Oxygen Evolution Reaction Properties Research Articles

Construction of mesoporous Ni-Co-Mo oxide/sulfide composite composite nanosheet arrays as bifunctional material for charge storage and oxygen evolution reaction applications

At present, energy conversion and energy storage devices are gradually integrated together, which puts forward higher requirements for the design and construction of electrode materials. Herein, bi-functional Co-Mo oxides and Ni/Co sulfides (NCMOS) composite nanosheet arrays on Ni foam are constructed for supercapacitors and oxygen evolution reaction (OER) of water splitting. The Ni-Co-Mo nanosheet precursor is firstly synthesized by stepwise hydrothermal processes and then converted into Ni-Co sulfide and Co-Mo oxide by in-situ sulfurization. The nanoarray and in-situ sulfurization of active materials bring more reactive active sites, optimize reaction kinetics, and shorten the transport path of electrons and charges, which enhance energy storage performance and OER catalytic activity of NCMOS material. In terms of supercapacitor applications, NCMOS exhibits high specific capacity (1332.1 C g–1) and good cycle stability. For OER application, NiCMOS shows lower OER overpotential (290 mV at 100 mA cm–2), smaller Tafel slope (87.2 mV dec–1) and excellent catalytic stability in oxygen evolution for 60 h. The excellent charge storage and OER properties suggest that bi-functional oxide/sulfide composites have great potential in energy conversion and storage-integrated devices.

Heterostructure of Fe-Doped CoMoOx/CoMoOx as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) plays a crucial role as a counter half-reaction for both electrochemical hydrogen production through water splitting and the generation of valuable carbon compounds via CO2 reduction. To overcome the sluggish kinetics of the OER, significant efforts have been devoted to developing cost-effective, sustainable, and efficient electrocatalysts, with transition-metal-based catalysts emerging as promising candidates. Herein, we successfully synthesized a core-shell type nanostructure of Fe-doped CoMoOx/CoMoOx (CMFO), which exhibits excellent electrocatalytic properties for OER. The presence of an amorphous layer of Fe-doped CoMoOx with abundant oxygen vacancies, along with the stability of a key OER intermediate, *O, contributes to the enhanced activity of CMFO catalyst compared to pristine CoMoOx (CMO). The optimized catalyst of CMFO-550 achieved much lower overpotential and Tafel slope and also exhibited better remarkable long-term stability for over 90 h compared to CMO-550. These findings highlight the potential of CMFO-550 as a cost-effective and highly efficient electrocatalyst for the OER. The successful development of this core-shell nanostructure opens up a new opportunity for the design and synthesis of advanced electrocatalysts for the OER, with implications for various applications in energy conversion and storage.

In Situ Modulation of Oxygen Vacancies on 2D Metal Hydroxide Organic Frameworks for High-Efficiency Oxygen Evolution Reaction.

The discovery of non-precious catalysts for replacing the precious metal of ruthenium in the oxygen evolution reaction (OER) represents a key step in reducing the cost of green hydrogen production. The 2D d-MHOFs, a new 2D materials with controllable oxygen vacancies formed by controlling the degree of coordination bridging between metal hydroxyl oxide and BDC ligands are synthesized at room temperature, exhibit excellent OER properties with low overpotentials of 207 mV at 10mA cm-2. High-resolution transmission electron microscopy images and density functional theory calculations demonstrate that the introduction of oxygen vacancy sites leads to a lattice distortion and charge redistribution in the catalysts, enhancing the OER activity of 2D d-MHOFs comprehensively. Synchrotron radiation and in situ Raman/Fourier transform infrared spectroscopy indicate that part of oxygen defect sites on the surface of 2D d-MHOFs are prone to transition to highly active metal hydroxyl oxides during the OER process. This work provides a mild strategy for scalable preparation of 2D d-MHOFs nanosheets with controllable oxygen defects, reveals the relationship between oxygen vacancies and OER performance, and offers a profound insight into the basic process of structural transformation in the OER process.

