Surface Oxidation of Stainless Steel: Oxygen Evolution Electrocatalysts with High Catalytic Activity

Stainless Steel Activation for Efficient Alkaline Oxygen Evolution in Advanced Electrolyzers

Designing robust and cost-effective electrocatalysts for efficient alkaline oxygen evolution reaction (OER) is of great significance in the field of water electrolysis. In this study, an electrochemical strategy to activate stainless steel (SS) electrodes for efficient OER is introduced. By cycling the SS electrode within a potential window that encompasses the Fe(II)↔Fe(III) process, its OER activity can be enhanced to a great extent compared to using a potential window that excludes this redox reaction, decreasing the overpotential at current density of 100 mA cm-2 by 40 mV. Electrochemical characterization, Inductively Coupled Plasma - Optical Emission Spectroscopy, and operando Raman measurements demonstrate that the Fe leaching at the SS surface can be accelerated through a Fe → γ-Fe2O3 → Fe3O4 or FeO → Fe2+ (aq.) conversion process, leading to the sustained exposure of Cr and Ni species. While Cr leaching occurs during its oxidation process, Ni species display higher resistance to leaching and gradually accumulate on the SS surface in the form of OER-active Fe-incorporated NiOOH species. Furthermore, a potential-pulse strategy is also introduced to regenerate the OER-activity of 316-type SS for stable OER, both in the three-electrode configuration (without performance decay after 300 h at 350 mA cm-2) and in an alkaline water electrolyzer (≈30 mV cell voltage increase after accelerated stress test-AST). The AST-stabilized cell can still reach 1000 and 4000 mA cm-2 at cell voltages of 1.69 and 2.1 V, which makes it competitive with state-of-the-art electrolyzers based on ion-exchange membrane using Ir-based anodes.

In-situ fabrication of Cr doped FeNi LDH on commercial stainless steel for oxygen evolution reaction

Commercial stainless steel has attracted increasing interest due to their rich content in transition metal elements and corrosion resistance properties. In this work, we design a facile and rapid route to in-situ fabricate the Cr doped FeNi layered double hydroxides nanosheets (LDHs) on modified stainless steel (Cr-FeNi LDH @ ESS) under ambient condition.The ultra small scaled 2D structure only around 20 nm diameter and metal ions with multivalent oxidation state were observed on the in situ fabricated LDHs, which provides high active area and active sites and thus promote excellent oxygen evolution reaction (OER). The Cr-FeNi LDH @ESS electrocatalysts exhibit an over potential of 280 mV at 10 mA cm-2 and achieves a Tafel slope of 44 mV dec-1 for OER in the 1.0 M KOH aqueous solution. We anticipate that the operating strategy of our system may promote the development of commercial non-precious productions as the efficient electrocatalysts for energy storage and conversion.

High-performance flower-like and biocompatible nickel-coated Fe3O4@SiO2 magnetic nanoparticles decorated on a graphene electrocatalyst for the oxygen evolution reaction

The electrocatalytic oxygen evolution reaction (OER) plays a crucial role in renewable clean energy conversion technologies and has developed into an important direction in the field of advanced energy, becoming the focus of basic research and industrial development. Herein, we report the synthesis and application of flower-like nickel-coated Fe3O4@SiO2 magnetic nanoparticles decorated on a graphene electrocatalyst for the OER that exhibit high efficiency and robust durability. The catalysts were optimized using a rotating ring-disk electrode to test their oxygen evolution properties in 1.0 M KOH solution. Importantly, owing to the high specific surface area and conductivity of C3N4 and graphene, the as-synthesized Fe3O4@SiO2@NiO/graphene/C3N4 exhibits a small Tafel slope of 40.46 mV dec-1, low overpotential of 288 mV at 10 mA cm-2, and robust OER durability within a prolonged test period of 100 h. The cytotoxicity of Fe3O4@SiO2, Fe3O4@SiO2@NiO, and Fe3O4@SiO2@NiO/graphene/C3N4 was evaluated in HeLa and MC3T3-E1 cells, demonstrating that they are efficient and biocompatible catalysts for the OER. Owing to its excellent electrocatalytic efficiency and eco-friendliness, Fe3O4@SiO2@NiO/graphene/C3N4 has considerable potential as a new multifunctional composite for large-scale applications in catalysis, biology, medicine, and high-efficiency hydrogen production.

