Electrocatalysts For Water Electrolysis Research Articles

Graphene‐Transition Metal Electrocatalysts for Sustainable Water Electrolysis

AbstractTransition metal compounds (TMCs) are potentially fruitful substitutes for noble metals for electrocatalytic splitting of water due to their intrinsic electrocatalytic activity, modifiable morphology, tunable electronic structure and their earth‐abundance. The combination of TMCs with graphene improves the dispersion of loaded catalysts, providing more catalytic active sites, enhancing the conductivity of hybrids, affording accelerated charge‐transfer kinetics, and minimizing catalyst bleaching, aggregation, and sintering under harsh reaction conditions. Additionally, graphene incorporation into TMCs modulates the electronic structure of active centers because of the synergistic interaction between them, thereby improving their catalytic performance. This review paper focuses on the recent progress made in designing different graphene‐transition metal‐based materials that can be used in the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and overall water splitting (OWS). In‐situ characterization methodologies and DFT calculations that facilitate catalyst development are discussed elaborately. Finally, the advancements made in the development of graphene‐supported transition metal compounds for use in a functional water electrolyzer have been explored. In conclusion, a few specific recommendations have been made about the current challenges related to the widespread production of effective HER/OER electrocatalysts for water electrolysis.

Pulse electrodeposition of Ni–P alloy coatings from Watts baths: P content, current efficiency, and internal stress

Ni–P alloy has been used as a protective coating for mechanical parts, a surface material for electronic parts, and an electrocatalyst for water electrolysis. Ni–P alloy electrodeposition was performed by adding H3PO3 to Watts baths under four different types of pulse current conditions and compared with direct current (DC) electrodeposition. When the peak current density was kept constant and the off time was extended, the P content increased, and the current efficiency decreased. When the off time was extended while the average current density remained constant, the P content peaked. This is thought to be due to a change in the phosphorus precipitation mechanism from indirect to direct. The internal stress trend of the Ni–P electrodeposition was measured in-situ using a spiral contractometer up to about 20 μm thickness. The results confirmed that it exhibited internal tensile stress due to hydrogen desorption. As the current efficiency decreased, the internal tensile stress tended to decrease because some excess hydrogen was not desorbed and remained inside. The internal tensile stress could be remarkably reduced to half that of DC electrodeposition while maintaining a high current efficiency by reducing the frequency of pulse electrodeposition to accelerate hydrogen desorption, or by applying a reverse current to consume the electrons that induce hydrogen production.

Perovskite oxides as electrocatalysts for water electrolysis: From crystalline to amorphous

Perovskite oxides as electrocatalysts for water electrolysis: From crystalline to amorphous

Orbital Occupancy Modulation to Optimize Intermediate Absorption for Efficient Electrocatalysts in Water Electrolysis and Zinc-Ethanol-Air Battery.

Spin engineering is a promising way to modulate the interaction between the metal d-orbital and the intermediates and thus enhance the catalytic kinetics. Herein, an innovative strategy is reported to modulate the spin state of Co by regulating its coordinating environment. o-c-CoSe2 -Ni is prepared as pre-catalyst, then in situ electrochemical impedance spectroscopy (EIS)and in situ Raman spectroscopy are employed to prove phase transition, and CoOOH/Co3 O4 is formed on the surface as active sites. In hybrid water electrolysis, the voltage has a negative shift, and in zinc-ethanol-air battery, the charging voltage is lowered and the cycling stability is greatly increased. Coordinated atom substitution and crystalline symmetry change are combined to regulate the absorption ability of reaction intermediates with balanced optimal adsorption. Coordinated atom substitution weakens the adsorption while the crystalline symmetry change strengthens the adsorption. Importantly, the tetrahedral sites are introduced by Ni doping which enables the co-existence of four-coordinated sites and six-coordination sites in o-c-CoSe2 -Ni. The dz2 + dx2 -y2 orbital occupancy decreases after the atomic substitution, while increases after replacing the CoSe6 -Oh field with CoSe6 -Oh /CoSe4 -Td . This work explores a new direction for the preparation of efficient catalysts for water electrolysis and innovative zinc-ethanol-air battery.

