Electrodes For Oxygen Evolution Reaction Research Articles

Elctrocatalytic oxygen evolution reaction on Mg, Al and Fe doped spinel oxides

Metal doped cobalt-base spinel type catalysts were prepared by co-precipitation route are considered suitable candidates for OER, ORR, metal air batteries, fuel cells, detoxification of water etc. For the purpose, metal doped oxides with formula MCo 2 O 4 , M= Mg, Al and Fe were prepared thermal decomposition of their metal carbonate precipitates and characterized by IR, XRD, CV, EIS and Tafel polarization techniques. The IR spectra of oxides showed absorption bands 650 cm -1 and 560 cm -1 for respective stretching and bending modes of vibration of Co-O bond at octahedral sites and formation of nano-size ( 18 nm) single phase cubical crystal with spinel geometry was confirmed by XRD powder patterns. The cyclic voltammetric (CV) curves of oxide electrodes in 1 M KOH solution showed a redox peak at E o = 434 -516 mV for Co 2+ /Co 3+ reactions. The electrocatalytic activity of oxide electrodes for oxygen evolution reaction in 1M KOH at 25 0 C was also studied by Tafel polarization technique and polarization curve of each oxides showed two Tafel slopes ( 63 and 115 mV/decade) and order of OER is unity.

In-situ grown metal-organic framework-derived carbon-coated Fe-doped cobalt oxide nanocomposite on fluorine-doped tin oxide glass for acidic oxygen evolution reaction

Development of stable and efficient non-noble metal based electrocatalysts for oxygen evolution reaction (OER) in acidic media is of great importance for proton exchange membrane based water electrolysis, which is indispensable for green hydrogen production. Herein, iron-doped, carbon-coated Co3O4 nanocomposite derived from a cobalt metal-organic framework, is grown in-situ on fluorine-doped tin oxide (FTO) glass (Fe-Co3O4@C/FTO) as an efficient and a stable binder-free electrode for acidic OER. Fe doping enhances both catalytic efficiency and stability of carbon coated Co3O4 toward acidic OER, through inducing small primary particle sizes and suitably modulated electronic structure of Co3O4, and better catalyst/substrate adhesion. Fe-Co3O4@C/FTO exhibits impressive electrocatalytic performances in 0.5 M H2SO4, with a low overpotential of 396 mV at 10 mA cm−2 and a small Tafel slope of 68.6 mV dec−1. Its electrochemical performances remain stable for over 50 h at 10 mA cm−2, making it a promising non-noble metal based electrocatalyst for acidic OER.

One-pot synthesis of Ni3S2/Co3S4/FeOOH flower-like microspheres on Ni foam: An efficient binder-free bifunctional electrode towards overall water splitting

Overall water splitting using highly effective and low-cost bifunctional electrocatalysts is a promising method for hydrogen production. Herein, Ni3S2/Co3S4/FeOOH flower-like microspheres composed of Ni3S2/Co3S4 nanosheets and FeOOH nanoparticles are in-situ generated on Ni foam (NF) by a facile one-step hydrothermal approach. The NF-supported Ni3S2/Co3S4/FeOOH can serve as an efficient binder-free bifunctional electrode for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline medium. The overpotentials at current density of 10 mA cm−2 are 158 and 181 mV for HER and OER, respectively. Moreover, the electrode exhibits remarkable performance for overall water splitting, requiring only a low voltage of 1.58 V to achieve the current density of 10 mA cm−2, and displaying a good long-term stability. The synergistic effect of different functional components and the unique hierarchical structure are responsible for the superior electrocatalytic performances of Ni3S2/Co3S4/FeOOH compared to Ni3S2, Ni3S2/Co3S4 and Ni3S2/FeOOH.