Tailored Heterojunction Active Sites for Oxygen Electrocatalyst Promotion in Zinc-Air Batteries

Rechargeable zinc-air batteries (ZABs) are promising energy storage systems due to their low-cost and safety. However, the working principle of ZABs is based on oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which display sluggish kinetic and low stability. Herein, this work proposes a novel method to design a heterogeneous CoP/CoO electrocatalyst on mesopore nanobox carbon/carbon nanotube (CoP/CoO@MNC-CNT) that enriched active sites and synergistic effect. Moreover, the well-defined heterointerfaces could lower the energy barrier for intermediate species adsorption and promote OER and ORR electrochemical performances. The CoP/CoO@MNC-CNT electrocatalyst presents a high half-wave potential of 0.838 V for ORR and a small overpotential of 270 mV for OER. The ZABs-based CoP/CoO@MNC-CNT air-cathode shows an open-circuit voltage of 1.409 V, the long-term cycle life of 500 h with a small voltage difference change of 7.7%. Additionally, the flexible ZABs exhibit highly mechanical stability, demonstrating their application potential in wearable electronic devices.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Highly porous Co-doped NiO nanorods: facile hydrothermal synthesis and electrocatalytic oxygen evolution properties

Highly porous 3d transition metal oxide nanostructures are opening up the exciting area of oxygen evolution reaction (OER) catalysts in alkaline medium thanks to their good thermal and chemical stability, excellent physiochemical properties, high specific surface area and abundant nanopores. In this paper, highly porous Co-doped NiO nanorods were successfully synthesized by a simple hydrothermal method. The porous rod-like nanostructures were preserved with the added cobalt dopant ranging from 1 to 5 at% but were broken into aggregated nanoparticles at higher concentrations of additional cobalt. The catalytic activity of Co-doped NiO nanostructures for OER in an alkaline medium was assayed. The 5%Co-NiO sample showed a drastically enhanced activity. This result could originate from the combination of advantageous characteristics of highly porous NiO nanorods such as large surface area and high porosity as well as the important role of Co dopant that could provide more catalytic active sites, leading to an enhanced catalytic activity of the nanocatalyst.

Engineering Microdomains of Oxides in High-Entropy Alloy Electrodes toward Efficient Oxygen Evolution

One important goal of the current electrocatalysis is to develop integrated electrodes from the atomic level design to multilevel structural engineering in simple ways and low prices. Here, a series of oxygen micro-alloyed high-entropy alloys (O-HEAs) is developed via a metallurgy approach. A (CrFeCoNi)₉₇ O₃ bulk O-HEA shows exceptional electrocatalytic performance for the oxygen evolution reaction (OER), reaching an overpotential as low as 196 mV and a Tafel slope of 29 mV dec^-1 , and with stability longer than 120 h in 1 m KOH solution at a current density of 10 mA cm^-2 . It is shown that the enhanced OER performance can be attributed to the formation of island-like Cr₂ O₃ microdomains, the leaching of Cr³⁺ ions, and structural amorphization at the interfaces of the domains. These findings offer a technological-orientated strategy to integrated electrodes.

Rapid Fabrication of High-Entropy Ceramic Nanomaterials for Catalytic Reactions

Although high-entropy alloys have been intensively studied in the past decade, there are still many requirements for manufacturing processes and application directions to be proposed and developed, but most techniques are focused on high-entropy bulk materials and surface coatings. We fabricated high-entropy ceramic (HEC) nanomaterials using simple pulsed laser irradiation scanning on mixed salt solutions (PLMS method) under low-vacuum conditions. This method, allowing simple operation, rapid manufacturing, and low cost, is capable of using various metal salts as precursors and is also suitable for both flat and complicated 3D substrates. In this work, we engineered this PLMS method to fabricate high-entropy ceramic oxides containing four to seven elements. To address the catalytic performance of these HEC nanomaterials, we focused on CoCrFeNiAl high-entropy oxides applied to the oxygen-evolution reaction (OER), which is considered a sluggish process in water. We performed systematic material characterization to solve the complicated structure of the CoCrFeNiAl HEC as a spinel structure, AB₂O₄ (A, B = Co, Cr, Fe, Ni, or Al). Atoms in A and B sites in the spinel structure can be replaced with other elements; either divalent or trivalent metals can occupy the spinel lattice using this PLMS process. We applied this PLMS method to manufacture electrocatalytic CoCrFeNiAl HEC electrodes for the OER reaction, which displayed state-of-the-art activity and stability.

