Electrocatalyst and uses thereof

Abstract

An electrocatalyst comprising a layered double hydroxide is disclosed, wherein the layered double hydroxide comprises intercalated charge-balancing anions and at least some of the charge-balancing anions are basic anions. The electrocatalyst is useful for alkaline seawater electrolysis (ASWE), and the latter can demonstrate stable operation at a high current density.

Description

ELECTROCATALYST AND USES THEREOFPRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024902736 titled “ELECTROCATALYST AND USES THEREOF” and fded on 30 August 2024, the contents of which are hereby incorporated by reference in their entirety.TECHNICAL FIELD

[0002] The present disclosure relates generally to an electrocatalyst and uses thereof. In a particular form, the present disclosure relates to an electrocatalyst comprising a layered double hydroxide and uses thereof.BACKGROUND

[0003] Green hydrogen produced through water electrolysis is increasingly recognized as a key contributor for a 2050 zero-carbon target1, 2. The current industrial production cost of green hydrogen, primarily reliant on alkaline pure water electrolysis3, generally falls within the range of US$ 4 - 5.5 kgm14. However, this cost is not yet competitive with that of grey hydrogen produced from fossil fuels (e.g., - US$ 2.5 kgH2-1)5, 6, limiting the widespread deployment of green hydrogen. Despite this, direct alkaline seawater electrolysis offers a practical route to producing economically competitive hydrogen.

[0004] Direct seawater electrolysis eliminates the demand for precious pure water input7, contributing to a significant reduction in annual operational expenditure (OPEX) (Figure la). Although one may suggest integrating a desalination system with an electrolysis system to avoid directly using seawater with complex components8, 9, the operation of such a desalination system would significantly increase the annual capital expenditure (CAPEX)10(Figure la). Collectively, direct alkaline seawater electrolysis demonstrates clear economic superiority compared to traditional pure water electrolysis and seawater desalination combined with electrolysis. More importantly, increasing the operating current from 0.2 - 0.3 A cm'2(current commercial standard) to at least 0.5 A cm'2in the high current zone can significantly lower hydrogen production costs (Figure lb). Therefore, developing large-current alkaline seawater electrolysis is economically crucial.

[0005] However, the current commercial alkaline pure water electrolyzer (AWE) electrodes (i.e., Raney Ni || Raney Ni) prove inadequate for seawater electrolysis due to severe anode corrosion and chlorine evolution reaction (C1ER), even at a low current density of 0.2 A cm'2(Figures Ic-le, 7, and 9). Therefore, achieving large-scale seawater electrolysis imposes higher demands on robust anodes.Currently, various anodes, such as nitrides11, phosphides12, 13, and sulfides14, 15, have been reported for seawater electrolysis, but they generally operate below 0.4 A cm'2and / or 400 hours due to the corrosion concern. These anodes normally undergo surface reconstruction, which creates surface defects that provide opportunities for Cl' to enter the electrode surface and trap active sites16, 17(Figure 1c). This process leads to gradual electrode degradation over long term operation. Meanwhile, the disordered anion distribution on the electrode surface may affect the adsorption of OER intermediates, potentially reducing OER activity18. It is therefore challenging for these types of anodes to maintain stability under more rigorous large-current (e.g., > 0.5 A cm'2) operating conditions.

[0006] An electrochemical water splitting process includes a hydrogen evolution reaction (HER) and an oxygen evolution reaction (OER). In general, for water electrolysis systems, the oxygen evolution reaction at the anode is significantly slower than the hydrogen evolution reaction at the cathode owing to its four-electron reaction step. Noble metal oxide catalysts (such as Ru02 and RO2) are widely used for OER because of their good catalytic performance, but the usage is restricted by their scarcity and high cost. Thus, there is a need to develop high-efficiency and low-cost OER anode catalysts for commercial water electrolysis.

[0007] The present inventors’ previous work, for the first time, demonstrated the feasibility of NiFe LDH-based anode in alkaline seawater electrolyzer (ASWE) by introducing anomalous CF adsorption on Fe sites19(Figure 1c). This feature enabled stable operation of pristine NiFe LDH in a 100 W-scale ASWE at 0.2 A cm'2. Unfortunately, the selective adsorption of CF on Fe sites failed to resist the more aggressive CF attack at a high current density (for example, at 0.5 A cm'2), resulting in severe anode corrosion (Figures Ic-lf, 8, and 9). Therefore, the pristine NiFe LDH (noted as AP NiFe LDH) is not well suited for application in ASWE at a high current density.

[0008] There is a need for new or improved electrocatalyst that can be used to mitigate or resolve one or more of the problems associated with water electrolysis, which include, but are not limited to, side reactions including chlorine evolution reaction (C1ER), electrode corrosion, scalability and production cost of an electrode made from the electrocatalyst for commercial or industrial uses, and direct alkaline seawater electrolysis at a high current density. Alternatively, or in addition, there is a need for an alternative to known electrocatalyst that can be used to mitigate or resolve one or more of the problems associated with water electrolysis.SUMMARY

[0009] According to a first aspect, there is provided an electrocatalyst comprising a layered double hydroxide, wherein the layered double hydroxide comprises intercalated charge-balancing anions and at least some of the intercalated charge -balancing anions are basic anions.

[0010] In some embodiments of the first aspect, the basic anions are not initially present within the layered double hydroxide and are introduced to the layered double hydroxide to replace at least some (or all) of the intercalated charge -balancing anions initially present within the layered double hydroxide. In some embodiments, the basic anions are introduced to the layered double hydroxide by ion exchange with at least some (or all) of the intercalated charge-balancing anions initially present within the layered double hydroxide. In some embodiments, the basic anions are present in the interlayer region of the layered double hydroxide. In some embodiments, the basic anions are uniformly distributed across the layered double hydroxide.

[0011] In some embodiments of the first aspect, the basic anions are selected from one or more of PO43, CO32, SO42, SeO42, VO43, HBO32, and BO33.

[0012] In some embodiments of the first aspect, the basic anions are highly basic anions. In some embodiments, the conjugate acids of the highly basic anions have a p Ta> about 10.0, for example > about 10.3 or > about 12.0. In some embodiments, the highly basic anions are selected from one or more of PO43and CO32.

[0013] In some embodiments of the first aspect, substantially all of the intercalated charge -balancing anions comprised in the electrocatalyst are basic anions, for example highly basic anions. In some embodiments, the layered double hydroxide remains in a crystalline state after at least some of the intercalated charge-balancing anions are exchanged with the basic anions.

[0014] In some embodiments of the first aspect, the electrocatalyst is for use in oxygen evolution reaction under alkaline conditions. In some embodiments, the electrocatalyst is for use as an anode catalyst, for example an OER anode catalyst. In some embodiments, the electrocatalyst is for use in water electrolysis, for example seawater electrolysis. In some embodiments, the electrocatalyst is for use in alkaline seawater electrolysis, for example, direct alkaline seawater electrolysis. In some embodiments, the electrocatalyst is for use in seawater electrolysis (for example alkaline seawater electrolysis) under a high current density of > about 0.5 A cm'2, for example, > about 0.8 A cm'2, or > about 1.0 A cm'2. In some embodiments, the electrocatalyst is for use in seawater electrolysis (for example alkaline seawater electrolysis) under a high current density for over 1,000 hours. In some embodiments, the electrocatalyst is for use in large-scale seawater electrolysis (for example alkaline seawater electrolysis), for example, kilowatt-scale.

[0015] In some embodiments of the first aspect, the intercalated charge-balancing anions are selected from the group consisting of F_, PC3-, CCh2-, VCE3-, HBO32-, BO33-, CF, Br, SCE2-, NCh’, CICE", SeCE2, and RCO2 (wherein R is an organic group, such as alkyl and phenyl).

[0016] In some embodiments of the first aspect, the layered double hydroxide without the basic anions being introduced is substantially crystalline or amorphous. In some embodiments, the layered double hydroxide with the basic anions being introduced is substantially crystalline. In some embodiments, the layered double hydroxide with or without the basic anions being introduced is in the form of nanosheets (for example hexagonal nanosheets). In some embodiments, the average lateral size of the nanosheets is about 10 nm to about 20 nm.

[0017] In some embodiments of the first aspect, the layered double hydroxide comprises a bimetallic layered double hydroxide and / or a trimetallic layered double hydroxide. In some embodiments, the layered double hydroxide is a bimetallic layered double hydroxide or a trimetallic layered double hydroxide. In some embodiments, the layered double hydroxide is selected from a nickel-based layered double hydroxide, a cobalt-based layered double hydroxide and a combination thereof. In some embodiments, the layered double hydroxide comprises a divalent metal ion and a trivalent metal ion. In some further embodiments, the divalent metal ion is selected from Ni and Co. In some further embodiments, the trivalent metal ion is selected from Fe, Co, Al, Mn, and Cr.

[0018] In some embodiments of the first aspect, the molar ratio between the divalent metal ion and the trivalent metal ion is about 4: 1 to about 1.6: 1, for example about 3: 1, about 2.5: 1 or about 2: 1. In some embodiments, the molar ratio between the divalent metal ion and the trivalent metal ion is about 3: 1.

[0019] In some embodiments of the first aspect, the layered double hydroxide is selected from Ni-Fe layered double hydroxide, Ni-Co layered double hydroxide, Ni-Al layered double hydroxide, Ni-Zn layered double hydroxide, Ni-Mn layered double hydroxide, Ni-Cr layered double hydroxide, Ni-Ir layered double hydroxide, Ni-Ru layered double hydroxide, Co-Fe layered double hydroxide, Ni-Fe and Ni-Cr coupled (NiFe@NiCr) layered double hydroxide, Co-Fe layered double hydroxide, Ni-Fe-Mn layered double hydroxide, and Ni-Co-Fe layered double hydroxide.

