Electrocatalyst, and process for its production

Abstract

Provided herein are electrocatalysts derived from metal-organic frameworks for energy storage and conversion applications, and processes for synthesizing and converting metal-organic frameworks to form electrocatalysts.

Description

[0001] Electrocatalyst, and process for its production

[0002] Related Applications

[0003] The present application claims priority from Australian Provisional Patent Application No. 2024903701, the entire contents of which is incorporated herein by this reference.

[0004] Field

[0005] The present disclosure relates to the field of electrochemistry, specifically to electrocatalysts derived from metal-organic frameworks for energy storage and conversion applications, and to the processes for synthesising and converting metal-organic frameworks to form electrocatalysts.

[0006] Background

[0007] The growing demand for clean energy has led to the development of technologies that can efficiently store and convert energy. In this context, metal-air batteries have emerged as promising candidates, due to their high theoretical energy density, superior safety profile, and cost-effectiveness compared to traditional lithium-ion batteries.

[0008] Despite their potential, the widespread adoption of metal-air batteries faces significant challenges. The primary hurdle lies in the sluggish kinetics of two critical electrochemical processes: the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). These reactions, fundamental to the operation of metal-air batteries, require complex molecular rearrangements for 0=0 bond formation in OER and involve a four-electron transfer pathway in ORR. The slow kinetics result in high charge / discharge overpotentials, low cycle efficiency, limited energy capacity, and reduced cycle life, impeding the practical implementation of these promising energy storage devices.

[0009] To address these challenges, the development of efficient and cost-effective electrocatalysts is crucial. Current approaches have explored various materials, each with its own set of limitations. Noble metal-based catalysts, such as Pt / C, Ru02, and IrO2, offer high energy densities but suffer from mono-functionality, scarcity, and high costs. Nitrogen-doped carbon materials (NCs) present a more cost-effective alternative with high electrical conductivity and large surface area, yet they often lack sufficient active sites and graphitization for efficient energy cycling. Metal-organic framework (MOF)-derived carbon has garnered recent attention due to their tuneable metal centres. However, balancing surface area and active site distribution remains a great challenge, and while these materials can show comparable performance to Ptbased materials, limitations remain in respect of synthesis, 0-0 bond cleavage efficiency, and efficiency OER / ORR efficiency.

[0010] The industry urgently needs novel electrocatalysts that can efficiently catalyse both OER and ORR while offering cost-effective alternatives to noble metals, which can significantly improve performance and lifespan of metal-air batteries. Developing such advanced electrocatalysts is essential for realizing the full potential of metal-air batteries and addressing the accelerating challenge of ensuring global energy supply.

[0011] Summary

[0012] A first aspect of the present disclosure provides a zeolitic imidazolate framework (ZIF), comprising:

[0013] zinc;

[0014] a ligand selected from benzimidazole, 6-chloropurine, and purine; and a further metal selected from the group consisting of cobalt, nickel, and iron as part of the framework, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1 : 10 to 1 :40.

[0015] The inventors have surprisingly discovered that a ZIF in accordance with the present disclosure provides for the production of electrocatalysts having advantageous metal density, metal connectivity, and porosity, and having favourable electrochemical performance. The presently disclosed ZIF advantageously comprises a ligand having pyridinic-type nitrogen atoms, which may form metal-nitrogen-carbon bonds within the ZIF framework and in the electrocatalyst, further improving electrochemical performance.

[0016] In some embodiments, the further metal to zinc molar ratio is in a range of from 1:20 to 1:40.

[0017] In some embodiments, the further metal is cobalt.

[0018] In some embodiments, the ZIF has a crystal structure that corresponds with a crystal structure ofZIF-11, ZIF- 12, ZIF-20, orZIF-21.

[0019] In some embodiments, the ZIF is impregnated with an additional metal which is different from the further metal. In some embodiments, the additional metal is selected from the group consisting of cobalt, nickel, iron and copper.

[0020] In some embodiments, the additional metal is iron.

[0021] Another aspect of the present disclosure provides an electrocatalyst comprising:

[0022] a porous carbon network with a nitrogen content of at least 2 atom%;

[0023] an electrocatalyst metal selected from the group consisting of cobalt, nickel, and iron, the metal being present in single sites within the carbon network; and

[0024] the electrocatalyst being derived from a zeolitic imidazolate framework (ZIF), wherein the ZIF comprises

[0025] zinc;

[0026] a ligand selected from benzimidazole, 6-chloropurine, and purine; and an electrocatalyst metal selected from the group consisting of cobalt, nickel, and iron, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1 : 10 to 1 :40.

[0027] An electrocatalyst in accordance with the present disclosure desirably comprises single metal atom sites distributed through a nitrogen-doped porous carbon network. The carbon network of the presently disclosed electrocatalyst is derived from a ZIF and may retain porosity and node connectivity of the ZIF.

[0028] The disclosed electrocatalyst suitably provides high performance in catalysing one or both of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The inventors have surprisingly discovered that an example electrocatalyst provides high electrochemical performance when incorporated into an electrochemical device, such as a metal-air battery.

[0029] In some embodiments, the electrocatalyst metal comprises an amount of from 0.3% to 5% by weight of the total weight of the electrocatalyst.

[0030] In some embodiments, the electrocatalyst is substantially free of zinc.

[0031] In some embodiments, the electrocatalyst has a porous nanosheet 2D structure. In some other embodiments, the electrocatalyst has a porous 3D structure.

[0032] In some embodiments, the electrocatalyst metal is cobalt.

[0033] In some embodiments, the electrocatalyst comprises an additional metal, which is different from the electrocatalyst metal. In some embodiments, the additional metal is selected from the group consisting of cobalt, iron, copper and nickel.

[0034] In some embodiments, the electrocatalyst comprises iron as an additional metal. In some embodiments, the electrocatalyst comprises a porosity of at least 100 cm3g. In some embodiments, the electrocatalyst has a surface area of at least 200 m2g-1. In some embodiments, the electrocatalyst has an electrical conductivity of at least 900 S / m.

[0035] In some embodiments, the electrocatalyst has a combined ORR and OER overpotential of no more than 700 mV.

[0036] Another aspect of the present disclosure provides a process for producing a zeolitic imidazolate framework (ZIF), comprising

[0037] combining

[0038] a zinc salt;

[0039] a further metal salt selected from cobalt, nickel, and iron salts, the further metal to zinc molar ratio being in the range of from 1 : 10 to 1 :40; and

[0040] a ligand selected from benzimidazole, 6-chloropurine, and purine; in a solvent to form a solid ZIF; and

[0041] separating the solid ZIF from the solvent.

[0042] In some embodiments, the process comprises forming a first mixture comprising the zinc salt and the further metal salts in a first solvent, and forming a second mixture comprising the ligand in a second solvent, the first and second mixtures then being combined to form the solid ZIF.

[0043] In some embodiments the first solvent is toluene.

[0044] In some embodiments, the second solvent is methanol.

[0045] In some embodiments, the toluene to methanol volume ratio is in the range of from 1 : 1 to 1:4.

[0046] In some embodiments, the total metal to ligand molar ratio is in the range of from 1:2 to 1:4.

[0047] In some embodiments, ammonium hydroxide is added.

[0048] In some embodiments, the zinc salt is zinc nitrate.

[0049] In some embodiments, the further metal salt is cobalt nitrate.

[0050] In some embodiments, the ZIF is impregnated with an additional metal which is different to the further metal.

[0051] In some embodiments, the additional metal is selected from the group consisting of cobalt, nickel, iron and copper. In some embodiments, following formation of a solid ZIF, the solid ZIF is treated with one or more metal salts selected from cobalt, nickel, iron, and copper salts thereby impregnating the solid ZIF with the additional metal.

[0052] In some embodiments, the ZIF is treated with an iron salt.

[0053] There is also provided a ZIF produced or producible by a process as defined herein. Another aspect of the present disclosure provides a process for forming an electrocatalyst, comprising:

[0054] pyrolyzing a ZIF as defined herein, or a ZIF produced by the process as defined herein. In some embodiments, the pyrolysis is conducted under conditions which evaporate zinc, such that the electrocatalyst comprises substantially no zinc.

[0055] In some embodiments, pyrolysis is carried out at a temperature in a range of from 800°C to 1000°C.

[0056] In some embodiments, pyrolysis is undertaken in the presence of a salt which is molten under the pyrolysis conditions.

[0057] In some embodiments, the salt is selected from the group consisting of zinc acetate and potassium chloride.

[0058] There is also provided an electrocatalyst produced or producible by the process as defined herein.

[0059] There is also provided an electrochemical device comprising the electrocatalyst as defined herein.

[0060] In some embodiments, the electrochemical device is an aqueous metal -air cell, fuel cell, water splitting electrode, or battery.

[0061] Brief Description of the Drawings

[0062] Figure 1: provides a synthesis flow diagram for an exemplary protocol to prepare a ZIF and ZIF-derived electrocatalyst in accordance with some embodiments of the disclosure.

[0063] Figure 2: provides a synthesis flow diagram for another exemplary protocol to prepare a ZIF and ZIF-derived electrocatalyst in accordance with some embodiments of the disclosure.

[0064] Figure 3: provides X-ray diffractograms for exemplary ZIF samples prepared in accordance with some embodiments of the disclosure.

[0065] Figure 4: provides scanning and transmission electron micrographs (SEM and TEM) of ZIF samples prepared in accordance with some embodiments of the disclosure, wherein (a) represents a SEM image of a ZIF sample; (b) represents a SEM image of a ZIF-derived electrocatalyst sample formed by pyrolysis of a ZIF; and c) represents a TEM images of a ZIF-derived electrocatalyst sample formed by pyrolysis of a ZIF.

[0066] Figure 5: provides at C) a linear sweep voltammogram for aZIF-derived electrocatalyst according to some embodiments of the invention, showing overall overpotential during the complete ORR and OER process; and (D) the overpotential gap between ORR and OER for some ZIF-derived electrocatalysts.

[0067] Figure 6: provides morphology, compositional, and spectroscopic analysis results of a ZIF according to some embodiments of the invention, comprising (A) SEM image of N-C-Blank, (B) SEM image, (C) TEM image, (D) HAADF-STEM image, (E) the enlarged image (the orange circle shows metallic atoms) and (F) Element-mapping (green: carbon, yellow: nitrogen, and blue: Co) of Co-N-C-1 / 40 catalyst. (G) Co K-edge XANES spectra and (H) Co FT-EXAFS spectra of Co foil, CoO, Co-N-C-1 / 10, and Co-N-C-1 / 40.

[0068] Figure 7: provides analytical results of the ORR electrocatalytic activity for a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) LSV curves of the electrocatalysts at a rotation rate of 1600 rpm at a scan rate of 5 mV s-1. (B) Tafel plots derived from ORR’s LSV curve. (C) Half-wave potential (E1 / 2) and kinetic current density (Jk) at 0.85 V. (D) LSV curves of Co-C-N-1 / 40 at a scan rate of 5 mV s-1and various rotation rates (400-2000rpm), and (E) the inset is the corresponding K-L plots obtained from LSVs. (F) LSV curves of Co-N-C-1 / 40 electrocatalyst before and after 800 CV in Ch-saturated 0.1 M KOH at scan rate 5mV / s.

[0069] Figure 8: provides analytical results of the OER and bi-functionality activity for a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) LSV curves in 1 M KOH solution at a rotation rate of 1600 rpm and a scan rate of 5 mV s-1. (B) Tafel plots derived from OER’s LSV curves. (C) The potential gap between ORR and OER as bifunctionality. (D) The effect of Nitrogen type and cobalt concentration on bi-functionality of the electrocatalysts.

[0070] Figure 9: provides analytical results of the electrocatalytic activity of Co-N-C-1 / 40 and Pt-Ru / GC catalysts in a ZAB system, comprising (A) discharge polarization curves and the corresponding power density. (B) Measurement of the voltage difference between the cathode and anode by open-circuit voltage. (C) Full discharge profile for a ZAB at a current density of 10 mA cm-2. (D) Discharge plateaus curves of the battery at various current densities.

[0071] Figure 10: provides analytical results of Galvanostatic charge and discharge profiles cycling stability at current density of 2 mA cm-2. Figure 11: provides analytical results of a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) SEM, (B) TEM, (C) EDS mapping, and (D) STEM images of CoFe-2DSA.

[0072] Figure 12: provides analytical results of a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) N2 adsorption-desorption isotherms, (B) XRD patterns after carbonization, (C) Raman spectra, (D) C si XPS spectra, (E) N si XPS spectra, and (F) Comparison of Nitrogen contents of CoFe-2DSA, CoFe-blank, Co-2DSA, Fe-2DSA.

[0073] Figure 13: provides ORR electrochemical results of a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) LSV curves at scan rate 5 mV. s'1and rotating rate 1600rpm in Ch-saturated 0.1 M KOH, (B) Corresponding Tafel plots, (C) Corresponding Half potential (E1 / 2) and kinetic current density (jk) at 0.85 V, (D) LSV curves of CoFe-2DSA catalyst at various rotating rates, (E) Koutecky-Levich plot at scan rate 5 mV. s'1, (F) LSV stability test for before and after 1000 CV cycles of CoFe-2DSA catalyst.

[0074] Figure 14: provides OER and bifunctionality electrochemical results of a ZIF-derived electrocatalyst according to some embodiments of the invention, comprising (A) LSV curves of OER at scan rate 5 mV. s'1and rotating rate 1600 rpm in 02-saturated 1 M KOH, (B) Corresponding Tafel plots, (C) The overall overpotential of CoFe-2D SA during the whole ORR and OER process, (D) The potential gap between ORR and OER,

[0075] Figure 15: provides analytical results of an aqueous Zn-Air Battery system comprising a ZIF-derived electrocatalyst according to some embodiments of the invention. (A) Opencircuit plots. (B) Discharge polarization curves and the corresponding power density. (C) Full discharge profile for a Zn-air battery at a current density of 10 mA cm-2. (D) Discharge plateaus curves of the battery at various current densities.

[0076] Figure 16: provides galvanostatic charge and discharge profiles cycling stability at current density of 2 mA cm-2and different charge-discharge cycle time for an aqueous Zn-Air Battery system comprising a ZIF-derived electrocatalyst according to some embodiments of the invention.

[0077] Figure 17: provides galvanostatic cycling stability (120 min charge-120 min discharge) at different current density for an aqueous Zn-Air Battery system comprising a ZIF-derived electrocatalyst according to some embodiments of the invention.

[0078] Detailed Description Definitions

[0079] Unless specifically defined otherwise, all technical and scientific terms used herein shall be taken to have the same meaning as commonly understood by one of ordinary skill in the art (e.g., chemistry, materials science, electrochemistry, and the like).

[0080] The present disclosure refers to the entire contents of certain documents being incorporated herein by reference. In the event of any inconsistent teaching between the teaching of the present disclosure and the contents of those documents, the teaching of the present disclosure takes precedence.

[0081] It is to be understood that if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art in Australia or any other country

[0082] As used herein, the term “and / or”, e.g., “X and / or Y” shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0083] As used herein, the term about, unless stated to the contrary, refers to + / - 10%, of the designated value.

[0084] As used herein, the terms “a”, “an” and “the” include both singular and plural aspects, unless the context clearly indicates otherwise.

[0085] Unless otherwise indicated, terms such as "first," "second," etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g., a “first” item) and / or a higher-numbered item (e.g., a “third” item).

[0086] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination. As used herein, the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.