Electrochemical mitigation of hydrogen sulfide in deep-pit swine manure storage

Hydrogen sulfide (H₂S) is a toxic and hazardous gas and is commonly present in livestock operations, which occasionally causes associated exposure accidents. This study evaluated the effectiveness of electrochemical control of H₂S in lab-scale swine manure storage using different electrode materials, and further selected suitable materials to demonstrate the performance of a pilot-scale field test in the deep-pit manure storage of a 200-head swine barn. In the lab-scale test, electrochemical sulfide oxidation mainly contributed to the H₂S mitigation, resulting in high H₂S removal efficiencies when using low carbon steel (LCS) and stainless steel 304 (SS304) as electrodes. Based on their better H₂S treatment performance and lower material costs, LCS and SS304 were selected for the pilot-scale test. In a 92-day operation, the pilot-scale demonstration showed H₂S removal efficiencies of 84.0% and 63.5% for LCS and SS304, respectively. A techno-economic assessment indicated that the installation and operation of the electrochemical system accounted for 16% of barn construction cost using LCS as electrodes. Further optimization may substantially decrease the electrode material consumption and the overall cost.

Preparation of nickel-iron hydroxides by microorganism corrosion for efficient oxygen evolution

Nickel–iron composites are efficient in catalyzing oxygen evolution. Here, we develop a microorganism corrosion approach to construct nickel–iron hydroxides. The anaerobic sulfate-reducing bacteria, using sulfate as the electron acceptor, play a significant role in the formation of iron sulfide decorated nickel–iron hydroxides, which exhibit excellent electrocatalytic performance for oxygen evolution. Experimental and theoretical investigations suggest that the synergistic effect between oxyhydroxides and sulfide species accounts for the high activity. This microorganism corrosion strategy not only provides efficient candidate electrocatalysts but also bridges traditional corrosion engineering and emerging electrochemical energy technologies.

Developing facile strategies to realize the precise construction of Ni-Fe structures is of significance for water oxidation. Here, the authors demonstrate a universal microorganism-assisted corrosion strategy for preparing highly efficient Ni-Fe composites towards oxygen evolution.

A review on fundamentals for designing oxygen evolution electrocatalysts

Electricity-driven water splitting can facilitate the storage of electrical energy in the form of hydrogen gas. As a half-reaction of electricity-driven water splitting, the oxygen evolution reaction (OER) is the major bottleneck due to the sluggish kinetics of this four-electron transfer reaction. Developing low-cost and robust OER catalysts is critical to solving this efficiency problem in water splitting. The catalyst design has to be built based on the fundamental understanding of the OER mechanism and the origin of the reaction overpotential. In this article, we summarize the recent progress in understanding OER mechanisms, which include the conventional adsorbate evolution mechanism (AEM) and lattice-oxygen-mediated mechanism (LOM) from both theoretical and experimental aspects. We start with the discussion on the AEM and its linked scaling relations among various reaction intermediates. The strategies to reduce overpotential based on the AEM and its derived descriptors are then introduced. To further reduce the OER overpotential, it is necessary to break the scaling relation of HOO* and HO* intermediates in conventional AEM to go beyond the activity limitation of the volcano relationship. Strategies such as stabilization of HOO*, proton acceptor functionality, and switching the OER pathway to LOM are discussed. The remaining questions on the OER and related perspectives are also presented at the end.

Heterolayered Ni-Fe Hydroxide/Oxide Nanostructures Generated on a Stainless-Steel Substrate for Efficient Alkaline Water Splitting