[0020] In some embodiments of the first aspect, the layered double hydroxide without the basic anions being introduced comprises or consists of a chloride form of Ni-Fe layered double hydroxide. In some embodiments, the electrocatalyst comprises or consists of a chloride form of Ni-Fe layered double hydroxide with at least some (or all) of the CF anion being exchanged with PC3’. In some embodiments, the electrocatalyst has a composition formula of [Ni3 / 4Fei / 4(OH)2](PO43)i / i2-nH2O or [NiswFe I / 4(OH)2] (PO43’)i / i2.

[0021] According to a second aspect, there is provided a use of the electrocatalyst according to the first aspect in seawater electrolysis.

[0022] In some embodiments of the second aspect, the electrocatalyst is used in alkaline seawaterelectrolysis. In some embodiments, the electrocatalyst is used in direct alkaline seawater electrolysis. In some embodiments, the electrocatalyst is used in seawater electrolysis (for example alkaline seawater electrolysis) under a high current density of > about 0.4 A cm'2, for example, > about 0.5 A cm'2, > about 0.8 A cm'2, > about 1.0 A cm'2, or even > 1.5 A cm'2. In some embodiments, the electrocatalyst is used in seawater electrolysis (for example alkaline seawater electrolysis) so that electrode corrosion is reduced or prevented. In some embodiments, the electrocatalyst is used in seawater electrolysis (for example alkaline seawater electrolysis) so that selectivity for chlorine evolution reaction (C1ER) is reduced or prevented and oxygen evolution reaction (OER) activity is stabilised or boosted. In some embodiments, the electrocatalyst is used as an anode catalyst.

[0023] In some embodiments of the second aspect, the seawater electrolysis using the electrocatalyst demonstrates a higher energy efficiency compared to the seawater electrolysis using a Raney Ni-based electrocatalyst. In some embodiments, the seawater electrolysis using the electrocatalyst demonstrates an about 20 % higher energy efficiency compared to the seawater electrolysis using a Raney Ni-based electrocatalyst. In some embodiments, the seawater electrolysis using the electrocatalyst demonstrates more than about 70 % energy efficiency (for example, about 73 % or about 74 %) at a current density of 0.5 A cm'2at about 2.0 V, for example, in a 1 kW-scale electrolyzer. In some embodiments, the seawater electrolysis using the electrocatalyst stably runs for over 100 hours at a current density of 0.5 A cm'2, for example, in a 1 kW-scale electrolyzer. In some embodiments, the seawater electrolysis using the electrocatalyst stably runs at a current density of 1.0 A cm'2for over 1,000 hours, for example, in a 2 W- scale alkaline seawater electrolyzer.

[0024] According to a third aspect, there is provided an electrode of an electrochemical device, which comprises the electrocatalyst according to the first aspect.

[0025] In some embodiments of the third aspect, the electrode is an anode. In some embodiments, the electrode is an anode of a water electrolyzer. In some embodiments, the electrocatalyst is supported on a substrate. In some embodiments, the substrate is selected from Ni foam, Ni foil, Ni mesh, Ti mesh, Ti felt, and stainless steel mesh.

[0026] In some embodiments of the third aspect, the electrochemical device is a water electrolyzer. In some embodiments, the electrochemical device is a seawater electrolyzer. In some further embodiments, the seawater supplied to the seawater electrolyzer has not been subjected to complex water purification, such as desalination.

[0027] According to a fourth aspect, there is provided an electrochemical device comprising the electrocatalyst according to the first aspect.

[0028] In some embodiments of the fourth aspect, the electrochemical device is a water electrolyzer. In some embodiments, the electrochemical device is a direct seawater electrolyzer, for example direct alkaline seawater electrolyzer. In some embodiments, the electrochemical device is a direct seawater electrolyzer comprising the electrocatalyst for oxygen evolution reaction. In some embodiments, the electrochemical device is a direct alkaline seawater electrolyzer under a high current density of > about 0.4 A cm'2, for example, > about 0.5 A cm'2, > about 0.8 A cm'2, > about 1.0 A cm'2, or even > 1.5 A cm'2. In some embodiments, the electrochemical device is a supercapacitor.

[0029] According to a fifth aspect, there is provided a method of manufacturing the electrocatalyst according to the first aspect, which comprises obtaining the layered double hydroxide and introducing the basic anions to the layered double hydroxide through anion exchange.

[0030] In some embodiments of the fifth aspect, the layered double hydroxide is obtained through coprecipitation.

[0031] According to a sixth aspect, there is provided a method for conducting water electrolysis, which comprises using the electrocatalyst according to the first aspect for oxygen evolution reaction.

[0032] In some embodiments of the sixth aspect, the water electrolysis is a seawater electrolysis. In some embodiments, the water electrolysis is an alkaline seawater electrolysis. In some embodiments, the water electrolysis is a direct alkaline seawater electrolysis. In some embodiments, the water electrolysis is a seawater electrolysis (for example alkaline seawater electrolysis) under a high current density of > about 0.4 A cm'2, for example, > about 0.5 A cm'2, > about 0.8 A cm'2, > about 1.0 A cm'2, or even > 1.5 A cm'2. In some embodiments, the electrocatalyst is used so that electrode corrosion is reduced or prevented. In some embodiments, the electrocatalyst is used so that selectivity for chlorine evolution reaction (C1ER) is reduced or prevented and oxygen evolution reaction (OER) activity is stabilised or boosted. In some embodiments, the electrocatalyst is used as an anode catalyst.

[0033] In some embodiments of the sixth aspect, the seawater electrolysis using the electrocatalyst demonstrates a higher energy efficiency compared to the seawater electrolysis using a Raney Ni-based electrocatalyst. In some embodiments, the seawater electrolysis using the electrocatalyst demonstrates an about 20 % higher energy efficiency compared to the seawater electrolysis using a Raney Ni-based electrocatalyst. In some embodiments, the seawater electrolysis using the electrocatalyst demonstrates more than about 70 % energy efficiency (for example, about 73 % or about 74 %) at a current density of 0.5 A cm'2at about 2.0 V in a 1 kW-scale electrolyzer. In some embodiments, the seawater electrolysis using the electrocatalyst stably runs for over 100 hours at a current density of 0.5 A cm'2in a 1 kW-scale electrolyzer. In some embodiments, the seawater electrolysis using the electrocatalyst stably runs at a current density of 1.0 A cm'2for over 1,000 hours, for example, in a 2 W-scale alkaline seawaterelectrolyzer.BRIEF DESCRIPTION OF FIGURES

[0034] Embodiments of the present disclosure will be discussed with reference to the accompanying figures.

[0035] Figure 1 provides a feasibility analysis of seawater utilization: (a) Operating current density dependence of annual capital expenditure (CAPEX) and operational expenditure (OPEX) for an ideal 1 MW-scale AWE plant, and the impacts of simply changing pure water-supply scheme to directly seawater-supply or to integrate a seawater desalination system; (b) Operating current density dependence of hydrogen-levelized production cost (HLPC) for plants with different water-supply schemes; (c) Schematics for ions' behaviours under different conditions; (d) Chronopotentiometry (CP) tests of Raney Ni- / AP NiFe LDH-based anode; (e) (f) Hypochlorite and metal cations amounts in electrolyte after CP tests.

[0036] Figure 2 depicts correlation between the properties of NiFe-LDH-[A] (A represents the anion that is exchanged with the intercalated charge -balancing anion) and the incorporated anions: (a) Schematic of anion exchange for NiFe-LDH-[A] synthesis; (b) X-ray diffraction (XRD) spectra and layer distances of AP NiFe LDH and NiFe-LDH-[A]; (c) Fourier-transformed magnitudes of Ni / Fe K- edge extended X-ray absorption fine structure (EXAFS) spectra; (d), (e) Linear sweep voltammetry (LSV) curves and Tafel plots for NiFe LDH-[A] in alkaline saline (1 M KOH + 0.5 M NaCl); (f), (g) polarized current density at 1.7 V vs. RHE and corrosion potentials of NiFe LDH-[A] in alkaline saline (1 M KOH +0.5 M NaCl) as a function of pKavalues of the corresponding conjugate acids for incorporated anions.

[0037] Figure 3 depicts OER activity and corrosion resistance of NiFe LDH-[PO43]: (a) (b) CP tests of AP NiFe LDH- / NiFe LDH- [PO43] -based anode under different current densities in alkaline seawater (Raw seawater collected from the Glenelg beach, Adelaide, Australia); hypochlorite, metal cations, and phosphate amounts in electrolyte after CP tests; (c) Schematic for a lab-scale ASWE; (d) Polarization curves for ASWEs assembled with different anodes; (e) Durability test of NiFe LDH- [PO43] -based ASWE at 1.0 A cm'2; (f) Comparison of operating current density and durability between this work and reported anodes.

[0038] Figure 4 depicts structure evolution of NiFe LDH-[A]: (a) Ni K-edge X-ray absorption nearedge (XANE) spectra of NiFe LDH-[A]; (b) Energy shifts of Ni / Fe K-edge XANE; (c) Operando Raman spectra for NiFe LDH-[A], peaks at 453 / 523 cm1, 470 / 553 cm1, and 695 cm'1correspond to a-Ni(0H)2, y-NiOOH, and y-FeOOH, respectively31’32 33, (d) Operando attenuated total reflectance-infrared absorption spectroscopy (ATR-IRAS) spectra for NiFe LDH-[A] anodes, the bands from 2,900 cm'1to3,700 cm1are assigned to the O-H stretching mode (VO-H) of surficial water34’35; (e) pH changing in the EDL upon NiFe LDH-[A] anodes surface during LSV scanning; (f) Schematic for effects of anions upon NiFe LDH-[A] anode surface.

