown to be enhanced under the influence of a magnetic field. This has been demonstrated for a variety of metal oxide catalysts and also for a nitrogen-coordinated single metal atom electrocatalyst (Applied Catalysis B: Environmental, 2019. 258: p. 1 17955). This enhancement has been effected using an electrolytic cell containing a catalyst within the magnetic field generated by a large magnet which is external to the to the cell itself. Such systems suffer disadvantages in terms of versatility, safety and cost as discussed above.

[0006] There is therefore a need for a means to supply a magnetic field to electrochemical reaction systems which overcomes, or at least ameliorates, the above disadvantages with current means.Summary

[0007] In a first aspect of the disclosure, there is provided a magnetic electrocatalyst comprising a transition metal catalyst species coupled to a magnetic species, said transition metal catalyst species comprising a transition metal.

[0008] The following options may be used in conjunction with the first aspect, either individually or in any suitable combination.

[0009] The transition metal catalyst species may comprise a transition metal complexed with a tetrapyrrole macrocycle, a transition metal oxide or metallate, a transition metal mixed oxide or metallate, or a M-N-C catalyst. The tetrapyrrole macrocycle may be an optionally substituted phthalocyanine. The M-N-C catalyst may be Fe-N-C.

[0010] The transition metal catalyst species may be coupled to adsorbent particles. The adsorbent particles may be supported on the magnetic species. The adsorbent particles may be, for example, carbon black.

[0011] The magnetic species may comprise magnetic nanoparticles. The magnetic species may have a coating separating the magnetic species from the transition metal catalytic species. The coating may be a polymeric coating. The coating may comprise, for example, polyvinylchloride or polydopamine.

[0012] The transition metal may be in the +II oxidation state. The transition metal may be selected from the group consisting of Co, Mn, Ni, Cu, Zn and Fe and mixtures of any two or more of these.

[0013] In an embodiment there is provided a magnetic electrocatalyst comprising a transition metal catalyst species coupled to a magnetic species having a coating separating the magnetic species from the transition metal species, said transition metal catalyst species comprising a transition metal complexed with a tetrapyrrole macrocycle and being coupled to adsorbent particles, said adsorbent particles being supported on the magnetic species.

[0014] In another embodiment there is provided a magnetic electrocatalyst comprising a transition metal catalyst species coupled to a magnetic species having a two layer coating separating the magnetic species from the transition metal species, said transition metalcatalyst species comprising a M-N-C catalyst, such as a Fe-N-C catalyst, said transition metal catalyst species being supported on the magnetic species.

[0015] In a second aspect of the disclosure there is provided method for conducting an electrocatalytic reaction comprising applying an electrical potential across an electrically conductive composition between a cathode and an anode, the electrically conductive composition comprising a substrate and a magnetic electrocatalyst according to the first aspect.

[0016] The following options may be used in conjunction with the second aspect, either individually or in any suitable combination.

[0017] The electrocatalytic reaction may be an oxygen reduction reaction or an oxygen evolution reaction

[0018] The substrate may be water. In this instance the electrocatalytic reaction may be hydrolysis, hydrogen may be evolved at the cathode and oxygen may be evolved at the anode.

[0019] In a third aspect of the disclosure there is provided use of a magnetic electrocatalyst according to the first aspect in an electrocatalytic reaction.

[0020] The electrocatalytic reaction may be one that generates hydrogen peroxide. It may be one that generates oxygen.

[0021] In a fourth aspect of the disclosure there is provided use of a magnetic electrocatalyst according to the first aspect in constructing an electrocatalytic cell.

[0022] In a fifth aspect of the disclosure there is provided a process for making a magnetic electrocatalyst comprising coupling a transition metal catalyst species to a magnetic species.

[0023] The following options may be used in conjunction with the fifth aspect, either individually or in any suitable combination

[0024] The magnetic species may comprise magnetic nanoparticles. The magnetic nanoparticles may have a coating. The coating may be a polymeric coating. The magnetic nanoparticles may have a polymeric coating and a silica coating.

[0025] The process may comprise coating the magnetic species with the coating prior to said coupling.

[0026] The transition metal catalyst species may comprise a transition metal complexed with a tetrapyrrole macrocycle, or a transition metal oxide or metallate, or a transition metal mixed oxide or metallate, or a M-N-C catalyst. The transition metal catalyst species may comprise a transition metal complexed with a tetrapyrrole macrocycle. In this instance the process may comprise adsorbing the transition metal catalyst species onto an adsorbent to form a coated adsorbent and coupling the coated adsorbent to the magnetic species. The transition metal catalyst species may comprise a M-N-C catalyst, such as Fe-N-C. In this instance, the process may comprise coupling the M-N-C catalyst to the magnetic species.

[0027] In an embodiment there is provided a process for making a magnetic electrocatalyst comprising:• applying a polymeric coating on the surface of magnetic nanoparticles to form coated magnetic nanoparticles;• adsorbing a transition metal phthalocyanine complex onto carbon black to form a coated carbon black; and• adsorbing the coated carbon black onto the coated magnetic nanoparticles so as to couple the transition metal phthalocyanine complex to the coated magnetic nanoparticles to form the magnetic electrocatalyst.

[0028] In another embodiment there is provided a process for making a magnetic electrocatalyst comprising:• applying a polymeric coating on the surface of magnetic nanoparticles to form coated magnetic nanoparticles;• applying a silica coating to the surface of the coated magnetic nanoparticles to form doubly coated magnetic nanoparticles; and• adsorbing a M-N-C catalyst, such as Fe-N-C, onto the doubly coated magnetic nanoparticles so as to couple the M-N-C catalyst to the doubly coated magnetic nanoparticles to form the magnetic electrocatalyst.Brief Description of the Drawings

[0029] Figure 1 . Molecular structure of the M-phthalocyanine precursor. M=Mn, Co, Ni, Cu or Zn.

[0030] Figure 2. Schematic drawing showing the method of synthesis of the magnetic electrocatalyst.

[0031] Figure 3. Electrochemical performance assessment, (a-d) ORR performance in 0.1 M HCIO4 electrolyte, (a) LSV (linear sweep voltammetry) curves (top panel) and corresponding FEH2O2 (bottom panel), (b) Kinetic current densities ( / K-H2O2, top panel) and the / k ratios of CoPc / CB-Mag against others (bottom panel), (c) EIS Nyquist plots, (d) Mass specific activity toward H2O2 synthesis. The inset shows the site-specific TOF values at 0.35 and 0.45V. (e-i) OER performance in 1 .0 M KOH electrolyte, (e) LSV curves, and (f) calculated magnetocurrent enhancement, (g) Tafel plots, (h) EIS Nyquist plots, (i) OER Stability performance tested at 50 mA. cm-2.