Efficient and Stable Dual-Active-Site of Core-Shell NiFe-Layered Double Hydroxide Anchored on FeMnON-N-Doped Carbon Nanotubes as Bifunctional Oxygen Electrocatalysts for Zn-Air Batteries

The bifunctional air electrodes with numerous dual-active sites and low cost are desirable to modify the performance of Zn-air batteries (ZABs). Metal–oxygen-nitrogen–carbon substrate (M = Mn, Fe, Ni, etc.) and NiFe-layered double hydroxide (NiFe-LDH) nanosheets are excellent catalysts in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, respectively. Hereby, we investigate a bifunctional electrocatalytic substrate with a 3D core–shell hierarchical architecture by anchoring high OER-active NiFe-LDH on ORR-active FeMnZIF-8@gC3N4-derived FeMnON-N doped carbon nanotubes bamboo like (NiFe-LDH@FeMnON-NC). This nanocomposite has unique features such as robust synergistic effects, high conductivity, balance, and optimization of surface chemical valences of Fe, Mn, and Ni atoms to boost the bifunctional ORR and OER properties and stability in ZABs. The NiFe-LDH@FeMnON-NC nanocomposite not only exhibited superior OER electroactivity with a low onset overpotential of 235 mV (10 mA cm−2) but also had excellent ORR activity with a current density of −5.48 mA cm−2 and onset potential of 1.04 V, which is better than or comparable to those of commercial Pt/C and RuO2. Rechargeable ZABs constructed by bifunctional NiFe-LDH@FeMnON-NC have a peak power density (235.41 mW cm−2), open-circuit potential (OCV) (1.53 V), small discharge/charge band gap of 0.74 V and excellent discharge stability.

Anisotropic structural carbon skeleton decorated with Co nanoparticles towards oxygen evolution reaction

Hierarchical carbon skeletons derived from natural wood can be employed as the substrates to fabricate self-supported catalysts. The typically three sections (cross section, radial section, and tangential section) of wood would significantly affect the electrocatalytic performance. Therefore, the correlations between anisotropy structure of wood derived hierarchical carbon skeletons and oxygen evolution reaction (OER) performances was systematically investigated. The cross-sectional wood-derived carbon decorated with Co nanoparticles requires an overpotential of 370 mV to deliver 50 mA cm−2 superior to those of radial-sectional and tangential-sectional counterparts. The cross-section of wood derived carbon skeleton possesses higher content of Co nanoparticles, which is accounted for the enhanced OER catalytic activity. This work highlights the critical contribution of anisotropy of carbon skeletons in promoting the OER properties and provides a new paradigm for designing advanced electrocatalysts.

Insights on MOF-derived metal-carbon nanostructures for oxygen evolution.

Electrochemical water splitting has been regarded a promising method for the production of green hydrogen, addressing the need for efficient energy conversion and storage. However, it is severely hindered by the oxygen evolution reaction (OER) because of its multi-step four-electron transfer pathway with sluggish reaction kinetics. Microporous metal-organic-frameworks (MOFs), by virtue of large specific surface area, high porosity, tunable composition and morphology, find widespread use as precursors of metal-carbon nanostructures. The resulting carbon nanomaterials can well inherit the characteristics and advantages of the crystalline MOF precursors, and exhibit versatile application prospects in the fields of environment and energy, particularly in OER. Herein, a meticulous overview of the synthesis strategy for MOF-derived metal-carbon nanostructures and the origins of their enhanced OER properties has been demonstrated. We comprehensively illustrate these aspects across three dimensions: MOF selection, metal introduction, and carbon structures. Finally, the challenges and future prospects for this emerging field will be presented.

Activation of Commercial Stainless-Steel Electrodes for Highly Efficient and Stable Anion-Exchange Membrane Electrolysis

Commercial stainless steel (SS) is gaining interest as a promising electrode material to be widely used for green hydrogen production from alkaline water electrolysis. Herein, low-cost 304-type SS meshes (SM) were engineered through a simple 2-step activation process, i.e., chemical etching and electrochemical activation. The modified electrodes exhibited comparable hydrogen and oxygen evolution reaction properties with commercially, noble metal-based electrodes available. The modified stainless steel-based electrodes were assembled and tested in an AEM electrolyzer cell, which displays more than 300 mV-voltage drops compared to the bare stainless steel-based cells. The in-situ impedance spectroscopy revealed a significant decrease in the resistances due to interfacial contact, charge transfer, and mass transport. In addition, we identified nanocrystalline Fe-NiCr2O4 and nanocrystalline Ni(OH)2/Fe(OH)2 active species for SS used in hydrogen and oxygen evolution side respectively which could explain the significantly higher performance. In addition, we also developed an electrolyzer system to assess the long-term durability of our cell reactors in which our cells exhibited exceptional durability at 5.0 A (1.0 A cm-2) for 250 h. Our results exemplify that such an approach has the potential for upscaling and deployment in the next-generation, low-cost AEM electrolysis for green hydrogen production.