[0039] Figure 5 depicts performances of ASWE and economic feasibility analysis: (a) Optical image for an industrial hydrogen production system; (b) Schematic for a 1 kW-scale electrolyzer stack; (c) Optical image for components included in a single cell; (d) Polarization curves for ASWEs assembled with different anodes; (e) Energy efficiencies of ASWEs as a function operating current density; (f) Durability test of NiFe LDH-[PO43’] -based ASWE at 0.5 A cm'2; (g) Comparison of HLPC under different conditions; (h) HLPC for an ideal 1 MW-scale ASWE plant as a function of operating current density and energy efficiency.

[0040] Figure 6 shows a breakdown of hydrogen production cost for an ideal 1 MW-scale alkaline pure water electrolyzer (AWE) plant.

[0041] Figure 7 shows sensitivity analysis of hydrogen-levelized production cost (HLPC) for an ideal 1 MW-based AWE plant.

[0042] Figure 8 shows (a) Digital photographs of standard solutions containing different CIO’ amounts ranging from 0.052 to 1.67 ppm. Red colour results from the reaction between CIO’ and N, N’-diethyl-p- phenylenediamine (DPD); (b) Calibration for CIO’ amount as a function of UV-vis absorbance of standard solutions at the wavenumber of 520 nm.

[0043] Figure 9 shows optical images and UV-vis absorbance results for electrolytes after CP tests and reacting with DPD: (a) Raney Ni as anode at 0.2 A cm’2for 2 hours; (b) (c) AP NiFe-LDH as anode at 0.2 and 0.5 A cm’2for 2 hours, respectively.

[0044] Figure 10 shows high-angle annular dark-field scanning transmission electron microscopy (HAADF-TEM) images of AP NiFe-LDH.

[0045] Figure 11 shows HAADF-TEM images and EDS elemental maps of NiFe LDH-[A]: NiFe LDH-[C1 ], NiFe LDH-[C1O4], NiFe LDH-[NO3], NiFe LDH-[SeO42’], NiFe LDH-[SO42’], NiFe LDH- [CO32], and NiFe LDH-[PO43’].

[0046] Figure 12 shows polarized current density at 1.7 V vs. RHE and corrosion potentials of NiFe LDH-[A] as a function of (a) (c) ionic radii and (b) (d) oxygen atom number of intercalated anions.

[0047] Figure 13 shows optical images and UV-vis absorbance results for electrolytes after CP testsacross various current densities ranging from 0.1 to 1.5 A cm'2and reacting with DPD: (a) AP NiFe LDH-based anode; (b) NiFe LDH-[PO43] -based anode.

[0048] Figure 14 shows Fe K-edge X-ray absorption near-edge (XANE) spectra of NiFe LDH-[A],

[0049] Figure 15 shows (a) Fe 2p, and (b) Ni 2p XPS spectra of AP NiFe LDH and NiFe-LDH-[A],When compared to AP NiFe-LDH, the Ni 2p peaks of the other NiFe LDH-[A] samples displayed a pronounced shift towards a lower binding energy region, whereas the Fe 2p peaks exhibited minimal shift. These findings imply an increase in electron densities at the Ni sites in the NiFe LDH-[A] intercalated with more basic anions, consistent with the X-ray Absorption Spectroscopy (XAS) results.

[0050] Figure 16 shows O K-edge XANE spectra of NiFe LDH-[A], The reduction in intensity of the broad peaks around ~ 533 eV with the incorporation of more basic anions indicates a decrease in unoccupied density of states, suggesting a higher electron density at O sites in the NiFe LDH-[A] intercalated with more basic anions.

[0051] Figure 17 shows CV curves of NiFe LDH-[A] with the incorporation of different anions in alkaline saline.

[0052] Figure 18 shows operando Raman spectra of NiFe LDH-[C1 ] and NiFe LDH-fPO ] electrodes at 1.55 and 1.60 V vs. RHE. At elevated potentials where Ni undergoes complete transformation into y- NiOOH, the oxidation state of Ni ceased to be a significant influencing factor. This was supported by the nearly identical I470 / I553 ratios at 1.55 and 1.6 V vs. RHE for NiFe LDH-[C1 ] and NiFe LDH-fPCfi3], suggesting similar oxidation states for both samples.

[0053] Figure 19 shows (a) (b) operando attenuated total reflectance -infrared absorption spectroscopy (ATR-IRAS) spectra of NiFe LDH-[C1 ] and NiFe LDH-fPCfi3] electrodes, and Gaussian fits of H-O-H bending mode; (c) Ratios of three types interfacial water as a function of polarized potential. The broad peak extending from 2,900 cm'1to 3700 cm'1is assigned to the O-H stretching mode (VO-H) of water. It can be further resolved into three types of VO-H associated with different interfacial water configurations: 4-coordinated hydrogen-bonded water (4-HB H2O), 2-coordinated hydrogen-bonded water (2-HB H2O), and weak hydrogen-bonded Na+ / K+-hydrated water (Na / K H2O).

[0054] Figure 20 shows CV curves required for IrOxdeposition on Pt-ring electrode at a scan rate of 1.0 V s’1.

[0055] Figure 21 depicts (a) Time and (b) pH dependence of open circuit potential (Eoc) for IrOxelectrodeposited Pt-ring electrode.

[0056] Figure 22 shows a schematic illustration for ion behaviours upon NiFe LDH-[C1 ] anode surface.

[0057] Figure 23 shows plant operating current density and energy efficiency dependence of hydrogen production cost for an ideal 1 MW-scale AWE plants utilizing (a) purchased deionized water (DI) water or (b) produced DI water from an integrated desalination system.

[0058] Figure 24 depicts dependence of CAPEX and OPEX upon alkaline seawater electrolyzer (ASWE) plant operating current density.

[0059] Figure 25 depicts sensitivity analysis of HLPC for an ideal 1 MW-based ASWE plant.DESCRIPTION OF EMBODIMENTS

[0060] The present disclosure arises from the inventors’ findings that introducing a basic anion (preferably a highly basic anion, such as a phosphate ion) to a layered double hydroxide comprised by an electrocatalyst (for example anode catalyst) used in seawater electrolysis (for example, alkaline seawater electrolysis) lowered selectivity for chlorine evolution reaction (C1ER), reduced or prevented electrode corrosion, and / or stabilised or boosted the oxygen evolution reaction (OER) activity. Specifically, the findings show that there is a strong interaction between basic anions (e.g., phosphate) and Fe sites and the basic anions are securely anchored to the Fe sites, which contributes to the enhanced stability of the layered double hydroxide with more basic anions compared to the layered double hydroxide with less basic anions. Moreover, the basic anions facilitated proton transfer, thereby maintaining a highly alkaline environment in the electric double layer (EDL), and effectively shielded the electrocatalyst from Cl" attack. The presence of a higher concentration of OH- led to reduced influx of Cl" into the EDL, resulting in lower C1ER selectivity and higher corrosion resistance. The highly alkaline environment with OH" is advantageous for maintaining stable OER activity when operating under high current density. Taking NiFe layered double hydroxide as an example, it has been found by the inventors that the basic anion selectively occupied Fe sites and the OER at Ni sites were not impeded and that minimal changes occurred with the coordination environment of Ni but there were significant alterations in the coordination environment of Fe.

[0061] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction. Examples of an electrochemical device include, but are not limited to, an electrolyzer, a battery, a flow battery, a supercapacitor, particularly an electrochemical device without use of a fuel.

[0062] The term “water electrolyzer” used herein refers to an electrolyzer that uses electrochemicalspliting of water into hydrogen and oxygen (2H2O = 2H2 + O2). In electrolysis process, the DC power can be generated from sustainable energy resources such as solar, wind and biomass. A water electrolyzer may be in the form of, for example, a diaphragm water electrolyzer and an anion exchange membrane electrolyzer.

[0063] The term “alkaline water electrolysis” used herein refers to a water electrolysis process that uses an alkaline electrolyte solution. The alkaline electrolyte solution may have a pH of > about 7.5. Examples of the electrolyte solution include, but are not limited to, an aqueous solution of KOH and / or NaOH. A concentration of the electrolyte may be about 20 %~30 %.The reaction at the cathode: 4H2O + 4e_—> 2H2 + 4OH-The reaction at the anode: 40 H -^ 62 + 2H2O + 4e_

[0064] The term “alkaline seawater electrolysis” used herein refers to a water electrolysis that can use seawater as the feedstock. For example, the alkaline seawater may comprise 1 M KOH and 0.5 M NaCl (0.5 M). The term “direct seawater electrolysis” used herein refers to a water electrolysis that can use seawater as the feedstock and does not need complex water purification, for example without predesalination. However, this does not exclude a simple pretreatment of seawater before it undergoes electrolysis. In an embodiment, the pretreatment may include one or more of the following: simply filtering seawater to remove solid impurities and / or microorganisms; allowing calcium (Ca) and / or magnesium (Mg) ions to precipitate (for example, by use of alkali) and removing the precipitate from seawater (for example, by filtration).

[0065] The term “pKa” refers to the negative base -10 logarithm of the acid dissociation constant of a solution. It measures how tightly a proton is held by a Bronsted acid. A pKaused herein represents the pKaof an anion’s conjugate acid. A higher pKacorresponds to a stronger basic anion. For example, the pKaof monohydrogen phosphate anion (HPO ) is about 12.32, the pKaof monohydrogen sulfate anion (HSO4 ) is about 1.99.

[0066] Nanomaterials are defined as materials with at least one external dimension in the size range from 1 nm to 100 nm. The term “nanosheet” used herein refers to a two-dimensional nanostructure with thickness in a scale ranging from 1 nm to 100 nm.

[0067] It should be appreciated that there may be or may not be another step between the steps described herein. That is, in some circumstances, the sequential steps described herein may be conducted immediately after one another.