[0032] Figure 4. Application of the CoPc / CB-Mag catalyst in a two-electrode electrolyzer, (a) A photo of a 100 cm2electrode, (b) Current-potential responses, and (c) continuously H2O2 production performance of different catalysts at 100 mA.cm-2and a DI water flow rate of 30 mL.hr1. All cell voltages are reported without iR-correction.

[0033] Figure 5. Schematic illustration (a) and photograph (b) of a 100 cm2two-electrode electrolyzer system for H2O2 production.

[0034] Figure 6. (a)-(c): ORR LSV curves and the calculated FEH2O2 for MPc-based catalysts; (d) OER LSV curves for MPc-based catalysts;, (e) magnetocurrent curves for MPc / CB-Mag catalysts; (f) magnetocurrent enhancement for MPc / CB-Mag catalysts.

[0035] Figure 7. Current density (a), and magnetoenhancement (b), for metal oxide and metallate catalysts.

[0036] Figure 8. LSV curves of Fe-N-C catalyst (dotted line) and Fe-N-C catalyst with magnetic particles (solid line) at 900 rpm in 02-saturated 0.1 M HCIO4 electrolyte.

[0037] Figure 9. Depiction of magnet arrangement from Applied Catalysis B: Environmental, 2019. 258: p. 117955.

[0038] Figure 10. Depiction of magnet arrangement from Angewandte Chemie International Edition, 2023. 62(28): p. e202304229.

[0039] Figure 1 1. Depiction of magnet arrangement from Journal of Materials Chemistry A, 2022. 10(4): p. 1760-1767.Description of embodiments

[0040] The present disclosure describes magnetic species coupled to transition metal catalyst species. It is known that in certain circumstances magnetic fields can enhance the catalytic effectiveness of transition metal catalysts. However hitherto, the magnetic field has commonly been applied by means of an external magnet, either a permanent magnet or an electromagnet. The present inventors have surprisingly found that the transition metal catalyst may be coupled to the magnet so as to avoid the problems inherent in the use of an external magnet.

[0041] The magnetic species of the present invention is typically a permanent magnet with a specific surface area of about 1 to 10 m2 / g. The specific surface area, for example as measured by a physisorption technique such as nitrogen adsorption, may be between about 1 to 5, 5 to 10, 1 to 7, 3 to 10 or 3 to 7 m2 / g, e.g. about 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10 m2 / g. The present disclosure has exemplified this using magnetic nanoparticles, several of which are available commercially. These may have mean particle diameter of from about 200 to about 2000nm, or about 200 to 1000, 200 to 500, 500 to 2000, 500 to 1000 or 800 to 1000nm, e.g. about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000nm. Important aspects of the magnetic species are the ability to support large amounts of transition metal catalytic species and the ability to be inserted into an electrocatalytic cell. The first of these requirements may be satisfied by a high surface area magnetic species, for example small particle size magnetic nanoparticles. Other structures than magnetic nanoparticles that may satisfy these requirements are high surface area magnetic sponges and microporous magnetic species. These may be monolithic or may be particulate.

[0042] The magnetic species are commonly metallic. They may be susceptible to corrosion when inserted into an electrocatalytic cell, particularly during operation of the cell. Therefore it is preferable to provide a coating to the magnetic species in order to protect it from such corrosion. Suitable coatings may be polymeric. These may be applied either by directly applying a polymer to the surface of the magnetic species or by polymerising a monomeric or oligomeric species on the surface of the magnetic species. An example of the former approach is the deposition of PVC on the surface, and an example of the latter approach is the polymerisation of dopamine on the surface to form a polydopamine (PDA) coating. Advantages of PDA as a coating include its ease of production under mild conditions, and its ability to adhere well to a range of surfaces. In some instances, polymers may be formed on the surface by interaction of two dissimilar monomers, for example polyurethanes may beformed by interaction of polyols with polyisocyanates. Suitable polymerisation reactions are well known.

[0043] A feature of the present invention is that the transition metal catalyst species is exposed on the surface of the magnetic catalyst so as to allow it to interact with substrates in the cell. Accordingly, the coating on the magnetic species is disposed between the magnetic species and the transition metal species. Commonly the coating will be disposed directly on the surface of the magnetic species.

[0044] The skilled person will readily recognise that there is a wide variety of transition metal catalysts that may be used in the presence of a magnetic field to enhance electrocatalytic reactions. One suitable class of catalysts comprises complexed transition metals. There are many known complexing agents that may be used and are well known. A commonly used class of complexing agents is the tetrapyrrole macrocycle. These include porphyrins and phthalocyanines. These may be substituted, for example by one or more halogens, one or more alkyl groups etc. Due to the known method of synthesising these complexing agents, they commonly have either 4 or 8 substituents, and the substituents are commonly all the same. Thus for example, the macrocycle may have 4 halogen substituents, or 8 halogen substituents, or 4 methyl substituents or 8 methyl substituents. The structure of metal- phthalocyanine complexes is shown in Fig. 1. In this example the phthalocyanine macrocycle is unsubstituted, however substitution on the macrocycle is possible on the benzenoid rings as described above. Another suitable class of catalysts comprises M-N-C catalysts, such as Fe-N-C, which comprise atoms of a metal, such as a transition metal, such as iron, complexed by 4 or more nitrogen atoms within a polycyclic aromatic hydrocarbon lattice or graphene.

[0045] Other suitable classes of transition metal catalyst species include transition metal oxides and transition metal metallates. The metalates may be oxometallates, which are salts in which the anion comprises a metal and oxygen. Examples include vanadate, ferrate, chromate, etc. Mixed metal oxides and mixed metal metallates may also be used. Suitable transition metal catalyst species include for example NiO, NiZnFeO4 and CoMnV04.

[0046] The transition metal of the transition metal catalyst species may be in the +II oxidation state. It may be a transition metal having one or more available higher oxidation state, e.g. +III, +III, +IV, +V or +VL This enables it to function as a reducing agent in an electrocatalytic reaction. However other transition metals may also be used. Suitable transition metals include Co, Mn, Cu, Zn and Fe. Mixtures of these may also be used.

[0047] A convenient means to couple the transition metal catalyst species to the magnetic species is to adsorb it onto an adsorbent and to then couple the adsorbent onto the magnetic species. Suitable adsorbents include carbon based adsorbents such as carbon black or activated carbon, or mineral based adsorbents such as nanoparticulate (e.g. fumed) silica, diatomaceous earth etc. Suitable adsorbents commonly are capable of readily adsorbing onto the magnetic species, or to the coating thereon. The adsorbent is particulate and may have a mean particle size of less than about 100nm, or less than about 50, 20 or 10nm, or of about 1 to about 10Onm, or about 1 to 50, 1 to 20, 1 to 10, 10 to 100, 20 to 100, 50 to 100, 10 to 50, 10 to 20 or 20 to 50nm, e. g. about 1 , 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100nm. However, the use of an adsorbent is not required for all transition metal catalyst species. For example where the transition metal catalyst species is a complexed transition metal, or a transition metal oxide or metallate, a transition metal mixed oxide or metallate, it may be adsorbed onto an adsorbent and the adsorbent coupled to the magnetic species. Where the transition metal catalyst species is a M-N-C catalyst, it may be coupled to the magnetic species directly.

