WO2023017495A1

WO2023017495A1 - A method of generating oxygen by electrochemical water splitting at optimized conditions of ph, temperature, and pressure

Info

Publication number: WO2023017495A1
Application number: PCT/IB2022/057592
Authority: WO
Inventors: Ananth Govind Rajan; John Mark P Martirez; Emily A Carter
Original assignee: Indian Institute of Science IISC; Princeton University
Current assignee: Indian Institute of Science IISC; Princeton University
Priority date: 2021-08-13
Filing date: 2022-08-13
Publication date: 2023-02-16
Anticipated expiration: 2024-02-13

Abstract

The present disclosure relates to an efficient method of water splitting for large/industrial scale production of oxygen at the anode in an electrolyzer, while at the same time permitting hydrogen production at the cathode of the same electrolyzer. More particularly, the present disclosure provides optimal operating conditions such as temperature, pressure, and pH for a range of potentials for an electrochemical water splitting reactor to generate the maximum amount of oxygen at a given voltage while supplying the minimum possible amount of alkali.

Description

“A METHOD OF GENERATING OXYGEN BY ELECTROCHEMICAL WATER SPLITTING AT OPTIMIZED CONDITIONS OF pH, TEMPERATURE, AND PRESSURE” STATEMENT REGARDING FEDERALLY SPONSPORED RESEARCH FOR DEVELOPMENT The present invention was made with US government support under Grant No. FA9550-14-1- 0254 awarded by the Air Force Office of Scientific Research. The US government has certain rights in the invention. TECHNICAL FIELD The present disclosure relates to the field of electrolysis and electrochemical water splitting into oxygen and hydrogen. In particular, the present disclosure relates to an efficient method of water splitting for large/industrial scale production of oxygen at the anode in an electrolyzer, while simultaneously permitting the large/industrial scale production of hydrogen at the cathode. More particularly, the present disclosure provides optimal operating conditions such as temperature, pressure, and pH for an electrochemical water splitting reactor to generate the maximum amount of oxygen at a given applied potential. BACKGROUND OF THE DISCLOSURE Oxygen (O₂) is a major component of the Earth’s atmosphere and is also one of the most abundant elements on Earth. Oxygen, apart from keeping us alive, has a variety of applications. In particular, the relatively pure form of oxygen (liquid or compressed) has numerous industrial and medical applications. For instance, pure oxygen finds application in steel manufacturing, the paper-pulp industry, metal production and fabrication, glass manufacturing, the petrochemical industry, as the breathing gas in space suits, etc. Furthermore, oxygen has several use cases in healthcare, including in hospitals, outpatient treatment centers, and people’s homes. Indeed, supplemental oxygen supply at home and in hospitals is critical for the survival of people suffering from breathing disorders such as emphysema, bronchitis, chronic obstructive pulmonary disease, etc. The primary method for the industrial production of oxygen is the fractional distillation of liquefied air. In recent years, however, another alternative has emerged – the electrolysis of water into molecular oxygen and hydrogen. The electrolysis of water is considered an environmentally friendly method to produce oxygen and hydrogen gases. Electrolysis involves the passage of electric current through two electrodes – known as the anode and the cathode – connected via an electric circuit, resulting in various chemical reactions involving constituents of the electrolyte solution. In water electrolysis, the electrolyte is an aqueous solution containing an acid or an alkali. Further, the electrodes are made using carefully chosen materials, with different types of materials considered for the anode and the cathode. The reactions taking place at the anode and the cathode are, respectively, the oxidation and reduction of various aqueous species within the electrolyte. Upon the application of a potential difference across the electrodes, the negatively charged hydroxide ions (OH⁻) migrate to the positively charged anode where water/OH- oxidation, i.e., the oxygen evolution reaction (OER) takes place and oxygen gas (O₂) evolves. Simultaneously, the positively charged protons (H⁺) diffuse to the negatively charged cathode where water/proton reduction, i.e., the hydrogen evolution reaction (HER) takes place and hydrogen gas ( H₂) evolves. The overall reaction during water electrolysis is: H₂O→H₂(g)+½O₂(g). The electrode potential, solution pH, temperature, and pressure are key operating conditions for any (photo)electrochemical water splitting reactor, as depicted in Figure 1A. Several studies have investigated the influence of the electrode potential and solution pH on OER kinetics. The temperature-dependent oxygen evolution activity of various electrocatalysts also has been investigated experimentally. Fewer experimental studies have dealt with the pressure- dependence of OER kinetics. One study investigated the oxygen partial pressure’s role in modulating the oxygen vacancy concentration in NdNiO₃, and thereby the OER activity. A second one studied the effect of pressure on the OER mechanism. Others have focused on the combined effect of temperature and pressure on water electrolysis. However, most of the studies of the thermodynamics and kinetics of the OER only consider conditions of room temperature (25°C) and pressure (1.013 bar) and there are no studies/research or experimentations examining the pressure-dependence of OER thermodynamics and kinetics under optimized reactor operating conditions which would result in improving the commercial water splitting reaction conditions. Thus, there is a need to understand the gaps pertaining to the direct effect of temperature and pressure on OER thermodynamics and kinetics and deployment of such understanding of the operating conditions to commercial water splitting reactions. Further, commercial water splitting electrolyzers need to operate at elevated temperatures (~90 °C) and pressure (~100 bar) to achieve faster kinetics and produce oxygen and hydrogen in commercially viable quantities. Between the two-half reactions, i.e., the OER and HER constituting electrochemical water splitting, the OER is significantly more sluggish and presents a thermodynamic and kinetic bottleneck to the electrolysis of water. Since the OER is favoured under alkaline operating conditions, researchers have examined the possibility of alkaline water electrolysis using aqueous solutions of potassium hydroxide (KOH) and sodium hydroxide (NaOH) as the electrolyte. However, achieving high current densities of > 1000 mA/cm² in an environmentally friendly and cost-effective manner is one of the key challenges that needs to be surmounted before such a technology can be commercialized. To increase the current density in the water electrolysis process, one needs to optimise the key operating conditions used in the electrochemical water splitting reactor, i.e., the pH, temperature, pressure, and potential. This objective needs to be met while at the same time reducing the concentration of the alkali used in the electrolyte, so as to make the process more environmentally friendly, less corrosive to the reactor, and more economically viable via the use of smaller quantities of alkali. The present disclosure tries to address these needs outlined above. SUMMARY OF THE DISCLOSURE The present disclosure provides an efficient, eco-friendly, and cost-effective method for the production of pure oxygen and hydrogen by electrochemical water splitting in an electrolyzer. In particular, the present disclosure provides optimized operating conditions of an electrochemical water oxidation reaction such as optimal temperature, pressure, and pH (i.e., alkali content), at a given voltage to drive the oxygen evolution reaction (OER) in the presence of a metal-doped oxide, hydroxide, or oxyhydroxide catalyst (or electrocatalyst) for the production of oxygen at the anode. Additionally, the present disclosure provides optimized operating conditions of an electrochemical water oxidation reaction, such as optimal temperature, pressure, pH, and potential, that result in a significant reduction in the required alkali concentration in the aqueous solution and improvement in the OER current density. In particular, the method of the present disclosure optimizes the pH of the electrolyte as a function of temperature and pressure, while consequently resulting in a significant reduction in the concentration of the alkali required in the electrolyte solution. Accordingly, the present disclosure provides a method of generating oxygen by electrochemical water splitting at optimized conditions of pH, temperature, and pressure for an oxygen evolution reaction (OER) current density ranging from about 10 mA/cm² to about 10000 mA/cm², said method comprising: a) contacting an anode of an electrolyzer with an electrolyte comprising water and alkali, in the presence of a metal-doped oxide, hydroxide, or oxyhydroxide catalyst; and b) applying a potential ranging from about 1.45 V to about 1.75 V versus (vs.) the reversible hydrogen electrode (RHE) at the anode to allow said generation of the oxygen; wherein pH of the electrolyte ranges from about 7.4 to about 10.9; wherein the pH is a function of temperature T at a given pressure P; and wherein the temperature T ranges from about 28 °C to 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the pH of the electrolyte is determined based on an unconstrained minimization function applied to the negative of an oxygen evolution reaction (OER) current density (equivalent to the maximization of the OER current density), and wherein the OER current density is a function of the applied potential. In some embodiments of the present disclosure, the pH of the electrolyte is maintained in a manner that allows concentration of OH- ions in the electrolyte to be less than 1 M. In some embodiments of the present disclosure, the OER current density is improved by at least twofold when compared to any method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28°C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density is improved by up to 1000-fold when compared to a method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode,

stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28 °C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density improves by at least about 80% when the method is carried out at said optimized conditions of pH, temperature and pressure for the potential range as described herein. In some embodiments of the present disclosure, the OER current density improves by up to 200% when the method is carried out at said optimized conditions of pH, temperature and pressure for the potential range as described herein. In some embodiments of the present disclosure, the potential is about 1.5 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 7.4 to about 10.7, and the temperature T ranges from about 28 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.5 to about 10.9, and the temperature T ranges from about 28 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.7 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 10.2 to about 10.9, and the temperature T ranges from about 28 °C to about 41 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, for maintaining the pH range of about 7.4 to about 10.9 of the present disclosure, the concentration or amount of the required alkali in the electrolyte range from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween. In some embodiments of the present disclosure, the alkali is selected from a group comprising potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide (Mg(OH)₂), or any other alkali or alkaline earth hydroxide. In some embodiments of the present disclosure, the pH reduces from about 10.7 to about 7.4 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.5 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.38 mM to about 0.07 mM at the given pressure P. In some embodiments of the present disclosure, the pH reduces from about 10.9 to about 8.5 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.6 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.14 mM at the given pressure P. In some embodiments of the present disclosure, the pH reduces from about 10.9 to about 10.2 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.7 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.47 mM at the given pressure P. In some embodiments of the present disclosure, the metal-doped oxide, hydroxide, or oxyhydroxide catalyst is an iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst, which is also referred to as a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material. In some embodiments of the present disclosure, the potential applied across the electrolyzer ranges from about 1.45 V to about 1.75 V, including all values and ranges therebetween. In some embodiments of the present disclosure, the electrolyzer further comprises a cathode within the electrolyte, and wherein application of a potential across the electrolyzer generates oxygen at the anode and hydrogen at the cathode.