Highly active and inexpensive anode materials are required for large-scale hydrogen production using alkaline water electrolysis (AWE). Here, heterolayered nanostructures of Ni-Fe hydroxides/oxides with high activity for the oxygen evolution reaction (OER) were synthesized on a 316 stainless steel (SS) substrate through constant current density electrolysis. The thicknesses, morphologies, and compositions of the nanostructures, generated through dealloying and surface oxidation of the SS elements with severe oxygen microbubble evolution, were dependent on the electrolysis time. Nanostructural analyses showed that the heterolayered Ni-Fe hydroxide/oxide nanostructures were generated during the initial stage of electrolysis, growing nanofiberlike Ni-Fe hydroxide layers with increasing electrolysis time of up to 5 h. The prolonged electrolysis resulted in densification of the nanofiber structures. The OER overpotential at 10 mA/cm² was estimated to be 254 mV at 20 °C, demonstrating better performance than a standard OER catalyst, for example, Ir oxide, and obtaining the value of the Ni-Fe layered double hydroxide (LDH). Furthermore, the OER property surpassed the Ni-Fe LDH catalysts at high current density regions greater than 100 mA/cm². Moreover, stable electrolysis was achieved for 20 h under conditions similar to that of the practical AWE of 400 mA/cm² in 20 and 75 °C solution. Therefore, the simple surface modification method could synthesize highly active nanostructures for alkaline water splitting anodes.

A Simple and Scalable Approach To Remarkably Boost the Overall Water Splitting Activity of Stainless Steel Electrocatalysts

The stainless steel mesh (SSM) has received growing consideration as an electrocatalyst for efficient hydrogen and oxygen evolution reactions. Recently, the application of SSM as an oxygen evolution reaction (OER) electrocatalyst has been more promising, while its hydrogen evolution reaction (HER) catalytic activity is very low, which definitely affects its overall water splitting activity. Herein, a simple chemical bath deposition (CBD) method followed by phosphorization is employed to significantly boost the overall water splitting performance of SSM. The CBD method could allow the voids between the SSM fibers to be filled with Ni and P. Electrocatalytic studies show that the CBD-treated and phosphorized stainless steel (denoted SSM-Ni-P) exhibits an HER overpotential of 149 mV, while the phosphorization-free CBD-treated SSM (denoted as SSM-Ni) delivers an OER overpotential of 223 mV, both at a current density of 10 mA cm^-2. An asymmetric alkaline electrolyzer assembled based on the SSM-Ni-P cathode (HER) and SSM-Ni anode (OER) achieved an onset and 10 mA cm^-2 current densities at an overall potential of 1.62 V, granting more prospects for the application of inexpensive and highly active electrocatalysts for electrocatalytic water splitting reactions.

Electromodified NiFe Alloys as Electrocatalysts for Water Oxidation: Mechanistic Implications of Time-Resolved UV/Vis Tracking of Oxidation State Changes

Facile electromodification of metallic NiFe alloys leads to a series of NiFe oxyhydroxide surface films with excellent electrocatalytic performance in alkaline water oxidation. During cyclic voltammetry and after sudden potential jumps between noncatalytic and catalytic potentials, Ni oxidation/reduction was tracked with millisecond time resolution by a UV/Vis reflectance signal. Optimal catalysis at intermediate Ni/Fe ratios is explained by two opposing trends for increasing Fe content: a) pronounced slowdown of the Ni²⁺ /Ni³⁺ oxidation step and b) increased reactivity of the most oxidized catalyst state detectable at catalytic potentials. This state may involve an equilibrium between Ni⁴⁺ ions and Ni²⁺ ions with neighboring ligand holes, possibly in the form of bound peroxides.

Non-Precious Electrodes for Practical Alkaline Water Electrolysis

Water electrolysis is a promising approach to hydrogen production from renewable energy sources. Alkaline water electrolyzers allow using non-noble and low-cost materials. An analysis of common assumptions and experimental conditions (low concentrations, low temperature, low current densities, and short-term experiments) found in the literature is reported. The steps to estimate the reaction overpotentials for hydrogen and oxygen reactions are reported and discussed. The results of some of the most investigated electrocatalysts, namely from the iron group elements (iron, nickel, and cobalt) and chromium are reported. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The experimental work is done involving the direct-current electrolysis of highly concentrated potassium hydroxide solutions at temperatures between 30 and 100 °C, which are closer to industrial applications than what is usually found in literature. Stable cell components and a good performance was achieved using Raney nickel as a cathode and stainless steel 316L as an anode by means of a monopolar cell at 75 °C, which ran for one month at 300 mA cm⁻². Finally, the proposed catalysts showed a total kinetic overpotential of about 550 mV at 75 °C and 1 A cm⁻².