[0087] As used herein, reference to “standard” temperature and / or pressure conditions refers to an approximation of the IUPAC definition of standard temperature and pressure, wherein an approximate temperature of 273.15 K (0 °C, 32 °F) and an approximate pressure of 105 Pa (100 kPa, 1 bar) is intended.

[0088] The present disclosure relates to ZIFs useful as intermediates for electrocatalysts, to process for preparing the ZIFs, to electrocatalysts comprising the ZIFs, to processes for preparing the electrocatalysts, and to electrochemical devices comprising the electrocatalysts.

[0089] Zeolitic imidazolate framework (ZIF) are a subclass of metal-organic frameworks (MOFs), comprising metal ions forming “nodes” that are coordinated and interconnected by imidazolate ligands as “linkers” between the metal nodes. ZIFs have porous, stable structures with high surface area and tuneable chemical reactivity, and have been explored for gas storage, drug delivery and membrane-based separations

[0090] Electrode materials for metal-air batteries have been a focus for research, which must overcome the slow kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), as these reactions require extensive molecular rearrangements to form 0=0 bonds (OER) and involve four-electron transfer pathways (ORR). ZIF-based materials have promise to provide electrocatalytic activity compatible with both OER and ORR, however achieving sufficient reactivity and porosity is challenging.

[0091] ZIF-derived materials, obtained by pyrolyzing ZIFs at high temperatures, can exhibit improved electrocatalytic properties over ZIFs due to the creation of conductive, carbon-based frameworks that retain the structural properties of the original ZIF. The inventors of the present disclosure have discovered that ZIF-derived electrocatalyst materials having the properties described below may be useful for catalysing OER and ORR in electrochemical devices.

[0092] Zeolitic imidazolate framework

[0093] Accordingly, in one aspect, there is provided a zeolitic imidazolate framework (ZIF), comprising:

[0094] zinc;

[0095] a ligand selected from benzimidazole, 6-chloropurine, and purine; and a further metal selected from the group consisting of cobalt, nickel, and iron as part of the framework, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1 : 10 to 1 :40.

[0096] A ZIF is a class of metal-organic frameworks (MOFs) with a three-dimensional structure, and which has zeolite-like topology. ZIFs are typically composed of tetrahedrally-coordinated transition metal ions connected by imidazolate-type linkers.

[0097] The ZIF of the present disclosure comprises zinc, which is coordinated and interconnected by the ligand and provides metal nodes of the ZIF. In accordance with embodiments of the present disclosure, zinc encompasses zinc ions, and the terms zinc and zinc ion are used interchangeably. Suitable zinc ions may be +2 valency, that is, the zinc ions have a zinc (II) redox state.

[0098] The ZIF of the present disclosure comprises a ligand. The ligand is capable of coordinating to two or more metals, and thereby linking those metals forming a framework. The framework of the ZIF may thereby be formed where a metal is coordinated to two or more ligands, where each ligand is coordinated to two or more metals. The ligand may also be called a linker. The ligand comprises at least two nitrogen atoms that are each capable of coordinating with a metal, such as zinc. The nitrogen atoms of the ligand may comprise one or more nitrogen species, such as pyridinic nitrogen, pyrrolic nitrogen, and / or graphitic nitrogen. The ligand further comprises carbon atoms that interconnect the nitrogen atoms, such that the ligand may interconnect two or more metals. The ligand is suitably an imidazolate-type compound that coordinates to a metal and interconnects metal nodes to form the framework of the ZIF. The metal can therefore be present at nodes within the framework. Suitable ligands are benzimidazole, 6-chloropurine, and purine.

[0099] The ZIF also comprises a further metal. The further metal is in addition to zinc The term metal encompasses metal ions, and the two terms metal and metal ion are used interchangeably. The further metal may be cobalt, nickel, or iron, or a mixture thereof.

[0100] In some embodiments, the further metal is cobalt. The further metal may be present in the ZIF in any redox state. For example, cobalt may be present in the ZIF as cobalt (II) ions.

[0101] In some embodiments, the further metal is nickel. Nickel may be present in the ZIF as nickel (II) ions.

[0102] In some embodiments, the further metal is iron. Iron may be present in the ZIF as iron (II) ions The further metal is present as part of the framework of the ZIF, i.e. the further metal is coordinated by multiple ligands together forming part of the 3 -dimensional structure of the ZIF, rather than, for example, occupying pores within the ZIF.

[0103] The distribution of the zinc and / or the further metal in the framework of the ZIF may be determined by any suitable analytical technique, for example X-ray absorption spectroscopy (XAS). In some embodiments, XAS analysis may show low or no signal associated with metalmetal interaction. In some embodiments, the further metal may be uniformly distributed, or substantially uniformly distributed, throughout the framework.

[0104] The further metal is suitably present in the ZIF in a molar ratio in a range of from 1:10 to 1:40 compared with zinc. In some embodiments the molar ratio of the further metal is in a range of from 1:20 to 1:40 compared with zinc. In some embodiments, the molar ratio of the further metal to zinc is about 1:10, about 1:20, about 1:30, or about 1:40.

[0105] The ZIF of the present disclosure is typically a crystalline material. A crystalline material comprises a majority of the volume of the material having a physical structure defined by a uniformly repeating unit cell of chemical units.

[0106] The degree of crystallinity in the ZIF may be determined by any suitable analytical technique known in the art, for example X-ray diffraction.

[0107] In some embodiments, the ZIF has a crystal structure that corresponds with a crystal structure of ZIF-11, ZIF-12, ZIF-20, or ZIF-21. By the ZIF having a corresponding crystal structure, the ZIF node connectivity and crystal unit cell of the ZIF are substantially the same or equivalent to the node connectivity and crystal unit cell of one of ZIF-11, ZIF-12, ZIF-20, or ZIF-21, for example as determined by X-ray diffraction analysis.

[0108] In some embodiments, the ZIF is impregnated with an additional metal. The additional metal may be cobalt, nickel, iron, or copper, or a mixture thereof.

[0109] In some embodiments, the additional metal is cobalt. In some embodiments, the additional metal is nickel. In some embodiments, the additional metal is iron. In some embodiments, the additional metal is copper.

[0110] Impregnation of the ZIF with an additional metal requires that the ZIF is formed first, (i.e. from zinc, a ligand, and a further metal as described above), and then the additional metal is added to the ZIF, being incorporated onto the surface of the framework, and / or into pores within the ZIF. In some embodiments, the additional metal does not form a node of the framework. When present, in some embodiments the additional metal is different from the further metal. For example, in some embodiments where the further metal is cobalt, the additional metal is a metal that is different than cobalt, such as iron.

[0111] In some embodiments, the additional metal is present as single atom sites on the surface of the ZIF. In other embodiments, the additional metal is present as clusters of metal atoms, or mixtures of clusters and single atoms sites.

[0112] In some embodiments, the additional metal is present in a molar ratio of between 1:3 and 3 : 1 compared with the further metal of the ZIF. In some embodiments, the additional metal is present in a molar ratio of about 1 : 1 compared with the further metal of the ZIF.

[0113] Preparation of Zeolitic Imidazolate Frameworks

[0114] The ZIFs of the present disclosure may be produced by any suitable process.

[0115] The ZIFs may for example be produced by a process comprising combining a zinc salt, with a further metal salt selected from cobalt, nickel, and iron salts, the further metal to zinc molar ratio being in the range of from 1 : 10 to 1 :40, and a ligand selected from benzimidazole, 6-chloropurine, and purine in a solvent to form a solid ZIF, and separating the solid ZIF from the solvent.

[0116] The zinc salt provides zinc ions to form nodes of the framework of the ZIF. In some embodiments, the zinc salt comprises zinc in a +2 valency, that is, the zinc is in a (II) redox state in the zinc salt. In some embodiments, the zinc salt is selected from zinc nitrate, zinc sulphate, zinc chloride, zinc carbonate, zinc acetate, zinc chlorate and zinc phosphate. In some embodiments, the zinc salt is zinc nitrate.

[0117] The further metal salt provides a further metal ion to form nodes of the framework of the ZIF. The further metal salt is a cobalt, nickel, or iron salt, or a mixture thereof. In some embodiments, the further metal salt is a nitrate, sulphate, chloride, carbonate, acetate, chlorate, or phosphate, or a mixture thereof. In some embodiments the further metal salt is cobalt nitrate.

[0118] The ratio of zinc salt to further metal salt that is combined according to the process provides a means to adjust the ratio of zinc and further metal in the so-formed ZIF. In some embodiments, the molar ratio of zinc salt to further metal salt is in the range of from 1:10 to 1:40. In some embodiments, the molar ratio of zinc salt to further metal salt is in the range of from 1 :20 to 1 :40. In some embodiments, the molar ratio of the zinc salt to further metal salt is about 1:10, or about 1:20, or about 1:30, or about 1:40. In some embodiments, the total metal to ligand molar ratio is in the range of from 1:2 to 1:4.

[0119] Combining the salts and ligand may for example involve mixing, blending, or otherwise homogenising the salts and ligand to form a single mixture comprising the salt and ligand components. In some embodiments, the zinc salt and further metal salt are combined first, then the combined salts are thereafter combined with the ligand. In some embodiments, the zinc salt, further metal salt, and ligand are combined at around ambient temperature and / or at standard pressure. In some embodiments, the zinc salt, further metal salt, and ligand are combined at elevated temperature. In some embodiments, the zinc salt, further metal salt and ligand are combined at a temperature which is lower than ambient temperature.

[0120] Any suitable apparatus may be used to combine the components.

[0121] In some embodiments, the salts and ligand are combined by mixing. In some embodiments, combining the salts and ligand is undertaken over a period of time, for example by mixing for a period of time. In some embodiments, the salts and ligand are combined for at least 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 1 hour, 2, hours, 3, hours, 4, hours, 5 hours, 6 hours, 8 hours, or at least 10 hours.

[0122] The zinc salt, further metal salt and ligand are combined in a solvent, or a mixture of solvents.

[0123] In some embodiments, two or more of the zinc salt, further metal salt, and ligand are combined first then added to a solvent.

[0124] In some embodiments the solvent is selected from the group consisting of methanol, toluene, ethanol, dimethylformamide, tetrahydrofuran, hexane, acetone, water, or a mixture thereof.

[0125] In some embodiments, the solvent is or comprises toluene. In some embodiments, the solvent is or comprises methanol.

[0126] In some embodiments, the solvent is a mixture of toluene and methanol.

[0127] In some embodiments, the process comprises forming a first mixture comprising the zinc salt and the further metal salts in a first solvent, and forming a second mixture comprising the ligand in a second solvent, the first and second mixtures then being combined to form the solid ZIF.

[0128] For example, the zinc salt and further metal salt may be first combined in a solvent to form a first solvent mixture. The first solvent mixture is then mixed for sufficient time to dissolve the salts. The ligand may be mixed with a second solvent to form a second solvent mixture, wherein the first and second solvents are thereafter combined.

[0129] In some embodiments, the solvent of the first mixture is toluene. In some embodiments, the solvent of the second mixture is methanol.

[0130] In some embodiments where toluene and methanol are the solvent, the toluene to methanol volume ratio is in the range of from 1:1 to 1:4. In some embodiments, the volume ratio may be about 1 : 1, or about 1 :2, or about 1 :3, or about 1 :4.

[0131] Combining the components in a solvent may be undertaken in any suitable apparatus, for example flasks, beakers, vats, tanks, pipes, or other known vessels. Combining may be promoted by mixing, agitating, bubbling, application of ultrasound, heating, or homogenising. In some embodiments, one or more steps of the process may be undertaken in batch, semibatch, or continuous flow.

[0132] In some embodiments, a base is added, for example to the mixture of ligand, zinc and further metal. Any suitable base may be used. In some embodiments, the base is ammonium hydroxide.

[0133] Combining the zinc salt, further metal salt and ligand in a solvent suitably results in formation of a ZIF.

[0134] In some embodiments, the solid ZIF is a crystalline solid.

[0135] In some embodiments, the ZIF is insoluble in the solvent at room temperature and atmospheric pressure and therefore precipitates from the solvent as a solid ZIF.

[0136] In some embodiments, the temperature and / or pressure of the solvent is modified to promote precipitation of the ZIF from solution. In some embodiments, one or more steps are taken to promote precipitation of the ZIF from solution, for example cooling, addition of an anti-solvent, or addition of seed crystals.

[0137] The solid ZIF is then suitably separated from the solvent. Separation of the solid ZIF from the solvent may be undertaken by any suitable means for separating a solid from a liquid. For example, centrifugation, filtration, decantation, or a similar process may be undertaken. In some embodiments, the solid ZIF is concentrated by centrifugation, and the solvent is decanted to separate the solid ZIF from the solvent.

[0138] In some embodiments, following separation, the solid ZIF is washed with a solvent, for example to remove byproducts such as unreacted salts and / or ligand.

[0139] In some embodiments, following separation, the solid ZIF is dried, for example at elevated temperature and / or under vacuum. In some embodiments, the ZIF is impregnated with an additional metal which is different to the further metal. For example, the solid ZIF, once formed, may be treated with one or more additional metal salts. The additional metal salt is in addition to the further metal salt used to form the solid ZIF.

[0140] In some embodiments, the solid ZIF is separated from the solvent prior to being treated with one or more additional metal salts.

[0141] In some embodiments, the one or more additional metal salts contains a different metal from the metal in the further metal salt used to form the ZIF. In some embodiments, the additional metal salt is selected from the group consisting of cobalt, nickel, iron, and copper salts, or mixtures thereof. In some embodiments, the additional metal salt is a cobalt salt. In some embodiments, the additional metal salt is a nickel salt. In some embodiments, the additional metal salt is an iron salt. In some embodiments, the additional metal salt is a copper salt.

[0142] In some embodiments the additional metal salt is a nitrate, sulphate, chloride, carbonate, acetate, chlorate, or phosphate salt.

[0143] In some embodiments, the additional metal salt is iron nitrate.

[0144] In some embodiments, a solution of the one or more additional metal salts is prepared in a solvent, and the solution is combined with the solid ZIF. In some embodiments, a solution of the one or more additional metal salts is added gradually to the ZIF, for example dropwise. In some embodiments, treatment of the ZIF with one or more additional metal salts is undertaken at ambient temperature and / or at standard atmospheric pressure.

[0145] In some embodiments, the additional metal is present in a molar ratio of between 1:3 and 3 : 1 compared with the further metal of the ZIF. In some embodiments, the additional metal is present in a molar ratio of about 1 : 1 compared with the further metal of the ZIF.

[0146] The present disclosure also relates to a ZIF which is produced or which is producible according to a process as defined herein.

[0147] Electrocatalysts

[0148] The present disclosure further relates to electrocatalysts. An electrocatalyst is a material that participates in redox reactions. The electrocatalyst of the present disclosure is a material capable of electron transfer when an electrical bias is applied to the material. An electrocatalyst under an applied electrical bias may transfer electrons to or from external chemical species. An external chemical species that is relevant in the context of metal-air batteries is molecular oxygen (O2). An electrocatalyst suitable for interacting with molecular oxygen suitably comprises reactive active sites with suitable energetic properties to undergo electron transfer with molecular oxygen, and high surface area and porosity to enable molecular oxygen access to the reactive active sites.

[0149] The electrocatalyst according to the present disclosure comprises:

[0150] a porous carbon network with a nitrogen content of at least 2 atom%;

[0151] an electrocatalyst metal selected from the group consisting of cobalt, nickel, and iron, the metal being present in single sites within the carbon network; and

[0152] the electrocatalyst being derived from a zeolitic imidazolate framework (ZIF), wherein the ZIF comprises

[0153] zinc;

[0154] a ligand selected from benzimidazole, 6-chloropurine, and purine; and an electrocatalyst metal selected from the group consisting of cobalt, nickel, and iron, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1 : 10 to 1 :40.