[0068] It should be understood that every maximum numerical limitation given throughout this disclosure is deemed to include each and every lower numerical limitation as an alternative, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this disclosure is deemed to include each and every higher numerical limitation as an alternative, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this disclosure is deemed to include each and every numerical range or number that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein. By way of example, the phrase from about 2 to about 4 includes the whole number and / or integer ranges from about 2 to about 3, from about 3 to about 4; each possible range based on real (e.g., irrational and / or rational) numbers, such as from about 2.1 to about 4.9, from about 2.1 to about 3.4 and so on; and the individual real numbers such as 2, 2.5, 3, 3.5, and 4.

[0069] The present disclosure provides an electrocatalyst comprising a layered double hydroxide, wherein the layered double hydroxide comprises intercalated charge -balancing anions and at least some of the intercalated charge-balancing anions are basic anions. In some circumstances, substantially all of the intercalated charge -balancing anions comprised in the electrocatalyst are basic anions.

[0070] The term “layered double hydroxide” (LDH) used herein refers to a class of layered materials, which consist of positively charged layers and an interlayer region with charge -balancing anions. The layers are brucite-like and are made up of edge-sharing octahedra. In some circumstances, the layered double hydroxide may be a bimetallic layered double hydroxide or a trimetallic layered double hydroxide . The layered double hydroxide can be used as prepared. Alternatively, the layered double hydroxide may be constructed to improve its performance, such as catalytic activity and OER selectivity. For this purpose, the LDH can be doped, for example by Ce, La, or Mo, and thus the electrocatalyst comprises a doped LDH. Alternatively, or in addition, the LDH can be a composite with another material, such as a carbonaceous material or a TiCL thin fdm, and thus the electrocatalyst comprises a LDH composite. Alternatively, or in addition, the LDH may be supported on a substrate, such as stainless steel fiber felt.

[0071] For the purpose of illustration, the layered double hydroxides may be represented by the chemical formula [MZ+I-XM3+X(OH)2]X+[(An)x / n]x-yH2O. When z=2, Mz+represents a divalent metal ion and can be for example Mn2+, Co2+, and Ni2+. Z may also be 1 and Mz+may be for example Li+. M3+represents a trivalent metal ion and can be for example Al3+, Fe3+, C ' . Co3+, Ga3+, and Mn3+.A" represents a charge -balancing anion in the interlayer region which neutralise the total charge of the layered double hydroxide. A" can be organic or inorganic and denote for example F’, PO? . CO,2. VO?’, HBO32’, BOs3’, Cl’, Br’, SO ’, NOs’, ClO-f, SeO?’, and RCO2- (R is an organic group, such as alkyl and phenyl). It is desirable for the charge -balancing anion to be capable of ion exchange. The layer charge x is typically in the range of 0.2-0.4, for example 0.2-0.33.

[0072] Examples of the layered double hydroxide include, but are not limited to, Ni-Fe layered double hydroxide, Ni-Co layered double hydroxide, Ni-Al layered double hydroxide, Ni-Zn layered double hydroxide, Ni-Mn layered double hydroxide, Ni-Cr layered double hydroxide, Ni-Ir layered double hydroxide, Ni-Ru layered double hydroxide, Co-Fe layered double hydroxide, Ni-Fe and Ni-Cr coupled (NiFe@NiCr) layered double hydroxide, Co-Fe layered double hydroxide, and Ni-Fe-Mn layered double hydroxide, Ni-Co-Fe layered double hydroxide. In some circumstances, Ni-Co layered double hydroxides and Ni-Fe layered double hydroxides (LDH) may be considered given their advantages including low cost, excellent electrocatalytic performance, tunable composition, and simple preparation methods.

[0073] Structural stability of the layered double hydroxide could be affected by the molar ratio between the divalent metal ion and the trivalent metal ion. It may also be desirable to select a molar ratio between the divalent metal ion and the trivalent metal ion so that suitable charge density exists in the interlayer region and is favourable for anion exchange with the basic anion. In some circumstances, the molar ratio between the divalent metal ion and the trivalent metal ion is about 4: 1 to about 1.6: 1, for example about 3.5: 1, about 3: 1, about 2.5: 1, about 2: 1, or about 1.6: 1. In an embodiment, the molar ratio between the divalent metal ion and the trivalent metal ion is about 3: 1. Taking Ni-Fe LDH as an example, excessive introduction of Fe can cause a complete destruction of the nanosheet structure of the LDH, that is, exfoliation of multilayers into monolayers and change from a crystalline state into an amorphous state.

[0074] In some circumstances, a nickel-based layered double hydroxide, a cobalt-based layered double hydroxide, or a combination thereof may be used as the layered double hydroxide. For the purpose of illustration, the layered double hydroxide can be a chloride form of Ni-Fe layered double hydroxide with a molar ratio of Ni:Fe being 3: 1 (N Fc LDH-C1).

[0075] It is believed that improving crystallinity of a layered double hydroxide might give rise to an increase of the OER overpotential. For the present purpose, the layered double hydroxide without the basic anions being introduced and the layered double hydroxide with the basic anions being introduced may be in a substantially crystalline state. The layered double hydroxide with or without the basic anion being introduced may be in the form of nanosheets, for example polygonal nanosheets, such as hexagonal nanosheets. A smaller size of the LDH particles might induce a higher surface area, which in turn may be beneficial for increasing catalytic activity. In the situation that the layered double hydroxide with or without the basic anion assumes hexagonal nanosheets, the crystal size corresponds to the average lateral size of a nanosheet and may range between 10 nm to 20 nm. The thickness of the nanosheet may be below 10 nm, for example about 3 nm to about 10 nm. In some embodiments, the layered double hydroxide may be in an amorphous state and the basic anions are introduced into the amorphous layered double hydroxide.

[0076] Any method for preparing a layered double hydroxide known in the art can be used for thepresent purpose, such as co-precipitation method, anion exchange method, alcohol / polyol method, and urea method. The coprecipitation can be carried out by direct precipitation of mixed metal hydroxides in a solution. Specifically, solutions of divalent and tri valent metal ions which contain the charge -balancing anions that are to be incorporated to the LDH are used as precursors. An alkaline condition can be applied to ensure simultaneous precipitation of the two metal ions. For example, the pH for this purpose is adjusted to 9—10. The precipitates can be washed to remove the remaining salts.

[0077] It has been found by the present inventors that introducing a basic anion (preferably a highly basic anion, such as a phosphate ion) to a layered double hydroxide comprised by an electrocatalyst (for example anode catalyst) used in seawater electrolysis (for example, alkaline seawater electrolysis) could lower selectivity for chlorine evolution reaction (C1ER), reduce or prevent electrode corrosion, and / or stabilise or boost the oxygen evolution reaction (OER) activity.

[0078] A suitable inorganic (for example an oxyanion), organic or metallate anion may be considered for the highly basic anions. Examples for a metallate anion are MnO ’ and CrO ’. It may be preferable that the basic anions are capable of ion exchange. In some embodiments, the basic anions are one or more selected from PO ’, CCE2’, SO ’, SeO?’, VO?’, HBOs2’, and BOs3’. The basic anions to be used for the present disclosure may be highly basic anions. The conjugate acid of the basic anions may have a p Ta> about 10.0, for example > about 10.3, > about 12.0. In some embodiments, the highly basic anions are one or more selected from PO?’ and COs2’.

[0079] In some embodiments, the layered hydroxide as prepared contains the basic anions as the charge -balancing anions. Alternatively, the basic anions are not initially present within the layered double hydroxide and are introduced to the layered double hydroxide to replace at least some of the intercalated charge -balancing anions initially present within the layered double hydroxide. For this purpose, the basic anions may be introduced to the layered double hydroxide by anion exchange with at least some of the intercalated charge-balancing anions within the layered double hydroxide. For example, a LDH intercalated with Cl’ or NOf may undergo anion exchange in an aqueous solution of K3PO4 so as to allow PO?’ to replace at least some of the Cl’ or NCE’. It may be preferable that the layered double hydroxide remains in crystalline state after at least some of the intercalated charge -balancing anions being exchanged with the basic anions.

[0080] Also disclosed herein is a method of manufacturing the electrocatalyst, which comprises obtaining the layered double hydroxide and introducing the basic anions to the layered double hydroxide through anion exchange. The anion exchange of the method can be performed at room temperature and atmospheric pressure, which does not require a high temperature or a high pressure and thus makes it easy to operate. As discussed hereinabove, the layered double hydroxide may be obtained through coprecipitation. The layered double hydroxide may also be commercially available. For example, two-dimensional NiFe Layered Double Hydroxide (NiFe-LDH) Powder is available from MSE Supplies® under MSE PRO™.

[0081] In selecting a suitable amount of the basic anions to be introduced to the layered double hydroxide, consideration may be given to factors such as stability under positive polarisation potentials, availability, and costs. In some embodiments, the intercalated charge -balancing anions comprised by the LDH within the electrocatalyst to substantially consist of the basic anions. In a specific embodiment, the electrocatalyst has a composition formula of [Ni3 / 4Fei / 4(OH)2](PO43')i / i2-nH2O or [Ni3 / 4Fei / 4(OH)2](PC>43)i / i2. Element analysis may be conducted by energy dispersive spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-mass spectrometry.

[0082] The basic anions are uniformly distributed across the layered double hydroxide. It may be preferable that the basic anions are present at the surface of the layered double hydroxide and in the interlayer region of the layered double hydroxide. When the basic anions are different from the intercalated charge-balancing anions within the layered double hydroxide and are introduced to the layered double hydroxide to replace at least some of the intercalated charge -balancing anions, it has been found by the present inventors that the same characteristic peaks appear in X-ray diffraction spectra before and after anion exchange, which suggests that alteration of anions do not substantially affect the structure of the layered double hydroxide. Incorporation of anions at the surface of and between the layers of a layered double hydroxide (for example NiFe LDH) may be determined by energy dispersive X-ray spectroscopy (EDS) elemental maps and X-ray photoelectron spectroscopy (XPS).