In some embodiments of the present disclosure, the method comprises an electrolyte comprising water and KOH or NaOH having a concentration of about 0.15 mM, and wherein the catalyst is a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.51 V versus the reversible hydrogen electrode (RHE), the temperature is about 90 ºC, the pressure is about 1 bar, the pH of the electrolyte is maintained at 8.6, and the OER current density is about 997 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.15 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, the pH of the electrolyte is maintained at 8.6, and the OER current density is about 770 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and alkali (KOH or NaOH) having a concentration of about 0.26 mM, the catalyst is a of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 100 ºC, the pressure is about 100 bar, the pH of the electrolyte is maintained at 8.6, and the OER current density is about 1241 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.27 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 110 ºC, the pressure is about 200 bar, the pH of the electrolyte is maintained at 8.5 and the OER current density is about 1960 mA/cm². BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where: Figure 1 depicts – (A) a schematic diagram of a water splitting electrolyzer with the OER and the HER occurring at the anode and the cathode, respectively. pH, applied potential (U), temperature (T), and pressure (p) constitute the main operating conditions of the electrolyzer. (B) a graph of the standard Gibbs free energies of H₂O(l), H₂(g), and O₂(g) as a function of temperature, referenced to their respective values at room temperature ( T_r =10 °C). (C) a graph of the standard Gibbs free energies of the four adsorbed species in the OER = mechanism on Fe- doped β-NiOOH, referenced to their respective values at T_r, calculated using the surface normal modes from another reference. (D) a graph of the standard reduction potentials of the OER and the four elementary steps in the OER mechanism on Fe-doped β-NiOOH(

) as a function of temperature, with the thermodynamic overpotential (η_thermo) indicated. Figure 2 illustrates graphs of the vapor-phase oxygen mole fraction,

_మ as a function of pressure at two different temperatures, 25 °C and 90 °C, and a fixed pH of 12.0. (A) depicts the vapor-phase oxygen mole fraction (B) depicts the aqueous activity of oxygen (

Figure 3 depicts graphs of: (A) The equilibrium constant for water dissociation, KW, as a function of temperature. (B) Water, (C) OH-, and (D) K⁺ activity as a function of pH under alkaline conditions at 25 °C and 90 °C (green). The system pressure is 1 bar in all cases. Figure 4 illustrates a plot of standard pH with respect to OH-, i.e., the pH at which a_OH- = 1 M, denoted as pH⁰, as a function of temperature. The optimal pH for maximal OER current density, pH^opt, calculated at an applied potential of 1.51 V vs. the RHE, is shown as a function of temperature. Figure 5 illustrates the OER current density as a function of temperature at an electrolyte pH of pH⁰(T) (blue) or pH^opt(T) (red) at an applied potential of 1.51 V vs. the (A) RHE and (B) standard hydrogen electrode (SHE). The vertical axis in panel A is in a linear scale while in panel B it is in a log scale. The system pressure is 1 bar in both cases. Figure 6 illustrates the K⁺ activity, i.e., the initially supplied KOH concentration, required to maintain the solution at the optimal pH (Fig.4) as a function of temperature.