Improved pseudocapacitor and water splitting in cobalt-anchored vanadium carbide MXene nanocomposite

Electrochemical capacitors and hydrogen production through water splitting into constituent hydrogen (H2) and oxygen (O2) molecules are promising methods for long-lasting energy storage. This work presents a simple synthesis of a cobalt ion-doped vanadium carbide MXene (Co@V2CTx) nanocomposite, utilized as an effective, durable, and stable electrode for supercapacitors and as an electrocatalyst for water electrolysis. In 1 M KOH, the Co@V2CTx nanocomposite produced a capacitance of 1071 Fg-1 at 5 mVs−1 (more than 8 times that of pristine V2CTx MXene) and an energy and power density of 26.7 Whkg−1 and 325 Wkg-1 respectively at 1 Ag-1. In addition, the Co@V2CTx nanocomposite showed good hydrogen evolution reaction (HER) catalytic activity, exhibiting a minimal overpotential of 103 mV at 10 mAcm−2 and Tafel slope of 83 mVdec−1. The excellent performance of the Co@V2CTx nanocomposite is due to the synergistic effects produced when cobalt ions are intercalated into the vanadium carbide MXene, preventing restacking of sheets and boosting ion transfer. This work presents an easy and effective method for synthesizing MXene-based nanocomposites for energy storage and conversion applications.

Controllable synthesis of crystal-amorphous heterostructures in transition metal phosphide and enhancement mechanism for overall water splitting

The crystal-amorphous (c-a) heterostructure is a promising structure for electrocatalysts in water electrolysis. In this study, stable, efficient, and abundant c-a interfaces were formed by synchronously synthesizing crystalline FeP and amorphous MoP on foam ferrum by controlling the crystalline phase transition temperature. In 1 M KOH, the a-MoP/FeP@FF catalyst showed overpotentials of 75 mV and 253 mV for HER and OER processes, respectively, at a current density of j10. The Tafel slopes were small at 60 mV∙dec−1 and 77 mV∙dec−1 for HER and OER, respectively. Theoretical calculations indicate that the c-a interface optimizes the overall electronic structure, enabling Mo and Fe to have excellent HER and OER activity, respectively. The two types of active sites collaborate fully to promote overall water splitting. This study confirms that the c-a heterostructure can significantly enhance the catalytic performance of transition metal phosphides and explains the mechanism of enhanced catalytic activity. This synthesis method and reaction mechanism not only apply to other transition metal phosphides but also provide reference for other types of catalysts.

ZnS-stabilized single atoms for highly-efficient water electrolysis

Efficient generation of hydrogen via water electrolysis provides a strategy for producing clean and sustainable fuel. Nevertheless, the sluggish cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) require much energy input to overcome the high overpotential. Rational design of electrocatalysts is of crucial importance for enhancing the HER and OER performance. Herein, metal single atoms stabilized on the ZnS support (M@ZnS) were systematically investigated as the electrocatalysts for HER and OER via the density functional theory (DFT) calculations. Volcano plots were established to screen HER and OER catalysts with excellent performance. The structural, thermodynamic and electrochemical stability of M@ZnS catalysts were investigated. Sn@ZnS and Ni@ZnS exhibit superior HER catalytic activity. In particular, the ΔGH∗ value of Sn@ZnS is 0.049 eV, which is lower than that of the well-known benchmark Pt catalyst. Sn@ZnS and Pt@ZnS show good OER activity, thus they are expected to be the promising OER electrocatalyst candidates. The overpotential values of Sn@ZnS and Pt@ZnS are 0.60 V and 0.42 V, respectively. Sn@ZnS can work as a bifunctional HER/OER electrocatalyst for water electrolysis. This work not only provides theoretical guidance on the design of low-cost electrocatalysts toward HER and OER, but also paves a new way to stabilize single atoms for the fabrication of single-atom catalysts.