In-situ etching synthesis of 3D self-supported serrated Ni-WO3 for oxygen evolution reaction

The slow kinetics of oxygen evolution reaction (OER) severely restricts the application of water splitting. In this paper, a free-standing serrated Ni-WO3 electrode for OER was synthesized by a simple in-situ etching method using (NH4)2SO4 as etchant. The effect of etchant on structures of Ni-WO3 were studied carefully, indicating that the NH4+ and SO42- have a synergistic effect on the unique structure. The serrated Ni-WO3-3 (where 3 is the mass of (NH4)2SO4) dramatically enhance OER performance, an over-potential of only 265 mV at 10 mA cm−2 as compared with that 365 mV of serrated-free Ni-WO3. Interestingly, the structure and composition of the serrated Ni-WO3 electrode undergoes a self-reconstruction process during OER, the finally catalyst is interconnected by low crystallinity nickel oxy-hydroxide nanoparticles. This work mainly explores the influence of etching agent type, usage and reaction time on the morphology and properties of materials, and the reconstruction phenomenon in OER pre-catalyst was confirmed.

Efficient preparation of Ni-M (M = Fe, Co, Mo) bimetallic oxides layer on Ni nanorod arrays for electrocatalytic oxygen evolution

Fabrication of economic and high-performance electrodes for electrocatalytic oxygen evolution reaction (OER) accounts for a crucial issue associated with developing powerful and practical water splitting systems. In this work, free-standing Ni/Ni-M (M = Fe, Co, Mo) bimetallic oxides core/shell nanorod arrays (Ni/Ni-M NRAs) were prepared through electroless deposition of transition metal species on black nickel sheet (nickel nanorod arrays (Ni NRAs)) followed by electrochemical oxidation. All three types of Ni/Ni-M NRAs demonstrated enhanced electrocatalytic activity toward oxygen evolution reactions (OER). Especially, Ni/Ni-Fe NRAs electrode exhibit small onset potential of 1.535 V at current density of 10 mA∙cm−2. In contrast, the OER durability of these three samples was distinct. At 500 mV constant overpotential, the current density loss in OER of Ni/Ni-Fe NRAs was merely 13.5% for a period of 20000 s; but Ni/Ni-Mo and Ni/Ni-Co NRAs had almost disappeared catalytic activity under the identical conditions. According to many reports, the results were different for the superior OER stability of Ni-based bimetallic catalysts. Electrochemical analysis revealed that the NRAs structure dramatically improves charge transfer efficiency and electrochemically active surface area (ECSA). The present study might provide a new insight to design and fabricate more practical and high-performance Ni-based electrodes for OER.

Synergistic metal-oxide interaction for efficient self-reconstruction of cobalt oxide as highly active water oxidation electrocatalyst

Developing catalysts with outstanding performance for oxygen evolution reaction (OER) is crucial to advance energy conversion technologies. In these regards, catalysts based on 3d transition metals have recently attracted much attention, yet further development is required. Here, we present a new type of heterostructure catalyst in which CoO nanowire arrays are hybridized with tungsten nanoparticles (W-CoO), and are self-supported on conductive carbon cloth (CC). Electronic coupling effects at the W-CoO heterointerface promote electron transfer and OER kinetics to expedite the formation of oxyhydroxide species, which are the active sites for OER processes. A variety of in situ and ex situ characterization methods are employed to reveal deep insights into surface transformations and investigate the relationship between the conversion to oxyhydroxide moieties and OER performance. This report presents new understanding of the rational design and synthesis of catalysts that exhibit outstanding performance as electrochemical water splitting electrode for OER.

Enriched oxygen vacancy promoted heteroatoms (B, P, N, and S) doped CeO2: Challenging electrocatalysts for oxygen evolution reaction (OER) in alkaline medium