Figure 7 illustrates (A) The potential versus the SHE required to obtain the maximum current density at pH^opt. (B) The difference between the absolute potentials (i.e., versus the SHE) at pH^opt and pH⁰ to obtain the same current density as at pH⁰. Figure 8 illustrates graphs of (A) Reaction Gibbs free energies of water splitting, the OER, and the HER as a function of pressure at a fixed temperature of 90 °C, assuming pure reactant and product species. Note the split vertical axis on the plot. Only the free energies at a pressure of 1 bar are standard values. O₂ and H₂ mole fractions assumed as 1.0 in their respective gas- evolution compartments. (B) Reduction potentials of the OER and the four elementary steps in the OER mechanism on Fe-doped β-NiOOH as a function of pressure at a fixed temperature of 90 °C. Figure 9 illustrates a graph of the solubility of oxygen in water as a function of the applied pressure with the vapor-phase oxygen mole fraction maintained at unity, at 10 °C and 90 °C. Figure 10 illustrates a graph of the OER current density as a function of pressure at an electrolyte pH of pH^opt and pH⁰ and applied potentials of (A) 1.46 V and (B) 1.51 V vs. the RHE. Note that the reactor (system) temperature, T, in both panels is 90 °C. DESCRIPTION OF THE DISCLOSURE Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, definitions for some terms are included for better understanding of the present disclosure. As used herein, the singular forms ‘a’, ‘an’ and ‘the’ include both singular and plural referents unless the context clearly dictates otherwise. The term ‘comprising’, ‘comprises’ or ‘comprised of’ as used herein are synonymous with ‘including’, ‘includes’, ‘containing’ or ‘contains’ and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints. The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed. As used herein, the term/phrase ‘electrolysis of water’, or ‘electrochemical water oxidation’, or ‘electrochemical water splitting’ are used interchangeably and refers to the process of using electricity to decompose water into oxygen and hydrogen gas as described in this disclosure. The overall process of water electrolysis consists of two half-cell reactions: the hydrogen evolution reaction (used hereinafter as “HER”) and the oxygen evolution reaction (used hereinafter as “OER”). In the HER, water/protons is/are reduced at the cathode to produce H₂, and in the OER, water/OH- ions is/are oxidized at the anode to produce O₂. Currently, three main types of electrolysis technologies are being examined: (1) proton exchange membrane (PEM) electrolysis, (2) alkaline electrolysis, and (3) high-temperature solid oxide water electrolysis. As used herein, the term/phrase ‘electrolyzer’ or ‘electrochemical water splitting reactor’ are interchangeable and refer to a system that uses electric current to decompose water into hydrogen and oxygen molecules in a process called electrolysis, as defined above. In its most basic form, an electrolyzer consists of a cathode (negatively charged electrode), an anode (positively charged electrode), and a membrane. The system also contains ancillary components, including, but not limited to, pumps, vents, measuring devices, storage tanks, a power supply, and a separator. As used herein, the term/phrase ‘current density’ refers to the measure of the amount of electric charge per unit time that flows through a unit area of the cross-section. The area is measured in the direction perpendicular to the flow of current, and the resultant current density is expressed in amperes per square meter (or in other derived units, such as milliamperes per square centimeter). Usually, the more the current in a conductor, the higher will be the current density. In the context of the present disclosure, the conductor is the catalyst material as defined above, and the higher the current density associated with the water splitting process, the higher will be the generation rate of oxygen and hydrogen. As used herein, the term/phrase ‘SHE’ or ‘standard hydrogen electrode’ refers to an electrode that is used as a reference for measuring the potential of a working electrode. The value of the SHE potential is, by convention, zero at all temperatures and forms the basis with respect to which cell potentials are measured. The SHE consists of a 1.0 M H⁺(aq) solution in a tube with a square piece of platinized platinum immersed in it. The SHE is connected via a platinum wire to the working electrode. As used herein, the term ‘RHE’ or ‘reversible hydrogen electrode’ refers to an electrode that is used as a reference for measuring the potential of a working electrode. Unlike the SHE, the electrolyte in the RHE is not a 1.0 M H⁺ (aq) solution, but is instead the same electrolyte in which the working electrode is immersed. Accordingly, with an aim to overcome the drawbacks associated with the currently existing methods of electrochemical water splitting, the present disclosure provides an improved method for production of oxygen by water electrolysis. Therefore, an objective of the present disclosure is to develop an efficient, eco-friendly, and cost-effective industrial/large scale method for the production of pure oxygen, while producing hydrogen as a by-product. Another objective of the present disclosure is to optimize the operating conditions of pH, temperature, and pressure for a range of potentials for electrochemical water splitting reaction for production of oxygen at an industrial scale. Another objective of the present disclosure is to optimize the pH as a function of temperature and pressure to produce the maximum possible amount of oxygen gas for a given applied potential. Another objective of the present disclosure is to reduce the concentration of the alkali solution required for maintaining the optimized pH as mentioned above and develop an eco-friendly, economical electrochemical water oxidation method. Still another objective of the present disclosure is to understand the gaps pertaining to the direct effect of temperature and pressure on OER thermodynamics and kinetics, rather than through indirect mechanisms such as phase stability and defect concentrations. Yet another objective of the present disclosure is to develop a method of water electrolysis that results in generation of oxygen with minimal impact on the kinetics of production by means of achieving a maximal current density. Another objective of the present disclosure is to develop a method for the production of oxygen by electrochemical water splitting that can be carried out in conjunction with a counter- electrode for the carbon-dioxide-emission-free production of hydrogen gas. Yet another objective of the present disclosure is to provide a device and a process for generation of oxygen by electrochemical water oxidation, that employ the method developed in the present disclosure, at optimal conditions of pH, temperature, and pressure. To achieve the aforesaid objectives, the present disclosure provides an efficient, eco-friendly, and cost-effective method for production of pure oxygen by electrochemical water oxidation in an electrolyzer. In particular, the present disclosure provides optimized operating conditions of an electrochemical water oxidation reaction such as optimal temperature, pressure, and pH (i.e., alkali content), at a given voltage to drive the oxygen evolution reaction (OER) in the presence of mixed iron/nickel oxide, hydroxide, or oxyhydroxide catalyst for the production of oxygen at the anode. More particularly, the present disclosure provides optimized operating conditions of an electrochemical water oxidation reaction such as optimal temperature, pressure, pH, and potential that results in a significant reduction in the required alkali concentration in the electrolyte and an improvement in the OER current density. In particular, the method of the present disclosure optimizes the pH of the electrolyte as a function of temperature and pressure, that consequently also results in significant reduction of the optimal alkali concentration in the electrolyte. The present inventors have analyzed the coupled effects of temperature, pressure, and pH on the thermodynamics and kinetics of the OER electrocatalyzed by a mixed iron/nickel oxyhydroxide catalyst, in order to understand overall electrochemical water-splitting cycles. To this end, the present inventors investigated the thermodynamics and kinetics of elementary steps in electrochemical water splitting and determined the temperature variations of the free energies of molecular and adsorbed species, respectively, to calculate the OER free energy as a function of temperature. In some embodiments, the present disclosure provides a method of generating oxygen by electrochemical water splitting at optimized conditions of pH, temperature, and pressure for an oxygen evolution reaction (OER) current density ranging from about 10 mA/cm² to about 10000 mA/cm², said method comprising: a) contacting an anode of an electrolyzer with an electrolyte comprising water and alkali, in presence of a iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst; and b) applying a potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode to allow said generation of the oxygen; wherein pH of the electrolyte ranges from about 7.4 to about 10.9; wherein the pH is a function of temperature T at a given pressure P; and wherein the temperature T ranges from about 28 °C to 151 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the pH of the electrolyte ranges from about 7.4 to about 10.9, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal pH of the electrolyte is about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, about 7.9, about 8.0, about 8.1, about 8.2, about 8.3, about 8.4, about 8.5, about 8.6, about 8.7, about 8.8, about 8.9, about 9.0, about 9.1, about 9.2, about 9.3, about 9.4, about 9.5, about 9.6, about 9.7, about 9.8, about 9.9, about 10.0, about 10.1, about 10.2, about 10.3, about 10.4, about 10.5, about 10.6, about 10.7, about 10.8, or about 10.9, including all values and ranges therebetween. In some embodiments of the present disclosure, the pH of the electrolyte is a function of temperature T at a given pressure P of the electrolyzer and a given potential applied at the anode. In some embodiments of the present disclosure, the pH of the electrolyte changes with the change in the temperature T at a given pressure P and a given potential applied at the anode. In some embodiments of the present disclosure, the pH of the electrolyte decreases with the increase in the temperature T at a given pressure P and a given potential applied at the anode. In some embodiments of the present disclosure, pH of the electrolyte is determined based on an unconstrained minimization function applied to the negative of an oxygen evolution reaction (OER) current density (equivalent to the maximization of the OER current density), and wherein the OER current density is a function of the applied potential. In some embodiments of the present disclosure, the pH of the electrolyte is maintained in a manner that allows concentration of OH- ions in the electrolyte to be less than 1 M. In some embodiments, the electrolyte is a fluid comprising water and alkali. In some embodiments of the present disclosure, the optimal temperature T ranges from about 28 ºC to about 151 ºC, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal temperature T is less than the boiling point of the electrolyte at a given pressure P. In some embodiments of the present disclosure, the optimal temperature T ranges from about 28 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P. In some embodiments of the present disclosure, the optimal temperature T ranges from about 28 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P, and does not include temperatures below 28 ºC. In some embodiments of the present disclosure, the optimal temperature T is about 28 ºC, about 30 ºC, about 35 ºC, about 40 ºC, about 45 ºC, about 50 ºC, about 55 ºC, about 60 ºC, about 65 ºC, about 70 ºC, about 75 ºC, about 80 ºC, about 85 ºC, about 90 ºC, about 95 ºC, about 100 ºC, about 105 ºC, about 110 ºC, about 115 ºC, about 120 ºC, about 125 ºC, about 130 ºC, about 135 ºC, about 140 ºC, about 145 ºC, about 150 ºC, or about 151 ºC, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal temperature T ranges from about 40 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P. In some embodiments of the present disclosure, the optimal temperature T ranges from about 50 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P. In some embodiments of the present disclosure, the optimal temperature T ranges from about 40 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P, and does not include temperatures below 40 ºC. In some embodiments of the present disclosure, the optimal temperature T ranges from about 50 ºC to about 151 ºC, including all values and ranges therebetween, and is less than the boiling point of the electrolyte at a given pressure P, and does not include temperatures below 50 ºC. In some embodiments of the present disclosure, the optimized temperature employed for generating oxygen by electrochemical water splitting is less than the boiling point of the electrolyte at a given pressure P. As is known to a person skilled in the art, the boiling point of electrolyte will also vary with change in pressure. Accordingly, the optimized temperature employed in the method of the present disclosure also changes depending on the pressure. In some embodiments of the present disclosure, the electrolyte comprises water and alkali, and therefore the optimized temperature employed for generating oxygen by electrochemical water splitting is less than the boiling point of the said electrolyte at a given pressure P. In some embodiments of the present disclosure, the optimal pressure P ranges from about 1 bar to about 210 bar, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal pressure P is about 1 bar, about 10 bar, about 20 bar, about 30 bar, about 40 bar, about 50 bar, about 60 bar, about 70 bar, about 80 bar, about 90 bar, about 100 bar, about 110 bar, about 120 bar, about 130 bar, about 140 bar, about 150 bar, about 160 bar, about 170 bar, about 180 bar, about 190 bar, about 200 bar, or about 210 bar, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal potential ranges from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, including all values and ranges therebetween. In some embodiments of the present disclosure, the optimal potential applied at the anode is about 1.45 V vs. the RHE, about 1.46 V vs. the RHE, about 1.47 V vs. the RHE, about 1.48 V vs. the RHE, about 1.49 V vs. the RHE, about 1.50 V vs. the RHE, about 1.51 V vs. the RHE, about 1.52 V vs. the RHE, about 1.53 V vs. the RHE, about 1.54 V vs. the RHE, about 1.55 V vs. the RHE, about 1.56 V vs. the RHE, about 1.57 V vs. the RHE, about 1.58 V vs. the RHE, about 1.59 V vs. the RHE, about 1.60 V vs. the RHE, about 1.61 V vs. the RHE, about 1.62 V vs. the RHE, about 1.63 V vs. the RHE, about 1.64 V vs. the RHE, about 1.65 V vs. the RHE, about 1.66 V vs. the RHE, about 1.67 V vs. the RHE, about 1.68 V vs. the RHE, about 1.69 V vs. the RHE, about 1.70 V vs. the RHE, about 1.71 V vs. the RHE, about 1.72 V vs. the RHE, about 1.73 V vs. the RHE, about 1.74 V vs. the RHE, or about 1.75 V vs. the RHE, including all values and ranges therebetween. In some embodiments of the present disclosure, the potential applied at the anode is about 1.5 V versus the RHE and preferably 1.51 V at the RHE. In some embodiments of the present disclosure, the potential applied at the anode is about 1.6 V versus the RHE. In some embodiments of the present disclosure, the potential applied at the anode is about 1.7 V versus the RHE. In some embodiments of the present disclosure, the OER current density ranges from about 10 mA/cm² to about 10,000 mA/cm², including all values and ranges therebetween. In some embodiments of the present disclosure, the OER current density ranges from about 400 mA/cm² to about 1000 mA/cm², including all values and ranges therebetween. In some embodiments of the present disclosure, the OER current density ranges from about 60 mA/cm² to about 1600 mA/cm², including all values and ranges therebetween. In some embodiments of the present disclosure, the OER current density ranges from about 60 mA/cm² to about 2500 mA/cm², including all values and ranges therebetween. In some embodiments of the present disclosure, the OER current density is about 10 mA/cm², about 20 mA/cm², about 30 mA/cm², about 40 mA/cm², about 50 mA/cm², about 100 mA/cm², about 200 mA/cm², about 300 mA/cm², about 400 mA/cm², about 500 mA/cm², about 600 mA/cm², about 700 mA/cm², about 800 mA/cm², about 900 mA/cm², about 1000 mA/cm², about 2000 mA/cm², about 3000 mA/cm², about 4000 mA/cm², about 5000 mA/cm², about 6000 mA/cm², about 7000 mA/cm², about 8000 mA/cm², about 9000 mA/cm², or about 10000 mA/cm² including all values and ranges therebetween. In some embodiments of the present disclosure, the OER current density is about 10 mA/cm². In some embodiments of the present disclosure, the OER current density is about 400 mA/cm². In some embodiments of the present disclosure, the OER current density is about 997 mA/cm². In some embodiments of the present disclosure, the OER current density is about 770 mA/cm². In some embodiments of the present disclosure, the OER current density is about 1241 mA/cm². In some embodiments of the present disclosure, the OER current density is about 1960 mA/cm². In some embodiments of the present disclosure, the OER current density is improved by at least twofold when compared to any method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28 °C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density is improved by up to 1000-fold when compared to a method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28 °C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density is improved in the range of about twofold to 1000-fold when compared to a method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28 °C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density is improved by about twofold, about fivefold, about 10-fold, about 50-fold, about 100-fold, about 200-fold, about 300-fold, about 400-fold, about 500-fold, about 600-fold, about 700-fold, about 800-fold, about 900-fold, or about 1000-fold when compared to any method performed outside the stated potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode, stated pH range of about 7.4 to about 10.9 and the stated temperature range from about 28 °C to about 151 °C at a given pressure P, wherein the temperature is less than the boiling point of the electrolyte at the given pressure. In some embodiments of the present disclosure, the OER current density improves by at least about 80% when the method is carried out at said optimized conditions of pH, temperature, potential, and pressure as described herein. This improvement is in comparison with a similar method performed under the same conditions of pressure and potential, but at a temperature of 20 °C. In some embodiments of the present disclosure, the OER current density improves by about 200% when the method is carried out at said optimized conditions of pH, temperature, potential, and pressure as described herein. This improvement is in comparison with a similar method performed under the same conditions of pressure and potential, but at a temperature of 20 °C. In some embodiments of the present disclosure, the OER current density improves by up to about 21700% when the method is carried out at a pressure of about 1 bar, potential of 1.5 V vs. the RHE at the anode and at optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 5000% when the method is carried out at a pressure of about 1 bar, potential of 1.6 V vs. the RHE at the anode and optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 5000% when the method is carried out at a pressure of about 10 bar, potential of 1.6 V vs. the RHE at the anode and optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 5000% when the method is carried out at a pressure of about 200 bar, potential of 1.6 V vs. the RHE at the anode and optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 200% when the method is carried out at a pressure of about 1 bar, potential of 1.7 V vs. The RHE at the anode and optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 200% when the method is carried out at a pressure of about 10 bar, potential of 1.7 V vs. the RHE at the anode and optimized temperature and pH conditions. In some embodiments of the present disclosure, the OER current density improves by up to about 200% when the method is carried out at a pressure of about 100 bar, potential of 1.6 V vs. the RHE at the anode and optimized temperature and pH conditions. Accordingly, in some embodiments of the present disclosure, the potential is about 1.5 V vs. the RHE, the pH of the electrolyte ranges from about 7.4 to about 10.7, and the temperature T ranges from about 28 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.5 V vs. the RHE, the pH of the electrolyte ranges from about 7.4 to about 10.6, and the temperature T ranges from about 40 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.5 V vs. the RHE, the pH of the electrolyte ranges from about 7.4 to about 10.3, and the temperature T ranges from about 50 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.6 V vs. the RHE, the pH of the electrolyte ranges from about 8.5 to about 10.9, and the temperature T ranges from about 28 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.6 V vs. the RHE, the pH of the electrolyte ranges from about 8.5 to about 10.7, and the temperature T ranges from about 40 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.6 V vs. the RHE, the pH of the electrolyte ranges from about 8.5 to about 10.3, and the temperature T ranges from about 50 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.7 V vs. the RHE, the pH of the electrolyte ranges from about 10.2 to about 10.9, and the temperature T ranges from about 28 °C to about 41 °C and is less than boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the potential is about 1.7 V vs. the RHE, the pH of the electrolyte ranges from about 10.2 to about 10.6, and the temperature T ranges from about 40 °C to about 41 °C and is less than boiling point of the electrolyte at the given pressure P. Accordingly, in some embodiments of the present disclosure, the pressure is about 1 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 8.6 to about 10.7, including all values and ranges therebetween, for temperatures ranging from about 28 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 10 mA/cm² to about 770 mA/cm². In some embodiments of the present disclosure, the pressure is about 10 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.4 to about 10.7, including all values and ranges therebetween, for temperatures ranging from about 32 °C to about 151 °C. Consequently, the OER current density at these conditions ranges from about 10 mA/cm² to about 10000 mA/cm². In some embodiments of the present disclosure, the pressure is about 10 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.4 to about 10.4, including all values and ranges therebetween, for temperatures ranging from about 40 °C to about 151 °C. Consequently, the OER current density at these conditions ranges from about 25 mA/cm² to about 9800 mA/cm². In some embodiments of the present disclosure, the pressure is about 20 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.5 to about 10.0, including all values and ranges therebetween, for temperatures ranging from about 50 °C to about 151 °C. Consequently, the OER current density at these conditions ranges from about 60 mA/cm² to about 9800 mA/cm². In some embodiments of the present disclosure, the pressure is about 50 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.7 to about 9.4, including all values and ranges therebetween, for temperatures ranging from about 70 °C to about 140 °C. Consequently, the OER current density at these conditions ranges from about 250 mA/cm² to about 6800 mA/cm². In some embodiments of the present disclosure, the pressure is about 100 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.6 to about 9.2, including all values and ranges therebetween, for temperatures ranging from about 80 °C to about 150 °C. Consequently, the OER current density at these conditions ranges from about 435 mA/cm² to about 9800 mA/cm². In some embodiments of the present disclosure, the pressure is about 150 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.6 to about 9.0, including all values and ranges therebetween, for temperatures ranging from about 90 °C to about 150 °C. Consequently, the OER current density at these conditions ranges from about 740 mA/cm² to about 9800 mA/cm². In some embodiments of the present disclosure, the pressure ranges from about 1 bar to 210 bar, the potential is about 1.5 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 7.4 to about 10.9, including all values and ranges therebetween, for temperatures ranging from about 28 °C to about 151 °C. Consequently, the OER current density at these conditions ranges from about 10 mA/cm² to about 10000 mA/cm² In some embodiments of the present disclosure, the pressure is about 1 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.6 to about 10.6, including all values and ranges therebetween, for temperatures ranging from about 30 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 370 mA/cm² to about 9300 mA/cm². In some embodiments of the present disclosure, the pressure is about 10 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.6 to about 10.3, including all values and ranges therebetween, for temperatures ranging from about 40 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 700 mA/cm² to about 9300 mA/cm². In some embodiments of the present disclosure, the pressure is about 20 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.7 to about 10, including all values and ranges therebetween, for temperatures ranging from about 50 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 1200 mA/cm² to about 9300 mA/cm². In some embodiments of the present disclosure, the pressure is about 50 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.8 to about 9.8, including all values and ranges therebetween, for temperatures ranging from about 60 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 2195 mA/cm² to about 9220 mA/cm². In some embodiments of the present disclosure, the pressure is about 150 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 8.9 to about 9.6, including all values and ranges therebetween, for temperatures ranging from about 70 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 3600 mA/cm² to about 9200 mA/cm². In some embodiments of the present disclosure, the pressure is about 200 bar, the potential is about 1.6 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 9 to about 10, including all values and ranges therebetween, for temperatures ranging from about 60 °C to about 90 °C. Consequently, the OER current density at these conditions ranges from about 2180 mA/cm² to about 9180 mA/cm². In some embodiments of the present disclosure, the pressure ranges from about 1 bar to 210 bar, the potential is about 1.6 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 8.5 to about 10.9, including all values and ranges therebetween, for temperatures ranging from about 28 °C to about 92 °C. Consequently, the OER current density at these conditions ranges from about 300 mA/cm² to about 10000 mA/cm² _. In some embodiments of the present disclosure, the pressure is about 1 bar, the potential is about 1.7 V vs. the RHE at the anode, the pH of the electrolyte ranges from about 10.2 to about 10.9, including all values and ranges therebetween, for temperatures ranging from about 30 °C to about 40 °C. Consequently, the OER current density at these conditions ranges from about 5700 mA/cm² to about 9900 mA/cm². In some embodiments of the present disclosure, the pressure ranges from about 1 bar to 210 bar, the potential is about 1.7 V vs. the RHE at the anode, and the pH of the electrolyte ranges from about 10.2 to about 10.9, including all values and ranges therebetween, for temperatures ranging from about 28 °C to about 41 °C. Consequently, the OER current density at these conditions ranges from about 5500 mA/cm² to about 10000 mA/cm² _. As is apparent from the embodiments above, the criticality of the present disclosure lies in the optimized conditions of pH, temperature, and pressure for a potential range that have been arrived at herein, for generating oxygen by electrochemical water splitting. A person skilled in the art will therefore readily realize that these conditions are unaffected by the type or make of the device or system that employs these conditions for electrochemical water splitting. Hence, any device or system such as an electrolyzer will be able to electrochemically split water equally well and with higher efficiency of the OER, as long as the electrolyzer functions at the optimized conditions of pH, temperature, and pressure for the potential range as described herein. As mentioned above, since pH is one of the important conditions that has been optimized in the present disclosure, a direct impact of the stated optimization is visible on the concentration or amount of alkali employed in the method for maintaining the stated optimal pH. Accordingly, in some embodiments of the present disclosure, for maintaining the pH range of about 7.4 to about 10.9 of the present disclosure, the concentrations or amounts of the required alkali in the electrolyte range from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween. In some embodiments of the present disclosure, the concentration of the alkali in the electrolyte is about 0.07 mM, about 0.08 mM, about 0.09 mM, about 0.1 mM, about 0.2 mM, about 0.3