Facet-Dependent Selectivity of Rutile IrO2 for Oxygen and Chlorine Evolution Reactions

Water electrolysis is a promising route for sustainable production of hydrogen as an energy storage medium and valuable precursor for industrial chemical syntheses such as ammonia and methanol. Direct electrolysis of seawater circumvents costly desalination and purification steps to reduce the price of renewable hydrogen to achieve cost parity with carbon-intensive steam reforming. However, the significant concentration of chloride salts in seawater poses a challenge to selectivity of seawater electrolysis. In aqueous chloride electrolytes, the chlorine evolution reaction (CER) is kinetically favored over the oxygen evolution reaction (OER). Rutile-type iridium dioxide (IrO2) is a state-of-the-art electrocatalyst for water electrolysis but is also a benchmark chlorine evolution electrocatalyst in the industrial chlor-alkali process. Understanding OER/CER selectivity is needed to make seawater electrolysis a viable energy conversion technology in the future.In this work, we seek to understand the relationship between crystallographic facet and competitive reaction pathway between OER and CER on epitaxial, rutile IrO2 thin films. We investigate facet-dependent OER and CER activity on a series of single-crystalline IrO2 thin films using a rotating disk electrode geometry. The OER/CER selectivity, reaction rate order, and reaction intermediate electroadsorption affinities are explored to add fundamental insight into the reactivity of rutile IrO2 surface. To gain further insight into OER intermediate adsorption affinities, we paired electrochemical measurements with surface-sensitive ambient pressure x-ray photoelectron spectroscopy (AP-XPS). Moving forward, our facet-dependent study of OER/CER selectivity of rutile IrO2 can be used to design selective seawater electrocatalysts for cost-effective and sustainable hydrogen production.

Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting

The development of non-noble-metal-based electrocatalysts for water electrolysis is essential to produce sustainable green hydrogen. Highly active and stable non-noble-metal-based electrocatalysts are greatly needed for the replacement of the benchmark electrocatalysts of iridium, ruthenium, and platinum oxides. Herein, we synthesized non-noble-metal-based, Fe-doped, β-Ni(OH)2 interconnected hierarchical nanosheets on nickel foam via a conventional hydrothermal reaction. Iron doping significantly modified the electronic structure of β-Ni(OH)2 due to the electron transfer of iron to nickel hydroxide. Fe-doped β-Ni(OH)2 was investigated both as a cathode and anode electrode for hydrogen and oxygen evolution reactions (OERs and HERs). It facilitated significant improvements in electrochemical performance due to its huge intrinsic active sites and high electrical conductivity. As a result, the electrocatalytic activity of Fe-doped Ni(OH)2 exhibited a lesser overpotential of 189 and 112 mV at a current density of 10 mA cm−2 and a Tafel slope of 85 and 89 mV dec−1 for the OER and HER, respectively. The Fe-doped β-Ni(OH)2 displayed excellent durability for 48 h and a cell voltage of 1.61 V @ 10 mA cm−2. This work demonstrates that Fe-doped β-Ni(OH)2 is an efficient electrocatalyst with superior electrocatalytic performance towards overall water splitting that can be useful at the industrial scale.

Activity of electrodeposited rhodium in acidic and basic water electrolysis

Hydrogen (H2) is increasingly seen as a future fuel and a potential alternative to fossil fuels, as it is the cleanest and ideal energy carrier. Water electrolysis is one of the easiest methods to produce H2, offering the advantage of simplicity. Rhodium (Rh) is considered one of the best electrocatalysts for water electrolysis. This research was conducted to investigate the activity of electrodeposited Rh for its potential electrocatalytic application in acidic and basic water electrolysis. The electrode was fabricated from a 5 g/L solution of rhodium sulfate [Rh2(SO4)3] electrodeposited at 3.0 V for 3 min in a 92.5% silver (Ag) alloy substrate. Electrochemical characterizations were performed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in a three-electrode set-up. The acidic electrolyte was a sulfuric acid (H2SO4) solution while the basic electrolyte was a sodium hydroxide (NaOH) solution. Stability tests were done on a 48-h continuous run of water electrolysis. Results showed onset potentials of 1.4 V and −0.2 V for acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, while 0.6 V and −0.9 V for basic OER and HER, respectively. A consistent absolute value of limiting current, 8.00 × 10−3 A was observed for both reactions of the two electrolytes. Electrodeposited Rh as an anode showed excellent stability on both acidic and basic media but may fail as a cathode in long-term water electrolysis. The stability was observed to decrease with increasing electrolyte concentration at a higher rate on an acidic medium.