Increasing worldwide energy consumption has prompted considerable study into energy generation and energy storage systems in recent years. Chemical fuels may be produced efficiently via electrocatalytic water splitting, which uses electric and solar power. The development of efficient anodic electrocatalysts for efficient oxygen evolution reaction (OER) is a greater concern of present energy research. Cerium oxide (CeO2) are promising electrocatalysts that exhibit outstanding OER but their reduced stability obstructs the practical application. A novel strategy was established to construct an effective catalyst of heteroatom (N, B, P and S) doped CeO2 matrix were prepared. Moreover, the doping of heteroatoms into the CeO2 matrix processes the improved electronic conductivity, reactive sites, increases the electrochemical catalytic activity, which enhances the water oxidation reaction. Consequently, well-suited alkaline electrolysers were brought together for water oxidation to ideal OER electrocatalytic activity. The OER activity of the electrocatalysts follows the order of S–CeO2 (190 mV@10 mA cm−2), N– CeO2 (220 mV @10 mA cm−2), P– CeO2 (230 mV @10 mA cm−2), B–CeO2 (250 mV @10 mA cm−2) and CeO2 (260 mV @10 mA cm−2) in 1 M of KOH. From the kinetics analysis, Tafel slope value achieved for catalysts CeO2, B–CeO2, P–CeO2, N–CeO2 and S–CeO2 are 142 mV dec−1,121 mV dec−1, 102 mV dec−1, 98 mV dec−1 and 83 mV dec−1 respectively. These results validate that the S–CeO2 electrode is prominent for OER performance with the requirement of cell voltage of 1.42 V at 10 mA cm−2 current density. In addition, sulphur doped CeO2 relatively have excellent stability through chrono-potentiometric analysis lasting for 20 h. Although the heteroatoms doped CeO2 is acts as anode material, the preparation method is widespread, which will reduce the synthesis cost and streamline the preparation of electrode for OER. This research effort delivers a complete advantage for the development of robust, environmentally friendly and highly dynamic electrocatalysts for OER activity.

Chemical synthesis of a microsphere-like copper molybdate electrode for oxygen evolution reaction

The sluggish mechanism of oxygen evolution reaction (OER) inhibits the efficiencies of different energy storage systems. Thus, recent studies have mainly focused on designing highly active electrocatalysts to enhance OER. Here, a porous microsphere-like copper molybdate (CuMoO4) is synthesized via a simple hydrothermal route. Further, the crystalline nature of CuMoO4 is confirmed via X-ray diffraction (XRD). The chemical states of the designed sample are determined via X-ray photoelectron spectroscopy (XPS). The morphology and elemental composition of CuMoO4 are determined via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, as well as energy-dispersive X-ray (EDX) analyses. The CuMoO4 microspheres exhibit interconnected nanoflake-like structures, which can improve the active surface area and efficiency of CuMoO4. Furthermore, the active surface area of the CuMoO4 microspheres is calculated via the Brunauer–Emmett–Teller (BET) method. The obtained catalytic performance of CuMoO4 is compared with those of its basic metal oxides, such as MoO3 and CuO. The obtained overpotentials (η) for CuO, MoO3, IrO2, and CuMoO4 were 286, 294, 267, and 247 mV with Tafel slope values of 65, 84, 58, and 53 mV/dec, respectively. The study for long-term stability of the CuMoO4 electrode reveals that it can sustain the electrochemical activity for 12 h.

Recent Progress in the Development of Advanced Functionalized Electrodes for Oxygen Evolution Reaction: An Overview.

Presently, the global energy demand for increasing clean and green energy consumption lies in the development of low-cost, sustainable, economically viable and eco-friendly natured electrochemical conversion process, which is a significant advancement in different morphological types of advanced electrocatalysts to promote their electrocatalytic properties. Herein, we overviewed the recent advancements in oxygen evolution reactions (OERs), including easy electrode fabrication and significant action in water-splitting devices. To date, various synthetic approaches and modern characterization techniques have effectively been anticipated for upgraded OER activity. Moreover, the discussed electrode catalysts have emerged as the most hopeful constituents and received massive appreciation in OER with low overpotential and long-term cyclic stability. This review article broadly confers the recent progress research in OER, the general mechanistic approaches, challenges to enhance the catalytic performances and future directions for the scientific community.