mM, about 0.4 mM, about 0.5 mM, about 0.6 mM, about 0.7 mM, about 0.8 mM, about 0.9 mM, about 1 mM, about 1.1 mM, about 1.2 mM, about 1.3 mM, about 1.35 mM, or about 1.38 mM, including all values and ranges therebetween. In some embodiments of the present disclosure, the pH reduces from about 10.7 to about 7.4 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.5 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.38 mM to about 0.07 mM at the given pressure P. In some embodiments of the present disclosure, the pH reduces from about 10.9 to about 8.5 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.6 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.14 mM at the given pressure P. In some embodiments of the present disclosure, the pH reduces from about 10.9 to about 10.2 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.7 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.47 mM at the given pressure P. In some embodiments of the present disclosure, the alkali is selected from a group comprising potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide (Mg(OH)₂), and any other alkali or alkaline earth hydroxide, or any combination thereof. Accordingly, in some embodiments of the present disclosure, for maintaining the stated pH range of about 7.4 to about 10.9 of the present disclosure, the amount/concentration of the required alkali in the electrolyte ranges from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween, and wherein the alkali is potassium hydroxide (KOH). In some embodiments of the present disclosure, for maintaining the stated pH range of about 7.4 to about 10.9 of the present disclosure, the amount/concentration of the required alkali in

the electrolyte ranges from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween, and wherein the alkali is sodium hydroxide (NaOH). In some embodiments of the present disclosure, for maintaining the stated pH range of about 7.4 to about 10.9 of the present disclosure, the amount/concentration of the required alkali in the electrolyte ranges from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween, and wherein the alkali is calcium hydroxide (Ca(OH)₂). In some embodiments of the present disclosure, for maintaining the stated pH range of about 7.4 to about 10.9 of the present disclosure, the amount/concentration of the required alkali in the electrolyte ranges from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween, and wherein the alkali is magnesium hydroxide (Mg(OH)₂). In some embodiments of the present disclosure, for maintaining the stated pH range of about 7.4 to about 10.9 of the present disclosure, the amount/concentration of the required alkali in the electrolyte ranges from about 0.07 mM to about 1.38 mM, including all values and ranges therebetween, and wherein the alkali is any alkali or alkaline earth hydroxide. As mentioned above, in the present disclosure, the anode of the electrolyzer is contacted with an electrolyte comprising water and alkali, in the presence of a metal-doped oxide, hydroxide, or oxyhydroxide catalyst. In some embodiments of the present disclosure, the stated metal- doped oxyhydroxide catalyst is an iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst, also referred to as a mixed iron/nickel oxide, hydroxide or oxyhydroxide material. In some embodiments of the present disclosure, the electrolyzer further comprises a cathode within the electrolyte. In some embodiments of the present disclosure, application of the potential across the electrolyzer generates hydrogen at the cathode. In some embodiments of the present disclosure, the electrolyzer further comprises a cathode within the electrolyte, and wherein application of the potential across the electrolyzer generates oxygen at anode and hydrogen at cathode.