[0083] The electrocatalyst disclosed herein may be used in oxygen evolution reaction. In some embodiments, the oxygen evolution reaction is conducted under an alkaline condition. The electrocatalyst disclosed herein may also find use in water electrolysis (for example direct alkaline seawater electrolysis). An alkaline electrolyte solution used for alkaline seawater electrolysis may have a pH of > about 7.5, for example, pH of 11 to 14. The electrolyte solution may be an aqueous solution of KOH and / or NaOH, for example a 6 M KOH in natural seawater.

[0084] It would be appreciated that the electrocatalyst disclosed herein may be used to fabricate an electrode and an electrochemical device. In a particular form, the electrode is an anode comprising the electrocatalyst disclosed herein. For this purpose, the electrocatalyst may be supported on a substrate, such as Ni foam, Ni foil, Ni mesh, Ti mesh, Ti felt, and stainless steel mesh. The electrocatalyst may be dispersed in ethanol with an aqueous Nafion perfluorinate resin solution to form a slurry, which is then applied onto the surface of a glassy carbon electrode to fabricate an anode. The electrocatalyst may be loaded at about 1.6 mg cm'2to 2.5 mg cm'2.

[0085] The electrochemical device may be a water electrolyzer, for example an alkaline seawaterelectrolyzer, wherein the anode comprising the electrocatalyst is assembled with a cathode. Examples of a cathode for a water electrolyzer include, but are not limited to, a Raney Ni-based cathode and a Pt / C cathode. A water electrolyzer known in the art may be adapted for the purpose of the present disclosure. The water electrolyzer may further comprise, an electrolyte solution, a current collector (gas diffusion layers) such as porous titanium plates and / or a separator (or diaphragm). An example of the electrolyte solution consists of 1 M KOH and 0.5 M NaCl. The separator is placed between the electrodes to prevent the direct mixing of the product gases inside the electrolyzer. Examples of the separator are asbestos, woven polymer film and a porous separator having zirconium dioxide (ZrO2) on a polymeric basis and marketed under the name Zirfon™ (Agfa-Gevaert N.V.). The water electrolyzer may be operated under industrial conditions where 30 % KOH and seawater are used and a temperature of 60 °C to 80 °C is applied.

[0086] Using the electrocatalyst may advantageously allow seawater electrolysis (for example, alkaline seawater electrolysis or direct alkaline seawater electrolysis) to run under a high current density of > about 0.5 A cm'2, for example, > about 0.8 A cm'2, > about 1.0 A cm'2, or even > 1.5 A cm'2. In some circumstances, the current density may be about 1.5 A cm'2. In some circumstances, a seawater electrolyzer utilising the electrocatalyst disclosed herein (for example, in a 2 W-scale alkaline seawater electrolyzer) can operate under a high current density of about 1.0 A cm'2for over 1,000 hours. In some circumstances, a seawater electrolyzer (for example a 1 kW-scale electrolyzer) using the electrocatalyst can stably run for over 100 hours at a current density of 0.5 A cm'2. Furthermore, a seawater electrolyzer using the electrocatalyst disclosed herein may demonstrate a higher energy efficiency compared to a seawater electrolyzer using a Raney Ni-based electrocatalyst. For example, a seawater electrolyzer using the electrocatalyst disclosed demonstrates an about 20 % higher energy efficiency compared to the seawater electrolysis using a Raney Ni-based electrocatalyst. In some circumstances, the seawater electrolysis demonstrates more than about 70 % energy efficiency (for example, about 73 % or about 74 %) at a current density of 0.5 A cm'2at about 2.0 V, for example in a 1 kW-scale electrolyzer. During the seawater electrolysis, electrode corrosion (for example anode corrosion) may be reduced or prevented, selectivity for chlorine evolution reaction (C1ER) may be reduced or prevented, and / or oxygen evolution reaction (OER) activity may be stabilised or boosted. The electrocatalyst can enable a stable operation of alkaline seawater electrolysis under industrial conditions and at an industrial scale. For example, it can be used in a kilowatt-scale alkaline seawater electrolysis and lead to a 20 % reduction in hydrogen-levelized production cost.

[0087] Also disclosed herein a method for conducting water electrolysis, which comprises using the electrocatalyst for oxygen evolution reaction. The water electrolysis can be a seawater electrolysis, for example direct alkaline seawater electrolysis. Further details may refer to the description and discussion given hereinabove.EXAMPLES

[0088] Chemical agents

[0089] Nickel chloride, ferric chloride, formamide, nickel nitrate, ferric nitrate, sodium hydroxide, potassium hydroxide, sodium chloride, sodium perchlorate, sodium nitrate, sodium sulfate, sodium selenate, sodium carbonate, and sodium phosphate (ACS reagent,98.0 %) were purchased from Sigma- Aldrich, Australia. Nafion perfluorinated resin solution (10 wt.%) were purchased from Fuelcell Store, USA.

[0090] Synthesis of NiFe LDH intercalated with A anion (NiFe LDH-[A ])

[0091] For the synthesis of initial AP NiFe LDH, a 10 mL aqueous solution containing 75 mM NiCL 6H2O (0.1783 g) and 25 mM FeCE 6H2O (0.06757 g) was added dropwise to 20 mL formamide solution (23 vol.%) under magnetic stirring at 80 °C. The solution pH was simultaneously maintained at 9—10 with dropwise adding 0.25 M NaOH. The reaction was completed within 10 minutes. After cooling to room temperature, the product was washed for several times using ethanol and deionized water, then kept in a wet state, and noted as ‘AP NiFe LDH’. For the synthesis of synthesis of NiFe LDH-[A], about 5 mg of AP NiFe LDH was added into a 5 mL aqueous solution containing 1 M NaOH and 0.1 M sodium salt, such as NaCl, NaC104, NaNO Na2SeO4, Na2SO4, NaiCO’,. or NasPCL, respectively. The obtained slurries were firstly sonicated for 1 hour and magnetically stirred for another 12 hours at room temperature. Note that the “0.25 M NaOH” and the “I M NaOH + 0. 1 M sodium salt” solutions were freshly prepared just before using to avoid the reaction between CO2 in air and the generation of COs2-. For example, the NiFe LDH-[A]s prepared include [Ni3 / 4Fei / 4(OH)2](Cl )i / 4, [Ni3 / 4Fei / 4(OH)2](ClO4-)i / 4, [Ni3 / 4Fei / 4(OH)2](NO3-)i / 4, [Ni3 / 4Fei / 4(OH)2](SeO42’)i / 8, [Ni3 / 4Fei / 4(OH)2](SO42’)i / 8, [Ni3 / 4Fei / 4(OH)2](CO32-)i / 8 and [Ni3 / 4Fei / 4(OH)2](PO43)i / i2.

[0092] Characterisation

[0093] X-ray diffraction (XRD) spectra were collected on a Rigaku MiniFlex 600 X-Ray diffractometer using Cu Ka X-ray source. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and the corresponding energy dispersive X-ray spectroscopy (EDS) elemental maps were obtained via a FEI Titan Themis 80-200 operating at 200 kV. Inductively coupled plasma-mass spectrometry (ICP-MS) detected by an Agilent 7500cx instrument was used to analyse the dissolved ions concentration in an electrolyte. X-ray photoelectron spectroscopy (XPS) analysis was performed on a Kratos Axis Ultra with a Delay Line Detector photoelectron spectrometer using an Al monochromatic X-ray source. The C Is peak at 284.8 eV was used as a reference to correct for charging effect. Synchrotron-based X-ray absorption spectroscopy (XAS) spectra were collected on the X-rayspectroscopy beamline at the Australian Synchrotron.

[0094] The layer distances (d) of AP NiFe LDH and NiFe LDH-[A] were calculated according to Bragg's law n- = 2t / -sin , where n is the diffraction order, n = 1; z is the X-ray wavelength, z = 1.5406 A; 0 is the glancing angle, obtained according to the X-ray diffraction (XRD) spectra of samples (Figure 2b).

[0095] The integration area of reduction peak in stabilized CV curve of NiFe LDH-[A] (noted as P[A]) can be related to the amount of involved Ni sites for OER1 2. Assuming that the involved Ni sites for OER in a NiFe LDH-[C1 ] sample exactly covers a geometrical area of 1 cm2. Then the relative electrochemical active surface area (ECSA) of the other NiFe LDH-[A] sample could be determined as P[A] / P[C1’]. As reported, the ECSA normalized OER activities of samples using both the reduction peak integration method and the double-layer capacitance (Cai) method present consistent trends1, 3.

[0096] Electrochemical measurements

[0097] Electrochemical measurements shown in Figure 2d was performed using a rotating disk electrode (RDE) in alkaline saline (1 M KOH + 0.5 M NaCl). NiFe LDH-[A] inks were prepared via 2 mg catalyst, 20 pL 10 wt. % Nafion perfluorinated resin solution, and 1980 pL ethanol mixed and sonicated for 90 minutes. 10 pL ink was dropped onto RDE for each test. Catalysts were firstly activated by 20 cycles of CV at a scanning rate of 0.1 V s’1, and then LSV curves were collected at a scanning rate of 0. 1 V s’1. The independent measurement was repeatedly performed at least three times for each catalyst. Electrochemical measurements shown in Figure 2e was performed using a typical three -electrode setup with alkaline saline as electrolyte. 50 pL NiFe LDH-[A] ink was dropped onto a Ti-foil (1 x 0.5 cm2) as work electrode. The corrosion polarized curve was firstly obtained at a scanning rate of 5 mV s’1, and then transferred to Tafel plots by taking the logarithm of current density. Note that the alkaline saline electrolyte used for each measurement was freshly prepared and sealed in a glass bottle protected with argon (Ar) gas during the whole measurement process to avoid the reaction between CO2 in air and the generation of CO,2. Potentials for all three -electrode measurements were referenced to the reversible hydrogen electrode (RHE), calculated by adding, 0. 197 + 0.059 x pH V to the potential vs. Hg / HgO electrode. Potentials were displayed without / ^-compensation.