[0155] An electrocatalyst in accordance with the present disclosure comprises a porous carbon network. It is believed that having a porous carbon network may be advantageous for electrocatalytic performance, by providing high surface area and / or facilitating electrical conductivity.

[0156] The carbon network of the electrocatalyst is porous. Porosity refers to the presence of interconnected internal voids within the volume of the carbon network. Porosity is advantageous for an electrocatalyst to reduce the impact of reactant / product mass transport on catalysis, wherein external species such as molecular oxygen may diffuse to the active catalytic sites through the internal pores of the structure. The term porosity encompasses the volume ratio of the internal voids compared with the volume of the carbon network, as well as the shape, size, shape / size distribution, and connectivity of the internal voids. The porosity further refers to multi-scale porosity, that is the relative presence of micropores, mesopores, and macropores in the structure.

[0157] In some embodiments, the electrocatalyst has a porosity of at least 50, or at least 75, or at least 100, or at least 150, or at least 200, or at least 250, or at least 300 cm3g’1.

[0158] In some embodiments, the electrocatalyst has a porosity in the range of from 50 to 1000, or from 100 to 1000, or from 200 to 1000, or from 500 to 1000, or from 50 to 500, or from 100 to 500, or from 200 to 500, or from 50 to 200, or from 100 to 200 cm3g’1. The porosity of the electrocatalyst may be determined by any suitable analytical technique, for example by nitrogen adsorption / desorption isotherms.

[0159] In some embodiments, porosity is determined by ASTM D3663-20 (Standard Test Method for Surface Area of Catalysts and Catalyst Carriers), e.g. as being used in November 2024.

[0160] A carbon network in the context of the present disclosure refers to a carbon-based material comprising an ordered, interconnected network of atoms.

[0161] The carbon network comprises nitrogen within the network, and the porous carbon network has a nitrogen content of at least 2 atom%. In some embodiments, the porous carbon network comprises nitrogen in an amount of at least 2, 3, 4, 5, 6, 8, 10, or 12 atom%. In some embodiments, the carbon network comprises from 2 to 10, or from 2 to 8, or from 2 to 6, or from 2 to 4, or from 4 to 10, or from 4 to 8, or from 4 to 6, or from 6 to 10, or from 6 to 8 atom% nitrogen.

[0162] The presence and concentration of nitrogen in the carbon network may be determined by any suitable analytical technique. For example, the presence and concentration of nitrogen in the carbon network may be determined by X-ray Photoelectron Spectroscopy (XPS) and / or Inductively Coupled Plasma (ICP) spectroscopy.

[0163] The electrocatalyst is derived from a ZIF. Being derived from a ZIF means that a ZIF is first prepared, then converted to form the electrocatalyst.

[0164] In some embodiments, the electrocatalyst retains crystal structure and / or metal connectivity associated with the ZIF. In some embodiments, the electrocatalyst retains porosity, pore size and / or pore connectivity properties associated with the ZIF.

[0165] The ZIF from which the electrocatalyst is derived comprises:

[0166] zinc;

[0167] a ligand selected from benzimidazole, 6-chloropurine, and purine; and a further metal selected from the group consisting of cobalt, nickel, and iron, and copper, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1:10 to 1:40.

[0168] The ZIF from which the electrocatalyst is derived comprises zinc, which is coordinated and interconnected by the ligand and provides metal nodes of the ZIF. In accordance with embodiments of the present disclosure, zinc encompasses zinc ions, and the terms zinc and zinc ion are used interchangeably. Suitable zinc ions may be +2 valency, that is, the zinc ions have a zinc (II) redox state. However, typically during production of the electrocatalyst, zinc is removed. In some embodiments, the electrocatalyst is free, or substantially free, of zinc. Zinc is a relatively volatile species that may be removed by treatment with heat.

[0169] In some embodiments, the total amount of zinc present in the electrocatalyst is less than 1%, less than 0.5%, or less than 0.1% based on the number of atoms in the network.

[0170] In some embodiments, the total amount of zinc present in the electrocatalyst is less than 1%, less than 0.5%, or less than 0.1% by weight of the electrocatalyst.

[0171] The ZIF from which the electrocatalyst is derived comprises a ligand. The ligand is capable of coordinating to two or more metals and thereby linking those metals forming a framework. The framework of the ZIF may thereby be formed where a metal is coordinated to two or more ligands, where each ligand is coordinated to two or more metals. The ligand may also be called a linker. The ligand comprises at least two nitrogen atoms that are each capable of coordinating with a metal, such as zinc. The nitrogen atoms of the ligand may comprise one or more nitrogen species, such as pyridinic nitrogen, pyrrolic nitrogen, and / or graphitic nitrogen. The ligand further comprises carbon atoms that interconnect the nitrogen atoms, such that the ligand may interconnect two or more metals. The ligand is suitably an imidazolate-type compound that coordinates to a metal and interconnects metal nodes to form the framework of the ZIF. The metal can therefore be present at nodes within the framework. Suitable ligands are benzimidazole, 6-chloropurine, and purine.

[0172] The carbon and nitrogen of the porous carbon network is primarily derived from the ligand of the ZIF.

[0173] The ZIF from which the electrocatalyst is derived also comprises an electrocatalyst metal. The term metal encompasses metal ions, and the two terms metal and metal ion are used interchangeably. The electrocatalyst metal may be cobalt, nickel, or iron, or a mixture thereof. In some embodiments, the electrocatalyst metal is cobalt. The electrocatalyst metal may be present in the ZIF in any redox state. For example, cobalt may be present in the ZIF as cobalt (II) ions. In some embodiments, the electrocatalyst metal is nickel. In some embodiments, the electrocatalyst metal is iron. The electrocatalyst metal is present as part of the framework of the ZIF, i.e. the electrocatalyst metal is coordinated by multiple ligands together forming part of the 3 -dimensional structure of the ZIF, rather than, for example, occupying pores within the ZIF.

[0174] The electrocatalyst metal is suitably present in the ZIF from which the electrocatalyst is derived, in a molar ratio in a range of from 1:10 to 1:40 compared with zinc. In some embodiments the molar ratio of the electrocatalyst metal is in a range of from 1:20 to 1:40 compared with zinc. In some embodiments, the molar ratio of the electrocatalyst metal to zinc is about 1:10, about 1:20, about 1:30, or about 1:40.

[0175] The ZIF from which the electrocatalyst is derived is typically a crystalline material. A crystalline material comprises a majority of the volume of the material having a physical structure defined by a uniformly repeating unit cell of chemical units. The degree of crystallinity in the ZIF may be determined by any suitable analytical technique known in the art, for example X-ray diffraction. In some embodiments, the ZIF has a crystal structure that corresponds with a crystal structure of ZIF-11, ZIF-12, ZIF-20, or ZIF-21. By the ZIF having a corresponding crystal structure, the ZIF node connectivity and crystal unit cell of the ZIF are substantially the same or equivalent to the node connectivity and crystal unit cell of one of ZIF-11, ZIF-12, ZIF-20, or ZIF-21, for example as determined by X-ray diffraction analysis.

[0176] The concentration of the electrocatalyst metal in the electrocatalyst may be determined by any suitable means, for example by inductively-couple plasma mass spectrometry (ICP-MS). In some embodiments, the electrocatalyst metal is present in an amount of from 0.1% to 10%, or 0.2% to 8%, or 0.3% to 6%, or 0.3% to 5%, or from 0.5% to 4%, or about 0.3%, about 0.5%, about 1%, about 2%, about 3%, about 4%, or about 5%, by weight of the total weight of the electrocatalyst.

[0177] In some embodiments, the electrocatalyst metal is coordinated to nitrogen groups in the carbon network of the electrocatalyst. It is believed that metal-nitrogen-carbon bonds formed in some embodiments enhance the electrocatalytic activity of the metal. The presence of metal -nitrogen coordination bonds may be determined by any suitable analysis technique, for example X-ray diffraction spectroscopy. In some embodiments, metal-nitrogen bonds constitute at least 80%, 85%, 90%, 95%, 97%, or at least 99% of the bonds coordinating the electrocatalytic metal in the carbon network.

[0178] The electrocatalyst metal is present in single sites within the carbon network. Single atom sites refers to there being sites containing single electrocatalyst metal atoms within the porous carbon network.

[0179] The presence of single sites and / or absence of clusters of two or more further metal atoms within the porous carbon network may be determined by any suitable analytical technique, for example an analytical technique suitable for detecting interactions between metal atoms, such as X-ray absorption spectroscopy, Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, and / or X-ray Absorption Near Edge Structure (XANES) spectroscopy. In some embodiments, at least 90% of the electrocatalyst metal species, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99%, or at least 99.5%, or at least 99.9% of the electrocatalyst metal species present in the porous carbon network are present in single sites.

[0180] In some embodiments, less than 10% of the electrocatalyst metal species, or less than 5%, or less than 4%, or less than 3%, or less than 2%, or less than 1%, or less than 0.5%, or less than 0.1% of the electrocatalyst metal species present in the porous carbon network are present in the form of clusters.

[0181] In some embodiments, the electrocatalyst metal is present as single atom sites that are uniformly distributed, or substantially uniformly distributed, throughout the porous carbon network.

[0182] In some embodiments, the electrocatalyst metal is coordinated to nitrogen groups in the carbon network of the electrocatalyst. It is believed that metal-nitrogen-carbon bonds formed in some embodiments enhance the electrocatalytic activity of the metal. The presence of metal -nitrogen coordination bonds may be determined by any suitable analysis technique, for example X-ray diffraction spectroscopy. In some embodiments, metal-nitrogen bonds constitute at least 80%, 85%, 90%, 95%, 97%, or at least 99% of the bonds coordinating the electrocatalytic metal in the carbon network.

[0183] In some embodiments, the electrocatalyst has a 2D nanosheet structure. A 2D nanosheet structure is a thin, sheet-like structure having atomic or near-atomic thickness. A 2D nanosheet comprises a network extending predominantly in two dimensions, with relatively less network extension in a third dimension. It is believed that a 2D nanosheet structure may be advantageous for some electrocatalysis applications, owing to the high surface area, high electrical conductivity and good mechanical properties.

[0184] In some embodiments of the 2D nanosheet structure, the electrocatalyst has a ratio of (length + width) / depth of at least 20:1, or at least 30:1, or at least 40:1, or at least 50:1, or at least 100:1.

[0185] In some embodiments of the 2D nanosheet structure, the electrocatalyst has a depth, also referred to as thickness, of no more than 100 nm, 80 nm, 60 nm, 40 nm, 20 nm, 15 nm, 12 nm, 10 nm, 8 nm, 6 nm, 4 nm, 2 nm, 1 nm, or no more than 0.5 nm, or about 0.4 nm, or about 0.3 nm.

[0186] In some embodiments, the electrocatalyst has a 3D structure. In some embodiments of the porous 3D structure, the electrocatalyst has a ratio of (length + width) / depth of less than 5:1. In some embodiments of the 3D structure, the electrocatalyst has a depth, also referred to as thickness, of at least 3 pm, or at least 5 pm, or at least 10 pm, or at least 15 pm, or at least 20 pm.

[0187] In some embodiments, the electrocatalyst comprises an additional metal. The additional metal may be cobalt, nickel, iron, or copper, or a mixture thereof.

[0188] In some embodiments, the additional metal is cobalt. In some embodiments, the additional metal is nickel. In some embodiments, the additional metal is iron. In some embodiments, the additional metal is copper.

[0189] When present, in some embodiments the additional metal is different from the electrocatalyst metal. For example, in some embodiments where the electrocatalyst metal is cobalt, the additional metal is a metal that is different than cobalt, such as iron.

[0190] In some embodiments, the additional metal is present in a molar ratio of between 1:3 and 3 : 1 compared with the electrocatalyst metal. In some embodiments, the additional metal is present in a molar ratio of about 1 : 1 compared with the electrocatalyst metal.

[0191] In some embodiments, the ZIF from which the electrocatalyst has been derived was formed, then impregnated with the additional metal, and the resulting material then converted into an electrocatalyst.

[0192] In some embodiments, the additional metal does not form a node of the porous carbon network. In some embodiments, the additional metal is located on the surface of the porous carbon network.

[0193] In some embodiments, the additional metal is present as single atom sites on the surface of the pores of the electrocatalyst. In other embodiments, the additional metal is present as clusters of metal atoms, or mixtures of clusters and single atom sites.

[0194] High surface is beneficial for an electrocatalyst to increase exposure of catalytic active sites of the electrocatalyst to external chemical species. In some embodiments, the electrocatalyst has a surface area of at least 50, at least 75, at least 100, at least 150, at least 200, at least 250, at least 300, or at least 400 m2g-1. In some embodiments, the electrocatalyst has a surface area in the range of from 50 to 1000, or from 100 to 1000, or from 200 to 1000, or from 500 to 1000, or from 50 to 500, or from 100 to 500, or from 200 to 500, or from 50 to 200, or from 100 to 200 m2g-1.

[0195] The surface area of the electrocatalyst may be determined by any suitable analytical technique, for example using the Brunauer-Emmett-Teller (BET) method based on N2 gas adsorpti on / desorpti on . Preparation of Electrocatalyst

[0196] The present disclosure relates further to a process for deriving an electrocatalyst from a ZIF in accordance with the first aspect or a ZIF produced by the process according to the second aspect. The process comprises pyrolyzing a ZIF as defined herein, or a ZIF produced by the process as defined herein.

[0197] The ZIF is exposed to heat sufficient to pyrolyze the ZIF to form the electrocatalyst. Pyrolysis can decompose the organic ligand of the ZIF to form a carbon-rich network, which may enhance electrocatalytic activity of the structure.

[0198] In some embodiments, the pyrolysis conditions are sufficient to substantially or completely remove zinc from the ZIF. Zinc is a volatile material, such that heating under sufficient conditions can exclude zinc from the ZIF by evaporation.

[0199] In some embodiments, the pyrolysis conditions are sufficient to remove at least 95%, 97%, 99%, 99.5%, or 99.9% of zinc from the ZIF structure, for example as determinable by ICP-MS.

[0200] In some embodiments, the ZIF is heated to at least 700 °C, 750 °C, 800 °C, 850°C, 900°C, 950°C, 1000°C, or at least 1050°C to pyrolyze the ZIF.

[0201] In some embodiments the heat applied to pyrolyze the ZIF is in the range of from 800°C to 1000°C.

[0202] In some embodiments, the ZIF is heated under a controlled atmosphere. A suitable controlled atmosphere is a nitrogen or argon rich atmosphere, or under a reduced pressure, such as under vacuum. In some embodiments, pyrolysis is undertaken under nitrogen.

[0203] In some embodiments, the ZIF is exposed to pyrolysis conditions for a period of at least 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or at least 8 hours.

[0204] Pyrolysis may be undertaken in any suitably resilient vessel or apparatus. In some embodiments pyrolysis is undertaken in a crucible. In some embodiments, pyrolysis is undertaken in a fixed-bed reactor.

[0205] In some embodiments, pyrolysis of the ZIF is undertaken in the presence of a salt, which is molten under the process conditions. It is believed that the presence of a molten salt during pyrolysis of the ZIF improves porosity and surface area of the electrocatalyst that is derived.