[0048] The magnetic electrocatalyst described herein may be used for catalysing a wide range of electrocatalytic reactions without the need for an external source of magnetic field. Two such reactions, described elsewhere herein, are oxygen reduction reactions (ORR) to generate hydrogen peroxide, and oxygen evolution reactions (OER), to generate oxygen gas. Simply put, any reaction which relies on, or is enhanced by, application of a magnetic field to an electrocatalytic reaction can employ a magnetic catalyst according to the present invention. Since the magnetic field is provided by the magnetic catalyst itself, the reaction is carried out in much the same way as conventionally, but without applying an external magnetic field. Thus, to generalise, an electrocatalytic reaction is performed by applying an electrical potential between two electrodes in an electrochemical cell which contains substrate and the magnetic electrocatalyst. The skilled person will readily appreciate the nature and range of reactions to which this technology may be applied. Several illustrative examples are provided herein.

[0049] The magnetic electrocatalyst may be made by coupling a transition metal catalyst species to a magnetic species. Commonly the transition metal catalyst species will first be adsorbed onto an adsorbent particle, although it may in some instances be coupled directly onto, e.g. adsorbed onto, the magnetic species or onto a coating on the magnetic species.

[0050] In order to facilitate adsorption of the transition metal catalyst species onto the adsorbent particle, the adsorbent particle may be first cleaned. The nature of this cleaning will depend on the nature of the adsorbent particle. In the case of a carbon based adsorbent particle, this may for example include heating in an inert or reducing atmosphere. Suitabletemperatures for this may be from about 1000°C to about 2000°, or about 1000 to 1500, 1500 to 2000 or 1200 to 1700°C, e.g. about 1000, 1 100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000°C. The reducing atmosphere may comprise hydrogen gas. It may comprise an inert gas, for example helium, neon or argon. It may comprise a mixture of such gases.

[0051] Adsorption of the transition metal catalyst species onto the adsorbent particles may be effected by exposing the adsorbent particles to a solution of the transition metal catalyst species. The adsorbent particles may be agitated in the solution. They may be sonicated therein. The solvent for the solution should be one that is a solvent for the transition metal catalyst species and one that can wet the surface of the adsorbent particles. For organometallic transition metal catalyst species, this is commonly a polar organic solvent. Suitable solvents may for example include DMF, DMSO, HMPT, HMPA etc. The solvent may be one that adsorbs to the surface of the adsorbent particles less strongly than the transition metal catalyst species. The concentration of the transition metal catalyst species in the solution is not critical and may depend on the solubility of the transition metal catalyst species in the solvent. It may for example be between about .001 and about 1%w / v or between about 0.01 and 1 , 0.1 and 1 , 0.001 and 0.1 , 0.001 and 0.01 or 0.01 and 0.1 %w / v, e.g. about 0.001 , 0.005, 0.01 , 0.05, 0.1 , 0.5 or 1%w / v. The ratio of transition metal catalyst to adsorbent particles may be from about 1 :2 and about 1 :20, or from about 1 :2 and 1 :10 or 1 :2 and 1 :5 or 1 :5 and 1 :10 or 1 :10 and 1 :20. It may be for example 1 :20, 1 :15, 1 :10, 1 :5, 1 :4, 1 :3 or 1 :2 on a w / w basis. There may be a greater weight of adsorbent particles than transition metal.

[0052] As discussed above, the magnetic species may be in the form of magnetic nanoparticles. Suitable nanoparticles include NdFeB, iron oxide (ferrite: mahegmite or magnetite), iron alloys (FePt, FePd), iron carbides etc. As discussed, these may have coatings in order to prevent corrosion in use. The coating may be polymeric. The process of applying the coating may comprise exposing the uncoated magnetic species to a solution of a polymer, such as PVC (polyvinylchloride). Other suitable polymers include polyacrylonitrile (PAN), polyetherimide (PEI), polyethylene oxide (PEO), polyimide (PI) and cellulose. As this process relies on dissolving the polymer, only polymers for which a suitable solvent can be found are suitable for this process of applying the polymer. Suitable solvents for this process include DMF, acetone, THF, ethyl acetate, isopropanol etc. Suitable pairings of polymer and solvent are well documented, or are readily determinable by routine experiment. A typical procedure involves dispersing the magnetic nanoparticles in a solution of the polymer or immersing the magnetic species in a solution of the polymer. This may be accompanied by suitable agitation and / or sonication. A suitable ratio of magnetic species to polymer in this procedure is from about 2:1 to about 20:1 , or about 5:1 to 20:1 , 10:1 to 20:1 , 2:1 to 10:1 , 2:1 to 5:1 or 5:1 to 10:1 ,e.g. about 2:1 , 3:1 , 4:1 , 5:1 , 10:1 , 15:1 or 20:1 on a w / w basis. The solvent may be removed by evaporation.

[0053] A second process for coating the magnetic species is to expose it to a polymerizable species and polymerise that species on the surface of the magnetic species. A suitable monomer for this purpose is dopamine, which can be polymerised simply by means of pH adjustment. Polydopamine (PDA) is thought to comprise dihydroxyindole, indoledione, and dopamine units, which are considered to be covalently linked. Thus in a representative procedure, the magnetic species is immersed in, optionally dispersed in, water buffered to pH7. A similarly buffered pH7 solution of dopamine hydrochloride is then added and adjusted to pH8.5 so as to promote polymerisation of the dopamine to polydopamine (PDA). A suitable ratio of magnetic species to polymerizable species in this procedure is between about 1 :1 and about 1 :5, or about 1 :1 and 1 :3, 1 :3 and 1 :5 or 1 :2 and 1 :4, e.g. about 1 :1 , 2:3, 1 :2, 2:5, 1 :3, 1 :4 or 1 :5 on a w / w basis. Other polymers that may be formed by polymerisation on the surface of the magnetic species include polyimides, polyetherimides, polyurethanes and polysilicates.