Enhancing the d/p‐Band Center Proximity with Amorphous‐Crystalline Interface Coupling for Boosted pH‐Robust Water Electrolysis

AbstractRationalizing non‐precious pH‐robust electrocatalysts is a crucial priority and required for multi‐scenario hydrogen production customization. Herein, an amorphous–crystalline CoBOx/NiSe heterostructure is theoretically profiled and constructed for efficient and pH‐robust water electrolysis. The crystalline lattice confinement induces a CoCo bond shortening and a B‐site delocalization on amorphous CoBOx, resulting in a decreased d‐p band center difference (Δεd‐p) toward the balanced intermediates adsorption/desorption. Accordingly, the CoBOx/NiSe heterostructure exhibits efficient and robust hydrogen/oxygen evolution reaction (HER/OER) catalytic activity in different electrolytes. Of particular note, it achieves ultralow overpotentials in both the beyond‐Pt HER (14.5 mV) and OER (229.1 mV) at 10 mA cm−2under an alkaline electrolyte, and reaches an industrial‐level OER current density of 2 A cm−2. Water electrolysis is stably delivered with a low η10voltage of 1.48 V. The incorporation of such d‐p orbitals at the amorphous–crystalline interface puts forward new opportunities in rationally designing advanced non‐precious electrocatalysts for water electrolysis.

MOF-Derived Iron-Cobalt Bimetallic Selenides for Water Electrolysis with High-Efficiency Oxygen Evolution Reaction.

Highly active and stable oxygen evolution reaction (OER) electrocatalysts for water electrolysis are currently in high demand. Herein, a rationally designed three-dimensional (3D) CoFe selenide porous array (Fe-CoSe PA) is synthesized through ion exchange from zeolitic imidazolate framework-L (ZIF-L) nanoarray, followed by a facile selenization under hydrothermal conditions for OER electrocatalysis. During the OER process, the surface of Fe-CoSe PA is rapidly oxidized to CoFe oxides/hydroxides, which prevents the inner layer from being oxidized. Benefiting from the high porosity, abundant active sites, and the high conductivity of inner Fe-CoSe, Fe-CoSe PA exhibits excellent OER performance, with an overpotential of 285 mV at a current density of 10 mA cm-2, and a small Tafel slope of 68 mV dec-1, as well as high stability under 50 h of continuous testing. The present work could provide a facile route for fabricating 3D porous selenides for highly efficient OER catalysis.

Electrochemical activation construction of LaCo1-x-yNixFeyO3 promoted by optimized lattice Ni doping toward water oxidation

Iron sites with high intrinsic activity for oxygen evolution reaction (OER) can effectively enhanced the performance of perovskite oxide as electrocatalyst for water electrolysis. However, doping of iron in perovskite LaCoO3 remains a challenge owing the strong Co–O bond and robust structure of LaCoO3. Herein, the lattice doping of Ni in LaCoO3 has been adopted to promote the interaction between iron ions and Co site in LaCoO3. Firstly, molten salt of Ni(NO3)2 provides free-moving Ni ions to substitute Co sites in the lattice of LaCoO3 forming LaCo1-xNixO3 at the optimized Ni doping condition. Then, iron ions can easily be absorbed to LaCo1-xNixO3 due to the strong interaction between Ni and Fe by electrochemical activation at room temperature. The prepared LaCo1-x-yNixFeyO3 nanoparticles keep the coarse surface for maximizing the exposure of active sites. The high-valence Co and oxygen vacancy from LaCo1-x-yNixFeyO3 contribute to the better intrinsic activity for OER, demonstrating the overpotential of ƞ10 of approximately 315 mV and good stability. The strategy of by introducing the lattice doping of other metal ion can realize the facile and effective construction of iron doped perovskite oxide for water oxidation.

Recent Research Advances in Ruthenium‐Based Electrocatalysts for Water Electrolysis Across the pH‐Universal Conditions

Electrocatalytic water splitting including oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as a mild, green, and sustainable technology, is recognized as a great potential pathway to defeat the current environmental and energy‐related crisis. Electrode materials resisting the corrosion of electrolytes in the full pH range are attracting the attention of the research community, which can adapt to more complicated conditions and significantly reduce expenditure. Accordingly, considerable efforts have been made to upgrade the availability of pH‐universal electrode materials. Ruthenium‐based materials with prominent activity, pH‐universal window, cheaper price, etc. have been universally acknowledged to be the feasible alternative to platinum. Herein, the recent knowledge of the Ru‐based electrocatalysts toward HER, OER, and overall water splitting across all pH conditions, including reaction mechanism, construction of advanced electrocatalysts, and regulation strategy of activity is focused. Finally, the current challenges and future prospects are highlighted, aiming to guide the design and synthesis of the universal pH‐stable Ru‐based electrocatalysts.