Mesoporous nanostructures of NiCo-LDH/ZnCo2O4 as an efficient electrocatalyst for oxygen evolution reaction

Increasing energy demands for pollution-free and renewable energy technologies have stimulated intense research on the development of inexpensive, highly efficient, and stable non-noble metal electrocatalysts for oxygen evolution reaction (OER). In this study, a superior OER performance was achieved using a tri-metallic (Zn, Co, Ni) high-performance electrocatalyst. We successfully fabricated a peony-flower-like hierarchical ZnCo2O4 through an additive-free hydrothermal reaction followed by heat treatment. Then NiCo-LDH (layered double hydroxides) nano-flakes was electrodeposited on the ZnCo2O4/GCE surface to prepare NiCo-LDH/ZnCo2O4/GCE which was used as electrode for OER. The structure and morphology of the catalysts were characterized by several techniques including Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping and Brunauer–Emmett–Teller method. The NiCo-LDH/ZnCo2O4 catalyst provided high catalytic activity toward OER under alkaline condition (1.0 M KOH) with a low overpotential of 260 mV to drive the benchmark current density of 10 mA cm−2 and Tafel slope of 62 mV dec−1, as well as long-term stability and high turnover frequency of 0.0641 s−1 at overpotential of 340 mV. The NiCo-LDH/ZnCo2O4 catalyst was found to perform significantly better than NiCo-LDH, ZnCo2O4, NiCo-LDH/Co3O4, Co3O4, and commercial RuO2 catalysts. The outstanding OER performance of NiCo-LDH/ZnCo2O4 catalyst, which may be attributed to the large specific surface area, accelerated mass and electron transport, and synergistic effect of multiple hybrid materials, makes it a promising catalyst for OER.

Layer‐by‐Layer Assembly‐Based Electrocatalytic Fibril Electrodes Enabling Extremely Low Overpotentials and Stable Operation at 1 A cm−2 in Water‐Splitting Reaction

AbstractFor the practical use of water electrolyzers using non‐noble metal catalysts, it is crucial to minimize the overpotentials for the hydrogen and oxygen evolution reactions. Here, cotton‐based, highly porous electrocatalytic electrodes are introduced with extremely low overpotentials and fast reaction kinetics using metal nanoparticle assembly‐driven electroplating. Hydrophobic metal nanoparticles are layer‐by‐layer assembled with small‐molecule linkers onto cotton fibrils to form the conductive seeds for effective electroplating of non‐noble metal electrocatalysts. This approach converts insulating cottons to highly electrocatalytic textiles while maintaining their intrinsic 3D porous structure with extremely large surface area without metal agglomerations. To prepare hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrodes, Ni is first electroplated onto the conductive cotton textile (HER electrode), and NiFe is subsequently electroplated onto the Ni–electroplated textile (OER electrode). The resulting HER and OER electrodes exhibit remarkably low overpotentials of 12 mV at 10 mA cm−2 and 214 mV at 50 mA cm−2, respectively. The two‐electrode water electrolyzer exhibits a current density of 10 mA cm−2 at a low cell voltage of 1.39 V. Additionally, the operational stability of the device is well maintained even at an extremely high current density of 1 A cm−2 for at least 100 h.

Conductivity Modulation of 3D‐Printed Shellular Electrodes through Embedding Nanocrystalline Intermetallics into Amorphous Matrix for Ultrahigh‐Current Oxygen Evolution

AbstractScaling up commercial hydrogen production by water electrolysis requires efficient oxygen evolution reaction (OER) electrodes that can deliver large current densities (more than 500 mA cm−2) at low overpotentials. Here, a highly active and conductive shell‐based cellular (Shellular) electrode is developed through a strategy of embedding nanocrystalline Ni3Nb intermetallics into an amorphous NiFe‐OOH matrix. The tailor‐made laser remelting process enables the dispersive precipitation of corrosion‐resistant nanocrystalline Ni3Nb in large numbers. After in situ electrochemical activation in the self‐developed growth‐mode‐control electrolyte, the amorphous NiFe‐OOH nanosheets and nanocrystalline Ni3Nb are formed on the as‐printed Inconel 718. The conductive atomic force microscopy (C‐AFM) studies and density functional theory (DFT) calculations elucidate that nanocrystalline Ni3Nb can simultaneously enhance the conductivity and activity of the catalyst film. Additionally, a Shellular structure inspired by nature is designed, interestingly, its specific surface area keeps constant with increases in porosity. This design can result in a large surface area and high porosity but with less material cost. Using this electrochemically activated Shellular electrode for OER, a high current density of 1500 mA cm−2 is achieved at a record‐low overpotential of 261 mV with good durability. This development may open the door for large‐scale industrial water electrolysis.