[0098] Electrochemical measurements shown in Figures Id, 3a, and 3b were performed in a two- electrode setup using alkaline seawater (I M KOH + seawater) as electrolyte. The raw seawater collected from Glenelg beach, Adelaide, Australia was fdtered in advance to remove solid impurities and microorganisms. Commercial NiMo alloy foam was used as cathode. AP NiFe LDH and NiFe LDH [PO43] -based anodes were prepared by spraying the catalyst inks onto commercial Ni foams (1 x 1 cm2). The loadings of catalysts were weighted as about 2.5 mg cm’2. The anolytes were collected after each CPtest for produced hypochlorite and dissolved ions tests. Voltages were displayed with / ^-compensation.

[0099] Measurements on alkaline seawater electrolyzers (ASWEs)

[0100] The 2 W-scale ASWE was a single-cell configuration with a reactive area of 1 cm2. The industrial 1 kW-scale ASWE was a multi -cell configuration assembled with 17 stacked cells, and the total anode or cathode area was 1,081.2 cm2. Commercial woven polymer film and Raney Ni was used as diaphragm and cathode, respectively. All the performances of ASWEs were determined using 6 M KOH + seawater as initial electrolyte and precipitation-treated seawater as feedstock. The raw seawater collected from Bohai Sea, China was filtered in advance to remove solid impurities and microorganisms. Voltages were displayed without / ^-compensation.

[0101] N, N’-diethyl-p-phenylenediamine (DPD) colorimetric method

[0102] After each CP test, 10 mb electrolyte was collected and adjusted to pH ~ 7 using H2SO4. A DPD kit, including 0.05 g of DPD, 0.05 g of ethylene diamine tetra-acetic acid (EDTA), and 0.4 g of Na2HPC>4 (buffer), was then added into the anolyte. The solution was shaken fiercely to dissolve the DPD and was tested using the portable ultraviolet-visible (UV-Vis) spectrophotometer (HACH, DR900). The CIO’ amount in electrolyte was calculated based on the calibration results shown in Figure 8.

[0103] Ir(),-modified rotating ring-disk electrode (RRDE) technique

[0104] The pH evolution upon the surface of disk electrode surface can be established by monitoring the open circuit potential (OCP) changes of IrOx-modified ring electrode4. IrOxwas firstly electrodeposited onto Pt-ring electrode of RRDE by CV cycling (-0.45 - 0.75 V vs. Ag / AgCl, 1.0 V s’1, 300 cycles starting in the negative direction, Figure 20). Electrolyte for the electrodeposition was prepared as reported4, and was saturated using Ar gas before and during the electrodeposition. Then, the OCP (Eoc) of the IrOx-modified ring electrode was recorded in 0.5 M NaCl electrolyte at different pH (Figure 21), which was adjusted by gradually adding NaOH or H2SO4. The pH dependence relationship of the Eoc was established by linear fitting (Figure 21). The pHring were obtained by converting Eoc following equation (1): pHring = -(Eoc - b) / a, where a and b are the slope and intercept values of the fitted line, respectively.

[0105] The pH evolution upon catalyst surface during OER was measured in Ar-saturated alkaline saline. 10 pL of the abovementioned NiFe LDH-[A] ink was dropped onto the disk electrode. LSV was performed on the disk electrode at a scanning rate of 1 mV s’1, and simultaneously Eoc of the IrOx- modified ring electrode was recorded. The pHring of the IrOx-modified ring was calculated from the Eoc using equation (1). Then the pHdisk of the catalyst-loaded disk electrode was calculated based on the pHring following equation (2): Cn+.rmg ~ C OH- ring — Nn CH+,disk ~ Con-disk) + (1—No)(CH+,bulk ~ CoH-bulk), wlldCCm,nis the concentration of species m on the ring or disk electrode, or in the bulk electrolyte, respectively; ND is defined as detection efficiency and was calculated as 0.37.

[0106] Operando Raman measurements

[0107] Raman spectra were determined using a confocal Raman microscope (Horiba LabRAM HR Evolution) with a 100X objective (Olympus) equipped with an excitation of 532 nm laser. Operando measurements were conducted in a homemade three -electrode cell, assembled with a catalyst-loaded carbon paper work electrode, a graphite rod counter electrode, an Ag / AgCl (saturated KC1) reference electrode, and freshly prepared alkaline saline electrolyte.

[0108] Operando attenuated total reflectance-infrared absorption spectroscopy (ATR-IRAS)

[0109] Operando ATR-IRAS measurements were determined on a Thermo-Fisher Nicolet iS20 equipped with liquid nitrogen-cooled HgCdTe (MCT) detector and VeeMax III ATR accessory (Pike Technologies). A germanium (Ge) prism coated with catalyst as working electrode was fixed in a commercial PIKE three-electrode cell with an Ag / AgCl (saturated KC1) reference electrode, a Pt-wire counter electrode, and freshly prepared alkaline saline electrolyte. All IR spectroscopies were obtained via averaging 32 scans at a spectral resolution of 4 cm1.

[0110] Results

[0111] Engineered NiFe LDH with intercalated anions

[0112] The pristine hexagonal nanosheet-like NiFe LDH (noted as AP NiFe LDH) with a diameter less than 20 nm was synthesised by coprecipitation (Figures 2a, 2b, and 10). Afterwards, seven types of engineered NiFe LDH (noted as NiFe LDH-[A]) were obtained by exchanging a series of anions, including chloride (Cl ), perchlorate (CIO4 ), nitrate (NO3 ), selenate (SeO ), sulfate (SO42), carbonate (CO32), and phosphate (PO43) (Figures 2a, 2b, and 11) which include, for example, [Ni3 / 4Fei / 4(OH)2](Cl_)i / 4, [Ni3 / 4Fei / 4(OH)2](ClO4-)i / 4, [Ni3 / 4Fei / 4(OH)2](NO3-)i / 4, [Ni3 / 4Fei / 4(OH)2](SeO42’)i / s, [Ni3 / 4Fei / 4(OH)2](SO42)i / 8, [Ni3 / 4Fei / 4(OH)2](CO32)i / 8 and [Ni3 / 4Fei / 4(OH)2](PO43)i / i2. X-ray diffraction (XRD) spectra indicate that the alteration of anions does not affect the structure of NiFe LDH, while a slight increase in the (003) peaks suggests a reduction in layer distance induced by the successful intercalating of anions20, 21(Figure 2b). In addition, minimal changes in the coordination environments of Ni but significant alterations in those of Fe provide evidence of selective anions bonding with Fe sites rather than Ni sites (Figure 2c).

[0113] The OER activity and corrosion resistance of NiFe LDH-[A] were initially assessed in alkalinesaline (I M KOH + 0.5 M NaCl). As shown in Figure 2d, while the onset potentials of NiFe LDH-[A] remained unaffected by the incorporation of various anions, their electrochemical active surface area (EC'S A (-normalized OER activities displayed noticeable differences with increasing potential. Similarly, Figure 2e illustrates the variation in the corrosion resistance of NiFe LDH-[A] with different intercalated anions. Collectively, positive correlations were established between the OER activity and corrosion resistance of NiFe LDH-[A] and the basicity, described by pKavalues22, 23, of intercalated anions (Figures 2f and 2g, Table 1). This indicates the OER activity and corrosion resistance of NiFe LDH-[A] improve with the incorporation of more basic anions. In addition, the dependence of the performance enhancement on the structural parameters of anions, such as ionic radii and oxygen atom number, was excluded (Figure 12). The nature of pKainspires us that these positive correlations are related to the distinct interaction of anions with protons / metal cations. For example, NiFe LDH-fPO ] with the most basic anion intercalation was chosen to ensure stable operation of ASWE under large-current conditions.Table 1 pKavalues of anions’ conjugate acids

[0114] Performance of NiFe LDH-[A ] in ASWE

[0115] The comparison of AP NiFe LDH and NiFe LDH-[PO43]-based anodes in alkaline seawater electrolysis were initially evaluated using a two-electrode H-cell setup. As shown in Figures 3a and 3b, NiFe LDH-| PO / I -based anode displayed a significant improvement in both OER activity and corrosion resistance; it operated more stably across various current densities ranging from 0.1 A cm'2to 1.5 A cm'2. Though the AP NiFe LDH-based anode exhibited good resistance to CF and stability at current densities lower than 0.5 A cm'2, it experienced severe electrode corrosion and C1ER when the current density increases to higher current densities (Figures 3a and 13). This evolution also indicates a more severe CF attack on the electrodes at higher current density. In contrast, NiFe LDH-fPO ] -based anode exhibited mild C1ER and lower dissolved Ni / Fe concentrations at current densities from 0.1 A cm'2to 1.5 A cm'2(Figures 3b and 13). These findings demonstrate the notable CF resistance and stability achieved by phosphates incorporation. Furthermore, the minimal phosphate and Fe leaching observed throughout the tests suggest the strong bonding force of phosphates with Fe sites (Figure 3b), which contributes to theoverall stability of whole structure24.

[0116] To verify its scale-up potential, the NiFe LDH-fPO ] -based anode was assembled into a 2 W- scale alkaline electrolyzer with a commercial Raney Ni-based cathode and operated under industrial conditions (Figure 3c). The target ASWE achieved a high current density of 1.0 A cm'2at a low cell voltage of about 2.0 V, which presented a significant advantage compared to commercial Raney Ni- and AP NiFe LDH-based ASWEs (Figure 3d). Notably, the NiFe LDH-fPO ] -based ASWE worked stably at 1.0 A cm'2for over 1,000 hours (Figure 3e). This remarkable durability surpasses that of several reported anodes utilized in alkaline seawater electrolysis. These anodes were evaluated across various electrode configurations, including three-electrode, two -electrode, and electrolyzer systems, and typically operated below 0.4 A cm'2and / or 400 hours (Figure 3f, Table 2).Table 2 Comparison of performance for reported electrocatalysts in alkaline simulated / natural seawater.