Front Cover: Cobalt Oxide Nanowires with Controllable Diameters and Crystal Structures for the Oxygen Evolution Reaction (Eur. J. Inorg. Chem. 18/2022)

The Front Cover shows an illustration of replication of mesostructured cobalt oxide and its utilization as electrocatalyst for water electrolysis. The impact of the nanowire diameters of the two-dimensional ordered mesoporous spinel (Co3O4) and rock-salt (CoO) cobalt oxides on their electrochemical oxygen evolution reaction (OER) activity has been systematically studied. The magnifying glass reveals an operando Raman spectroscopy technique that is used to monitor the alteration of the electrocatalyst during the OER. A phase transformation from rocksalt (CoO) to a distorted spinel (Co3O4) phase is observed, which was found to be responsible for a high OER activity in the starting rocksalt crystal phase. More information can be found in the Research Article by E. Budiyanto and H. Tüysüz.

The Pivotal Role of s-, p-, and f-Block Metals in Water Electrolysis: Status Quo and Perspectives.

Transition metals, in particular noble metals, are the most common species in metal-mediated water electrolysis because they serve as highly active catalytic sites. In many cases, the presence of nontransition metals, that is, s-, p-, and f-block metals with high natural abundance in the earth-crust in the catalytic material is indispensable to boost efficiency and durability in water electrolysis. This is why alkali metals, alkaline-earth metals, rare-earth metals, lean metals, and metalloids receive growing interest in this research area. In spite of the pivotal role of these nontransition metals in tuning efficiency of water electrolysis, there is far more room for developments toward a knowledge-based catalyst design. In this review, five classes of nontransition metals species which are successfully utilized in water electrolysis, with special emphasis on electronic structure-catalytic activity relationships and phase stability, are discussed. Moreover, specific fundamental aspects on electrocatalysts for water electrolysis as well as a perspective on this research field are also addressed in this account. It is anticipated that this review can trigger a broader interest in using s-, p-, and f-block metals species toward the discovery of advanced polymetal-containing electrocatalysts for practical water splitting.

Repurposing metal containing wastes and mass-produced materials as electrocatalysts for water electrolysis

Recycling metal containing waste is an attractive option to generate water splitting electrocatalysts for green hydrogen production. This will help alleviate future pressure on endangered elements that are required for the future energy transition.

Metal‐Organic Framework Derived Nanostructured Bifunctional Electrocatalysts for Water Splitting

AbstractWith continuously increasing energy requirements, electrochemical water splitting is a solution to generate hydrogen as a carbon‐free fuel for future energy demands. Water splitting reaction is made up of two half electrochemical reactions ‐ hydrogen evolution (HER) and oxygen evolution (OER). The principal components of these electrochemical reactions are electrode materials, which are currently facing challenges in performance improvement, thus developing advanced electrode materials or electrocatalysts is essential. Metal‐organic frameworks (MOFs) are crystalline porous materials that have recently exhibited great potential as precursor for designing excellent water splitting electrocatalysts. These MOF‐derived materials are not attractive just because of high‐performance in electrocatalysis but also owing to their fascinating nanostructures, which are difficult to achieve by other synthetic methods. Search for well‐shaped nanostructured materials using MOF as a precursor for water splitting have attracted the attention in recent time and is a rapidly growing research area. This review summarizes the progress towards MOF‐derived electrocatalysts for water electrolysis especially focusing on nanostructure engineering, structure‐property correlations, and their bifunctional HER/OER performances. Performance of these bifunctional catalysts in two‐electrode electrolyzers are also discussed. Finally, existing obstacles and the future prospects of MOF‐derived bifunctional water splitting electrocatalysts are elaborated.