[0054] In some embodiments, for example where the magnetic electrocatalyst is to be used in acidic conditions, a multiple coating layers may be applied to the magnetic species. Two to five, or two to ten coating layers may be applied to the magnetic species. Two, three, four, five, six, seven, eight, nine, ten, or more coating layers may be applied to the magnetic species. Two coating layers may be applied to the magnetic species. The coating layers may be the same, or may be different. For example, the magnetic species may be coated with PDA as described above, and then coated with silicate. In a representative procedure, PDA coated magnetic species may be prepared as described above. Then, the PDA coated magnetic species may be dispersed in a solvent, such as an ethanol water solution which is made basic with a base such as ammonia, and treated with an orthosilicate, such as a tetraalkyl orthosilicate, such as tetraethyl orthosilicate.

[0055] In order to form the final magnetic electrocatalyst, the magnetic species, optionally coated, and the transition metal catalyst species, optionally adsorbed onto adsorbent particles, are mixed in a suitable solvent. Thus options include an uncoated magnetic species with an unsupported transition metal catalyst species (i.e. not adsorbed onto adsorbent particles), a coated magnetic species with an unsupported transition metal catalyst species, an uncoated magnetic species with a supported transition metal catalyst species (i.e. adsorbed onto an adsorbent) and a coated magnetic species with a supported transition metal catalyst species. Coated magnetic species encompasses coating with one, two, or more coating layers, such as polymeric layers, silica layers, etc. as described above. Suitable solvents for forming the magnetic electrocatalyst are those that are capable of dispersing both components. Thesolvent may be a volatile solvent to facilitate its removal after formation of the magnetic electrocatalyst. Suitable solvents include isopropanol, n-butanol, isobutanol, n-propanol, ethanol, acetone, ethyl acetate etc. The mixing may be facilitated by suitable agitation, sonication etc. The solvent may conveniently be removed by evaporation and optionally final drying for example in a vacuum oven. A suitable ratio of transition metal catalyst species, optionally adsorbed onto adsorbent particles, to optionally coated magnetic species may be from about 1 :1 to about 1 :10, or about 1 :1 to 1 :5, 1 :1 to 1 :2, 1 :2 to 1 :10, 1 :5 to 1 :10, 1 :2 to 1 :5 or 1 :3 to 1 :7 on a w / w basis. In the event that the transition metal catalyst species is not adsorbed onto adsorbent particles, this ratio may be up to 1 :100 or more w / w.

[0056] Reactions using the magnetic electrocatalyst of the present invention may be conducted in a standard cell containing substrate(s) and / or reagent(s) together with the magnetic electrocatalyst. The cell may be stirred in order to maintain the particles of magnetic electrocatalyst dispersed through the cell. Alternatively the electrocatalyst may be retained as a layer between the anode and the cathode. The magnetic electrocatalyst may be in the form of particles disposed on one or both of the anode and the cathode. The loading of the magnetic electrocatalyst particles may be less than about 5mg of particles per cm2of electrode area, or less than about 5, 3, 2 or 1 mg.cm-2, or from about 0.5 to 5, 0.5 to 2, 0.5 to 1 , 1 to 5, 0.5 to 2 or 0.5 to 1 mg.cm-2, e.g. about 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 mg.cm-2. In the event that the magnetic electrocatalyst is a monolithic high surface area (e.g. microporous) material, it may be in the form of a thin sheet which may then be inserted between the anode and the cathode in the cell. The magnetic electrocatalyst may be present in the cell at about 0.1 to about 10mg / cm2of electrode surface area, or about 0.1 to 5, 0.1 to 2, 0.1 to 1 , 0.1 to 0.5, 0.1 to 0.2, 0.2 to 10, 0.5 to 10, 1 to 10, 2 to 10, 5 to 10, 0.5 to 5, 1 to 5 or 0.5 to 2mg / cm2, e.g. about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1 .5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10mg / cm2. Following the reaction, the magnetic electrocatalyst may be recovered from the reaction mixture. This may be accomplished by filtration, centrifugation, magnetic separation or other suitable method. The magnetic electrocatalyst may then be washed in a suitable solvent and dried so as to be useable in a subsequent electrocatalytic reaction.

[0057] As discussed earlier, electrocatalytic reactions in which the magnetic electrocatalyst may be used include oxygen reduction and evolution reactions (ORR and OER respectively). Understanding the spin-dependent activity of nitrogen-coordinated single metal atom (M-N-C) electrocatalysts for these reactions remains challenging due to the lack of structure-defined catalysts and effective spin manipulation tools. The examples provided herein address both challenges using a magnetic field integrated heterogeneous molecular electrocatalystprepared by anchoring metal(ll) phthalocyanine (MPc) deposited carbon black (CB) on polymer-protected magnetic nanoparticles.

[0058] MPcs were selected as the molecular precursor, as they bear a structurally well-defined M-N4 active centre with appreciable electrocatalytic activity and unique magnetic properties. They were deposited on a conductive CB substrate (MPc / CB) and further anchored on polymer-protected permanent magnet nanoparticles, forming a hierarchically structured catalyst, denoted as MPc / CB-Mag, with defined and fully exposed M-N4-C active sites and a built-in magnetic field for spin manipulation.

[0059] Exemplified by CoPc, the built-in magnetic field can shift the low-spin cobalt centre to high-spin without structure modification, affording one-order higher turnover frequency and a 50% increased hydrogen peroxide selectivity for ORR, and a nearly 4000% enhanced magnetocurrent for OER. This catalyst can minimize magnet usage by up to 7 orders, and It can be easily employed in a 100 cm2two-electrode electrolyzer, enabling safe and continuous production of a pure hydrogen peroxide solution for 100 hours. The new strategy demonstrated here also applies to other MPc / CB and metal oxide catalysts, offering a universal platform for studying spin-related electrochemical processes and applications, including fuel cells, water electrolysis and carbon dioxide reduction.Definitions

[0060] The following are some definitions that may be helpful in understanding the description of the present disclosure. These are intended as general definitions and should in no way limit the scope of the present disclosure to those terms alone, but are put forth for a better understanding of the following description.

[0061] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The term "include" and its variants have a similar meaning.

[0062] The terms "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0063] In the context of this specification the term "about" is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in thecontext of achieving the same function or result. Commonly this is understood to refer to ±10% of the recited value. However context may indicate otherwise. For example, a parameter which is stated as being "about 1 , 2 or 3" is clearly not intended to exclude values between 1 .1 and 1.8 or between 2.2 and 2.7 (i.e. values not between 1 + / -10%, 2+ / -10% and 3+ / -10%), and should be understood to include those intermediate values.

[0064] Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of 1 .0 to 5.0 is intended to include all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 5.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 5.0, such as 2.1 to 4.5. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited herein is intended to include all higher numerical limitations subsumed therein.

[0065] The term "may" should be taken to encompass both positive and negative statements unless the context implies otherwise. Thus, for example, the phrase "A may be B" should be taken to contemplate both the statement "A is B" and "A is not B".

[0066] Any description of prior art documents herein, or statements herein derived from or based on those documents, is not an admission that the documents or derived statements are part of the common general knowledge of the relevant art.