Enhance the water oxidation performance of electrodeposited Ni(OH)2 through structure modulation by glutamic acid

Ni(OH)2 has been extensively studied as a promising electrocatalyst for the oxygen evolution reaction (OER). However, enhancing its OER properties is still required and challenging. Here we reported that the OER activity of Ni(OH)2 can be improved with the structure modulation by glutamic acid (GA) through a simple co-electrodeposition process. The coordination effect of GA leads to the reduction of Ni2+ ions and enhances the generation of NiOOH sites during the activation process by cyclic voltammetry. The Ni(OH)2-GA anode shows remarkably enhanced OER activity than pristine Ni(OH)2 in alkaline media. Additionally, Fe-doping realizes further improvement in the OER activity of Ni(OH)2-GA, suggesting the possibility of achieving highly efficient electrocatalysts with cheap materials and an easy fabrication process.

Understanding the synergistic catalysis effect on the dual-metal-N4 embedding single-walled carbon nanotubes from first principles

Developing high-efficiency electrocatalysts for the oxygen evolution reaction (OER) remains a crucial bottleneck on the way to the water splitting for producing clean fuel (H2). Compared with single atom catalysis (SACs), dual-atom catalysts (DACs) have attracted great interest due to higher OER catalytic efficiency. In this work, the OER properties of dual-metal-N4 embedding armchair single-walled carbon nanotubes (D-MN4/CNTs) were systematic studied by density functional theory (DFT) simulations. Our results indicate that CoN4 embedding armchair CNTs exhibit higher OER activity than the corresponding planar structure, especially for CoN4 embedding in armchair CNT (4, 4) (CNT4). For MN4-CoN4 co-embedding CNTs, the TiN4-CoN4/CNTs have good OER synergistic effect with the lowest overpotential. Besides, the diameter of CNTs have a significant impact on the OER efficiency. The lowest reaction overpotential 0.47 V were obtained in TiN4-CoN4/CNT4 with a 5.69 Å tube diameter. Interestingly, compressive stress will further enhance the synergistic effect between two metal atoms in the OER reaction. The OER overpotential of CoN4-TiN4 embedding armchair CNT4 can reduce to 0.40 V under the −4 % uniaxial compression strain. These works were expected to better understand the synergistic mechanisms and design high-efficiency dual-atom OER electrocatalysts.

Electrochemical Investigations of Double Perovskite M2NiMnO6 (Where M = Eu, Gd, Tb) for High-Performance Oxygen Evolution Reaction

Double perovskites are known for their special structures which can be utilized as catalyst electrode materials for electrochemical water splitting to generate carbon-neutral hydrogen energy. In this work, we prepared lanthanide series metal-doped double perovskites at the M site such as M2NiMnO6 (where M = Eu, Gd, Tb) using the solid-state reaction method, and they were investigated for an oxygen evolution reaction (OER) study in an alkaline medium. It is revealed that the catalyst with a configuration of Tb2NiMnO6 has outstanding OER properties such as a low overpotential of 288 mV to achieve a current density of 10 mAcm−2, a lower Tafel slope of 38.76 mVdec−1, and a long cycling stability over 100 h of continuous operation. A-site doping causes an alteration in the oxidation or valence states of the NiMn cations, their porosity, and the oxygen vacancies. This is evidenced in terms of the Mn4+/Mn3+ ratio modifying electronic properties and the surface which facilitates the OER properties of the catalyst. This is discussed using electrochemical impedance spectroscopy (EIS) and electrochemical surface area (ECSA) of the catalysts. The proposed work is promising for the synthesis and utilization of future catalyst electrodes for high-performance electrochemical water splitting.