A Review and Perspective on Electrocatalysts Containing Cr for Alkaline Water Electrolysis: Hydrogen Evolution Reaction

Transition metal-based catalysts are the next most efficient catalysts for hydrogen generation in alkaline media, after Pt-group metal catalysts. Research employing transition metal-based catalysts has progressed exponentially in recent years, resulting in catalysts with excellent activity and stability. Compared to other neighbour d-metals (Ni, Fe, Co, Cu) which receive proper preference, research on Zn, Mn, and Cr containing electrocatalysts for water electrolysis is limited. Chromium in general has received limited consideration but has begun to attract the attention of researchers in the past few years. This review provides a brief discussion and evaluation of different catalysts (oxides, hydroxides, nitrides, phosphides, sulphides, carbides, etc.) incorporating different phases of the Cr component, together with a perspective on the catalytic significance of using Cr as a co-catalyst for hydrogen evolution in alkaline media. With advancements in catalysis research, electroactivity and stability showcased by Cr-based catalysts, some even competitive against precious metal catalysts, can be lucrative solutions for H2 generation.

Ex-Situ Investigation of Activated Stainless Steel As Oxygen Evolution Reaction Electrode in Alkaline Media

Transition metal mixed oxides have been considered as promising catalysts for OER in alkaline media due to high catalytic activity, possible long lifetime and cheap alternatives to precious metal oxides [1-3]. Increasing research interest has been dedicated to Ni-based OER catalysts in particular, which possesses all desired qualities for a catalyst including being earth-abundant and have theoretically high catalytic activity [1]. Iron impurities in nickel hydroxide was found to lower OER overpotential in Ni-based alkaline batteries [4, 5], which paved the way for NiFe catalysts as active OER electrocatalysts in water electrolysis [5-9]. Large use of Ni-rich materials is becoming an increasing difficulty in alkaline electrolysis, and the search for cheaper bulk materials has recently been intensified. In particular, cheaper stainless steels being a source of both Fe and Ni have shown promise as OER electrode. However, the as-received stainless steel has low OER activity and some surface treatment, enriching the surface with nickel is necessary.In this work, we activate as-received 316 stainless steel bulk material by electrooxidation at 1.72 V vs RHE in KOH electrolyte at room temperature. We study the effect of electrolyte pH during activation as well as oxidation time. The electrode surface layer is studied using XPS, GDOES and SEM, while the surface activity is studied electrochemically using potential step and linear sweep voltammetry in a three-electrode Teflon cell. The active surface area was assessed using cyclic voltammetry. Reaction order and Tafel slope are determined to specify the reaction mechanism.We show that surface treatment of 316 stainless steel in the highest concentration of KOH (7.5 M) gives the highest activity for a minimum of 240 minutes oxidation time. Longer oxidation times did not improve electrochemical activity. Surface analysis by XPS, SEM and GDOES show a significant increase in surface Ni after activation, which was correlated to the improved activity. The surface content of Ni increased in general with increasing electrolyte pH during activation. SEM indicates small crystals on the surface, which could be due to precipitation of dissolved species on the activated samples. The best pretreatment performed in this study leads to an overvoltage of 320 mV at 10 mA cm-2. Krasil’shchikov reaction pathway is assigned as the OER reaction mechanism corresponding to the measured reaction order and Tafel slope. All the samples have the same Tafel slope. Repetitive polarization curves after 24h chronoamperometry indicate negligible change in performance with time. This indicates that the activated stainless steel is a promising electrode material for oxygen evolution. Han, L., S. Dong, and E. Wang, Transition‐metal (Co, Ni, and Fe)‐based electrocatalysts for the water oxidation reaction. Advanced materials, 2016. 28(42): p. 9266-9291. Singh, R., J. Singh, and A. Singh, Electrocatalytic properties of new spinel-type MMoO4 (M= Fe, Co and Ni) electrodes for oxygen evolution in alkaline solutions. international journal of hydrogen energy, 2008. 33(16): p. 4260-4264. Song, F., et al., Transition metal oxides as electrocatalysts for the oxygen evolution reaction in alkaline solutions: an application-inspired renaissance. Journal of the American Chemical Society, 2018. 140(25): p. 7748-7759. Conway, B. and P. Bourgault, The electrochemical behavior of the nickel–nickel oxide electrode: Part I. Kinetics of self-discharge. Canadian Journal of Chemistry, 1959. 37(1): p. 292-307. Lyons, M.E. and M.P. Brandon, The oxygen evolution reaction on passive oxide covered transition metal electrodes in aqueous alkaline solution. Part 1-Nickel. Int. J. Electrochem. Sci, 2008. 3(12): p. 1386-1424.