[0067] For the purposes of description, all documents referred to herein are hereby incorporated by reference in their entirety unless otherwise stated.Examples

[0068] The present disclosure is further described below by reference to the following nonlimiting examples.Example 1Materials:

[0069] Metal phthalocyanines (MPcs: MnPc, CoPc, FePc, NiPc), cerium(IV) sulfate (Ce(SC>4)2), N,N-dimethylformamide (DMF, >99%), isopropanol (IPA, 99.9%), Nation® 117 solution (5%), nitric acid (HNO3, 70%), perchloric acid (HCIO4, 70%,), dopamine hydrochloride, tris(hydroxymethyl)aminomethane hydrochloride (Trizma), polyvinylchloride (PVC, low molecular weight, Mw~48000), cyclohexanone (>99.0%), potassium hydroxide (KOH), andNation® 212 membrane (thickness 50.8 microns) were obtained from Sigma-Aldrich. CB (Vulcan XC-72R) and the core / shell Ir / lrOx catalyst were purchased from Fuelcell Store. Argon (Ar, 99.999%) and oxygen (O2, 99.999%) gas cylinders were obtained from BOC Gas Australia. NdFeB (about 800-1000 nm in size) permanent magnet nanoparticles were purchased from Nanochemazone. Deionized water (18 MO- cm) was produced from a laboratory water purification system (Milli-Q®). MPcs were purified by sublimation. Other chemicals were used as received.Preparation of polymer shell-encapsulated magnetic nanoparticles:

[0070] A polydopamine (PDA) shell was applied to avoid possible corrosion of the magnet nanoparticles. 50 mg of the as-received magnet nanoparticles was dispersed in 50 mL Trizma buffer (10 mM, pH 7). Afterwards, a further 10 mL of Trizma buffer (10 mM), containing 100 mg dopamine hydrochloride, was added under vigorous stirring (2500 rpm), and the mixture was adjusted to pH 8.5 to initiate dopamine polymerization to form a PDA coating on the magnet nanoparticles. The mixture was further mechanically stirred for 12 h at room temperature, and the PDA-coated magnetic nanoparticles (PDA-mag) were recovered by filtration, followed by ethanol washing and drying in an oven overnight.

[0071] PDA-coated demagnetized nanoparticles were also prepared following the same method, except that the nanoparticles were thermally annealed under argon at 400°C (well above its Curie temperature at around 310~370°C). The PDA-coated demagnetized nanoparticles were also recharged for reference experiments.

[0072] A PVC polymeric shell was coated on the magnetic nanoparticles to avoid their potential corrosion during electrochemical reactions in alkaline electrolytes. About 100 mg of PVC powder was first dissolved in 4 mL of cyclohexanone under stirring at 70°C to form a homogeneous solution. 500 mg of NdFeB magnetic powder was added to the resulting solution under sonication. The solution was further stirred, and then the solvent was slowly removed by heating. The resulting viscous mixture was added dropwise to ethanol under vigorous stirring. The particulate solids were then recovered by centrifugation and washed with ethanol before they were dried under vacuum at 60°C overnight.Preparation of multi-layered polymer shell-encapsulated magnetic nanoparticles:

[0073] Dopamine was firstly polymerised onto a magnetic particle surface. Briefly, 100 mg Neodymium-lron-Boron (NdFeB) magnetic particles and 5 mg dopamine (0.05 mass ratio to magnetic particles) were combined in a tris(hydroxymethyl)aminomethane (Tris) buffer solution under 2500 rpm stirring. The solution pH was adjusted to 8.5 by adding 1 M KOHsolution. The solution was constantly stirred at room temperature for 24 hours resulting in the formation of PDA-coated magnetic particles. The product was collected by filtration and dried under ambient conditions.

[0074] Next, the a second coating layer of SiC>2 was prepared using tetraethyl orthosilicate (TEOS) in a sol-gel method. 100 mg of the PDA-magnetic particles were dispersed in a 10 mL 80 vol% ethanol water solution under sonication for 30 minutes before 0.5 mL of 28 wt% ammonia solution was added dropwise under 2500 rpm stirring. The dispersion was kept stirring for 30 minutes, followed by addition of 5 mL of 10 mg / mL TEOS solution over 1 hour using a syringe injector. The dispersion was stirred for a further 12 hours before the SiO2- PDA-magnetic particles were collected by filtration and dried under ambient conditions.Synthesis of magnet-integrated hierarchically structured catalysts:CoPc / CB on PDA-coated magnetic particles

[0075] Prior to catalyst preparation, the CB substrate was purified by annealing in a 5% H2 / Ar gas flow at 1500°C for 2 hours to clean the surface. The CoPc / CB catalyst was synthesized by depositing CoPc on CB. About 5 mg of CoPc and 50 mg of CB were dispersed in 50 mL DMF. After 30 minutes ultrasonication, the mixture was further stirred under argon protection for 24 h before the solids were recovered by filtration. The solids were washed with DMF and ethanol before being dried in a vacuum oven at 80°C overnight.

[0076] The resulting CoPc / CB was mixed with PDA-coated magnetic particles at a mass ratio of 0.33:1 in IPA. After sonication for 30 minutes, the mixture was first gradually dried by evaporation and then dried in a vacuum oven at 80°C overnight. The resulting catalyst was denoted as CoPc / CB-Mag. A diagram illustrating this process is shown in Fig. 2 Other catalysts of different mass ratios were also prepared. Using the same method, CoPc / CB- Demag was also synthesized using the polymer-coated demagnetized nanoparticles. Other MPcs (M=Mn, Fe, and Ni) were used to prepare MPc / CB and MPc / CB-Mag catalysts following the same method.Fe-N-C on Si02-PDA-coated magnetic particles and electrodeSynthesis of Fe-N-C catalyst

[0077] Fe-N-C catalyst was synthesised according to literature procedures Nature Catalysis, 2023, 6, 1215). Briefly, 10 mg of Fe2O3 nanoparticles (5 nm particle size) and 6.78 g of zinc nitrate hexahydrate were dispersed and dissolved into 150 mL of methanol. 7.88 g of 2- methylimidazole was dissolved in another 150 mL of methanol. Both solutions were mixed andheated at 60 °C for 24 h. The precipitant was then collected by centrifuging, washed with ethanol three times, dired in a vacuum oven at 60 °C for 12 hours, and finely ground into powder. 300 mg of the powder was pyrolysed in a tube furnace at 1100 °C for 1 hour under 10 mol% H2in Ar to provide the Fe-N-C catalyst.Electrode preparation