[0206] In some embodiments, the molten salt may comprise zinc salts and / or potassium salts. In some embodiments the molten salt may comprise zinc acetate and / or potassium chloride. In some embodiments where a molten salt is employed that comprises zinc acetate and potassium chloride, the zinc to potassium molar ratio is in the range of from 1 :5 to 1:1.

[0207] The present disclosure relates further to an electrocatalyst produced or producible according to a process as defined herein.

[0208] Uses of Electrocatalysts

[0209] Properties of the electrocatalyst according to the third aspect or the electrocatalyst produced according to the fourth aspect may be advantageous for use in an electrochemical device.

[0210] Electrocatalysts in accordance with the present disclosure have been found to have good electrical conductivity. The electrical conductivity may be determined by any suitable analytical technique, for example by potentiometry, and / or Electrochemical Impedance Spectroscopy (EIS). In some embodiments, the electrocatalyst has an electrical conductivity of at least 500, 700, 900, 1000, 1200, 1400, or at least 1600 S / m.

[0211] In some embodiments, the electrocatalyst is capable of catalysing one or both of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In some embodiments, the electrocatalyst catalyses both OER and ORR. The performance of the electrocatalyst for catalysing ORR and / or OER may be analysed by any suitable technique, for example Linear Sweep Voltammetry. In some embodiments where Linear Sweep Voltammetry is used to analyse catalytic performance, the half-wave potential (E’A) may be measured to determine ORR, which corresponds to the potential at half of the maximum current. In some embodiments where Linear Sweep Voltammetry is used to analyse catalytic performance, the onset potential may be recorded to determine OER, which is the potential at a current density of 10 mA / cm2where significant oxygen evolution begins. In some embodiments, the overall overpotential is then calculated as the difference between the ORR half-wave potential and the OER onset potential.

[0212] The overall overpotential (AE=Ejio-Ei / 2) of an oxygen electrode provides an indicator of the combined OER and ORR activity of an electrocatalyst, wherein lower values may indicate superior electrocatalytic performance (Yan, L. et al. (2023) Advanced Energy Materials 13, 2204245). In some embodiments, the electrocatalyst exhibits low overall overpotential. In some embodiments the overall overpotential is no more than 900, 850, 800, 750, 700, 680, 660, 640, 620, 600, 580, or no more than 560 mV. In some embodiments, the electrocatalyst provides stable electrocatalytic performance over numerous cycles. Stable performance refers to substantially unchanged electrochemical properties during cycling the electrocatalyst through repeated redox reactions. In some embodiments, the electrocatalyst maintains substantially unchanged performance over at least 50, 700, 1000, 1500, 2000, 3000, or at least 4000 cycles.

[0213] Products and Devices

[0214] In some embodiments the electrocatalyst according to the third aspect or the electrocatalyst produced according to the fourth aspect may be employed in an electrochemical product or device. In some embodiments the electrocatalyst is employed in an electrode of a product or device.

[0215] In some embodiments the product or device is an aqueous metal-air cell, fuel cell, supercapacitor, water splitting electrode, carbon dioxide reduction device, electrochemical sensor, or battery. In some embodiments the product or device is an electrode of a metal-air cell.

[0216] Examples

[0217] Non-limiting examples will now be described, to further illustrate exemplary embodiments of the present disclosure.

[0218] Reagents and General Methodology

[0219] Suitable chemicals were sourced from Sigma-Aldrich without further refinement and included methanol (99 %), toluene (99 %), ammonium hydroxide (NH4OH), zinc nitrate hexahydrate (Zn(NO3)2 6H2O), cobalt nitrate hexahydrate (Co(NO3)2 6H2O), benzimidazole (C7H6N2), Nafion® solution (5 %). The washing process utilized ultrapure water and methanol as required. Solutions were prepared using only ultrapure water.

[0220] Physicochemical and Electrochemical Characterisation

[0221] ZIF and ZIF-derived electrocatalyst samples were prepared according to an exemplary procedure, as detailed in Figures 1 and 2. ZIF or ZIF-derived electrocatalyst samples were analysed using a range of techniques, including powder X-ray diffraction on a PANalytical X'Pert Pro Diffractometer with Cu Ka radiation at 40kV and 15mA (as shown in Figure 3), field emission scanning electron microscopy Phenom XL SEM for in-depth microstructural analysis, 10 KV and SED, transmission electron microscopy FEI Tecnai G2 T20 TWIN TEM instrument with an acceleration voltage of 200 kV, high angle annular dark-field scanning transmission electron microscopy on a Hitachi HD-2700C (as shown in Figure 4). Figure 4 shows scanning and transmission electron micrographs (SEM and TEM) of ZIF samples, wherein (a) represents a SEM image of a ZIF sample; (b) represents a SEM image of a ZIF-derived electrocatalyst sample formed by pyrolysis of a ZIF; and c) represents a TEM images of a ZIF-derived electrocatalyst sample formed by pyrolysis of a ZIF.

[0222] The EDX data were collected using a FEI Tecnai G2 F20 FEGTEM operating at 200 kV with a Bruker EDX detector.

[0223] The elemental components of the ZIF or ZIF-derived electrocatalyst were analysed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) Thermo iCAP TQe Triple Quadrupole ICP-MS.

[0224] X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific Nexsa spectrometer with a hemispherical analyser. Monochromatic Al Ka X-rays (1486.6 eV) at 72 W were used (6 mA, 12 kV) with a 400 pm x 250 pm spot. Wide survey and high-resolution scans were taken with analyser pass energies of 150 and 50 eV, respectively. Survey scans had a 1.0 eV step size and a 10 ms dwell time, while high-resolution scans used a 0.1 eV step size and a 50 ms dwell time. The analysis chamber maintained a base pressure below 5.0 x 10-9 mbar, and a low-energy dual -beam flood gun compensated for surface charging. Data analysis was conducted using Avantage software, with energy calibration referenced to the C Is peak at 284.8 eV.

[0225] The specific surface area of the catalysts was calculated from nitrogen physisorption isotherms collected at 77 degrees Kelvin Micromeritics 3Flex system, using adsorption data in the pressure range of P / P0 = 0.05 to 0.3 for Brunauer-Emmett-Teller (BET) surface area calculations. Pore size distributions were determined using the Barrett- Joy ner-Halenda (BJH) method.

[0226] Sample names, the total surface area (SBET) and pore volume (Vrotai) from BET analysis, varying cobalt concentrations from ICP analysis, graphitic-N, and pyridinic-N content from high-resolution XPS, and measured electrical conductivity are described in Table 1.

[0227] The ZIF and ZIF-derived electrocatalyst materials were also assessed for surface area, pore volume, pore size and cobalt / iron content, as shown in Table 2. Table 1. Comparison of textural properties, nitrogen content and ICP-Cobalt concentration after carbonization.

[0228] After Co / Zn Surface Pore volume Pore size Pyridinic-N Graphitic -N ICP-Co Electrical carbonization (mol) area (m2 / g) (cm3 / g) (run) (At%) (At%) (wt%) conductivity (S / m) N-C-Blank 0 / 100 474.2 0.30 4.3 4.4 1.27 - 1421 Co-N-C-1 / 40 1 / 40 411.4 0.28 4.5 3.46 1.14 0.59 1361 Co-N-C-1 / 30 1 / 30 393.1 0.24 4.6 3.23 1.35 1.63 1234 Co-N-C-1 / 20 1 / 20 348.2 0.21 5.6 2.35 1.18 3.74 1184 Co-N-C-1 / 10 1 / 10 311.7 0.20 7.1 1.85 1.19 4.11 975

[0229] Table 2. BET Surface Characterization and ICP Analysis.

[0230] Before After Surface Pore Volume Pore ICP-Co ICP-Fe Carbonization Carbonization Area (m2 / g) (cm3 / g) Size (A) (wt%) (wt%) ZIF-ll-Co / Fe *CoFe-Blank 95.29 0.130 59.45 0.55 1.61 ZIF-ll-Co / Fe CoFe-2DSA 1041.07 0.739 97.8 0.42 0.35 ZIF-ll-Co CO-2DSA 1014.63 0.593 74.7 0.51 0 ZIF-ll-Fe Fe-2DSA 963.45 0.719 109.6 0 0.74 *Pyrolysed without salt treatment

[0231] Electrochemical measurements

[0232] Experiments were undertaken to evaluate the electrochemical properties of ZIF-derived electrocatalysts for undertaking ORR and OER, as shown in Figure 5. The tests were performed at a temperature of 25 °C using a rotating disk electrode (RDE) system on a VMP3 electrochemical workstation (Biologic Science Instruments SAS). A rotating disk electrode with a platinum disk with a surface area of 0.125 cm'2was used as the main substrate for these measurements. The reference electrode was made of Ag / AgCl (saturated with 3.5 mol L-1KC1), while a Pt foil rod acted as the counter electrode. The experiments were conducted using a KOH solution (0.1 M) as the electrolyte. Using the Nemst equation, the potentials were converted to the reversible hydrogen electrode (RHE) scale. Electrical conductivity was analysed in accordance with Banerjee, et al. (2015).

[0233] To prepare the catalyst inks, 6 mg of catalyst was added to a small container. 150 pL of deionized water was added, 300 pL of ethanol, and 20 pL of Nafion® solution (from Sigma Aldrich). The mixture was then subjected to ultrasonication for 2 hr to ensure that the catalyst was evenly dispersed. After the ultrasonication process, 10 pL of the resulting ink was transferred onto platinum working disk area. To compare the effectiveness of different catalysts, a graphitized carbon powder containing 20% Pt and 10% Ru, referred to as Pt-Ru / GC, was also prepared with the same ink preparation method. This sample was then tested along with the other catalysts as a benchmark catalyst.

[0234] Before conducting experiments to test their activity in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the electrolyte solution was purged with high- purity oxygen for 30 minutes to ensure it was fully saturated with oxygen.

[0235] The electrochemical behaviour of the freshly prepared samples was initially examined using cyclic voltammetry (CV) with a scan rate of 5 mV.s'1in a 0.1 M KOH that was saturated with nitrogen and oxygen at 25 °C. Linear sweep voltammetry (LSV) tests were also conducted in an 02-saturated 0.1 M KOH at various rotation speeds, ranging from 400 to 1600 rpm, with a scan rate of 5 mV s'1.

[0236] To find the kinetic current density and electron transfer number (n), The Koutecky- Levich equation was used in accordance with Nguyen, et al. (2023).

[0237]

[0238] The equation describes the relationship between the measured current density (Jmeasured), the kinetic current density (Jk), the rotation speed (co), the number of electron transfers in the ORR system (n), the effective area of the glassy carbon electrode (A), Faraday Constant (F: 96485 C.mol'1), the kinetic viscosity (v: l.l*10'2.cm2.s-1), the saturated concentration of oxygen in a 0.1 M KOH solution (CO: (1.2* 10'3mol.L'1)), and the diffusion coefficient of oxygen in a 0.1 M KOH solution (DO: (1.9* 10'5cm. s'1) (Ding, et al. (2022)).

[0239] Figure 5 shows A) a linear sweep voltammogram for a ZIF-derived electrocatalyst according to some embodiments of the invention, showing overall overpotential during the complete ORR and OER process; and (B) the overpotential gap between ORR and OER for some ZIF-derived electrocatalysts.

[0240] Zn-Air Battery (ZAB) Characterisation

[0241] To evaluate the effectiveness of ZIF-derived electrocatalysts in aZABs, a two-electrode device was constructed and employed for testing purposes. The air electrode, composed of carbon cloth, consisted of a gas diffusion layer on the side exposed to the air and a catalyst layer on the side facing the water. The gas diffusion layer, with an effective area of 1.0 cm2, facilitated the movement of oxygen from the surrounding air to the catalyst sites. The catalyst layer was formed by applying catalyst ink onto the carbon cloth using a drop-casting method, resulting in a catalyst loading density of 1 mg cm-2for all studied catalysts. The same ink preparation method and electrocatalytic performance measurement were applied for the synthesised material and Pt-Ru / GC as benchmark catalyst.

[0242] The anode of the device was a polished zinc plate, 1.0 mm thick, with a purity of 99.99 wt%. The electrolyte employed was a solution comprising a 6.0 M KOH and 0.2 mol M Zn(Ac)2. To make a rechargeable battery, a commercial a graphitized carbon powder containing 20% Pt and 10% Ru, referred to as Pt-Ru / GC, was also utilized for comparative purposes. All battery testing was carried out under ambient atmospheric conditions.

[0243] Polarization curves were obtained by conducting LSV (Linear Sweep Voltammetry) measurements using the Biologic Science Instruments SAS electrochemical workstation with EC -Lab-Software. The measurements were performed at a scan rate of 5 mV / s. Current density and power density were adjusted according to the effective surface area of the air electrode. The specific capacity and energy density were calculated based on the consumed metal zinc, using equations 3 and 4, respectively (Nguyen, et al. (2023)).

[0244] Current* Services Hour

[0245]

[0246] Weight of Consumed Zinc

[0247]

[0248] „ „ Current*Services Hour*Average Discharge Voltagez.

[0249] Energ

[0250] OJy Density

[0251] J= - — - — —5- — (4) Weight of Consumed Zincv 7

[0252] To evaluate the rechargeability of the made batteries, charge-discharge test at different current density and different charge / discharge cycles were carried out.

[0253] Example 1: Electrocatalyst based on cobalt-doped-nitrogen-carbon network (Co-N-C) from modified ZIF-derived carbon

[0254] Single atom sites cobalt-doped-nitrogen-carbon structure (Co-N-C) were created from modified ZIF- 11 -derived carbon by optimizing the cobalt to zinc ratio from 1:10 to 1:40. HAADF-STEM images and EXAFS spectra confirmed that the structure with the lowest cobalt concentration (Co-N-C- 1 / 40) contains single cobalt atoms coordinated with four nitrogen atoms (C0-N4). Electrochemical tests showed that the Co-N-C-1 / 40 electrocatalyst performed exceptionally well in both ORR (El / 2 ~ 0.859 V) and OER (Ej=10: 1.544 V), with excellent stability. When used as the bi-functional electrocatalyst in air cathode of a rechargeable ZAB, the Co-N-C-1 / 40 electrocatalyst achieved a peak power density of 178.6.1 mW cm-2and a specific capacity of 799 mA.h.gzn'1. Furthermore, the battery demonstrated long-term stability, lasting for 33 days and enduring 1580 charge / discharge cycles. Density functional theory (DFT) calculations reveal the effect of location and concentration of pyridinic nitrogen on the efficiency of the 4-electron ORR. The position of pyridinic nitrogen with Co plays a critical role in determining the overpotential of the C0N4 electrocatalyst for ORR. The record-breaking performance achieved by the ZAB significantly overcomes current performance shortcomings, making it a promising candidate for safe and efficient energy storage technology.

[0255] Synthesis of ZIF

[0256] In detail, 1.2 g of benzimidazole was dissolved in 46 ml of toluene to form solution A. Separately, 3 g of zinc nitrate was dissolved in 48 ml of methanol to form solution B. Both solutions were separately stirred for 5 minutes until a clear solution was obtained, following which solution B was added to solution A and stirred for an additional 10 minutes. Subsequently, 1.2 g of ammonium hydroxide was introduced to the solution and stirred at room temperature for a period of 3 hours. The resulting crystals were collected through centrifugation, washed repeatedly with methanol, and then vacuum-dried at 80 °C overnight. The above procedure was applied to synthesize the ZIF- 11 -Co structure through the introduction of cobalt as a dopant into the ZIF-11 structure. This was achieved by varying the molar ratio of cobalt to zinc. The metal salt quantity remained consistent, while the Co to Zn molar ratios were adjusted to 1 :40, 1 :30, 1 :20, and 1:10. The ensuing samples were designated as ZIF-ll-Co-X / Y, where X / Y corresponded to the Co to Zn molar ratio, the sample names described in Table 1.