Investigating the role of 3D hierarchical Ni-CAT/NiFe-LDH/CNFs in enhancing the oxygen evolution reaction and Zn-air battery performance

NiFe layered double hydroxide (NiFe-LDH) is an efficient and widely available catalyst for the oxygen evolution reaction (OER), but further improvement of its OER property remains a challenge. Therefore, a conductive Ni-organic framework is triumphantly synthesized in-situ on NiFe-LDH/carbon nanofibers (Ni-CAT/NiFe-LDH/CNFs) through a hydrothermal treatment. This configuration utilizes the exposed surface area and the electron transfer pathways of Ni-CAT and CNFs, resulting in exceptional OER kinetics in alkaline conditions. A low overpotential of 370 mV at 10 mA cm−2 and a small Tafel slope of 79 mV dec−1 are achieved. The liquid-state Zn-air batteries, featuring Ni-CAT/NiFe-LDH/CNFs catalyst as an air cathode, indicate a significant peak power density of 292.1 mW cm−2 and an extended cycle durability of over 66 h. Solid-state Zn-air batteries demonstrate stable cycling at various flat/bent/flat states, showing great potential for flexible electronic device applications. According to experimental measurements and computational analysis, the in-situ growth of Ni-CAT on the NiFe-LDH matrix can optimize intermediate adsorption and alter hydrophilicity, resulting in improved performance of Zn-air batteries.

A novel sea urchin like nanostructure as a bifunctional catalyst for overall water splitting

The aim of this study is to construct a high-activity platinum-anchored WO3 electrocatalyst and investigate the effect of platinum content on the catalytic performance. This strategy compared the electrocatalytic performance under acidic conditions by discussing the platinum content and significantly enhances the electrocatalytic activity through nanoscale structure creation and electronic synergies. Therefore, anchoring Pt atoms on WO3 nanoarrays is very important for boosting the activity and stability of electrocatalysis via a hydrothermal co-precipitation approach, Ptx/WO3@NF (x = 0.1 mmol∼0.3 mmol) named as Pt1/WO3, Pt2/WO3 and Pt3/WO3, which enhanced hydrogen evolution reaction(HER) and oxygen evolution reaction (OER) activities. The prepared Pt2/WO3@NF microspheres showed excellent electrocatalytic activity. When the current density was 10 mA cm−2, the HER overpotential was 77 mV, the OER overpotential was 126 mV, and the two-electrode water decomposition voltage was 1.4418 V. The bifunctional catalyst shows excellent stability, with virtually no decay in the curves after 100 h stability tests. In addition, nanosheet surface has abundant defects and interface structure, which can maintain excellent conductivity of catalyst and expose more active sites clarify the increased H2 adsorption for HER activity enhancement. The synthesis of a bifunctional electrocatalyst with both HER and OER properties, presents a novel and intriguing concept that contributes to the advancement of green hydrogen development.

“Polyoxometalate electron sponge” induces the accurate regulation of electron states at Ni sites to enhance oxidation of water

Because of their special features, NiFe-LDHs (nickel iron layered double hydroxides) are prospective OER (oxygen evolution reaction) catalysts that might be utilized to catalyse the electrolysis of water and produce hydrogen to address the energy crisis. In this work, the electronic structure and electrocatalytic performance of the NiFe-LDH were accurately regulated by optimizing the Ni sites, which was enabled by adjacent metal sites coordinated with the “polyoxometalate electron sponge”. With extension of the modification time, the Ni 2p binding energy, the Ni3+/Ni2+ ratio and the OER properties were gradually tuned, which indicated accurate regulation of active Ni sites by the “polyoxometalate electron sponge” on a temporal scale. Additionally, NiFe-LDH-PW12-12 h (NiFe-LDH modified by polyoxometalate anions for 12 h) showed the highest OER performance along with fast electron transfer, superior reaction kinetics and electrochemical durability, with an overpotential ∼68 mV lower than that of NiFe-LDH. This work provides an accurate strategy for regulating the electronic structures of active metal sites for the OER.