[0117] Correlation between NiFe LDH performances and anion basicity

[0118] The intrinsic effects of anion basicity on the OER activity and corrosion resistance performances of NiFe LDH were then investigated to understand the boosted performances of NiFe LDH- [A] in seawater electrolysis. Initially, the electron density was found to increase on Ni / O sites but no change on Fe sites with the incorporation of higher basic anions (Figures 4a, 4b, and 14-16). This observation aligns with the inhibited Ni oxidation and the delayed transition from c / .-Ni(OH)2 to y-NiOOH in operando Raman tests (Figures 4c, 17, and 18). These results confirm the electron-donating nature of basic anions in NiFe LDH-[A], As a result, the electron-withdrawing effect of Fe on the electrons of Ni / O was mitigated through the Ni-O-Fe^A bond20. Importantly, this heightened electron-donating effect leads to a stronger interaction between basic anion (e.g., phosphate) and Fe sites, which contributes to the enhanced stability of NiFe LDH-fPO ’]. The resultant inhibited Fe leaching was evidenced by the delayed diminishing of y-FcOOH within NiFe LDH-| PO4| compared to that within NiFe LDH-[C1 ] (Figure 4c).

[0119] In addition to anchoring metal cations, the electron -donating nature of basic anions enables their interaction with protons to influence proton transfer during OER. Specifically, the absolute intensity of O-H stretching mode (VO-H) of water upon NiFe LDH-| PO4| electrode decreased gradually with increasing potential (Figure 4d). This suggests that the NiFe LDH-fPO ’] electrode strongly interacts with the surface water as the polarized potential increases25. This enhanced interaction facilitates water supply and enhances proton transfer efficiency26. Moreover, no detectable shift in the VO-H position and configuration of the interfacial water was observed upon the NiFe LDH-fPO ’] electrode (Figures 4d and 19). This lack of shift indicates consistent components, such as OH’ concentration, in the EDL upon the NiFe LDH-| PO4| electrode25. In contrast, the VO-H position generally showed a red-shift with the increasing ratio of strongly bonded water upon the NiFe LDH-[C1 ] electrode (Figures 4d and 19). This indicates a strengthened hydrogen-bond network with increasing potential27, which hinders water supply and efficient proton transfer in the EDL. The change in OH’ concentration in the EDL upon electrodesurface were then quantitatively assessed using the IrOx-modified rotating ring-disk electrode (RRDE) technique28. Notably, the pH in the EDL, referred to as pHdisk, upon the NiFe LDH-fPCE3] electrode was found to remain elevated compared to that upon NiFe LDH-[C1 ] electrode during OER (Figures 4e, 20, and 21). This result provides evidence of the consistent components upon the NiFe LDH-fPO ’] electrode.

[0120] These spectroscopic and electrochemical observations directly reflect the effect of phosphates in facilitating proton transfer, and thereby a highly alkaline environment can be maintained in the EDL (Figures 4f). The presence of a higher concentration of OH’ leads to reduced Cl’ influx into the EDL according to the electroneutrality principle29, 30, resulting in less C1ER and better corrosion resistance (Figure 4f). On the other hand, adequate OH’ supply is crucial for maintaining stable OER activity when operating under high current density. In contrast, without basic anions steering, slow proton transfer presents challenge for adequate OH’ supplementation. As a result, Cl’ influxes with OH’ into the EDL to balance the positive surface charge, leading to severe electrode corrosion and C1ER (Figure 22).

[0121] Industrial-scale ASWE and TEA

[0122] The scale-up performance of NiFe LDH-fPO ’] -based anode was assessed in an industrial hydrogen production system (John Cockerill company), which includes a 1 kW-scale electrolyzer stack with 17 cells connected in series (Figures 5a and 5b). This is the state-of-the-art largest-scale device for alkaline seawater electrolysis reported in lab research. The electrode area for a single cell is about 63.6 cm2, while the total electrode area for the entire stack is about 1,081.2 cm2. Each cell primarily consists of a commercial Raney Ni- or NiFe LDH-based anode, a commercial Raney Ni-based cathode, a commercial woven polymer diaphragm, and other components (seal rings and electrode plates, etc.) (Figures 5b and 5c). The commercial Raney Ni-based AWE achieved a current density of 0.2 A cm’2at 2.0 V using pure 6 M KOH as electrolyte (Figure 5d). In contrast, our NiFe LDH-based ASWE, with 6 M KOH + raw seawater as electrolyte, achieved about 0.33 A cm’2and 0.5 A cm’2on AP NiFe LDH- and NiFe LDH-fPO ’] -based anodes, respectively (Figure 5d). Moreover, the NiFe LDH- [PO43] -based ASWE demonstrated higher energy efficiencies (AAs), calculated based on the higher heating value (HHV) of hydrogen36, across different current densities. It achieved 73.4 % AA at 0.5 A cm’2at about 2.0 V, which is nearly 20 % better than that of commercial Raney Ni-based AWE (Figure 5e). Notably, the target ASWE exhibited stable operation for over 100 hours at a high current density of 0.5 A cm’2(Figure 5f). During the duration test, about 2.24 Nm3, equivalent to 0.2 kg, of pure hydrogen was produced every 10 hours; about 8.6 g of KOH was consumed per kilogram seawater for Ca2+ / Mg2+precipitation treatment; seawater after precipitation and filtration treatments was used as feedstock. This achievement represents the first successful implementation of an industrial-scale seawater hydrogen production system under rigorous large-current conditions.

[0123] TEA was then conducted to preliminarily evaluate the economic feasibility of the ASWE based on the electrocatalyst disclosed herein. Considering a current electricity price of USS 0.05 kWh1and a 10-year plant lifetime, the HLPC for an AWE plant was calculated at US$ 5.28 kgm’1under cell conditions of 0.2 A cm'2and 2.0 V (Figure 5g). Replacing pure water with seawater directly reduced the HLPC for an ASWE plant by USS 0.49 kgm1(Figure 5g). Increasing the operating current density to 0.5 A cm'2decreased the HLPC by an additional USS 0.64 kg H21(Figure 5g). Utilizing offshore renewable electricity (i.e., USS 0.02 kWh1) and updating plant equipment (i.e., 30-year plant lifetime) could further decrease the HLPC to USS 1.96 kgH2-1(Figure 5g). This cost of green hydrogen is competitive compared to that of grey hydrogen and meets the 2030 global targets (e.g., USS 2.0-2.5 kgH2-1)37(Figure 5h). In contrast, the HLPC for an AWE plant would be challenged to meet these targets under the same conditions (Figure 23).

[0124] As shown in Figure 24, annual CAPEX showed a strong correlation with operating current density, as the total cell area and BOP required to achieve the target 1 MW net power fluctuated with different operating current densities. For example, operating the ASWE plant at 0.2 A cm'2instead of 0.5 A cm'2could lead to an increase in CAPEX by approximately USS 62,777, resulting in a HLPC of USS 4.79 kgH2-1(Figures 5g and 24). However, as the operating current density surpasses 0.5 A cm'2, the impact of CAPEX on HLPC diminishes (Figure 24). Further reduction of CAPEX and HLPC could be achieved through future engineering technology upgrades, such as extending the plant lifetime to 30 years (Figure 5g).

[0125] Moreover, potential concerns arising from the utilization of seawater were carefully considered. Firstly, the consumption of stack and auxiliary equipment is expected to increase due to inevitable corrosion induced by seawater, leading to higher OPEX. However, the HLPC appears to be less sensitive to these issues, including increased maintenance rate, labour cost, and decreased electrode lifetime (Figure 25, Table 3). Secondly, the KOH consumption will increase due to the deposition of calcium and magnesium ions present in seawater. Addressing these cations could result in an additional annual cost of ~ USS 35,732 for consuming at least 44.7 tons of KOH. However, it is worth noting that approximately 24.4 tons of hydroxides could be separated for potential profit, particularly considering that magnesium is a valuable resource that typically requires other technologies for extraction from seawater29. Thus, the cost of KOH consumption could be offset. In summary, while utilizing seawater may pose challenges, the overall benefits of achieving a lower HLPC outweigh these concerns. Particularly with the advancements in ASWE technology capable of stable operation under high current density, the long-term advantages of seawater utilization become more pronounced.Table 3 Range of parameter values for sensitivity analysis

[0126] Discussion

[0127] Enhanced OER activity and corrosion resistance were achieved with the NiFe LDH-based anode by intercalating basic anions (e.g., phosphates). Owing to their strong basicity, the phosphates effectively shielded NiFe LDH from CF attack and facilitated proton transfer for OER. The engineered NiFe LDH-based anode exhibited remarkable high-current stability in a 2 W-scale ASWE. The hydrogen production cost was determined as US$ 1.96 kgH2-1through a comprehensive TEA based on our 1 kW- scale ASWE system. The present disclosure provides a comprehensive exploration including mechanism, technology, and economics within the realm of alkaline seawater electrolysis for hydrogen production.

[0128] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0129] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0130] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

[0131] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, thesemultiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.REFERENCES

[0132] [1] International Energy Agency (IEA). Net zero by 2050: A roadmap for the global energy sector, https: / / www.iea.org / reports / net-zero-by2050 (2021).

[0133] [2] International Energy Agency (IEA). Global hydrogen review 2021. https: / / www.iea.org / reports / global-hydrogen-review2021 (2021).

[0134] [3] Qin, Z., et al. Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting. Energy Environ. Sci. 12, 572-581 (2019).