[0257] Synthesis of ZIF-derived Electrocatalyst

[0258] For the preparation of ZIF-derived electrocatalysts, the obtained ZIF-ll-Co-X / Y samples were placed in a corundum crucible and heated at 930 °C for 3 h under nitrogen. Due to the low boiling point of Zn atoms (with a melting point of 420 °C and boiling point of 907 °C), it can evaporate at high temperatures above 800 °C. The resulting structures were then named Co-N-C-X / Y, where X / Y represents the molar ratio of Co to Zn in the initial ZIF structures, the sample names described in Table 1. The process of synthesizing can be observed through the diagram depicted in Figures 1 and 2.

[0259] Morphology and Structure

[0260] The morphology and chemical composition of the samples were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray spectroscopy (EDS).

[0261] SEM shows all the samples with various Co / Zn ratios had a clear rhombic dodecahedron shape prior to carbonization and adhered to the ZIF-11 morphology. Even after carbonization at 930 °C, the morphology remains intact with a size of 10 pm, preserving the same morphology of the original material (Figure 6 (A) and (B) illustrate the SEM images of the N-C-Blank and Co-N-C-1 / 40, respectively. Both samples exhibit well-defined rhombic dodecahedron structures with a uniform size distribution. The consistent morphology between N-C-Blank and Co-N-C-1 / 40 suggests that the introduction of cobalt does not significantly alter the overall shape of the particles, maintaining a high degree of crystallinity.

[0262] Figure 6 (C) provides a closer look at the internal structure of the Co-N-C-1 / 40 electrocatalyst through TEM. It reveals a homogeneous dispersion of cobalt with no aggregation within the carbon matrix, indicating successful incorporation of cobalt into the structure. The HAADF-STEM image (Figure 6 (D)) highlights the detailed atomic arrangement within the Co-N-C-1 / 40 electrocatalyst. Bright spots, corresponding to cobalt atoms, can be observed within the structure, showcasing the atomic-scale distribution of these metallic atoms. Figure 6 (E) presents an enlarged HAADF-STEM image, providing a detailed view of the atomic structure. Yellow circles highlight the positions of metallic atoms (brighter and larger diameter atoms within the Co, N and O matrix, presumably Co),), confirming the presence of uniform dispersed cobalt single atom sites within the carbon matrix, which is crucial for catalytic activity. Elemental mapping through EDS illustrates the distribution of different elements within the Co-N-C-1 / 40 electrocatalyst (Figure 6 (F)). The maps indicate that carbon (green), nitrogen (yellow), and cobalt (blue) are uniformly distributed throughout the sample. This homogeneous dispersion of elements suggests a well-synthesized electrocatalyst with a potentially high catalytic activity due to the uniform presence of active sites. To clarify the composition of synthesized ZIF structures before and after carbonization, an X-ray diffraction (XRD) analysis is carried out. As seen in Figure 5, the XRD patterns before carbonization showed that the samples had highly crystalline and well-ordered structures. This was confirmed by the similarity of the diffraction peaks to those found in the literature. The peaks at 3.2°, 4.47°, 6.28°, 7.66°, 8.83°, 9.14°, 9.87°, 11.13°, 11.53°, 12.37°, 13.06°, 13.83°, 14.16°, 15.27°, 15.58°, 15.86°, 16.95°, and 18.52° correspond to the (100), (110), (200), (211), (220), (300), (310), (222), (320), (321), (322), (331), (420), (500), (510), (520), (521) and (600) planes of the cubic ZIF-11 structure, respectively, and demonstrate the highly crystalline structure of the synthesized materials. The lattice parameters of the ZIF-ll-Co-1 / 40 were also determined using the XRD data. The unit cell parameters were found to be a=b=c=28.43 A and a=P=y=90°, in good agreement with the literature values. These results indicate that the highly crystalline structures were synthesized. The XRD analysis was also performed on the samples after carbonization at 930 °C. There are two broad peaks at 29=23.7° and 43.7°, which correspond to the graphitic carbon (002) and (101) planes.

[0263] The Raman spectra of the samples were analysed and revealed the presence of two prominent peaks at 1348 cm'1(D-band) and 1592 cm'1(G-band). The D-band is typically associated with disordered or amorphous structures, while the G-band is indicative of more ordered or crystalline structures. The analysis of the D-band to G-band ratio (ID / IG) in the Raman spectra of all samples with varying Co / Zn ratios showed ID / IG ratio close to 1 indicates that there are defects or disorder in the carbon structure, which are likely due to the introduction of metal ions into the ZIF framework.

[0264] The surface area and porosity of catalysts have a significant impact on their catalytic activity. To investigate this, nitrogen adsorption-desorption experiments were conducted at 77 K on the carbonized samples. The results reveal that the samples exhibit typical isotherms features of type IV, with a steep nitrogen uptake at ultra-low pressures (P / Po<O.Ol), signalling the microporous structure of the materials with narrow pore channels. The pore size distribution (PSD) curves, demonstrate the microporous structure of the as-prepared catalysts. According to Table 1, the total surface area (SBET) and pore volume (Vrotai) of bimetallic ZIF-derived carbons gradually decreased by increasing the amount of cobalt from Co-N-C-1 / 40 (411.47 m2g-1and 0.284 cm3g'1) to Co-N-C-1 / 10 (311.72 m2g-1and 0.203 cm3g'1), while all were less than those of N-C-Blank (474.26 m2g-1and 0.305 cm3g'1). It can be attributed to the Zn evaporation and its pore formation mechanism during the high-temperature annealing process. During carbonization, the organic linkers are decomposed, and metallic zinc is produced through the reduction of Zn ions, which function as sacrificial templates. This process creates vacancies in the crystal structure, resulting in the formation of a highly porous carbon material with a high surface area. Hence, the partial substitution of Zn with cobalt throughout the ZIF structure limits Zn evaporation at temperatures above 800 °C, resulting in the formation of less porosity into the framework. Additionally, increasing the amount of cobalt can highly increase the likelihood of aggregated cobalt formation and block narrow pores of the material, thereby reducing SBET and Vrotai.

[0265] The ICP analysis revealed varying cobalt concentrations in the carbonized samples. According to Table 1, Co-N-C-1 / 40 (0.59 wt%) and Co-N-C-1 / 10 (4.11 wt%) exhibited the lowest and highest amount of cobalt in their structure, respectively.

[0266] The composition and chemical state of the samples were analysed using X-ray photoelectron spectroscopy (XPS). The C is spectra of all the samples can be broken down into four peaks that represent different types of chemical bonds, including C-C (284.7 eV), C-N (285.8 eV), C-0 (287.3 eV), and O-C-OH (288.2 eV). The presence of C-N bonds makes the catalysts particularly effective for adsorbing oxygen-containing intermediates on its surface by providing Lewis basic sites on the surface of the material. These basic sites can interact with Lewis acidic sites on oxygen-containing intermediates, such as hydroxyl (OH) groups or carbonyl (C=O) groups, through hydrogen bonding or electrostatic interactions. This interaction between the C-N material and the oxygen-containing intermediates can facilitate their adsorption on the surface of the material and enhance the catalytic activity of the material. Therefore, it is possible that the presence of C-N bonds in a catalyst can make it particularly effective for adsorbing oxygen-containing intermediates on its surface.

[0267] The O Is spectra of the catalysts have been evaluated and identified to have three separate peaks. The first peak, referred to as 01, is located at ~529 eV and is believed to be related to the metal-oxygen bond or lattice oxygen. The second peak, 02, is located at ~531 eV and represents defective oxygen vacancies on the surface of the catalyst. The third peak, 03, is associated with the presence of OH" species and chemically adsorbed oxygen. The main difference observed in 01, 02, and 03 peaks is related to Co-N-C-1 / 40 that has significantly higher 03 concentration (3 wt%), compared to Co-N-C-1 / 30 (1.04 wt%), Co-N-C-1 / 20 (1.88 wt%), Co-N-C-1 / 10 (1.94 wt%), and N-C-Blank (1.58 wt%).

[0268] The Co 2p spectra of the samples and their corresponding deconvoluted concentrations are shown in Figure S4 (D) and Table S3. The peaks include Co0(780.1 and 795.4 eV), Co2+(783.4 and 798.1 eV), Co-N (781.4 and 796.7 eV), and a shake-up satellite (786.8 and 802.5 eV). The concentration of Co-N was observed to be the highest in the Co-N-C-1 / 40 at a value of 0.412%. In addition, it was revealed that increasing the proportion of cobalt in the sample had an undesired effect on the Co-N concentration, decreasing its value from 0.412% in Co-N-C-1 / 40 to 0.157% in Co-N-C-1 / 10. The Co-N bond at the interface can serve as a pathway for electron transfer, leading to efficient modulation of charge transfer dynamics by accelerating electron transfer.

[0269] The incorporation of nitrogen contents within the carbon lattice leads to a variety of benefits, specifically in the form of pyrrolic-N, graphitic-N, and pyridinic-N. Out of these three types, graphitic-N and pyridinic-N species in the carbon lattice promote 7t-bonding, which can significantly enhance electron transport and stabilize the carbon atoms. To have a better understanding of the nitrogen species of the prepared materials, their high-resolution N Is spectra were analysed. Five distinct peaks were detected, indicating the existence of pyridinic-N (-398.4 eV), pyrrolic-N (-399.7 eV), Co-N (-400.3 eV), graphitic-N (-401.0 eV), and oxidized-N (-404.1 eV). According to the data presented in Table 1, the total combination of pyridine and graphite nitrogen, as the main beneficial parameter for the ORR and OER, was found to be 4.6, 4.58, 3.53, 3.04, and 5.67 % in Co-N-C-1 / 40, Co-N-C-1 / 30, Co-N-C-1 / 20, Co-N-C-1 / 10, and N-C-Blank, respectively. By conducting a thorough analysis of the effect of the ratio of cobalt to Zn on nitrogen types in the samples, Co-N-C-1 / 40 is notable for having the highest amount of total nitrogen (9.57 %) among the samples studied with varied cobalt concentrations, as well as the highest levels of pyridinic and graphitic nitrogen (4.6 %). This suggests that Co-N-C-1 / 40 may have a high potential for catalytic activity and could potentially serve as a more efficient catalyst compared to the other samples.

[0270] The impact of nitrogen content on the structural properties is corroborated by the measurement of electrical conductivity, as evidenced in Table 1. Specifically, the highest electrical conductivity is observed in the Co-N-C-1 / 40 sample (1361 S / m), surpassing that of Co-N-C-1 / 30 (1234 S / m), Co-N-C-1 / 20 (1184 S / m), and Co-N-C-1 / 10 (975 S / m), in accordance with the respective nitrogen concentrations.

[0271] X-ray absorption spectroscopy (XAS) was used to gain deeper insights into the coordination environment and local electronic structure around the Co atoms in the catalysts, Co-N-C-1 / 40, and Co-N-C-1 / 10. The Co K-edge X-ray absorption near-edge structure (XANES) spectra in Figure 6 (G) show a pre-edge feature at 7709 eV for Co-N-C-1 / 40, like that of CoO due to the ls^3d electron transition of Co, thereby validating that the average oxidation state of Co in the Co-N-C-1 / 40 approximates +2. In addition, compared to Co-N-C- 1 / 10, Co-N-C-1 / 40 displays a stronger and sharper white-line peak related to ls^4p transitions, suggesting more electron transfer from Co to the coordinators in Co-N-C-1 / 40.

[0272] Detailed analysis was performed using Fourier-transformed k2-weighted %(k)-function Co K-edge extended X-ray absorption fine structure (FT-EXAFS) spectra (Figure 6 (H)). No Co-Co peak at -2.18 A was identified in Co-N-C-1 / 40, suggesting the absence of crystalline Co and that Co atoms are atomically dispersed as single atom sites. A major peak at -1.42 A, corresponding to Co-N b ackscattering, was observed in Co-N-C-1 / 40. In comparison, there is a sharp peak at -2.18 A and an absent peak at -1.42 A in Co-N-C-1 / 10, indicating more crystalline Co in the form of Co-Co clusters are present. To further understand the fine coordination structure of Co atoms and to prove that Co atoms are likely to coordinate only with N atoms in the first shell, FT-EXAFS fitting of Co-N-C-1 / 40 was analysed (Figure S5). The fitting results suggest that Co-Nxmoieties can be accurately observed at 1.95 A and 1.91 A with degeneracies of 2 each for Co-N-C-1 / 40 (See Table 5S for fitting details). The presence of pyridinic nitrogen extends the Co-N bond distance between two adjacent nitrogen atoms due to conjugation, thereby influencing the charge transfer between the Co and N atoms at the Co-N4 site. Wavelet transform EXAFS (WT-EXAFS) analysis of Co-N-C-1 / 40 significantly differs from that of Co foil, hence confirming the non-existence of Co-Co bonds. Concentrated signal contours of Co-N-C-1 / 40 resemble those of Co coordinated with light atoms, and the slight negative shift of the maximum signal in Co-N-C-1 / 40 shows the coordination of Co-N, different from that of Co-O, showing a high degree of concordance with Co-N-C-1 / 40. This confirms that Co single atoms are uniformly dispersed and coordinated as C0-N4 within the structure of Co-N-C-1 / 40.

[0273] Electrochemical Catalytic Performance

[0274] A thorough assessment of the catalytic properties of synthesized materials was conducted utilizing the standard three-electrode system. The effectiveness of the synthesized material as a bi-functional electrocatalyst for the ORR and OER was evaluated through the utilization of cyclic voltammetry (CV) and linear sweep voltammetry (LSV), executed using a rotating disk electrode (RDE) in an alkaline environment (saturated with O2) at a rotation rate of 1600 rpm. All potentials were converted to the reversible hydrogen electrode reference (RHE). To compare the effectiveness of different electrocatalysts, Pt-Ru / GC electrocatalyst was also prepared and tested along with the other electrocatalysts as a benchmark catalyst. The half potential, onset potential, electron transfer number, and Tafel slope were identified using the LSV data, allowing for an evaluation of the performance of the synthesized electrocatalysts.