In some embodiments of the present disclosure, the generated oxygen and hydrogen are further captured. In some embodiments of the present disclosure, the generated oxygen is further captured in compressed cylinders or tanks. In some embodiments of the present disclosure, the generated hydrogen is further captured in compressed cylinders or tanks Accordingly, the present disclosure provides a method of generating oxygen by electrochemical water splitting at optimized conditions of pH, temperature, and pressure for an oxygen evolution reaction (OER) current density ranging from about 10 mA/cm² to about 10000 mA/cm², said method comprising: a) contacting an anode of an electrolyzer with an electrolyte comprising water and alkali, in presence of a iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst, wherein the alkali is selected from potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide (Mg(OH)₂), another alkali or alkaline earth hydroxide or any combination thereof; and b) applying a potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode to allow said generation of the oxygen; wherein the pH of the electrolyte ranges from about 7.4 to about 10.9; wherein the pH is a function of temperature T at a given pressure P; and wherein the temperature T ranges from about 28 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.61 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.7; wherein the temperature T is about 28 °C at a pressure P of 1 bar; and wherein the OER current density is about 10 mA/cm².

In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.7 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.4; wherein the temperature T is about 40 °C at a pressure P of 10 bar; and wherein the OER current density is about 28 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.071 mM NaOH, in the presence of an iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 7.5; wherein the temperature T is about 150 °C at a pressure P of 10 bar; and wherein the OER current density is about 10000 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.26 mM KOH, in the presence of a mixed iron/nickel hydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.8; wherein the temperature T is about 90 °C at a pressure P of 50 bar; and wherein the OER current density is about 761 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.86 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.1; wherein the temperature T is about 50 °C at a pressure P of 50 bar; and wherein the OER current density is about 54 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.26 mM KOH or NaOH, in the presence of a mixed iron/nickel oxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.6; wherein the temperature T is about 100 °C at a pressure P of 100 bar; and wherein the OER current density is about 1241 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.24 mM NaOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.4; wherein the temperature T is about 110 °C at a pressure P of 150 bar; and wherein the OER current density is about 1966 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.22 mM KOH, in the presence of an iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.2; wherein the temperature T is about 120 °C at a pressure P of 200 bar; and wherein the OER current density is about 3032 mA/cm². In some embodiments of the present disclosure, the method comprises

a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.12 mM NaOH, in the presence of a mixed iron/nickel oxyhydroxide catalyst; and b) application of a potential of about 1.5 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 7.7; wherein the temperature T is about 150 °C at a pressure P of 210 bar; and wherein the OER current density is about 9691 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.14 mM Ca(OH)₂, in the presence of an iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE the electrolyzer to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.5; wherein the temperature T is about 92 °C at a pressure P of 1 bar; and wherein the OER current density is about 10000 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.32 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 8.9; wherein the temperature T is about 92 °C at a pressure P of 100 bar; and wherein the OER current density is about 10000 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.70 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.4; wherein the temperature T is about 40 °C at a pressure P of 10 bar; and

wherein the OER current density is about 704 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.52 mM Mg(OH)₂, in the presence of a mixed iron/nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10; wherein the temperature T is about 50 °C at a pressure P of 10 bar; and wherein the OER current density is about 1271 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.65 mM KOH, in the presence of a mixed iron/nickel hydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 9.8; wherein the temperature T is about 60 °C at a pressure P of 50 bar; and wherein the OER current density is about 2196 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.63 mM NaOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 9.6; wherein the temperature T is about 70 °C at a pressure P of 100 bar; and wherein the OER current density is about 3653 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.56 mM Ca(OH)₂, in the presence of an iron-doped nickel oxyhydroxide catalyst; and

b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 9.3; wherein the temperature T is about 80 °C at a pressure P of 150 bar; and wherein the OER current density is about 5880 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.47 mM Mg(OH)₂, in the presence of a mixed iron/nickel oxyhydroxide catalyst; and b) application of a potential of about 1.6 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 9.02; wherein the temperature T is about 90 °C at a pressure P of 200 bar; and wherein the OER current density is about 9182 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.47 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.2; wherein the temperature T is about 40 °C at a pressure P of 1 bar; and wherein the OER current density is about 10000 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 0.85 mM NaOH, in the presence of an iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.8; wherein the temperature T is about 30 °C at a pressure P of 10 bar; and wherein the OER current density is about 5706 mA/cm².

In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 1.05 mM KOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.5; wherein the temperature T is about 40 °C at a pressure P of 50 bar; and wherein the OER current density is about 9848 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 1.18 mM NaOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.9; wherein the temperature T is about 30 °C at a pressure P of 100 bar; and wherein the OER current density is about 5688 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 1.30 mM KOH, in the presence of an iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.6; wherein the temperature T is about 40 °C at a pressure P of 150 bar; and wherein the OER current density is about 9818 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 1.27 mM Ca(OH)₂, in the presence of a mixed iron/nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen;

wherein the pH of the electrolyte is about 10.9; wherein the temperature T is about 30 °C at a pressure P of 200 bar; and wherein the OER current density is about 5669 mA/cm². In some embodiments of the present disclosure, the method comprises a) contacting an anode of an electrolyzer with an electrolyte comprising water and 1.38 mM NaOH, in the presence of a iron-doped nickel oxyhydroxide catalyst; and b) application of a potential of about 1.7 V vs. the RHE at the anode to allow generation of the oxygen; wherein the pH of the electrolyte is about 10.6; wherein the temperature T is about 40 °C at a pressure P of 210 bar; and wherein the OER current density is about 9801 mA/cm². . In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH, the catalyst is of a mixed iron/nickel oxide, hydroxide or oxyhydroxide material, the potential applied at the anode is 1.51 V versus the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, and the pH of the electrolyte is maintained at 8.6. In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.51 V versus the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, the pH of the electrolyte is maintained at 8.6 and the OER current density is about 997 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.51 V versus the RHE, the temperature is about 90 ºC, the pressure is about 100 bar, and the pH of the electrolyte is maintained at 8.9. In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.51 V versus the RHE, the

temperature is about 90 ºC, the pressure is about 100 bar, the pH of the electrolyte is maintained at 8.9 and the OER current density is about 985 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.15 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, and the pH of the electrolyte is maintained at 8.6. In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.15 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, the pH of the electrolyte is maintained at 8.6, and the OER current density is about 770 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and alkali (KOH or NaOH) having a concentration of about 0.26 mM, the catalyst is a of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 100 ºC, the pressure is about 100 bar, and the pH of the electrolyte is maintained at 8.6. In some embodiments of the present disclosure, the method comprises electrolyte comprising water and alkali (KOH or NaOH) having a concentration of about 0.25 mM, the catalyst is a of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 100 ºC, the pressure is about 100 bar, the pH of the electrolyte is maintained at 8.6, and the OER current density is about 1241 mA/cm². In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.27 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 110 ºC, the pressure is about 200 bar, and the pH of the electrolyte is maintained at 8.5.

In some embodiments of the present disclosure, the method comprises electrolyte comprising water and KOH or NaOH having a concentration of about 0.27 mM, the catalyst is of a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material, the potential applied at the anode is 1.5 V versus the RHE, the temperature is about 110 ºC, the pressure is about 200 bar, the pH of the electrolyte is maintained at 8.5 and the OER current density is about 1960 mA/cm². The present disclosure also provides a device for generation of oxygen by electrochemical water oxidation. In particular, the device of the present disclosure for generating oxygen by electrochemical water oxidation, comprises a) a reaction chamber comprising a plurality of walls defining an internal cavity; b) an anode within the internal cavity comprising a metal-doped oxide, hydroxide, or oxyhydroxide catalyst; and c) an electrolyte within the internal cavity, in contact with the anode, said electrolyte comprising water and alkali; wherein the device is configured to carry out the electrochemical water oxidation under optimal temperature and pressure conditions as described above. In some embodiments of the present disclosure, the device further comprises a cathode within the internal cavity, the cathode being in contact with the electrolyte and a membrane separating the anode from cathode. In embodiments relating to the device for generation of oxygen, the features and characteristics of the optimal temperature, pressure, or other conditions, and metal-doped oxide, hydroxide, or oxyhydroxide catalyst is as described by any of the embodiments above. For the sake of brevity, and avoiding repetition, each of those embodiments are not being reiterated here again. However, each of the said embodiments, completely fall within the purview of the device for generation of oxygen described herein. The present disclosure refers to a system for generating oxygen by electrochemical water oxidation. In particular, the system for generating oxygen by electrochemical water oxidation comprises the device as described above, and a power supply configured to receive power from a power source for application of a potential across the device.

In some embodiments of the present disclosure, the system further comprises at least one processor configured to control the temperature, pressure, applied potential, or a combination thereof. In embodiments relating to the device for generation of oxygen, the features and characteristics of the device, optimal temperature, pressure, or other conditions, and metal-doped oxide, hydroxide, or oxyhydroxide catalyst is as described by any of the embodiments above. For the sake of brevity, and avoiding repetition, each of those embodiments are not being reiterated here again. However, each of the said embodiments, completely fall within the purview of the system for generation of oxygen described herein. Nonetheless, having said the above, it is important to emphasize that regardless of the device and system described herein, the criticality of the present disclosure lies in the optimized conditions of pH, temperature, potential, and pressure that have been arrived at in the present disclosure, for generating oxygen by electrochemical water splitting. A person skilled in the art will therefore readily realize that these conditions are unaffected by the type or make of the device or system that employs these conditions for electrochemical water splitting. Hence, any device or system such as an electrolyzer will be able to electrochemically split water equally well and with higher efficiency and OER, as long as the electrolyzer functions at the optimized conditions of pH, temperature, and pressure for a range of potentials as described herein. Overall, the method of the present disclosure possesses at least the following advantages: a) Gives an overview of the coupled effect and relationship of temperature, pressure, and pH for a range of potentials on the thermodynamics and kinetics of the OER electrocatalyzed by metal-doped oxide, hydroxide, or oxyhydroxide catalyst to understand overall electrochemical water-splitting cycles; b) Provides optimized operating conditions for electrolyzer that results in high OER current densities (up to 1000-fold higher) and can be used for industrial or large- scale production of pure oxygen; c) Provides significant reduction in the concentration of alkali to be used in the electrolyte. Accordingly, the operation conditions would not be highly corrosive (at high temperatures) in an alkaline water electrolyzer and its operational life would also increase substantially, as well as providing more favourable scalability and economics; d) Involves a negligible trade-off in kinetics, thereby leading to cost-savings due to an obviation of downstream hydrogen compression; and e) Provides an efficient, eco-friendly, cost-effective and industrially scalable method for production of pure oxygen by electrochemical water splitting/oxidation in an electrolyzer. It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein. Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein. EXAMPLES The analysis is based on the standard hydrogen electrode (SHE), whose potential at all temperatures is zero by convention, so that:

where are the standard Gibbs free energies of the proton-electron

couple and gaseous hydrogen at temperature T. The superscript ⁰ denotes standard-state conditions (1 bar pressure and pure water and oxygen). Hydrogen gas is at 1 bar pressure in the reference electrode at the considered temperature. The OER consists of four proton(hydroxide)-coupled electron transfer reactions, presented as follows: I₁ ⇄ I₂ + (H⁺+e-) or I₁ + OH- ⇄ I₂ + H₂O +e- I2 + H₂O ⇄ I3 + (H⁺+e-) + O₂ or I2 + OH- ⇄ I3 + e- + O₂ I₃ + H₂O ⇄ I₄ + (H⁺+e-) or I₃ + OH- ⇄ I₄ + e- I₄ ⇄ I₁ + (H⁺+e-) or I₄ + OH- ⇄ I₁ + H₂O +e- where I₁ = HO*OH + ^γOH, I₂ = HO*O + ^γOH, I₃ = HO* + ^γOH₂, and I₄ = HO*OH₂ + ^γOH, * denotes the Fe active site, and ^γ a Ni atom in the surface layer. Since Fe/Ni are only four-fold- lattice-oxygen-coordinated in the considered surface facet of (Ni,Fe)OOH, two adsorbates can adsorb simultaneously onto the active site, as in I₁, I₂, and I₄. Example 1: Effect of arbitrary temperature (below the water boiling point) on OER thermodynamics The standard Gibbs free energies of molecular (H₂, O₂, and H₂O) and ionic (H⁺+e-) species were first obtained at T_r = 25°C at any temperature T lower than the boiling point of water:

where i denotes either H₂(g) or H₂O(g), the species’ density functional theory (DFT) total

energy at zero Kelvin, its zero-point vibrational energy from DFT, and and

its standard enthalpy and entropy at T, respectively. We determine

through Shomate equations from the National Institute of Standards and Technology (NIST) database:

where

are experimentally derived constants for each molecular species

is directly obtained from the same database. We subsequently obtain the standard Gibbs free energy of liquid water at temperature T as:

where is the standard Gibbs free energy of condensation of water vapor. The

subscript “c” denotes condensation; later, subscripts “r” and “f” will denote reaction and formation, respectively. We calculate at any temperature T as:

where is obtained from the NIST database and denotes the standard

Gibbs free energy change incurred in changing the temperature of species i from T_r to T; the latter quantity for both liquid water and water vapor is estimated readily using Shomate equations. Finally, we calculate the standard Gibbs free energy of O₂(g) at room temperature as: denotes the standard Gibbs free energy of reaction for water splitting:

Here, denotes the standard free energy of formation of liquid water. Note that a

factor of two appears on the right-hand side because is defined per molecule of O₂

and is defined per molecule of H₂O; the minus sign appears because water

decomposes in the former reaction and forms in the latter one. We estimate in a

manner similar to Eq. (6) above:

where Δ is obtained from the NIST database and is calculated using

the respective Shomate equation. Because the SHE potential at all temperatures and 1 bar pressure is defined to be zero, , such that the standard Gibbs free energy of the

OER equals exactly the standard Gibbs free energy of water splitting, i.e

. At the outset, graphs depicting the free energies of liquid water and gaseous

hydrogen and oxygen as a function of temperature from 10 °C to 90 °C were plotted (Figure 1B). Next, the free energies of adsorbed species were determined as a function of temperature for solids as:

where is the standard Gibbs free energy of the i^th adsorbed species, its quantum-

mechanical DFT energy at one-quarter per metal site surface coverage E_vib,i its vibrational internal energy, and S_vib,i its vibrational entropy. Based on the above equation, the standard Gibbs free energies of each adsorbed species were plotted as a function of temperature in Figure 1C. It was observed that these free energies vary by ~0.15 eV over the temperature range considered. Moreover, the changes in the free energies of the adsorbed species with temperature are comparable to that of the gaseous species. Further, the standard Gibbs free energy change associated with the j^th step in the OER mechanism, was calculated as:

where N_s,j denotes the number of species participating in reaction j and v_ij represents the signed stoichiometric coefficient of species i in reaction j (>0 for products and <0 for reactants). Next, the standard potentials of each of the four reactions in the OER mechanism as a function of temperature were plotted in Figure 1C. Figure 1C also depicts the standard reduction potential of the OER measured vs. the RHE as a function of temperature. Further,

for both the SHE and RHE, the hydrogen pressure is set to 1 bar; therefore, for the latter, the sole potential variation arises due to its proton activity. EXAMPLE 2: Effect of arbitrary temperature (below the water boiling point) on OER kinetics In this example, OER kinetics as a function of temperature at 1 bar pressure was determined. The rate constant for each reaction j, k_j, is given as:

where λ_J and Δ w_j are Marcus parameters denoting the reorganization free energy and the net (product-reactant) work term, respectively, incurred in reaction j. Further,

the standard reduction potential of the j^th step at temperature T and applied potential U, and is obtained as is obtained

from the Computational Hydrogen Electrode framework (see Figure 1D for values) and U is referenced to the RHE through the solution pH. Note th is referenced to

the RHE through the standard pH (pH⁰=0 for protons and pH⁰=14 for hydroxide ions). The rate constant, k_j , for each reaction j is converted to a reaction rate, r_j, via multiplying by the reactant activities, a_i , raised to the absolute value of their respective stoichiometric coefficients, |v_ij| as

The activation free energies of forward and backward reactions are simply

related via the free energy of reaction as where

corresponds to the reaction free energy change assuming bulk liquid water, solvated ions, and O₂ gas phases. Δ w_i converts the bulk reaction free energy to the surface reaction free energy by including the work done to transport reactants/products to the catalyst surface, as required for application of Marcus theory. We used the appropriate standard states for H₂O, H⁺, OH-, H₂ and O₂. The species activities (a_i) are defined as follows:

where is the standard-state molarity of pure water, calculated using its molar mass and its

density at temperature is the solubility (mol/L) of O₂ in water at temperature T while

is the standard solubility (at 1 bar pressure) of O₂ in water at temperature T. K_W is the

equilibrium constant for water autoionization, which depends primarily on the temperature of the system. θ_l is the fraction of adsorbed species I_l, and is the concentration of adsorbed ecies I_l. C_sites is equal to 2.27 × 10¹

sp ² cm^-2, as mentioned above. The effective concentration of water is accounting for the degree of autoionization (H₂O = H⁺ + OH-).

To maintain the process at steady state, electrolyte at the appropriate pH must be fed continually into the reactor to make up for water losses due to water splitting and evaporation. Evaporated water can be recovered and reintroduced into the system by condensing out water vapor from the anodic product gas stream. Further, we consider the effects of these phenomena on the vapor-phase composition, i.e., vapor-phase mole fraction of oxygen and water vapor, which does affect the water-splitting rate via the concentration of dissolved oxygen. The oxygen solubility in water

is a function of both temperature and pressure, and is calculated as:

where p denotes the total pressure of the system, the vapor phase mole fraction of O₂(g), and

the inverse Henry’s law constant for

O₂(g). in units of mol O₂/kg water, is obtained from:

Here is determined based on the water vapor saturation pressure and oxygen partial

pressure under the relevant reactor conditions. The vapor phase mole fraction of O₂(g) can be calculated as:

where is the partial pressure of O₂(g) and is given in terms of the total system pressure

and the water saturation pressure, h can be

calculated using Raoult’s law as:

wher is the saturation pressure of water vapor, which depends on temperature and can

be calculated using Antoine’s relation:⁶⁹

Here, is expressed in bar, T in K (255.9 ≤ T ≤ 373), and A_p = 4.6543, B_p =

1435.264, and C_p = -64.848, as specified in the NIST database.⁷⁰ Given the system temperature, standard pressure, and the electrolyte pH,

, and K_W can be determined. To obtain the remaining six species activities, i.e.,

(O₂ dissolved in water)

(O₂ in the vapor phase) Eqs. (13), (16),

(20), and (23) have to be solved in conjunction with the following constraints:

Eq. (25) represents the equilibrium condition for the dissociation of KOH into K⁺ and OH- ions, because KOH, being a strong base, dissociates completely. Eq. (26) enforces electroneutrality in the system. Implicit in the above system of equations is the assumption that water/KOH dissociation and water evaporation are much faster than the OER and can be taken to have reached equilibrium. It follows that all the ionic/gaseous activities are defined solely based on thermodynamics, and the effect of kinetics appears via the adsorbed intermediate activities. Moreover, water lost due to evaporation and oxidation is replenished, as would be in any continuous (flow) reactor system. Finally, the net (forward-backward) rates of the elementary steps are summed over and multiplied by the charge on an electron and the active site density, to obtain the OER current density. EXAMPLE 3: Effect of pressure on vapor-phase mole fraction Figure 2A depicts the vapor-phase oxygen mole fraction as a function of pressure at two

different temperatures, 25°C and 90°C, and a fixed pH of 12.0. It is observed that is lower

at higher temperature due to the increased evaporation of water. Furthe increases with

increasing pressure because the saturation pressure of water can be reached easily, e.g., ~0.03 and 0.7 bar at 25°C and 90°C, respectively, and the head space is expected to be continuously filled with O₂ gas until the desired internal pressure is reached. Further, the aqueous oxygen activity , is depicted in Figure 2B at the same temperatures and under the same pressures. It was s

een that the aqueous oxygen activity is higher at the lower temperature of 25°C due to the increased solubility of oxygen. Moreover, the aqueous oxygen activity increases with increasing pressure, again due to the higher oxygen solubility in water and higher mole fraction in the vapor phase (Figure 9). EXAMPLE 4: The activities of other aqueous species as a function of temperature and pH It is noted that K_W varies from 1.01 × 10^-14 at 25°C to 3.83 × 10^-13 at 90°C, as given in Figure 3A. The increase in K_W with temperature indicates an increased tendency for water to autoionize. The activities of H₂O, OH-, and K⁺ at 25°C and 90°C as a function of the pH is given in Figures 3B through 3D, respectively. As can be seen from Figures 3A through 3D, as the pH increases, the ionic activity increases, with a corresponding decrease in the water activity. Further, as temperature increases, water activity decreases due to increased dissociation of water. Finally, it is apparent that pH=14, which can be attained readily at room temperature, is physically unattainable at elevated temperatures because, e.g.,

would need to be as high as ~21 at a temperature of 90°C for the pH to be 14. Accordingly, moving forward, two pHs were considered (see Figure 4): pH=pH⁰ (i.e., the pH where and pH=pH^opt, i.e., the optimal pH for maximizing the OER current

density at an applied potential of 1.51 V vs. the RHE. At pH⁰ and pH^opt, the aqueous species activities adopt reasonable values at all temperatures considered, thereby allowing comparisons between various temperatures. From Figure 4, it is apparent that the optimal pH for water splitting is less than 12 and that pH⁰ > pH^opt at all temperatures between 10°C and 90°C. Specifically, at 25°C, pH⁰ = 14.0 and pH^opt = 10.8, while at 90°C, pH⁰ = 12.4 and pH^opt = 8.6. Because the applied potentials ( U ) vs. the SHE and RHE are related by

it follows that the absolute potential required (i.e., vs. the SHE) to obtain a fixed

current density would be lower at pH⁰ than at pH^opt. However, not only is the amount of base required lower at pH^opt but also the current density is slightly higher at the same potential. EXAMPLE 5: Determining the OER current density as a function of the reactor temperature The OER current density as a function of the reactor temperature is given in Figures 5A and 5B at an applied potential of 1.51 V vs. the RHE and the SHE, respectively. As mentioned above, the results are shown for two pHs: pH=pH⁰(T) and pH=pH^opt(T). A potential of 1.51 V was chosen vs. the RHE because it leads to an OER current density of ~10 mA/cm² at room temperature, which is a benchmark in most experimental studies. A potential of 1.51 V was also considered vs. SHE as the reference electrode to present a contrasting example (however the pH^opt(T) is optimized for 1.51 V vs. RHE, and the two references are only equivalent at pH = 0). As temperature rises, in both Figure 5A and 5B, the OER current densities increase, as expected. However, unlike in Figure 5B, the current densities at pH=pH⁰ and pH=pH^opt are qualitatively comparable at all temperatures in Figure 5A. This follows from the use of the RHE as a reference electrode. Nevertheless, quantitatively they differ by around 60 mA/cm² at 90°C for a fixed potential of 1.51 V vs. the RHE, indicating a difference of around 6% between the current densities at pH=pH⁰ and pH=pH^opt. In contrast, in Figure 5B, one sees that the OER current density is much higher than seen in Figure 5A, and it is greater at pH⁰, rather than at pH^opt. This is because pH⁰ > pH^opt and due to the use of SHE as a reference electrode (higher the pH, the lower the equilibrium potential for OER, when measured against the SHE). It was noted that the OER current density for a fixed U of 1.51 V vs. the RHE(T) increases to 595 mA/cm² at 80°C, indicating Fe-doped β-NiOOH is a suitable catalyst for commercial electrolyzers that operate at current densities > 400 mA/cm² at a temperature of ~80°C. Moreover, the OER current density for the same potential further increases to 997 mA/cm² at a temperature of 90 °C, allowing one to achieve a current density as high as ~1 A/cm². EXAMPLE 6: Determination of concentration of alkali as a function of temperature and pH The operation of the anodic water-splitting half-cell at pH^opt < pH⁰ can enable the use of less alkali but with concomitant production of less oxygen. Figure 6 illustrates the activity of K+ ions as a function of temperature when the solution is maintained at the optimal pH, i.e., pH^opt. Because KOH dissociates fully, the activity of K⁺ corresponds to the concentration of alkali added initially to the system, assuming a constant volume of the liquid phase. Thus, at pH^opt, the concentration of KOH to be introduced is ~0.7 mM at 25°C, which further decreases to ~0.15 mM at 90°C. However, this reduction in the amount of alkali required does not come without a cost. Indeed, operating at pH^opt will require a larger absolute potential, if one wants to maintain the same current density as obtained by operating at pH⁰. Figure 7A depicts the potential versus the SHE that would be required to obtain a potential of 1.51 V versus the RHE at pH^opt. Figure 7B shows the extra potential that would be needed at pH^opt to obtain the same current density as at pH⁰, which is ~0.28 V at 90°C. At 25°C, operating at pH^opt, compared to pH⁰, leads to 3 orders of magnitude reduction in the alkali requirement (0.7 mM vs. 1 M). If one increases the temperature to 90°C, an additional factor of 4-5 reduction in the amount of alkali is possible. EXAMPLE 7: Effect of temperature-modulated OER thermodynamics on OER kinetics In this example, the effect of temperature-modulated OER thermodynamics on OER kinetics was quantified, beyond the usual Arrhenius effect, as the temperature varies from 10°C to 90°C. To this end, the OER current density was calculated at a fixed pH of 13.0, applied potential of 1.51 V vs. the RHE, and pressure of 1 bar, under three different conditions: (i) at 10°C, (ii) at 90°C assuming the OER potential to be unchanged from 10°C, and (iii) at 90°C. The OER current densities in these three cases were found to be ~1.5 mA/cm², 197 mA/cm², and 808 mA/cm², respectively. Thus, by solely accounting for Arrhenius-type effects and not changes in the OER potential, an increase in temperature from 10°C to 90°C would increase the OER current density by about two orders of magnitude. However, the reduction in OER equilibrium potential from 1.24 V (10°C) to 1.18 V (90°C) enables a further increase in the OER current density by nearly an extra order of magnitude, thereby indicating that even minor changes in the OER thermodynamics significantly affect OER kinetics. EXAMPLE 8: Effect of pressure on OER thermodynamics The effect of system pressure on OER thermodynamics was tested in this analysis. Although it is possible to operate water electrolyzers under conditions of differential pressure, wherein the anodic (oxygen) headspace is maintained at low pressures and the cathodic (hydrogen) headspace at high pressures, such operation can cause gas flow from one compartment to another. Thus, we consider the case of uniform reactor pressure. The free energy as a function of pressure using data from the NIST database is calculated as:

where represents the free energy change of pure species

when the system pressure changes from p₀ = 1 bar (standard pressure) to any arbitrary pressure p . We calculate at a fixed temperature T by linearly interpolating

between tabulated values withp varying from 1 bar to 100 bar with a linear spacing of 1 bar. The free energy of pure O₂(g) at arbitrary pressure is calculated as:

Further,

However at any arbitrary

pressure (these equalities hold only at standard pressure). This is because:

where the two terms on the right-hand side differ because the free energy of the proton-electron couple is always calculated under standard (1 bar) conditions of the SHE. The OER free energy is calculated as follows:

Using Eqs. (29) through (31), the Gibbs free energies of water splitting, oxygen evolution, and hydrogen evolution at a temperature of 90°C was plotted and provided in Figure 8A. Note that the change in the OER free energy with pressure solely occurs due to the change in the free energy of step 2 (i.e., the one involving O₂(g)) with pressure. Indeed, the free energies of steps 1, 3, and 4 in the OER do not change with pressure (Figure 8B). This is because pressure effects on adsorbed species and the proton-electron couple are respectively negligible (due to adsorbed intermediates being condensed phase entities) and exactly zero (due to the use of 1 bar pressure as a reference). EXAMPLE 9: Effect of pressure on OER kinetics The effect of pressure on the kinetics of the OER was determined. The main parameter that changes as a function of pressure is oxygen solubility in water; we assess this quantity self- consistently using Eqs. (20) through (24). Note that the rate constant does not change with pressure; the sole effect of pressure is on the oxygen activity that multiplies the reverse rate constant for reaction 2. The O₂ solubility, as a function of pressure at two different temperatures, 25°C and 90°C is

given in Figure 10. Naturally, the O₂ solubility increases with pressure and decreases with temperature. The OER current density as a function of the electrolyzer pressure at a fixed temperature of 90°C is given in in Figure 10A, B for two different cases: (i) an applied potential of 1.46 V vs. the RHE (Figure 10A; corresponding to an overpotential of 0.28 V vs. a fixed

_, = 1.18 V) and (ii) an applied potential of 151 V vs the RHE (Figure 11B; corresponding to an overpotential of 0.28 V vs. a fixed Although the reactor temperature in both cases is 90°C, we conside in case (ii). It is noted that the

OER current density decreases mildly in Figure 10A and negligibly in Figure 10B, as pressure changes from 1.013 to 100 bar. This is because the sole effect of pressure is to increase the reverse rate of reaction 2, via an increase in the oxygen activity. As a result, the pressure variation of the OER current density is mild at fixed potentials, with the OER current density decreasing by ~55 mA/cm² in case (i) and ~11 mA/cm² in case (ii) over the same pressure range at pH = pH^opt. It was also noted that the OER current density is higher at pH = pH^opt than at the standard pH = pH⁰ (see Figure 10A-B) by construction. Finally, by operating the electrolyzer with an anode potential of 1.51 V vs. the RHE at 90°C and 100 bar pressure, the OER current density would only reduce by ~12 mA/cm² to ~985 mA/cm² at pH = pH^opt (Figure 10B). This suggests that one could obtain compressed hydrogen directly, with no concomitant compromise in the OER kinetics. However, one would need to maintain the pH^opt ~8.6 (compared to pH⁰ = 12.4) at 90°C, as discussed above. This has the advantage of requiring less amount of alkali. To summarize the above analysis, the inventors have found that the maximum anodic OER current density is ~997 mA/cm² at a temperature of 90°C, as opposed to ~10 mA/cm² at room temperature, for an optimal pH = 8.6, standard pressure (1 bar), and an applied potential of 1.51 V vs. the RHE. This finding indicates Fe-doped NiOOH is an appropriate candidate for use in commercial electrolyzers, which typically function under alkaline conditions at current densities of ~400 mA/cm² and a temperature of 80 °C. It is also shown that at elevated temperatures (close to 90°C), a pH of 14 corresponds to unphysical species activities, and that one should consider the standard pH⁰ defined appropriately at each temperature.