[0135] [4] Glenk, G. & Reichelstein, S. Economics of converting renewable power to hydrogen. Nat.Energy 4, 216-222 (2019).

[0136] [5] Bartels, JR., Pate, MB. & Olson, NK. An economic survey of hydrogen production from conventional and alternative energy sources. Int. J. Hydrogen Energ. 35, 8371-8384 (2010).

[0137] [6] Liang, J., et al. Efficient bubble / precipitate trafficenables stable seawater reduction electrocatalysis at industrial -level current densities. Nat. Commun. 15, 2950 (2024).

[0138] [7] Jin, H., et al. Emerging materials and technologies for electrocatalytic seawater splitting.Sci. Adv. 9, eadi7755 (2023).

[0139] [8] Hausmann, JN., et al. Is direct seawater splitting economically meaningful? Energy Environ.Sci. 14, 3679-3685 (2021).

[0140] [9] Zhang, S., et al. Concerning the stability of seawater electrolysis: A corrosion mechanism study of halide on Ni-based anode. Nat. Commun. 14, 4822 (2023).

[0141]

[0010] Tong, W., et al. Electrolysis of low-grade and saline surface water. Nat. Energy 5, 367-377(2020).

[0142]

[0011] Yu, L., et al. Non-noble metal-nitride based electrocatalysts for high-performance alkaline seawater electrolysis. Nat. Commun. 10, 5106 (2019).

[0143]

[0012] Xu, W., et al. Ag nanoparticle-induced surface chloride immobilization strategy enables stable seawater electrolysis. Adv. Mater. 36, e2306062 (2024).

[0144]

[0013] Wu, L., et al. Heterogeneous bimetallic phosphide Ni2P - Fe2? as an efficient bifunctional catalyst for water / seawater splitting. Adv. Funct. Mater. 31, 2006484 (2020).

[0145]

[0014] Kuang, Y ., et al. Solar-driven, highly sustained splitting of seawater into hydrogen and oxygen fuels. Proc. Natl. Acad. Sci. U. S. A. 116, 6624-6629 (2019).

[0146]

[0015] Yu, L., et al. Ultrafast room-temperature synthesis of porous S-doped Ni / Fe(oxy)hydroxide electrodes for oxygen evolution catalysis in seawater splitting. Energy Environ. Sci. 13, 3439-3446 (2020).

[0147]

[0016] Liu, W., et al. Ferricyanide armed anodes enable stable water oxidation in saturated saline water at 2 A / cm2. Angew. Chem. Int. Ed. 62, e202309882 (2023).

[0148]

[0017] Kang, X., et al. A corrosion-resistant RuMoNi catalyst for efficient and long-lasting seawater oxidation and anion exchange membrane electrolyzer. Nat. Commun. 14, 3607 (2023).

[0149]

[0018] Duan, X., et al. Dynamic chloride ion adsorption on single iridium atom boosts seawater oxidation catalysis. Nat. Commun. 15, 1973 (2024).

[0150]

[0019] Liu, H., et al. High-performance alkaline seawater electrolysis with anomalous chloride promoted oxygen evolution reaction. Angew. Chem. Int. Ed. 62, e202311674 (2023).

[0151]

[0020] Yuan, S., et al. Tunable metal hydroxide -organic frameworks for catalysing oxygen evolution. Nat. Mater. 21, 673-680 (2022).

[0152]

[0021] Dionigi, F., et al. In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution. Nat. Commun. 11, 2522 (2020).

[0153]

[0022] Lide, D. R., et al. CRC Handbook of Chemistry and Physics (CRC Press, 2005).

[0154]

[0023] Dean, J. A. Lange ’s Handbook of Chemistry (McGraw-Hill, 1999).

[0155]

[0024] Liao, H., et al. Oxyanion engineering suppressed iron segregation in nickel-iron catalysts toward stable water oxidation. Adv. Mater. 35, e2300347 (2023).

[0156]

[0025] Yang, X., et al. Understanding the pH dependence of underpotential deposited hydrogen on platinum. Angew. Chem. Int. Ed. 58, 17718-17723 (2019).

[0157]

[0026] Hou, L., et al. Grain boundary tailors the local chemical environment on iridium surfacefor alkaline electrocatalytic hydrogen evolution. Angew. Chem. Int. Ed. 63, e202315633 (2023).

[0158]

[0027] Wang, Y.H., et al. In situ Raman spectroscopy reveals the structure and dissociation of interfacial water. Nature 600, 81-85 (2021).

[0159]

[0028] Yokoyama, Y ., et al. In situ local pH measurements with hydrated iridium oxide ring electrodes in neutral pH aqueous solutions. Chem. Lett. 49, 195-198 (2020).

[0160]

[0029] Guo, J., et al. Direct seawater electrolysis by adjusting the local reaction environment of a catalyst. Nat. Energy 8, 264-272 (2023).

[0161]

[0030] Chen, C., et al. Local reaction environment in electrocatalysis. Chem. Soc. Rev. 53, 2022-2055 (2024).

[0162]

[0031] Zhai, P., et al. Regulating electronic states of nitride / hydroxide to accelerate kinetics for oxygen evolution at large current density. Nat. Commun. 14, 1873 (2023).

[0163]

[0032] Louie, MW. & Bell, AT. An investigation of thin-fdm Ni-Fe oxide catalysts for the electrochemical evolution of oxygen. J. Am. Chem. Soc. 135, 12329-12337 (2013).

[0164]

[0033] Lee, S., et al. Oxygen isotope labeling experiments reveal different reaction sites for the oxygen evolution reaction on nickel and nickel iron oxides. Angew. Chem. Int. Ed. 58, 10295-10299 (2019).

[0165]

[0034] Sun, K., et al. Interfacial water engineering boosts neutral water reduction. Nat. Commun.13, 6260 (2022).

[0166]

[0035] Xu, J., et al. IrCk ntLO with lattice water-assisted oxygen exchange for high-performance proton exchange membrane water electrolyzers. Sci. Adv. 9, eadhl718 (2023).

[0167]

[0036] Lamy, C. & Millet, P. A critical review on the definitions used to calculate the energy efficiency coefficients of water electrolysis cells working under near ambient temperature conditions. J. of Power Sources 447, 227350 (2020).

[0168]

[0037] International Renewable Energy Agency (IRENA). Green hydrogen cost reduction: scaling up electrolyzers to meet the 1.5 °C climate goal. Abu Dhabi (2020).

Claims

CLAIMS1. An electrocatalyst comprising a layered double hydroxide, wherein the layered double hydroxide comprises intercalated charge -balancing anions and at least some of the charge -balancing anions are basic anions.

2. The electrocatalyst according to claim 1, wherein the basic anions are not initially present within the layered double hydroxide and are introduced to the layered double hydroxide to replace at least some of the intercalated charge -balancing anions initially present within the layered double hydroxide.

3. The electrocatalyst according to either claim 1 or claim 2, wherein the basic anions are introduced to the layered double hydroxide by ion exchange with at least some of the intercalated charge - balancing anions initially present within the layered double hydroxide.

4. The electrocatalyst according to any one of claims 1 to 3, wherein the basic anions are one or more selected from PO43, CO32, SO42', SeO42; VO43, HBO32, and BO33.

5. The electrocatalyst according to any one of claims 1 to 4, wherein the conjugate acids of the basic anions have a p Ta> about 10.0, for example > about 10.3, > about 12.0.

6. The electrocatalyst according to any one of claims 1 to 5, wherein the electrocatalyst is for use in water electrolysis, for example seawater electrolysis.

7. The electrocatalyst according to any one of claims 1 to 6, wherein the electrocatalyst is for use in seawater electrolysis under a high current density of > about 0.4 A cm'2, for example, > about 0.5 A cm'2, > about 0.8 A cm'2, > about 1.0 A cm'2, or even > about 1.5 A cm'2.

8. The electrocatalyst according to any one of claims 1 to 7, wherein the layered double hydroxide with or without the basic anions being introduced is substantially crystalline or amorphous.

9. The electrocatalyst according to any one of claims 1 to 8, wherein the layered double hydroxide comprises a divalent metal ion and a tri valent metal ion.

10. The electrocatalyst according to claim 9, wherein the divalent metal ion is selected from Ni and Co.

11. The electrocatalyst according to either claim 9 or claim 10, wherein the trivalent metal ion is selected from Fe, Co, Al, Mn, and Cr.

12. The electrocatalyst according to any one of claims 9 to 11, wherein the molar ratio between the divalent metal ion and the trivalent metal ion is about 4: 1 to about 1.6: 1, for example about 3: 1, about 2.5 : 1 or about 2: 1.

13. The electrocatalyst according to any one of claims 1 to 12, wherein the layered double hydroxide without the basic anions being introduced comprises or consists of a chloride form of Ni-Fe layered double hydroxide.

14. The electrocatalyst according to any one of claims 1 to 13, wherein the electrocatalyst has a composition formula of [Ni3 / 4Fei / 4(OH)2](PO43)i / i2-nH2O or [Ni3 / 4Fei / 4(OH)2](PC>43)i / i2.

15. Use of the electrocatalyst according to any one of claims 1 to 14 in seawater electrolysis.

16. An electrode of an electrochemical device, which comprises the electrocatalyst according to any one of claims 1 to 14.

17. An electrochemical device comprising the electrocatalyst according to any one of claims 1 to 14.

18. A method of manufacturing the electrocatalyst according to any one of claims 1 to 14, which comprises obtaining the layered double hydroxide and introducing the basic anions to the layered double hydroxide through anion exchange.

19. The method according to claim 18, wherein the layered double hydroxide is obtained through coprecipitation.

20. A method for conducting water electrolysis, which comprises using the electrocatalyst according to any one of claims 1 to 14 for oxygen evolution reaction.

Images