[0275] The data illustrates the cathodic peak voltages observed by CV tests of Co-N-C-1 / 40, Co-N-C-1 / 30, Co-N-C-1 / 20, and Co-N-C-1 / 10 in a 0.1 M KOH solution. The results reveal a trend in which the cathodic peak voltage decreases to lower voltage with increasing cobalt concentration. Specifically, the sample with the lowest cobalt concentration (Co-N-C-1 / 40) exhibited the most active cathodic peak at 0.869 V, then by increasing the cobalt concentration in sample Co-N-C-1 / 30, Co-N-C-1 / 20, and Co-N-C-1 / 10 the cathodic peak voltage shift to 0.845 V, 0.819 V, and 0.814 V, respectively. To investigate the ORR process in greater detail, RDE measurements were performed at a rotation rate of 1600 rpm in a 0.1 M KOH solution that was saturated with oxygen. The results, depicted in Figure 2 (A), indicated that the Co-N-C-1 / 40 electrocatalyst exhibited superior ORR activity, as evidenced by half-wave potential (EI / 2= 0.858 V) when compared to the Co-N-C-1 / 30 (EI / 2= 0.842 V), Co-N-C-1 / 20 EI / 2= 0.832 V), and Co-N-C-1 / 10 (EI / 2= 0.817 V) and Pt-Ru / GC (EI / 2= 0.829 V) and other previously reported electrocatalysts. Tafel slope is a widely used parameter to evaluate the electrocatalytic activity of an electrode and is calculated by determining the rate of change of the current density with respect to the overpotential. The Co-N-C-1 / 40 electrocatalyst demonstrates the highest rate of reaction for the ORR with a Tafel slope of 46 mV dec-1, which surpasses the performance of Co-N-C-1 / 30, Co-N-C-1 / 20 , Co-N-C-1 / 10 , and Pt-Ru / GC electrocatalysts with a Tafel slope of 61 mV dec-1, 72 mV dec-1, 92 mV dec-1, and 70 mV dec-1, respectively, Figure 7 (B). Furthermore, the Co-N-C-1 / 40 electrocatalyst exhibits a significantly higher kinetic current density, 3.38 mA cm-2, in comparison to other materials such as Co-N-C-1 / 30 (2.58 mA cm-2), Co-N-C-1 / 20 (1.6 mA cm-2), Co-N-C-1 / 10 (0.54 mA cm-2), and Pt-Ru / GC (1.59 mA cm-2), as depicted in Figure 2 (C) which can be because of having higher electrical conductivity (1361 S / m).

[0276] The Koutecky-Levich (K-L) plots were generated to analyse the ORR process, and the slopes of these plots were used to calculate the average electron transfer numbers (n). The results, depicted in Figure 7 (E), showed that the average electron transfer number for the Co-N-C-1 / 40 electrocatalyst was ~ 4, indicating a strong preference for the 4-electron ORR process. The ZAB can benefit from a 4-electron pathway, which can improve the battery's stability and performance by increasing energy efficiency, prolonging cycle life, and minimizing the production of hydrogen peroxide. The stability of the electrocatalyst is a vital aspect of the ORR process over an extended period. To determine this, we conducted CV on the Co-N-C-1 / 40 electrocatalyst for 800 cycles and compared the LSV curve potential to that of a fresh electrocatalyst at a scan rate 5 mV s'1, as shown in Figure 7 (F). The results indicate that after 800 cycles, the LSV potential mostly shifts to a lower potential by 21.6 mV suggesting that the electrocatalyst can maintain its performance for a prolonged period.

[0277] In Figure 8 (A), the electroactivity of all the electrocatalysts in terms of OER is displayed through the presentation of OER polarization curves. The Co-N-C-1 / 40 electrode exhibits a high level of OER electroactivity, as demonstrated by its low overpotential (r|j ) value of 314 mV. This value is comparable to that of Pt-Ru / GC (309 mV) and surpasses other electrodes such as Co-N-C-1 / 30 (360 mV), Co- Co-N-C-1 / 20 (370 mV), and Co-N-C-1 / 10 (400 mV). In Figure 8 (B), the Tafel slopes of the electrodes were presented to provide insight into their intrinsic OER activity. The Tafel slope of the Co-N-C-1 / 40 electrode was quantitatively determined to be 204 mV dec'1through experimentation. This value was found to be the lowest among the other CO-N-C tested electrocatalyst, including Co-N-C-1 / 30 (215 mV dec'1), Co-Co-N-C-1 / 20 (400 mV dec'1), and Co-N-C-1 / 10 (484 mV dec'1). This observation suggests that the Co-N-C-1 / 40 electrocatalyst may exhibit faster charge and / or mass transfer kinetics along with superior intrinsic activity for the OER compared to the other electrocatalysts. This indicates that the Co-N-C-1 / 40 electrode can facilitate the OER process at a faster rate than the other electrodes, making it an efficient and effective electrocatalyst for OER. The overall overpotential (AE=Ejio-Ei / 2) of an oxygen electrode serves as a key indicator of its bi-functional activity, with lower values indicating superior electrocatalytic performance. Co-N-C-1 / 40 was found to exhibit a notably low overall overpotential of 686 mV, as depicted in Figure 8 (C). This value is comparable to that of high-efficiency bi-functional electrocatalysts such as Pt-Ru / GC (710 mV) and significantly outperforms other electrocatalysts such as Co-N-C-1 / 30 (748 mV), Co-N-C-1 / 20 (768 mV), and Co-N-C-1 / 10 (813 mV). The Co-N-C-1 / 40 has outstanding performance as a bifunctional electrocatalyst in ORR and ORR.

[0278] Mechanistic Analysis

[0279] The effect of nitrogen content and cobalt concentration on ORR and OER was thoroughly investigated by exploring the correlation between half-wave potential as an indicator of ORR and overpotential at jlO as an indicator of OER, followed by assessing the bi-functionality potential to determine the overall impact of Nitrogen content and cobalt concentration on both reactions, Figure 8 (D) illustrates the observed trends.

[0280] In the analysis, it was found that the variation in graphitic nitrogen content had a negligible impact, and the change in pyrrolic-N content showed only a mild effect on the electrocatalytic performance. However, a significant influence on the reaction outcomes was observed with the variation of pyridinic-N content. Interestingly, a decrease in pyridinic-N content was observed with an increase in cobalt concentration, indicating a complex interplay between cobalt concentration and pyridinic-N species. Notably, the electrocatalyst with the most desirable performance for both ORR and OER was obtained with the highest pyridinic-N content and the lowest cobalt concentration. Exceptional performance in promoting reversible oxygen electrocatalysis was demonstrated by this Co-N-C-1 / 40 electrocatalyst. The observed results strongly support the combination of pyridinic-N and low cobalt concentration (in the form of single atom sites) plays a pivotal role in enhancing electrocatalytic activity, likely due to the facilitation of crucial reaction pathways and the optimization of active sites.

[0281] Zinc-Air Battery (ZAB) Performance

[0282] Motivated by the ability of the Co-N-C-1 / 40 electrocatalyst to perform both ORR and OER, a rechargeable ZAB was constructed using the Co-N-C-1 / 40 electrocatalyst. The performance of the Co-N-C-l / 40-based ZAB was evaluated by comparing it to traditional ZAB utilizing Pt-Ru / GC as the air cathode.

[0283] The discharge polarization and peak power density plots revealed that the Co-N-C-1 / 40-based ZAB had smaller voltage, and higher current densities, and higher peak power density compared to the Pt-Ru / GC electrode, Figure 9 (A). Co-N-C-l / 40-based ZAB has a peak power density of 178.6 mW cm'2at a current density of 235 mA cm'2, compared to 89.9 mW cm'2and 150 mA cm'2, respectively, for Pt-Ru / GC -based ZAB. Therefore, Co-N-C- 1 / 40-based ZAB can produce higher power output per unit area, making it a promising alternative to the Pt-Ru / GC electrode for use in energy conversion and storage devices. Additionally, the lower voltage of the Co-N-C- 1 / 40-based ZAB implies that it can potentially operate at a lower voltage and still achieve the same power output as the Pt-Ru / GC electrode, which can result in lower energy consumption and higher efficiency in practical applications. This observation aligns with the previously discussed ORR and enhanced half wave potential of the Co-N-C-1 / 40 electrocatalyst. The open-circuit voltage (OCV) was applied for both Co-N-C-l / 40-based ZAB and the Pt-Ru / GC -based ZAB to measure the voltage difference between the cathode and anode of the batteries as shown in Figure 9 (B). The higher OCV for the Co-N-C-l / 40-based ZAB (1.45 V vs 1.41 V) indicates that it has a higher energy density and can deliver more electrical energy per unit of mass than the Pt-Ru / GC -based ZAB.

[0284] The discharge-specific capacity of Co-N-C- 1 / 40-based and Pt-Ru / GC -based ZABs was measured by determining the amount of zinc metal consumed during a full discharge process. Figure 9 (C) displays the data indicating a discharge voltage of 1.19 V at a current density of 10 mA cm'2, which is relatively high. The Co-N-C-l / 40-based ZAB demonstrates a discharge specific capacity of 799 mAh gzn'1, which is close to the theoretical capacity of zinc at 820 mA h gzn'1and greater than the Pt-Ru / GC -based ZABs, which have a capacity of 764 mA h gzn'1. Moreover, the energy density of this ZAB type is calculated to be 879 Wh kgzn'1, implying that it is a high-performing rechargeable ZAB. Therefore, the battery can provide larger energy per unit mass of consumed zinc, which makes it a high-performing rechargeable battery.

[0285] In Figure 9 (D), the average discharge voltages were compared across a range of current densities to measure the rate performance, which showed that the Co-N-C-1 / 40 cathode performed well even at high operating rates of up to 48 mA cm-2. Specific voltages at 2, 12, 24, 36, and 48 mA cm-2were 1.25, 1.2, 1.12, 1, and 0.95 V, respectively, which were significantly higher than those of ZABs with Pt-Ru / GC cathode (1.06, 0.75, 0.37, and 0.13 V). Notably, the cell voltage fully recovered once the current density was reduced to 2 mA cm-2after 25 hours and remained stable for an additional 15 hours, indicating that the Co-N-C-1 / 40 cathode not only demonstrated high-rate performance but also good reversibility.

[0286] The Co-N-C- 1 / 40-based ZAB’s charge-discharge performance was evaluated at two C-rates (4C and 1C), corresponding to 15 and 60-minute charge or discharge cycles, respectively, to assess its rechargeability and compare it with a Pt-Ru / GC -based ZAB (Figure 10). At 4C, the Co-N-C- 1 / 40-based ZAB displayed a voltage gap of only 1.23 V, resulting in a round-trip efficiency of 44 %. Notably, the charge-discharge profiles remained steady even after 33 days and 1580 cycles, with a slight increase in the voltage gap to 1.34 V, while maintaining a roundtrip efficiency of 43 %. Compared to this, the voltage gap of Pt-Ru / GC -based ZABs started to increase after two days; and after 110 cycles and 2.5 days, the battery ceased to function. In addition, at 1C, Figure 5 (G), the Co-N-C-l / 40-based ZAB exhibited a voltage gap of 1.07 V, resulting in a remarkable round-trip efficiency of 48.2 % after 4 days. The charge-discharge profiles remained mostly unchanged even after 17 days and 213 cycles, with a slight increase in the voltage gap to only 1.1 V, while maintaining a round-trip efficiency of 48 %.

[0287] The ZAB using Co-N-C-1 / 40 as an electrocatalyst shows exceptional power density, specific capacity, and cycling performance compared to the recently reported bi-functional electrocatalysts.

[0288] Further investigations were carried out to evaluate the battery performance under higher current densities. The charge-discharge cycles were measured at current densities of 10 mA.cm'2and 20 mA.cm'2for a duration of 8 days. These tests aimed to examine the battery's behaviour under increased stress conditions. Notably, as the current density rose from 2 mA.cm2to 10 mA.cm2, and subsequently to 20 mA.cm2, a progressive increase in the voltage gap was observed. Specifically, the voltage gaps after ten days recorded were 1.08, 1.24, and 1.54 V, respectively, indicating a significant amplification in voltage drop as the current density escalated. The round efficiency of the battery exhibited a distinct downward trend with increasing current densities- 48.2%, 41.1% and 35.7% at 2 mA.cm2, 10 mA.cm2and 20 mA.cm2, respectively.

[0289] Example 2: Electrocatalyst based on dual metal-doped nitrogen-carbon structure from modified ZIF-derived carbon

[0290] A dual-metal electrocatalyst, CoFe-2DSAmade up of Fe and Co sites on 2D porous N-doped carbon nanosheets, was developed and used as the electrocatalyst in oxygen redox reaction. CoFe-2DSA electrocatalyst showed excellent bifunctionality for both the oxygen reduction reaction (ORR, with EI / 2=0.886 V) and the oxygen evolution reaction (OER, with r|=290 mV at 10 mA cm'2) in alkaline media, making it a promising bifunctional catalyst for oxygen redox electrocatalysis (AV= 0.634 V). When used as the cathode in a ZAB, CoFe-2DSA exhibited an open-circuit voltage of 1.48 V, peak power density of 229.6 mW cm'2, specific capacity of 811.5 mA h g'1, and energy density of 997 W h kg'1, with excellent cycling stability (74 days with 3570 cycles). These results highlight the potential of dual-site designed electrocatalyst to improve activity and accessibility in advanced bifunctional air cathodes for oxygen redox electrocatalysis.

[0291] Design and Structural Analysis of Catalysts

[0292] The production of the CoFe-2DSA catalyst can entail two main steps: first, the synthesis of a 3 -dimensional ZIF structure; followed by the conversion of the 3 -dimensional framework into a 2-dimensional dual-metal site carbon catalyst, achieved through a pyrolysis technique assisted by molten salt (S. Liu, et al. (2022))

[0293] Initially introducing iron by incorporating it into ZIF-ll-Co results in the creation of a composite structure known as ZIF-ll-Co / Fe. The composite of ZIF-ll-Co / Fe was blended thoroughly with a mixture of potassium chloride and zinc acetate, with a weight composition of 36.3% and 63.7%, respectively. The mixture is then placed in a corundum crucible and heated at 930°C for 3 hours under nitrogen atmosphere.

[0294] To investigate the influence of molten salt treatment on the resultant carbon structure SEM and TEM, and STEM was used prior and following the molten salt treatment (Figure 11). The ZIF-ll-Co / Fe possesses a remarkable ortho-dodecahedral shape before carbonization. After undergoing molten salt assisted pyrolysis, the CoFe-2DSA has transformed into a 2D sheet-like morphology. In contrast to the CoFe-2DSA, the control sample synthesized without the use of eutectic salts, CoFe-Blank, displayed a polyhedral architecture inherited from the ZIF-11 precursor. The eutectic salts are believed to facilitate the formation of the 2D morphology by preventing the collapse and aggregation of the material during the pyrolysis process. The salts also act as an efficient porogen agent, generating porosities in the 2D nanosheets due to the etching effect of the high-energy Cl'1and the rapid evaporation of Zn during the pyrolysis process. Fe and Co species are then trapped by the N-rich porous carbon and anchored onto the formed 2D nanosheet matrix. After the annealing process is completed and cooled down to room temperature, the resulting products are dissolved in 3M H2SO4 and to extract any remaining impurities including salts, aggregated metals, and free metals over the catalyst structure. The products are then washed several times with deionized water to remove the recrystallized salts and metal particles. This preparation process allows for the creation of an CoFe-2DSA dual site catalyst with unique properties.

[0295] Further analysis of CoFe-2DSA was conducted using STEM elemental mapping analysis, Figure 11 (C). These methods showed that CoFe-2DSA a homogenous distribution of iron, cobalt, nitrogen, and carbon atoms, with no iron and cobalt-related aggregates present. To confirm the uniform dispersion of Fe and Co atoms within the sample, aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was also utilized, Figure 11 (D). These results showed a uniform distribution of metal atoms on the 2D nanosheet without any aggregation, highlighted by yellow circles. The content of Co and Fe in CoFe-2DSA was measured by ICP and was found to be 0.42 and 0.35 wt%, respectively, as can be seen in Table 1. Nitrogen adsorption-desorption isotherms were employed to analyse the surface area and pore structure of CoFe-2DSA, following the Brunauer-Emmett-Teller (BET) method. The results showed the sample with molten salt CoFe-2DSAhas a high surface area of 1041 m2g'1and a pore volume of 0.74 cm3g’1, which are significantly larger than those of the CoFe-Blank (95.29 m2g'1and 0.13 cm3g'1), 11 (A) and Table 2. Molten salts can act as a porogen agent and improve the surface area and porosities.