Amorphous-crystalline heterostructures enable energy-level matching of cobalt sulfide/nickel iron layered double hydroxide for efficient oxygen evolution reaction

Interface engineering of heterostructures has emerged as a promising approach to enhance the catalytic activity of nonprecious electrocatalysts. Herein, a novel amorphous cobalt sulfide-crystalline nickel iron layered double hydroxide (a-CoS@NiFe-LDH) hybrid material is presented for application as an electrocatalyst for oxygen evolution reaction (OER). Benefitting from the well-matched energy level structures, the a-CoS@NiFe-LDH catalyst delivers a low overpotential of 221 ± 14 mV at an OER current density of 20 mA cm−2 and a small Tafel slope of 83.1 mV dec-1, showing good OER properties. First-principle computations reveal that the electronic interaction between amorphous cobalt sulfide (a-CoS) and crystalline nickel iron layered double hydroxide (NiFe-LDH) components within a-CoS@NiFe-LDH promotes the adsorbate evolution mechanism and reduces the adsorption energies for oxygen intermediates, thereby enhancing the activity and stability for OER. This work opens up a new avenue to enhance the OER catalytic efficiency via the construction of amorphous-crystalline heterostructures.

Outstanding oxygen evolution reaction properties released at the interface of NiMoO4 and FeNi layer double hydroxide heterostructures

For the alkaline oxygen evolution reaction (OER), FeNi layered double hydroxide (FeNi LDH) exhibits good activity and stability. For the sake of saving freshwater, the use of abundant seawater as an electrolyte poses new requirements for its OER performance. A novel method was designed based on a corrosion reaction to convert commercial Fe foam into a high-performance OER catalyst (FeNiM), which consisted of FeNi LDH layers and NiMoO4 nanoparticles modified on its surface. FeNiM exhibited excellent OER activity, only requiring an overpotential of 250 mV to achieve a current density of 100 mA cm−2. Experimental results indicated that the heterostructures formed by NiMoO4 and FeNi LDH was conducive to exposing active sites, promoting the adsorption of active intermediates, and generating highly active oxyhydroxides. In addition, the heterostructure was beneficial to stabilizing the electrode surface structure and inhibiting seawater corrosion. Therefore, FeNiM could maintain high current density activity in both alkaline freshwater and alkaline seawater, which only required low overpotentials of 326 mV and 304 mV to achieve a high current density of 1500 mA cm−2, respectively. This catalyst preparation method has the advantages of economic efficiency, industrial compatibility, and significantly promoting the development of green hydrogen economy and industrial seawater desalination.

Unravelling the trifunctional electrochemical properties of WSe2 nanosheets for self-powered hydrogen production

Two dimensional materials have received increasing recognition for their utility in electrochemical energy storage and conversion devices, as well as for self-powered systems. In this work, we are reporting the trifunctional electrochemical properties (such as energy-storage, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) of WSe2 nanosheets (prepared by a solvothermal method) towards the development of a self-powered system for uninterrupted hydrogen (H2) production. First, we have examined the energy storage properties of the WSe2 nanosheets in the form of flexible solid-state supercapacitor (FSSC) that shows the presence of ion-intercalation pseudocapacitance in the WSe2 nanosheets. The fabricated WSe2 FSSC possess a high device capacitance, energy density, and power density with 119% capacitance retention over 5,000 cycles. Second, we explored the electrocatalytic properties of WSe2 nanosheets that indicated they possess effective HER and OER properties with low overpotential (115 mV for HER and 312 mV for OER), respectively. Finally, a proof-of-concept self-powered system comprising a solar cell, WSe2 FSSC, and lab-scale WSe2 electrolyzer (with a low overpotential of 1.604 V at 10 mA cm−2) was demonstrated to overcome the power fluctuation issues for effective and uninterrupted H2 production.

CoFe Alloys Dispersed on Se, N Co-Doped Graphitic Carbon as Efficient Bifunctional Catalysts for Zn-Air Batteries.

The development of a stable and efficient non-noble metal catalyst with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is paramount to achieving the widespread application of Zn-air batteries (ZABs) but remains a great challenge. Herein, a novel Co3 Fe7 alloy nanoparticle dispersed on Se, N co-doped graphitic carbon (denoted as CoFe/Se@CN) was prepared through a facile hydrothermal and pyrolysis process. The synthesized CoFe/Se@CN exhibits outstanding ORR and OER properties with an ultralow potential gap of 0.625 V, which is mainly attributed to the abundant porous structure, the rich structural defects formed by doping Se atoms, and the strong synergistic effects between the CoFe alloys and graphitic carbon nanosheet. Furthermore, the ZAB fabricated by CoFe/Se@CN shows a high peak power density of 160 mW cm-2 and a large specific capacity of 802 mA h g-1 with favorable cycling stability, outperforming that of Pt/C+RuO2 . Our study offers a plausible strategy to explore bifunctional carbon-based materials with efficient electrocatalytic properties for rechargeable ZABs.