[0078] As-purchased 5 wt.% Nation® solution was diluted into 0.1 wt% and 0.05 wt% dilution using 90 vol% isopropyl alcohol. 20 mg SiO2-PDA-magnetic particle was dispersed in 1 mL 0.1 wt% Nation® dilution, and 5 mg Fe-N-C catalyst was dispersed in 1 mL 0.05 wt% Nation® dilution. The electrode was prepared by firstly dropcasting 9 pL of the SiCh-PDA-magnetic particle dispersion and secondly dropcasting 12 pL of the Fe-N-C catalyst dispersion onto a 0.2 cm2rotating disk electrode. Another electrode was dropcast using 12 pL of the Fe-N-C catalyst dispersion only. The electrodes were dried in ambient air for 3 hours before electrochemical tests.Electrochemical tests with CoPc / CB on PDA-coated magnetic particles:

[0079] Electrochemical performance tests were carried out using a conventional three- electrode configuration on an Autolab PGSTAT302N electrochemical workstation at 25°C. An RRDE (rotating ring-disc electrode: E6R1 , Pine Research, with a calibrated collection efficiency of 0.249) equipped with a glassy carbon disc and a platinum ring was used for testing ORR performance in a 0.1 M HCIO4 (pH=1.2) electrolyte. A glassy carbon tip RDE (rotating disc electrode: E3PK, Pine Research) was used for OER in a 1 M KOH electrolyte (pH=13.6). An Ag / AgCI electrode (3M KCI filling, Basi, MF-2056) and a graphite rod electrode (AFCTR3B, Pine Research) were used as the reference and counter electrodes respectively, for ORR. A Hg / HgO with 1 M KOH filling was used as a reference electrode for OER.

[0080] All reported potentials were calibrated against RHE (reversible hydrogen electrode). The catalyst ink was prepared by dispersing 5 mg of as-synthesized catalysts in 1 mL water / ethanol solution (1 / 9 = v / v, containing 0.05% Nation® 117) by 30minutes bath sonication. For the ORR test, the CoPc / CB-Mag mass loading was kept at 0.1 mg.cm-2, unless otherwise stated. CoPc / CB was deposited at 0.025 mg.cm-2to keep the same Co mass loading. For the OER test, the mass loading was increased to 0.4 mg.cm-2for CoPc / CB-Mag and 0.1 mg.cm-2for CoPc / CB. LSV polarization curves were recorded at 5 mV.s-1 without iR- compensation for all tests.Flow-cell electrolyzer test:

[0081] CoPc / CB-Mag and CoPc / CB catalysts were deposited on a carbon paper gas diffusion electrode (10 x 10 cm2, Toray TGP-H-090 with 30% Teflon) at 0.2 mg.cm-2on CoPc / CB basis by spray coating. I rC I r nanoparticles were deposited on a Ti felt at 1 mg.cm-2and hot pressed on a Nation® 212 membrane as the anode for OER. A 0.5 M H2SO4 anolyte was circulated at 10 mL.hr1. Humified O2 gas was injected into the cathode chamber at a flow rate of 200 seem. A poly(divinylbenzene) copolymer cationic exchange resin (CGC50x8, batch#015X / 10 / 0, about 30-50 pm, Purolite) was used as a porous solid-state electrolyte. Deionized water flow was supplied by a peristaltic pump to wash out the as-produced H2O2 at about 6 mL.min-1, and the effluent was collected for analysis. The electrochemical performance of the electrolyzer was collected on a Gamry Reference 3000 workstation coupled with a Reference 30K Booster.H2O2 concentration determination:

[0082] The H2O2 concentration (CH2O2) in the solution produced by the electrolyzer was determined by a Ce+3 / +4titration method. The UV-vis absorbance at 316 nm was used to establish the calibration curve.Results:Half-cell ORR and OER performances:

[0083] As shown in Figure 3a, without the built-in magnetic field, CoPc / CB shows moderate ORR activity that is comparable to previous reports. It requires a potential of 0.43 and 0.39V (versus a reversible hydrogen electrode, RHE) to reach an appreciable current density on the disk (-0.05mA cm-2) and ring (0.025 mA. cm-2) electrodes. The H2O2 Faradic efficiency (FEH2O2) is about 50 to 60% between 0.5 and 0.1 V (bottom panel of Figure 3a), corresponding to an H2O2 molar selectivity (XH2O2) up to 74%.

[0084] The built-in magnetic field in CoPc / CB-Mag can significantly enhance activity, improving the disk and ring onset potentials by 60 and 90mV to 0.49 and 0.48V, respectively. A 30% increment of the current density (j) at 0.1 V and 81 mV shift of the half-wave potential (E1 / 2, taken the j at 0.1 V as the limit) were obtained. The FEH2O2 also increased to a maximum of about 93%, corresponding to a H2O2 molar selectivity of over 96%. Figure 3b top panel further compares the total ORR kinetic current density (jk-total) calculated by the Koutechy-Levich equation. The jk-total of CoPc / CB-Mag is up to an order higher than that of CoPc / CB or CoPc / CB-Demag (bottom panel of Figure 3b). Tafel analysis assigned an electroncoupled proton transfer step as a universal rate-limiting step, in good agreement with previously reported Co-based single-atom catalysts for acidic ORR. Nevertheless, CoPc / CB- Mag has faster electron transfer kinetics with a reduced Tafel slope of 86mV.dec-1comparing to CoPc / CB (117mV.dec-1) and CoPc / CB-Demag (112mV.dec-1). From the electrochemical impedance Nyquist plots (EIS, Figure 3c), its charge-transfer resistance (Ret, 91 .4 ohm at 0.49V) is also much smaller.

[0085] The H2C>2-specific activity was further compared by using the H2O2 specific kinetic current density (jK-H2O2). The CoPc / CB-Mag can deliver an H2C>2-specific mass activity of about 56.3 A gcat-1and a site-specific turnover frequency (TOF) of 6.1 s-1at 0.35V (Figure 3d), which are over an order higher than CoPc / CB of 5.1 A gcat-1and 0.53 s-1respectively. Notably, all improved catalytic performances observed on CoPc / CB-Mag disappear on CoPc / CB-Demag, shedding light on the critical role played by the built-in magnetic field.