Enhanced Lifetime Cathode for Alkaline Electrolysis Using Standard Commercial Titanium Nitride Coatings

The use of hydrogen gas as a means of decoupling supply from demand is crucial for the transition to carbon-neutral energy sources and a greener, more distributed energy landscape. This work shows how simple commercially available titanium nitride coatings can be used to extend the lifetime of 316 grade stainless-steel electrodes for use as the cathode in an alkaline electrolysis cell. The material was subjected to accelerated ageing, with the specific aim of assessing the coating’s suitability for use with intermittent renewable energy sources. Over 2000 cycles lasting 5.5 days, an electrolytic cell featuring the coating outperformed a control cell by 250 mV, and a reduction of overpotential at the cathode of 400 mV was observed. This work also confirms that the coating is solely suitable for cathodic use and presents an analysis of the surface changes that occur if it is used anodically.

Life cycle assessment of a bioelectrochemical system as a new technological platform for biosuccinic acid production from waste

Waste management is a key environmental and socio-economic issue. Environmental concerns are encouraging the use of alternative resources and lower emissions to air, water and soil. Innovative technologies to deal with waste recovery that produce marketable bioproducts are emerging. Bioelectrochemical synthesis systems (BESs) are based on the primary principle of transforming organic waste into added-value products using microorganisms to catalyse chemical reactions. This technology is at the core of a research project called BIORARE (BIoelectrosynthesis for ORganic wAste bioREfinery), an interdisciplinary project that aims to use anaerobic digestion as a supply chain to feed a BES and produce target biomolecules. This technology needs to be driven by environmental strategies. Life Cycle Assessment (LCA) was used to evaluate the BIORARE concept based on expert opinion and prior experiments for the production of biosuccinic acid and waste management. A multidisciplinary approach based on biochemistry and process engineering expertise was used to collect the inventory data. The BES design and the two-step anaerobic digestion process have many potential impacts on air pollution or ecotoxicity-related categories. The comparison of the BIORARE concept with conventional fermentation processes and a water-fed BES technology demonstrated the environmental benefit resulting from the use of both the BES technology and a waste-based substrate as input thus supporting the BIORARE concept. Some trade-offs among the impact categories were identified but led to options to improve the concept. BES design and synergy management may improve the environmental performance of the BIORARE concept.

Sloughing a Precursor Layer to Expose Active Stainless Steel Catalyst for Water Oxidation

Hydrogen production by water electrolysis has been regarded as a promising approach to wean away from sourcing energy through fossil fuels, as the produced hydrogen gas can be converted to electrical or thermal energy without any harmful byproducts. However, an efficient hydrogen production is restricted by the sluggish oxygen evolution reaction (OER) at the counter anode. Therefore, the development of new OER catalysts with high catalytic activities is crucial for high performance water splitting. Here, we report a novel sloughing method for the fabrication of an efficient OER catalyst on a stainless steel (SS) surface. A chalcogenide (Fe-S) overlayer generated by sulfurization on the SS surface is found to play a critical role as a precursor layer in the formation of an active surface during water oxidation. Interestingly, a newly exposed catalytic layer after sloughing off the Fe-S overlayer has a nanoporous structure with changed elemental composition, resulting in a significant improvement in OER performance with an overpotential value of 267 mV at a current density of 10 mA cm^-2 (in 1 M KOH). Our novel method for the preparation of OER catalyst provides an important insight into designing an efficient and stable electrocatalyst for the water splitting community.

Iron Hydroxide-Modified Nickel Hydroxylphosphate Single-Wall Nanotubes as Efficient Electrocatalysts for Oxygen Evolution Reactions

Development of efficient electrocatalysts for oxygen evolution reaction (OER) is of great significance for future renewable energy applications. Herein, efficient OER electrocatalysts based on iron hydroxide-modified nickel hydroxylphosphate (NiPO/Fe(OH) _x) single-wall nanotubes (SWNTs) have been prepared by a facile stepwise surfactant-free solvothermal strategy, which possess diameters of about 6 nm and lengths of about several micrometers. Benefiting from the synergistic effect between iron hydroxides and NiPO SWNTs, the as-prepared NiPO/Fe(OH) _x SWNTs exhibit higher OER activity than primary NiPO SWNTs. Furthermore, the OER activity with different Fe contents displays a volcano-type shape, and the optimized NiPO/Fe(OH) _x SWNTs present excellent activity with a low overpotential of 248 mV to deliver a current density of 10 mA cm^-2 and 323 mV to achieve a large current density of 100 mA cm^-2, as well as a remarkably low Tafel slope of 45.4 mV dec^-1 in 1 M KOH electrolyte. The present work provides valuable insights to improve the OER performance by rational surface modification.