Simple activation effect on the EC hydrolysis performance of MOF structure

Transition metal-based metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) are considered as the ideal substitutes or supports for electrochemical catalysis field. However, due to the limited number of surface-active sites and the low conductivity of the bulk of MOFs/COFs, their electrocatalytic (EC) performance is usually promoted by the complicated multi-step decoration procedures. In this paper, a simple sequential-activation-step was verified to have the ability to improve considerably the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of pristine Co-MOF (ZIF-67) material. For example, NC@Co from the carbonized and electrochemical activated ZIF-67 exhibited enhanced OER properties, while NC@CoxOy obtained via a sequential carbonize-oxidized-electrochemical activated procedure on ZIF-67 exhibited outstanding HER performance relatively. Density Functional Theory (DFT) calculations indicated that the in situ generated CoOOH was attributed to the improved HER/OER performance of the corresponding ZIF-67 activated derivatives with the redistribution of electron density, increased conductivity, and the optimized adsorption Gibbs free energy of hydrolysis intermediates. This work presents potential directions for the application of MOFs or COFs in the fields of electrochemical energy conversion through the electrochemical pathways.

Exploiting synergistic effects: Co3O4/g-C3N4 composite catalyst for enhanced oxygen evolution reaction

In this study, we explore the potential of Co3O4/g-C3N4 composite catalysts for improving the oxygen evolution reaction (OER) performance. By employing a rotating disk electrode in 0.1 mol L−1 KOH electrolyte, we systematically investigate the OER properties of various ratios of Co3O4/g-C3N4 catalysts. Our findings reveal that Co3O4/g-C3N4-0.2 catalyst outperforms pure g-C3N4, exhibiting significantly higher current density (10 mA cm−2) and lower overpotential (627 mV). Furthermore, Tafel slope analysis demonstrates enhanced reaction kinetics, with Co3O4/g-C3N4-0.2 catalyst displaying the smallest Tafel slope (54 mV dec−1). Electrochemical impedance spectroscopy (EIS) confirms the superior charge transfer efficiency of Co3O4/g-C3N4-0.2 catalyst compared to other ratios and pure g-C3N4. Impressively, stability tests demonstrate only 5.4% performance decay after 1000 CV cycles, highlighting the excellent stability of Co3O4/g-C3N4-0.2 catalyst. These findings underscore the remarkable potential of Co3O4/g-C3N4 composite catalysts in OER applications. The synergistic effects between Co3O4 and g-C3N4 contribute to enhanced electrocatalytic performance, making it a promising candidate for future OER advancements.

Long-Term Stability of Ni–Sn–Fe-Based Coatings Prepared by Electrodeposition for the Oxygen Evolution Reaction

A coating comprising Ni, Sn, and Fe was deposited on a Ni mesh by cathodic polarization from a bath containing Ni2+, Sn2+, and Fe3+ salts in solution, and the oxygen evolution reaction properties of the thus obtained electrode were investigated. The lattice volume of the Ni–Sn–Fe-based coating was estimated to be 77.1 Å3, a much larger value than that (44.0 Å3) of the Ni–Fe-based coating obtained in the absence of Sn2+. The Ni–Sn–Fe-coated electrode manufactured by cathodic polarization at a current density of −120 mA cm−2 afforded a current density of 10 mA cm−2 at an overpotential of 276 mV in 1 M KOH. The said electrode’s Tafel slope was estimated to be 37 mV dec−1. When electrolyzed at constant current density (+50 mA cm−2 to +800 mA cm−2), it exhibited a stable potential for at least 162 h. The Ni–Sn–Fe-coated electrode was also used as the anode in a two-electrode cell (80 °C; 30 wt% KOH) and electrolyzed for 3 d. Evidence indicated a low cell voltage of 1.81 V at a current density of +600 mA cm−2, which is at an industrial level.