[0086] Considering that the adsorption of various OER intermediates (e.g., OH*, OOH* and O2*) on a single atom site all involves M-0 interactions, the inventors further demonstrated that the built-in magnetic field could also impact these crucial steps and improve the OER activity of CoPc / CB-Mag. The catalyst was prepared by replacing the PDA polymer protecting layer with cheaper polyvinylchloride (PVC), which has better tolerance to alkaline electrolytes. The OER LSV curves collected in a 1 M KOH electrolyte were compared in Figure 3e. Control experiments suggest that without CoPc, a carbon black loaded magnet shows negligible activity. The CoPc / CB-Mag catalyst exhibits an OER onset potential (defined as potential required to reach 0.5 mA. cm-2) of about 1 .46V vs. RHE, which is about 164mV lower CoPc / CB and CoPc / CB-Demag. The overpotential required to reach 10mA. cm-2(F]10), a common activity descriptor, also decreased by 14mV to 313mV. The magnetocurrent dominates the performance improvement, affording a maximum enhancement of 3829% at -1.56V (Figure 3f). As expected, improved kinetic performance is confirmed by a smaller Tafel slope of 57mV. dec-1 (Figure 3g) and drastically reduced RCT, i.e., from 50 ohms to 4 ohms with the built-in magnetic field (Figure 3h). The CoPc / CB-Mag also showed good stability. It can operate at 50mA.cm-2continuously for 48 hours with merely 34mV potential increment (Figure 3i), which is superior to CoPc / CB. The built-in magnetic field can effectively boost the oxygen redox reaction activity of the Co-N4 active center without atomic structure modification.Safe H2O2 production from a two-electrode electrolyzer with improved performance:

[0087] Large magnet blocks were hitherto required to provide magnetic fields with sufficient strength to influence electrochemical reactions. The mass ratio between magnet and catalysts is usually over 10000 (Table 1 ), which brings safety risks and scaling-up challenges. At a massratio of only 3, which is up to seven orders smaller, the amounts of magnetic materials required in CoPc / CB-Mag can be significantly reduced to improve process safety and scalability. CoPc / CB-Mag catalyst can be easily applied on a 100 cm2electrode (Figure 4a) to assemble an electrolyzer (Figure 5) with improved H2O2 production performance. Protons to the cathode are provided from lrC>2-catalyzed anodic OER across a Nation® 212 proton exchange membrane and a 1 mm thick solid state porous electrolyte assembled by a cation exchange resin. Electrolytic ion-free H2O2 solution can be produced with deionized water as the flowing phase. The potential-current response curves (Figure 4b) of the electrolyzer using CoPc / CB- Mag and CoPc / CB catalysts were collected without internal resistance (iR) correction. By eliminating the O2 diffusion limits, CoPc / CB-Mag can deliver an current density up to 300mA. cm-2at a full cell voltage of 4.27V, which is about 44% smaller than that of the CoPc / CB (6.16V). The cell was also operated at l OOmA.cm-2for 50 hours continuously, and the cell voltage responses are compared in Figure 4c. With the built-in magnetic field, the CoPc / CB- Mag electrode can stably produce an electrolytic-ion free H2O2 solution at about 2.99 with a small cell voltage increment of about 75mV after 50 hours. It also exhibited a stable FEH2O2 around 90% during the test. At a water flow rate of 30 mL.hr1, the H2O2 concentration in the effluent can reach 16.0wt% (by Ce(SC>4)2 titration), which corresponds to a H2O2 productivity of 1.68 mmol. cm-2. hr1or 16.79 mol gcat-1.hr1(CoPc / CB basis). By further increasing the operation current to 200 mA. cm-2, it reached a H2O2 productivity of 3.10 mmol.crrr2.hr1. In contrast, CoPc / CB showed much inferior performance. It required about 4.14V to reach 100 mA.cm-2and exhibited a greater voltage increment (233mV) after the test. It also delivered a much lower FEH2O2, around 42%, that is only half that of CoPc / CB-Mag.Extending to other MPc / CB-Mag and metal oxide catalysts:

[0088] The present strategy is shown to serve as a universal platform for other MPc-based catalysts, e.g., MnPc, FePc, and NiPc. They exhibit identical morphology to that of the CoPc / CB and are paramagnetic. Their ORR LSV curves and the calculated FEH2O2 are compiled in Figure 6a-c, showing varied activity changes under the influence of the built-in magnetic field. MnPc / CB-Mag and FePc / CBMag exhibited reduced disk currents and improved FEH2O2, i.e. from less than 20% to over 50% at 0.1 V. NiPc / CB-Mag delivered greater disk and ring current density, and an improved FEH2O2 from 50% to 86%. Their OER LSV curves are compared in Figure 6d. With the built-in magnetic field, the overpotential required for delivering 10mA. cm-2reduced by 160 ± 2, 33 ± 1 , and 79 ± 2 mV, for Mn, Fe and Ni respectively. Tafel analysis and EIS measurement results also confirm improved kinetic performance. NiPc / CB-Mag catalyst exhibits the greatest magnetocurrent density (Figure 6e) up to 80mA.cm-2. However, the MnPc / CB-Mag catalyst showed the greatest enhancement,up to 1200%, as shown in Figure 6f. In addition, this built-in magnetic field strategy is also applicable to some metal oxide OER catalysts, e.g., NiO, NiZnFeC , and CoMnVC (Figure 7), offering a promising approach to further enhance the performance of alkaline water electrolysis.

[0089] The MO (NiO, NiZnFeO4, CoMnVC ) were prepared by precipitating the metal hydroxides using respective metal nitrate salt and adjusting the pH with 0.1 M NH3H2O. Solid precipitates were collected, washed with DI H2O, dried in oven, and finely grounded. Afterwards, the solids were thermally annealed at 600°C for 4 hours to convert them into the metal oxides. Metal composition of NiZnFeO4 and CoMnV04 were confirmed by ICP-AES. The XRD patterns of the resulting products showed good agreement to the standard profiles.

[0090] The MO catalysts can be mixed with the PVC-protected magnet nanoparticles, affording MO-Mag catalyst that can be deposited on the current collector at the same mass loading of 0.1 mg.cm-2(catalyst basis). The mass ratio between MO catalyst and Mag was kept at 1 :3 for all samples. As shown above, NiZnFeO4 exhibited the best pristine performance with the smallest q10 of 1.783V, followed by NiO and CoMnVO4. However, NiO exhibited the greatest performance enhancement, with the greatest q10 decrement of 233mV and the magneto enhancement up to 7801 %.Electrochemical tests with Fe-N-C on SiO2-PDA-coated magnetic particles

[0091] Linear sweep voltammetry (LSV) tests were performed in a 0.1 M HCIO4 electrolyte using an Autolab PGSTAT302N electrochemical workstation connected to a Pine AFMSRCE electrode rotator. The rotating disk electrode was firstly wetted by deionised water and tested in O2-saturated electrolyte to record the LSV curves. Electrode rotating speed was 900 rpm. The resulting LSV curves are displayed in Figure 8. The onset potential and half-wave potential were improved by 46 mV and 37 mV, respectively. A 24% greater diffusion-limiting current was also obtained, demonstrating significantly improved acidic ORR performance.Industrial applicability

[0092] The catalyst and method described herein may be used for various electrochemical reactions, such as those involved in renewable energy conversion processes, from which products can be further used in a wide variety of applications.