[0296] The isotherms also revealed the presence of both micropores and mesopores in CoFe-2DSA, as indicated by the steep N2 uptake at low pressure and the well-defined hysteresis loop at high pressure, as shown by their type IV isotherms. The pore size distribution analysis, Figure 12 (A), further confirmed that CoFe-2DSA has a more microporous structure than the CoFe-Blank, a type I nitrogen adsorption isotherm. The ultra-thin 2D nanosheet structure of CoFe-2DSA, with its high BET and porosity, is expected to facilitate efficient mass and charge transfer during the reaction process by fully exposing the active sites. The clarity of the impact of the use of molten salt can also be seen by comparing Co-2DSA, Fe-2DSA, and CoFe-Blank, Table 2.

[0297] To provide a comprehensive analysis of the synthesized structures, an X-ray diffraction (XRD) analysis was conducted to elucidate their composition before and after carbonization. The obtained XRD patterns showcased distinctive features indicative of highly crystalline and well-ordered structures in the pre-carbonization samples. This observation was corroborated by the striking resemblance of the diffraction peaks to the established literature references. The diffraction peaks observed at 3.2°, 4.47°, 6.28°, 7.66°, 8.83°, 9.14°, 9.87°, 11.13°, 11.53°, 12.37°, 13.06°, 13.83°, 14.16°, 15.27°, 15.58°, 15.86°, 16.95°, and 18.52° can be assigned to the(lOO), (110), (200), (211), (220), (300), (310), (222), (320), (321), (322), (331), (420), (500), (510), (520), (521), and (600) crystallographic planes of the cubic ZIF-11 structure, respectively. These distinct peaks serve as a compelling demonstration of the highly crystalline nature of the synthesized materials. XRD analysis after carbonization shown in Figure 12 (B). The results revealed two distinct peaks at 23.7° and 43.7°, which correspond to the graphitic carbon (002) and (101) planes. No traces of metal nanoparticles were detected, as evidenced by the absence of any discernible peaks indicative of their presence. The concentration of metal particles within the resulting carbon framework was intentionally minimized to achieve a potentially singular atomic dispersion, which will be beyond the resolution of the XRD equipment. Raman spectroscopy was utilized to gain a deeper understanding of the sample's structural characteristics, Figure 12 (C). The Raman spectrum of CoFe-2DSA, a two-dimensional nanosheet matrix, was examined and revealed two distinctive peaks at 1348 cm'1and 1592 cm'1. These peaks, referred to as the D-band and G-band, are commonly found in materials and serve as markers for determining their structural and chemical properties. The D-band represents disordered or amorphous structures, while the G-band signifies ordered or crystalline structures. The D / G ratio was analysed in materials subjected to molten salt assessment, namely CoFe-2DSA, Co-2DSA, andFe-2DSA, as well as CoFe-Blank without the molten salt assessment. The results revealed a variation in the D / G ratio, with values ranging from 1.01 in the CoFe-Blank sample to 1.13, 1.10, and 1.11 in the corresponding evaluated molten salt assisted materials.

[0298] The surface chemical composition and elemental state of the samples were evaluated using X-ray photoelectron spectroscopy (XPS). The XPS survey spectra revealed the presence of carbon, nitrogen, oxygen, iron, and cobalt in the samples, as shown in survey spectrum. This analysis allowed for a thorough characterization of the surface properties of the samples. The C is XPS spectra shown in Figure 12 (D) were carefully studied and found to exhibit four distinct peaks at specific energy levels. These peaks, located at 284.27, 284.7, 285.28, 286.2, and 290.15 eV, were determined to correspond the presence of various types of bonding, including C=C, C-C, C-N, C-O-C, and 7t-7t*. The O ls XPS spectra revealed three separate forms of O bonding: Metal-O, O-C, and O-H. These bonding types can be identified at energy levels of 530.86, 531.81, and 533 eV, respectively. The key distinction can be observed in the quantity of C=O groups in the samples CoFe-2DSA, CoFe-blank, Co-2DSA, and Fe-2DSA, which are 2.68, 1.70, 1.89, and 2.16, respectively. The C=O group, also known as a carbonyl group, has a significant effect on the rate of OER. The carbonyl group acts as an electronwithdrawing group, increasing the electron density of the molecule and making the molecule more electrophilic. This makes it easier for the molecule to react with oxygen, increasing the rate of OER. Additionally, the carbonyl group can stabilize intermediate species (OH*, O*, and OOH*) in the OER reaction, which also contributes to the overall rate of the reaction.

[0299] The N Is XPS spectra shown in Figure 12 (E), the result is revealing there are four distinct types of nitrogen species that can be found in carbon materials, including pyridinic-N, pyrrolic-N, graphitic-N, and N-oxides. These nitrogen species can be distinguished by their corresponding energy levels, with pyridinic-N at 398.36 eV, pyrrolic-N at 399.47 eV, graphitic-N at 400.94 eV, and N-oxides at 404.1 eV. The amount of nitrogen, as well as specific nitrogen types such as pyridinic-N and graphitic-N, holds significant importance in influencing the electrocatalytic efficiency of catalysts in both the ORR and OER. The information on these parameters can be obtained from Figure 12 (F). The results show that the total nitrogen content of the samples treated with molten salt assisted pyrolysis decreased from 9.96 wt% in the CoFe-blank to 7.96, 7.56, and 7.44 wt% in the CoFe-2DSA, Co-2DSA, and Fe-2DSA, respectively.

[0300] Graphitic-N is particularly useful as an active site for ORR, due to its capability to donate electrons. Conversely, Pyridinic-N serves as an efficient active site for the OER, as it can accept electrons. Moreover, Pyridinic-N and graphitic-N with lone pair electrons can accept electrons from adjacent carbon atoms, thereby facilitating the adsorption of O2 or OOH, and ultimately promoting the reduction of OH to form H2O. The coordination interaction between nitrogen atoms and metals (Co and Fe) typically results in electrons being transferred from the nitrogen atoms to the metal sites. This electron transfer leads to a slight negative charge on the nitrogen atoms and a partial positive charge on the metallic surface. The combination of metal sites and nitrogen dopants significantly enhances the ORR and OER processes.

[0301] Electrochemical Performance for Oxygen Redox

[0302] Evaluation of Oxygen Reduction Electrocatalysis (ORR)

[0303] The unique microstructure of the CoFe-2DSA catalyst, makes it a promising candidate for catalysing ORR. The performance was evaluated by conducting cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements in a three-electrode system that consisted of a platinum rotating disk working electrode, an Ag / AgCl reference electrode, and a Pt foil rod counter electrode. Measurements were performed in 0.1 M KOH solutions that were saturated with O2. To assess the efficiency of various catalysts, a graphitized carbon powder containing 20% Pt and 10% Ru, obtained from Sigma Aldrich, and referred to as Pt-Ru / GC, was utilized as a standard material throughout the investigation. The same ink preparation method was employed to create ink, which was subsequently evaluated alongside the other catalysts to serve as a benchmark.

[0304] When the electrolyte solution was saturated by Ar, a quasi -rectangular voltammetry without any visible reduction peak was observed for CoFe-2DSA. However, in the Ch-saturated electrolyte, a distinctive cathode peak appeared at potential of 0.855 V which shows the potential of CoFe-2DSA as ORR electrocatalyst. The ORR capabilities of all samples and the commercial Pt-Ru / GC benchmark were further examined in 0.1 M KOH through LSV curve analysis using the RDE system, at a rotating speed of 1600 rpm and at a scan rate of 5 mV s'1. The ORR performance of CoFe-2DSA, CoFe-blank, Co-2DSA, Fe-2DSAand Pt-Ru / GC catalysis was compared by analysing their LSV curves as depicted in Figure 13 (A). Out of these catalysts, CoFe-2DSA displayed the highest half-wave potential at 0.886 V, while the others had half-wave potential of 0.801 V (CoFe-blank), 0.864 V (Co-2DSA), 0.858 V (Fe-2DSA), and 0.841 V (Pt-Ru / GC). Furthermore, CoFe-2DSA demonstrated not only exceptional ORR activity but also a remarkable kinetic current density of 7.19 mA cm'2at a potential of 0.85 V (Figure 13 (B)) which was 4.5 times larger than that of Pt-Ru / GC. Additionally, this level of activity surpasses or equals the activity of other high-performing Fe-Based / Co-based SA catalysts previously reported.

[0305] To provide further information about the rate of electrochemical reaction and the kinetics of the electrochemical process, Tafel slope was calculated based on LSV curves. As seen in Figure 13 (C), the Tafel slope of the CoFe-2DSA (70 mV.dec'1) catalyst is the smallest when compared to other catalysts such as CoFe-blank (294 mV.dec'1), Co-2DSA(107 mV.dec'1), Fe-2DSA(113 mV.dec'1), and Pt-Ru / GC (71 mV.dec'1).

[0306] The Koutecky-Levich method was employed to determine the electron transfer number, enabling the evaluation of the reaction pathway. The 4-electron pathway for ORR is considered more favourable in electrochemical devices, as it directly converts oxygen molecules to water. In contrast, the 2-electron pathway produces hydrogen peroxide as an intermediate product. The 4-electron pathway holds promise as a potential solution to overcome the slow kinetics associated with ORR. Figure 13 (E) displays the electron transfer number, obtained from the LSV curves, by Koutecky-Levich plots from Figure 13 (D). These plots reveal a close to linear relationship within the voltage range of 0.2 to 0.6 V. The electron transfer number for CoFe-2DSA was determined to be approximately 4, indicating that the catalyst promotes a four-electron transfer process during the ORR.

[0307] Stability is also a crucial factor in the ORR process, particularly over a long period of time. In this regard, the stability of CoFe-2DSA catalyst was evaluated by running CV for a long period of time and in between running LSV to see how the LSV curves change. As Figure 13 (F) exhibits, the CoFe-2DSA catalyst has shown excellent stability, maintaining its performance even after 1000 cycles as revealed by CV. The results indicated only a small decline of approximately 14 mV of LSV curve after 1000 CV cycles, which demonstrates the catalyst's ability to maintain its performance for extended periods. This impressive performance highlights the catalyst's exceptional effectiveness and reliability.

[0308] Evaluation of Oxygen Evolution Electrocatalysis (OER)

[0309] To investigate the performance of the CoFe-2DSA catalyst to overcome the sluggish kinetic of OER, LSV tests in a 1 M KOH electrolyte at 1600 rpm was applied Figure 14 (A) shows the CoFe-2DSA catalyst had an overpotential of r|=290 mV at a current density of 10 mA cm-2. This value is considered highly competitive in the field, with many researchers striving to achieve overpotentials below 400 mV to make the OER more practical and cost-effective. When comparing the overpotential of CoFe-blank (r|=450 mV), Co-2DSA (r|=350 mV), Fe-2DSA (r|=370 mV), and Ru / C (T|=310 mV), the CoFe-2DSA catalyst with the overpotential of r|=290 mV exhibits the lowest overpotential, demonstrating its exceptional performance in OER.

[0310] A lower Tafel slope indicates faster electron transfer and thus faster reaction rates, making the catalyst more efficient which is a measure of the kinetics of the OER and is considered a key parameter in the design of electrocatalysts. In this regard, the Tafel slopes were measured based on LSV results, Figure 14 (B). The CoFe-2DSA catalyst showed a Tafel slope of 128 mV dec-1. In comparison to other catalysts such as CoFe-blank, Co-2DSA, Fe-2DSA, and Pt-Ru / GC which has a Tafel slope of 284 mV dec-1, 168 mV dec-1, 196 mV dec-1, and 164 mV dec-1, respectively, the CoFe-2DSA catalyst exhibits excellent OER kinetics.

[0311] Evaluation of Bifunctionality

[0312] The bifunctional electrocatalytic activity of CoFe-2DSA was further evaluated through the potential gap (AE) between the half-wave potential for oxygen reduction (E1 / 2 of ORR) and the potential for oxygen evolution (Ejio of OER). A smaller AE value indicates excellent bifunctionality and electrode reversibility. As can be seen in Figure 14 (C and D), the smallest AE value of 634 mV is exhibited by CoFe-2DSA, while larger AE values are displayed by CoFe-blank (879 mV), Fe-2DSA (736 mV), Co-2DSA (722 mV), and Pt-Ru / GC (699 mV), The results demonstrate that CoFe-2DSA exhibits exceptional bifunctionality performance.

[0313] Our findings are in line with previous studies that have shown that nitrogen doping, specifically pyridinic and graphitic nitrogen as well as active metal sites, plays a crucial role in ORR / OER electrocatalysis. The high electrical conductivity along with the unique pore structure of CoFe-2DSA can potentially contribute to the development of increased number of active sites, enhancing the speed of electron transport during the reaction.

[0314] Nitrogen doping significantly impacts the overall catalytic mechanism by enhancing oxygen molecule adsorption on the catalyst surface through the modification of electron density around adjacent carbon atoms. This crucial process facilitates covalent bonding of oxygen on metal sites, such as cobalt. Furthermore, nearby nitrogen atoms play a pivotal role in aiding electron transfer throughout various reaction stages. During ORR a free O2 molecule, with its two unpaired electrons, requires the donation of two electrons from its surrounding environment. In pristine carbon frameworks, this donation comes from the dopants, as the pure carbon framework is chemically inert.

[0315] A summary of the potential mechanism:

[0316] • Electron-Rich Nitrogen Doping: The introduction of nitrogen atoms within the carbon lattice generates electron-rich sites. These nitrogen-doped carbon materials act as potent catalysts for oxygen-related reactions due to their ability to finely tune electron density.

[0317] • Enhanced Oxygen Adsorption: The electron-rich regions created by nitrogen doping facilitate the adsorption of oxygen molecules on the catalyst's surface. This favourable interaction occurs because oxygen molecules readily bond with electron-rich sites.

[0318] • Metal Sites Interaction: In the case of catalysts featuring metal sites like cobalt and iron dual-sites, oxygen molecules adhered to the catalyst surface interact with these metal sites. Metal sites exhibit a strong affinity for oxygen species, allowing them to form covalent bonds.

[0319] • Electron Transfer Assistance: During various reaction steps, where oxygen molecules transform into other oxygen-containing species, electron transfer is critical. Adjacent nitrogen atoms to metal sites can act as electron donors or acceptors, depending on their electronic configuration and local charge distribution. This dynamic involvement of nitrogen atoms facilitates electron transfer reactions, ultimately bolstering the overall ORR and OER.

[0320] • Synergistic Catalytic Environment: The synergy between nitrogen doping and the presence of metal sites establishes an active and efficient catalytic environment. Electron-rich nitrogen atoms enhance oxygen adsorption, while metal sites facilitate the formation of intermediate species and electron transfer, thereby driving the desired chemical transformations. The combination of nitrogen doping and metal coordination plays a pivotal role in the design of advanced electrocatalyst materials for ORR and OER. In specific of CoFe-2DSA, the synergy between cobalt and iron alters their original d-orbital energy levels, impacting their adsorption energy to the substrate. This alteration results in an optimal adsorption strength to the substrate, minimizing overpotential and promoting the absorption of key reaction intermediates like H*, OH*, and OOH* on the catalyst surface. This elucidates the superior catalytic activity of the dual-site catalyst (CoFe-2DSA) when compared to Co-2DSA and Fe-2DSA, as previously reported.