Self-Supported Stainless Steel Nanocone Array Coated with a Layer of Ni-Fe Oxides/(Oxy)hydroxides as a Highly Active and Robust Electrode for Water Oxidation

Highly efficient, robust, and cheap water oxidation electrodes are of great significance for large-scale production of hydrogen by electrolysis of water. Here, a self-supported stainless steel (SS) nanocone array coated with a layer of nanoparticulate Ni-Fe oxides/(oxy)hydroxides was fabricated by a facile, low-cost, and easily scalable two-step process. The construction of a nanocone array on the surface of an AISI 304 SS plate by acid corrosion greatly enlarged the specific surface area of the substrate, and the subsequent formation of a layer of Ni-Fe oxides/(oxy)hydroxides featuring the NiFe₂O₄ spinel phase on the nanocone surface by electrodeposition of [Ni(bpy)₃]²⁺ significantly enhanced the intrinsic activity and the stability of the SS-based electrode. The as-prepared electrode demonstrated superior activity for the oxygen evolution reaction (OER) in 1 M KOH, with 232 and 280 mV overpotentials to achieve 10 and 100 mA cm_geo^-2 current densities, respectively. The high activity of the electrode was maintained over 340 h of chronopotentiometric test at 20 mA cm_geo^-2, and the electrode also showed good stability over 100 h of electrolysis at high current density (200 mA cm^-2). More important for practical application, the used SS-based electrode can be easily regenerated with the original OER activity. The superior activity of this SS-based electrode stems from synergistic combination of high conductivity of the SS substrate, a large electrochemically active surface area of the nanocone array, and a uniformly coated nanoparticulate Ni-Fe oxide/(oxy)hydroxide layer with an optimal Ni/Fe ratio.

Steel-based electrocatalysts for efficient and durable oxygen evolution in acidic media

Upon electro-oxidation in LiOH, Ni42 alloy was rendered in an OER electrocatalyst that efficiently and durably works in the acidic regime.

Electro-oxidation of a cobalt based steel in LiOH: a non-noble metal based electro-catalyst suitable for durable water-splitting in an acidic milieu

The use of proton exchange membrane (PEM) electrolyzers is the method of choice for the conversion of solar energy when frequently occurring changes of the current load are an issue. However, this technique requires electrolytes with low pH. All oxygen evolving electrodes working durably and actively in acids contain IrO_x. Due to their scarcity and high acquisition costs, noble elements like Pt, Ru and Ir need to be replaced by earth abundant elements. We have evaluated a cobalt containing steel for use as an oxygen-forming electrode in H₂SO₄. We found that the dissolving of ingredients out of the steel electrode at oxidative potential in sulfuric acid, which is a well-known, serious issue, can be substantially reduced when the steel is electro-oxidized in LiOH prior to electrocatalysis. Under optimized synthesis conditions a cobalt-containing tool steel was rendered into a durable oxygen evolution reaction (OER) electrocatalyst (weight loss: 39 μg mm^-2 after 50 000 s of chronopotentiometry at pH 1) that exhibits overpotentials down to 574 mV at 10 mA cm^-2 current density at pH 1. Focused ion beam SEM (FIB-SEM) was successfully used to create a structure-stability relationship.

Fabrication of Nanoporous Nickel-Iron Hydroxylphosphate Composite as Bifunctional and Reversible Catalyst for Highly Efficient Intermittent Water Splitting

Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO₄) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO₄/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm^-2 at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm^-2 at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO₄/NF electrodes can obtain the current densities of 20 and 100 mA cm^-2 at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO₄/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.