[0093] An example of the utility of the present invention is in wastewater treatment. The exemplified CoPc / CB-Mag catalyst can produce an H2O2solution, which can be used to decompose organic contaminants in wastewater treatment facilities, for example by theFenton reaction. With Fe2+used as the transition metal in a catalyst, the H2O2 produced using this catalyst with improved efficiency, can form hydroxyl radicals, a powerful oxidant for the decomposition of contaminants. The wastewater may be acidified to pH=3~4. The H2O2 solution produced by the catalyst described herein by using an acidic electrolyte can be directly injected into the wastewater in order to effect oxidative decomposition of organic contaminants. A decentralized H2O2 production unit can be set up in a wastewater treatment plant. This may then eliminate safety hazards related to the transportation and storage of high- concentration H2O2.

[0094] A further example of the utility of the present invention is splitting of water in alkaline / neutral electrolytes or seawater. Water splitting in the alkaline / neutral electrolytes or sea water usually suffers from slow conversion rates and consequent unsatisfactory performance. As demonstrated here, the two critical electrochemical reactions in water splitting, namely hydrogen evolution reaction on the cathode and oxygen evolution reaction on the anode, can be substantially enhanced by means of the catalyst described herein. While the catalyst is used at a scale of mg per cm2of the electrode, its cost is not comparable to the savings in energy consumption and operating costs over the catalyst / electrode lifetime.

[0095] The strategy described herein offers a new route toward enhancing electrochemical performance by using a local magnetic field. It has the following advantages over existing catalysts and methods:• wide applicability. Various nanoparticulate catalysts which are sensitive to magnetic fields may be loaded on the magnetic nanoparticles to generate local magnetic field- enhanced catalysts. This advantage provides substantial versatility to the approach to preparing catalysts for a wide range of electrochemical reactions described herein. Such reactions include, but are not limited to, oxygen reduction, oxygen evolution and hydrogen evolution reactions.• process safety and cost. The method described herein only requires the magnet at an area loading of less than 1 mg.cm-2of magnetic particles on the electrode. This eliminates the safety concern of handling large magnetic blocks. It also obviates the need for additional electronic equipment to generate the magnetic field, which would incur additional equipment and running costs. The cost of the present catalyst is very small. Using the presented CoPc / CB-Mag catalyst as an example, the cost of cobalt phthalocyanine, carbon black and the magnetic nanoparticles is about A$13,000, 27 and 340 per kg respectively, resulting in a catalyst cost of A$295 per kg, where the majority of the cost comes from the magnetic nanoparticles. Further, the process for making the catalyst described herein does not involvethe use of high-temperature thermal annealing or solvent washing. The organic solvent used can be recycled, affording an environmentally friendly and cost-efficient process. At the tested catalyst loading of 0.5 mg.cm-2, 1 kg catalyst is sufficient to prepare 200 m2electrodes.Table 1 shows a comparison of the presently disclosed technology with competitive technologies. This highlights the large improvement in the ratio of catalyst to magnet mass provided by the invention disclosed herein.Table 1. Estimation of catalyst-magnet mass ratio used in recently reported studies.aMagnet density is taken as 7.5 g cm-3.bA disk-shaped magnet.cA ring-shaped magnet.dDAT=3,5-diamino-1 ,2,4-triazole.

[0096] Those skilled in the art will appreciate that the disclosure described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of a two or more of said steps, features, compositions and compounds.

Claims

Claims:1 . A magnetic electrocatalyst comprising a transition metal catalyst species coupled to a magnetic species, said transition metal catalyst species comprising a transition metal.

2. The magnetic electrocatalyst of claim 1 wherein the transition metal catalyst species comprises a transition metal complexed with a tetrapyrrole macrocycle, a transition metal oxide or metallate, a transition metal mixed oxide or metallate, or a M-N-C catalyst.

3. The magnetic electrocatalyst of claim 2 wherein the tetrapyrrole macrocycle is an optionally substituted phthalocyanine.

4. The magnetic electrocatalyst of claim 2 wherein the M-N-C catalyst is Fe-N-C.

5. The magnetic electrocatalyst of any one of claims 1 to 4 wherein the transition metal catalyst species is coupled to adsorbent particles, said adsorbent particles being supported on the magnetic species.

6. The magnetic electrocatalyst of claim 5 wherein the adsorbent particles are carbon black.

7. The magnetic electrocatalyst of any one of claims 1 to 6 wherein the magnetic species comprises magnetic nanoparticles.

8. The magnetic electrocatalyst of any one of claims 1 to 7 wherein the magnetic species has a coating separating the magnetic species from the transition metal catalytic species.

9. The magnetic electrocatalyst of claim 8 wherein the coating comprises polyvinylchloride or polydopamine.

10. The magnetic electrocatalyst of any one of claims 1 to 9 wherein the transition metal is selected from the group consisting of Co, Mn, Ni, Cu, Zn and Fe and mixtures of any two or more of these.11 . A method for conducting an electrocatalytic reaction comprising applying an electrical potential across an electrically conductive composition between a cathode and an anode, the electrically conductive composition comprising a substrate and a magnetic electrocatalyst according to any one of claims 1 to 10.

12. The method of claim 1 1 wherein the electrocatalytic reaction is an oxygen reduction reaction or an oxygen evolution reaction13. The method of claim 11 or claim 12 wherein the substrate is water, whereby the electrocatalytic reaction is hydrolysis, hydrogen is evolved at the cathode and oxygen is evolved at the anode.

14. A process for making a magnetic electrocatalyst comprising coupling a transition metal catalyst species to a magnetic species.

15. The process of claim 14 wherein the magnetic species comprises magnetic nanoparticles.

16. The process of claim 15 wherein the magnetic nanoparticles have a polymeric coating.

17. The process of any one of claims 14 to 16 comprising coating the magnetic species with a polymeric coating prior to said coupling.

18. The process of any one of claims 14 to 17 wherein the transition metal catalyst species comprises a transition metal complexed with a tetrapyrrole macrocycle, or a transition metal oxide or metallate, or a transition metal mixed oxide or metallate, or a M-N-C catalyst.

19. The process of claim 18 wherein the transition metal catalyst species comprises a transition metal complexed with a tetrapyrrole macrocycle and the process comprises adsorbing the transition metal catalyst species onto an adsorbent to form a coated adsorbent and coupling the coated adsorbent to the magnetic species.

20. The process of claim 14 comprising:• Applying a polymeric coating on the surface of magnetic nanoparticles to form coated magnetic nanoparticles;• Adsorbing a transition metal phthalocyanine complex onto carbon black to form a coated carbon black; andAdsorbing the coated carbon black onto the coated magnetic nanoparticles so as to couple the transition metal phthalocyanine complex to the coated magnetic nanoparticles to form the organometallic magnetic catalyst.

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