[0321] Evaluating the Electrochemical Performance of Materials as Electrocatalysts for Rechargeable Zinc- Air Battery

[0322] The remarkable bifunctionality performance exhibited by the CoFe-2DSA electrocatalyst prompted an investigation into its efficacy within the context of a rechargeable zinc-air battery (ZAB). The battery was assembled using a zinc plate as the anode, the CoFe-2DSA catalyst supported by carbon cloth as the air cathode, and a 6.0 M KOH and 0.2 M Zn(CH3COO)2 mixed solution as the electrolyte. To assess the effectiveness of the designed catalysts, the battery's performance was compared to a commercial Pt-Ru / GC benchmark as the air cathode. This comparison was based on measurements of the open circuit voltage (OCV), power density, specific capacity, and charge-discharge cycle stability. It is worth to mentioned that all the experimental conditions were kept same for CoFe-2DSA and Pt-Ru / GC electrocatalyst.

[0323] To evaluate the battery's level of charge and overall performance, an OCV test was conducted. This test involves measuring the voltage across the battery terminals when no external load is connected. The CoFe-2DSA-based ZAB exhibited a notably elevated OCV of 1.48 V, Figure 15 (A), approaching 90% of the theoretical voltage anticipated for ZAB. Under alkaline conditions, ZAB is theoretically capable of generating a maximum output voltage of 1.65 V, based on the electrochemical redox reactions occurring at both the cathode and the anode. In contrast, the Pt-Ru / GC -based battery showed a lower voltage, 60 mV. A higher OCV is desirable in a battery because it indicates the battery's capacity to deliver greater electrical potential when connected to a load. This implies that the battery can provide a higher voltage to power devices or perform work effectively.

[0324] The power density of ZABs plays a crucial role in assessing its ability to the amount of electrical power it can deliver per unit of area. In this context, the CoFe-2DSA-based battery showcased remarkable performance by achieving a power density of 229.6 mW cm'2, operating at a current density of 290 mA cm'2, Figure 15 (B). This power density surpassed that of the Pt-Ru / GC -Based battery, which recorded a power density of 89.9 mW cm'2at a current density of 110 mA cm'2.

[0325] The discharge-specific capacity of the made batteries was measured by determining the amount of zinc metal consumed during a full discharge process, Figure 15 (C). The CoFe-2DSA-based battery has exhibited impressive performance in terms of capacity and energy density. It has demonstrated a specific capacity of 811.55.2 mA h g'1and an energy density of 997 Wh kg'1which is comparable to ZAB theoretical (820 mAh g'1) and energy density (1080 Wh kg'1). In comparison, the Pt-Ru / GC -based battery has a specific capacity of 764 mA h g'1and an energy density of 825 Wh kg'1.

[0326] The CoFe-2DSA-based battery surpasses the Pt-Ru / GC -based battery in both specific capacity and energy density. This means that the CoFe-2DSA-based battery can store a greater amount of electrical energy per unit weight. Additionally, it has a higher power density, allowing for faster energy discharge. The results clearly demonstrate that the CoFe-2DSA electrocatalyst exhibits exceptional performance surpassing the reported values in previous studies.

[0327] The discharge performance rate of CoFe-2DSA-based ZAB was assessed by varying the current density from 2 mA cm'2to 12, 24, 26, and 48 mA cm'2. The battery was held at each current density for 5 hours to monitor the changes in discharge voltage. Subsequently, the current density was reduced back to 2 mA- cm'2to observe the recovery of the discharge voltage to its initial value. As depicted in Figure 15 (D), when the current density is increased from 2 mA cm'2to 12, 24, 36, and 48 mA cm'2, the discharge voltage decreases from 1.2 to 1.5, 1.06, and 0.97 V, respectively. Subsequently, upon reducing the current density back to 2 mA cm'2after 25 hours, the discharge voltage recovers to 1.18 V, which closely resembles the initial value.

[0328] To evaluate the long-term cycling stability of the CoFe-2DSA-based ZAB and its ability to maintain battery performance under repeated charge and discharge cycles, a series of galvanostatic charge and discharge tests were conducted. The tests were carried out at a constant current density of 2 mA cm'2, and four distinct charge-discharge cycle times were employed, namely 30 minutes, 60 minutes, 120 minutes, and 240 minutes for each cycle, as can be seen in Figure 16. The performance of the CoFe-2DSA-based ZAB was also compared with that of the Pt-Ru / GC -based ZAB battery. Under the given operational parameters of a current density of 2 mA cm'2and a 15-minute charge and 15-minute discharge cycle, the battery exhibited a voltage differential of 1.3 V and a round-trip efficiency of 44% after a period of 10 days. Subsequently, after 74 days and 3570 cycles, these values were modified to 1.64 V and 32.5% respectively. Notably, the catalyst continued to function effectively even after the prolonged 74-day duration, whereas the battery ceased to operate due to the complete consumption of the zinc foil within the anode region. Decreasing the voltage gap offers two main benefits: enhanced battery efficiency and improved voltage stability. It allows for more efficient energy utilization and ensures a consistent output voltage during discharge, resulting in reliable and long-lasting battery performance.

[0329] The performance of CoFe-2DSA-based ZAB was assessed under varying chargedischarge durations, as depicted Figure 16. Results indicate that as the charge-discharge cycle duration increased (30, 60, 120, and 240 minutes), the voltage gap decreased from 1.3 to 1.12, 1.1, and 0.88 V, while the round-trip efficiency increased from 44% to 45.6, 48.11, and 58.6%. However, due to different rates of zinc foil consumption, each battery ceased operation at different times. For instance, batteries with charge-discharge durations of 30, 60, 120, and 240 minutes stopped working after 74, 50, 40, and 30 days of operation, respectively. It should be noted that in each scenario, the batteries stopped functioning due to complete zinc foil consumption. It is noteworthy to mention that the performance evaluation of CoFe-2DSA-based ZAB was also conducted in comparison to the Pt-Ru / GC -based ZAB under two different cycle durations, namely 30 minutes and 120 minutes. The obtained results, as depicted in Figure 16, indicate that the Pt-Ru / GC -based ZAB ceased to function and experienced catalyst deactivation after 3.5 days 2.5 days of operation.

[0330] Increasing the charge-discharge cycle duration time in CoFe-2DSA-based ZAB leads to an improvement in round-trip efficiency. This can be attributed to enhanced electrochemical reactions, improved electrode kinetics, reduced side reactions, and minimized internal resistance effects. The longer cycle duration allows for more efficient conversion of electrical energy to chemical energy during charging and back to electrical energy during discharging. It also provides additional time for reactions to occur and facilitates better charge transfer processes.

[0331] After an initial assessment of CoFe-2DSA-based ZAB charge-discharge cycles conducted at a current density of 2 mA.cm2with varying charge-discharge duration times, further investigations were carried out to evaluate the battery's performance under higher current densities. Specifically, the charge-discharge cycles were measured at current densities of 12, 24, and 36 mA cm'2, while maintaining a constant charge and discharge duration (240 minutes each cycle), as depicted in Figure 17. The objective of these tests was to examine how the battery would behave when subjected to increased stress conditions.

[0332] The findings indicate that the voltage gap and round-trip efficiency of the system were influenced by the current density. Specifically, when the current density was increased from 2 mA cm'2to 12, 24, and 36 mA cm'2over a period of one day, the voltage gap exhibited a corresponding increase from 0.82 Vto 1.15, 1.36, and 1.58 V, respectively. Simultaneously, the round-trip efficiency experienced a decrease from 59.7% to 47%, 41%, and 35%, respectively. Furthermore, after a duration of 4.5 days, the voltage gap and round-trip efficiency displayed predominantly stable behaviour. The voltage gap values were recorded as 0.88 V, 1.2 V, 1.37 V, and 1.55 V, while the corresponding round-trip efficiency values were 58.4%, 46.1%, 40.2%, and 35.3%, respectively.

[0333] The CoFe-2DSA catalyst has demonstrated remarkable advancements in the ZAB, exhibiting superior catalytic activity and mass transfer when compared to both commercial Pt-Ru / GC catalysts and recently reported bifunctional electrocatalysts. The exceptional performance of CoFe-2DSAin facilitating the ORR and OER can be attributed to its distinctive structure composed of two-dimensional porous N-doped carbon nanosheets. This structure provides an extensive surface area and an abundance of active sites, resulting in enhanced catalytic activity. Moreover, the utilization of CoFe-2DSAas a catalyst in ZAB offers the added advantages of cost-effectiveness and environmental friendliness, surpassing traditional Pt-Ru / GC catalysts. References

[0334] Yan, L. et al. (2023) Advanced Energy Materials 13, 2204245

[0335] Banerjee, P. C. et al. Electrochemical capacitance of Ni-doped metal organic framework and reduced graphene oxide composites: more than the sum of its parts. ACS applied materials & interfaces 7, 3655-3664 (2015)

[0336] Nguyen, T. H. et al. Metal Single-Site Molecular Complex-MXene Heteroelectrocatalysts Interspersed Graphene Nanonetwork for Efficient Dual-Task of Water Splitting and Metal-Air Batteries. Advanced Functional Materials 33, 2210101 (2023).

[0337] Ding, K. et al. Robust Electronic Correlation of Co-CoN4 Hybrid Active Sites for Durable Rechargeable Zn-Air Batteries. Advanced Functional Materials, 2207331 (2022).

[0338] Gu, T. et al. Dual-sites coordination engineering of single atom catalysts for fulltemperature adaptive flexible ultralong-life solid-state Zn- Air batteries. Advanced Functional Materials 33, 2212299 (2023).

[0339] S. Liu, et al. Nitrogen-Doped Carbon Networks with Consecutive Conductive Pathways from a Facile Competitive Carbonization-Etching Strategy for High-Performance Energy Storage, Small, 18 (2022) 2104375.

Claims

Claims1. A zeolitic imidazolate framework (ZIF), comprisingzinc;a ligand selected from benzimidazole, 6-chloropurine, and purine; and a further metal selected from the group consisting of cobalt, nickel, and iron as part of the framework, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1 : 10 to 1 :40.

2. The ZIF of claim 1 comprising a further metal to zinc molar ratio in a range of from 1 :20 to 1:40.

3. The ZIF of claim 1 or 2, wherein the further metal is cobalt.

4. The ZIF of any of the preceding claims, wherein the ZIF has a crystal structure that corresponds with a crystal structure of ZIF-11, ZIF- 12, ZIF-20, or ZIF -21.

5. The ZIF of any of the preceding claims, wherein the ZIF is impregnated with an additional metal which is different to the further metal.

6. The ZIF of claim 5, wherein the additional metal is selected from the group consisting of cobalt, nickel, iron and copper.

7. The ZIF of claim 6, wherein the additional metal is iron.

8. An electrocatalyst comprising:a porous carbon network with a nitrogen content of at least 2 atom%;an electrocatalyst metal selected from the group consisting of cobalt, nickel, and iron, the metal being present in single sites within the carbon network; andthe electrocatalyst being derived from a zeolitic imidazolate framework (ZIF), wherein the ZIF compriseszinc;a ligand selected from benzimidazole, 6-chloropurine, and purine; anda further metal selected from the group consisting of cobalt, nickel, and iron, wherein the ZIF comprises a further metal to zinc molar ratio in a range of from 1:10 to 1:40.

9. The electrocatalyst of claim 8, wherein the electrocatalyst metal is present in an amount of from 0.3% to 5% by weight of the total weight of the electrocatalyst.

10. The electrocatalyst of claim 8 or 9, wherein the electrocatalyst is substantially free of zinc.

11. The electrocatalyst of any of claims 8 to 10, wherein the electrocatalyst has a porous 2D nanosheet structure.

12. The electrocatalyst of any of claims 8 to 10, wherein the electrocatalyst has a porous 3D structure.

13. The electrocatalyst of any of claims 8 to 12, wherein the electrocatalyst metal is cobalt.

14. The electrocatalyst of any of claims 8 to 13, wherein the electrocatalyst comprises an additional metal which is different from the electrocatalyst metal.

15. The electrocatalyst of claim 14, wherein the additional metal is selected from the group consisting of cobalt, iron, copper and nickel.

16. The electrocatalyst of claim 15, wherein the additional metal is iron.

17. The electrocatalyst of any of claims 8 to 16, wherein the electrocatalyst has a porosity of at least 100 cm3g’1.

18. The electrocatalyst of any of claims 8 to 17, wherein the electrocatalyst has a surface area of at least 200 m2g-1.

19. The electrocatalyst of any of claims 8 to 18, wherein the electrocatalyst has an electrical conductivity of at least 900 S / m.

20. The electrocatalyst of any of claims 8 to 19, wherein the electrocatalyst has a combined oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) overpotential of no more than 700 mV.

21. A process for producing a zeolitic imidazolate framework (ZIF), comprising combininga zinc salt;a further metal salt selected from cobalt, nickel, and iron salts, the further metal to zinc molar ratio being in the range of from 1 : 10 to 1 :40; and a ligand selected from benzimidazole, 6-chloropurine, and purine;in a solvent to form a solid ZIF; andseparating the solid ZIF from the solvent.

22. The process of claim 21, comprising:forming a first mixture comprising the zinc salt and the further metal salts in a first solvent, andforming a second mixture comprising the ligand in a second solvent, the first and second mixtures then being combined to form the solid ZIF.

23. The process of claim 22, wherein the first solvent is toluene, and the second solvent is methanol.

24. The process of claim 23, wherein the toluene to methanol volume ratio is in the range of from 1:1 to 1:4.

25. The process of any of claims 21 to 24, wherein the total metal to ligand molar ratio is in the range of from 1 :2 to 1:4.

26. The process of any of claims 21 to 25, wherein ammonium hydroxide is added.

27. The process of any of claims 21 to 26, wherein the zinc salt is zinc nitrate.

28. The process of any of claims 21 to 27, wherein the further metal salt is cobalt nitrate.

29. The process of any of claims 21 to 28, wherein the ZIF is impregnated with an additional metal which is different to the further metal.

30. The process of any of claims 21 to 28, wherein the additional metal is selected from the group consisting of cobalt, nickel, iron and copper.

31. The process of claim 30 wherein, following formation of a solid ZIF, the solid ZIF is treated with one or more metal salts selected from cobalt, nickel, iron, and copper salts thereby impregnating the solid ZIF with the additional metal.

32. The process of claim 31, wherein the ZIF is treated with an iron salt.

33. AZIF produced or producible by a process of any of claims 21 to 32.

34. A process for forming an electrocatalyst, comprising:pyrolyzing a ZIF according to any of claims 1 to 7, or a ZIF produced by the process of any of claims 21 to 32.

35. The process of claim 34, wherein the pyrolysis is conducted under conditions which evaporate zinc, such that the electrocatalyst comprises substantially no zinc.

36. The process of claim 34 or 35, wherein pyrolysis is carried out at a temperature in a range of from 800°C to 1000°C.

37. The process of any of claims 34 to 36, wherein pyrolysis is undertaken in the presence of a salt which is molten under the pyrolysis conditions.

38. The process of claim 37, wherein the salt is selected from the group consisting of zinc acetate and potassium chloride.

39. An electrocatalyst produced or producible by the process of any of claims 34 to 38.

40. The electrocatalyst of claim 11, wherein the electrocatalyst is produced or producible by a process according to claim 37 or claim 38.

41. The electrocatalyst of claim 12, wherein the electrocatalyst is produced or producible by a process according to any of claims 34 to 36.

42. An electrochemical device comprising the electrocatalyst of any of claims 8 to 28, or claims 39 to 41.

43. The electrochemical device of claim 42, wherein the product is an aqueous metal-air cell, fuel cell, supercapacitor, water splitting electrode, carbon dioxide reduction device, electrochemical sensor, or battery.

Images