Coupling mechanism between wear and oxidation processes of 304 stainless steel in hydrogen peroxide environments

Stainless steel is widely used in strongly oxidizing hydrogen peroxide (H₂O₂) environments. It is crucial to study its wear behaviour and failure mode. The tribological properties and oxidation of 304 stainless steel were investigated using a MMW-1 tribo-tester with a three-electrode setup in H₂O₂ solutions with different concentrations. Corrosion current densities (CCDs), coefficients of frictions (COFs), wear mass losses, wear surface topographies, and metal oxide films were analysed and compared. The results show that the wear process and oxidation process interacted significantly with each other. Increasing the concentration of H₂O₂ or the oxidation time was useful to form a layer of integrated, homogeneous, compact and thick metal oxide film. The dense metal oxide films with higher mechanical strengths improved the wear process and also reduced the oxidation reaction. The wear process removed the metal oxide films to increase the oxidation reaction. Theoretical data is provided for the rational design and application of friction pairs in oxidation corrosion conditions.

NiSe2/FeSe2nanodendrites: a highly efficient electrocatalyst for oxygen evolution reaction

NiSe₂/FeSe₂nanodendrites have been synthesized through a facile colloidal synthetic approach. Thanks to its unique 3D structure with branched architectures and the synergistic effect after Fe doping, the resulting Ni_0.5Fe_0.5Se₂catalyst exhibits superior OER activity with an overpotential of 235 mV at a current density of 10 mA cm⁻².

Hybrid Mn3O4–NiO nanocomposites as efficient photoelectrocatalysts towards water splitting under neutral pH conditions

Dual oxide Mn₃O₄–NiO nanocomposites synthesised by seed-mediated epitaxial growth have been exploited as electrocatalysts towards water splitting at an applied overpotential of 280 mV under neutral pH conditions.

Nanostructured hybrid NiFeOOH/CNT electrocatalysts for oxygen evolution reaction with low overpotential

The OER activity of nanostructured Ni-based LDH can be improved by doping with transition metals, which can be further enhanced by hybridizing with CNT.

PRED treatment mediated stable and efficient water oxidation performance of the Fe2O3 nano-coral structure

Herein, we demonstrate that an electrochemical surface treatment of Fe foil with simple pulse reverse electrodeposition (PRED) prior to thermal oxidation can substantially enhance the photoelectrochemical (PEC) stability and water splitting performance of Fe2O3/Fe photoanodes. Comprehensive structural (XRD, FESEM, and HRTEM), compositional (XPS depth profiling), and electrochemical (EIS and Mott-Schottky) analyses were performed to understand the effect of PRED treatment on the PEC performance of fabricated photoanodes. It is revealed that air-exposed Fe foil is prone to formation of a loosely bound surface oxide layer that, upon annealing at 800 °C, results in an unstable Fe2O3 nano-flake (2-3 μm long) morphology. In contrast, when such Fe foil is pre-treated with PRED to etch the loosely bound oxide layer, adherent inverse-opal-like nano-coral structures (60-100 nm thin) are formed. In addition to stability improvement, PRED-treatment also assists in exposing the photocatalytically active high index [104] facet sites of hematite. Thin hematite nano-coral structures with high index [104] facet sites significantly improved the separation of photo-generated charge carriers and oxygen evolution kinetics, resulting in performance enhancement with excellent photocurrent stability for extended duration in a 1 M NaOH solution under one sun illumination. The net photocurrent density for nano-coral morphology was 0.813 mA cm(-2) at 1.23 V vs. RHE, which is the highest reported value for pristine hematite photoanodes fabricated from Fe foil.

Oxidized Mild Steel S235: An Efficient Anode for Electrocatalytically Initiated Water Splitting

The surface of steel S235 was oxidized by Cl2 gas and checked for its electrocatalytic efficiency regarding oxygen formation in aqueous solution. If exposed to humid Cl2 gas for 110 min, steel S235 became an electrocatalyst that exhibits an overpotential for the oxygen evolution reaction (OER) of 462 mV at 1 mA cm(-2) at pH 7. The OER activity of the same sample at pH 13 was moderate (347 mV overpotential at 2.0 mA cm(-2) current density) in comparison with OER electrocatalysts developed recently. Potential versus time plots measured at a constant current demonstrate the sufficient stability of all samples under catalysis conditions at pH 7 and 13 for tens of hours. High-resolution X-ray photoelectron spectra could be reasonably resolved with the proviso that Fe2 O3 , FeO(OH), MnO(OH), and Mn2 O3 are the predominant Fe and Mn species on the surface of the oxidized steel S235.