Furthermore, the role played by the reduction in the OER potential with temperature in accelerating OER kinetics beyond simple Arrhenius effects is also determined.

It was also found that increasing pressure causes the OER potential to increase, thereby making the reaction less favourable thermodynamically. In terms of kinetics, for a fixed applied potential, increasing pressure reduces the OER current density marginally, due to an increased solubility of gaseous oxygen in water. As a result, producing compressed oxygen and hydrogen (~100 bar) involves a negligible trade-off in kinetics, while leading to cost-savings due to an obviation of downstream oxygen and hydrogen compression. Further, based on the above understanding between the coupled effects of temperature, pressure, and pH (alkali concentration) on the efficiency (OER current density), the present inventors have determined the optimal operating conditions – temperature, pressure and pH, for a range of potentials – for water electrolysis in an electrolyzer and the corresponding OER current density and concentration of alkali required in the method, as given hereinbelow in Table 1 and Table 2. The data generated herein is intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Table 1 therefore provides representative examples of optimal combinations of temperature, pressure, pH conditions along with corresponding current density and alkali concentrations required for the said pH at potentials of 1.5 V vs. the RHE (Table 1A), 1.6 V vs. the RHE (Table 1B) and 1.7 V vs. the RHE at the anode (Table 1C). Table 2 further provides representative examples of optimal combinations of temperature, pressure and pH conditions along with alkali concentrations required for the said pH at a potential of 1.5 V vs. the RHE (Table 2A-B) to obtain current density of 10 mA/cm² and 10000 mA/cm², respectively; at a potential of 1.6 V vs. the RHE (Table 2C) to obtain current density of 10000 mA/cm²; and at a potential 1.7 V vs. the RHE (Table 2D) at the anode to obtain current density of 10000 mA/cm². The data in Table 1 and Table 2 however is not exhaustive, and a person skilled in the art will be able to readily modulate the conditions to arrive at optimum values based on the teachings of the present disclosure. Accordingly, following examples should not be construed as limiting the scope of the disclosure herein. Table 1: Optimized operating conditions of temperature, pressure, and pH at an applied potential vs. the RHE at the anode and the corresponding OER current density and concentration of alkali for an iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst. Table 1A: At an applied potential of 15 V vs the RHE at the anode

Table 1B: At an applied potential of 1.6 V vs. the RHE at the anode

Table 1C: At an applied potential of 1.7 V vs. the RHE at the anode

Table 2: Optimized operating conditions of temperature, pressure, and pH at an applied potential at the anode along with concentration of alkali for an iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst to obtain the OER current density of about 10 mA/cm² and about 10000 mA/cm². Table 2A: At an applied potential of 1.5 V vs. the RHE at the anode to reach 10 mA/cm² current density

Table 2B: At an applied potential of 1.5 V vs. the RHE at the anode to reach 10 A/cm² current density

Table 2C: At an applied potential of 1.6 V vs. the RHE at the anode to reach 10 A/cm² current density

Table 2D: At an applied potential of 1.7 V vs. the RHE at the anode to reach 10 A/cm² current density

The foregoing description of the specific embodiments reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that

the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Throughout this specification, the term ‘combinations thereof’ or ‘any combination thereof’ or ‘any combinations thereof’ are used interchangeably and are intended to have the same meaning, as regularly known in the field of patent disclosures. As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned otherwise. Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

Claims

WE CLAIM: 1. A method of generating oxygen by electrochemical water splitting at optimized conditions of pH, temperature, and pressure for an oxygen evolution reaction (OER) current density ranging from about 10 mA/cm² to about 10000 mA/cm², said method comprising: a) contacting an anode of an electrolyzer with an electrolyte comprising water and alkali, in presence of a metal-doped oxide, hydroxide, or oxyhydroxide catalyst; and b) applying a potential ranging from about 1.45 V to about 1.75 V versus the reversible hydrogen electrode (RHE) at the anode to allow said generation of the oxygen; wherein the pH of the electrolyte ranges from about 7.4 to about 10.9; wherein the pH is a function of temperature T at a given pressure P; and wherein the temperature T ranges from about 28 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P.

2. The method as claimed in claim 1, wherein the pH of the electrolyte is determined based on an unconstrained minimization function applied to the negative of an OER current density, and wherein the OER current density is a function of the applied potential.

3. The method as claimed in claim 2, wherein the pH of the electrolyte is maintained in a manner that allows concentration of OH- ions in the electrolyte to be less than 1 M. 4. The method as claimed in claim 1, wherein when the potential is about 1.5 V vs. the RHE, the pH of the electrolyte ranges from about 7.

4 to about 10.7, and the temperature T ranges from about 28 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P. 5. The method as claimed in claim 1, wherein when the potential is about 1.6 V vs. the RHE, the pH of the electrolyte ranges from about 8.

5 to about 10.9, and the temperature T ranges from about 28 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P.

6. The method as claimed in claim 1, wherein when the potential is about 1.7 V vs. the RHE, the pH of the electrolyte ranges from about 10.2 to about 10.9, and the

temperature T ranges from about 28 °C to about 41 °C and is less than boiling point of the electrolyte at the given pressure P.

7. The method as claimed in any one of claims 4 to 6, wherein concentration or amount of the alkali required for maintaining the stated pH, ranges from about 0.07 mM to about 1.38 mM.

8. The method as claimed in claim 7, wherein the pH reduces from about 10.7 to about 7.4 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.5 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.38 mM to about 0.07 mM at the given pressure P. 9. The method as claimed in claim 7, wherein the pH reduces from about 10.

9 to about 8.5 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.6 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.14 mM at the given pressure P.

10. The method as claimed in claim 7, wherein the pH reduces from about 10.9 to about 10.2 with an increase in temperature and the corresponding increase in the OER current density at the potential of about 1.7 V vs. the RHE; and wherein the concentration or amount of the alkali required for maintaining the stated pH reduces from about 1.37 mM to about 0.47 mM at the given pressure P.

11. The method as claimed in any one of claims 1 to 10, wherein the pressure P ranges from about 1 bar to about 210 bar.

12. The method as claimed in claim 1, wherein the OER current density improves by at least about 80% when the method is carried out at said optimized conditions of pH, temperature, and pressure.

13. The method as claimed in claim 1, wherein the OER current density improves by about 200% when the method is carried out at said optimized conditions of pH, temperature, and pressure.

14. The method as claimed in claim 1, wherein the alkali is selected from a group of highly soluble hydroxides comprising potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide (Mg(OH)₂), and an alkali or alkaline earth hydroxide, or any combination thereof.

15. The method as claimed in claim 1, wherein the metal-doped oxide, hydroxide, or oxyhydroxide catalyst is an iron-doped nickel oxide, hydroxide, or oxyhydroxide catalyst, also referred to as a mixed iron/nickel oxide, hydroxide, or oxyhydroxide material.

16. The method as claimed in claim 1, wherein the electrolyzer further comprises a cathode within the electrolyte, and wherein applying a potential across the electrolyzer generates oxygen at the anode and hydrogen at the cathode.

17. The method as claimed in claim 1, further comprising capture of the generated oxygen.

18. The method as claimed in claim 1, further comprising capture of the generated hydrogen.

19. The method as claimed in claim 1, wherein the alkali is KOH or NaOH at a concentration or amount of about 0.15 mM, the catalyst is a mixed iron/nickel oxide, hydroxide, or oxyhydroxide catalyst, the potential applied at the anode is about 1.5 V vs. the RHE, the temperature is about 90 ºC, the pressure is about 1 bar, and the pH of the electrolyte is maintained at about 8.6.

20. The method as claimed in claim 1, wherein the alkali is KOH or NaOH at a concentration or amount of about 0.26 mM, the catalyst is a mixed iron/nickel oxide, hydroxide, or oxyhydroxide catalyst, the potential applied at the anode is about 1.5 V vs. the RHE, the temperature is about 100 ºC, the pressure is about 100 bar, and the pH of the electrolyte is maintained at about 8.6.

21. The method as claimed in claim 1, wherein the alkali is KOH or NaOH having a concentration or amount of about 0.27 mM, the catalyst is a mixed iron/nickel oxide, hydroxide, or oxyhydroxide catalyst, the potential applied at the anode is about 1.5 V vs. the RHE, the temperature is about 110 ºC, the pressure is about 200 bar, and the pH of the electrolyte is maintained at about 8.5.

22. The method as claimed in claim 19, wherein the OER current density is about 770 mA/cm².

23. The method as claimed in claim 20, wherein the OER current density is about 1241 mA/cm².

24. The method as claimed in claim 21, wherein the OER current density is about 1960 mA/cm².

25. The method as claimed in claim 1, wherein when the potential is about 1.5 V vs. the RHE, the pH of the electrolyte ranges from about 7.4 to about 10.6, and the temperature T ranges from about 40 °C to about 151 °C or from about 50 °C to about 151 °C and is less than the boiling point of the electrolyte at the given pressure P.

26. The method as claimed in claim 1, wherein when the potential is about 1.6 V vs. the RHE, the pH of the electrolyte ranges from about 8.5 to about 10.7, and the temperature T ranges from about 40 °C to about 92 °C or from about 50 °C to about 92 °C and is less than boiling point of the electrolyte at the given pressure P.

27. The method as claimed in claim 1, wherein when the potential is about 1.7 V vs. the RHE, the pH of the electrolyte ranges from about 10.2 to about 10.6, and the temperature T ranges from about 40 °C to about 41 °C and is less than boiling point of the electrolyte at the given pressure P.