Interrelationship between Extended Transport Pathways of Mixed Conducting Electrode and Delamination in Solid Oxide Electrolyzer Cells

Generating electricity using renewable energy such as solar and wind rather than fossil fuels like coal and natural gas reduces CO2 emissions and addresses climate change. However, due to the intermittency nature of renewables, highly efficient and massive scale energy storage method is the major enabler for its integration into the grid. Solid oxide electrolyzer cell (SOECs) (1), which is an electrochemical device to convert electricity into chemicals (such as hydrogen, syngas, ammonia or even methane, ethane, and ethylene), have received widespread attention. There have been tremendous improvements of the technology during the past 10 to 15 years. On the other hand, to drive the technology for commercialization, durability for long-term operation is still facing significant challenges (2). One degradation mechanism that has been widely reported is the delamination of the oxygen electrode/electrolyte interface. Pure ionic conductors such as 8 mol% Y2O3 doped ZrO2 (YSZ) and Gadolinium-doped ceria (GDC) are usually used as the dense electrolyte; mixed electronic and ionic conductors (MIEC) such as La1-xSrxMnO3-d(LSM), La1-xSrxCo1-yFeyO3-d (LSCF), Sm0.5Sr0.5CoO3 (SSC) are widely used as the oxygen electrode (3).The most popular delamination mechanism (2, 4) is attributed to the buildup of oxygen partial pressure at the LSM/YSZ interface and growth of microcracks caused by exceeding the fracture strength of the electrolyte. Another interesting explanation (5) from atomic level is that under high temperature the inter-diffusion of different cations across the LSM/YSZ interface significantly affect oxygen transport which develops pressure buildup and delamination. A mechanism (6) from a different angle has been proposed by analyzing SEM images of the LSM/YSZ interface at different stages of polarization. It is shown that the formation of nanoparticles caused by the migration or incorporation of oxygen ions from the electrolyte into the electrode, leading to the shrinkage of LSM lattice.Meanwhile, there have been modeling and experimental investigations of extended charge transport pathways from triple phase boundary (3PB) to two phase boundary (2TP) (3, 7) in MIEC electrodes, such as LSM and LSCF, as well as the multi-step charge transfer reaction (8-10) at gas/MIEC interface. It has been demonstrated that there is a transition voltage between two different transport pathways, and it can cause significant oxygen vacancy concentration variation at the electrode/electrolyte interface. In this work, we explore the correlation between the transition of transport pathways and the delamination phenomenon. We assume that large oxygen vacancy concentration variation will cause chemical-expansion-mismatch at the electrode/electrolyte interface, which leads to delamination of oxygen electrode from the electrolyte.Figure 1 shows a schematic of model domain constructed with details at the interface. A bilayer oxygen electrode structure consists of a commercial LSCF-GDC porous backbone coated by a thin SrCo0.9Ta0.1O3- d (SCT10) film. The new oxygen electrode has an inherently fast oxygen evolution reaction (OER) electrokinetics (or high oxygen evolution rate) and is capable of mitigating the delamination problem by minimizing the accumulation of oxygen in OER electrode lattice and thus chemical stresses. To understand the fundamental Electro-Chemical-Mechanical coupling mechanism and its contribution to SOEC performance degradation, we develop a rigorous Multiphysics model to explore the interplays between reaction rates and transport for two different pathways in delamination probability of the pristine and bilayer OER electrodes. The work will lead to a better understanding of the delamination mechanisms and effective mitigation plan and provide guidelines for the experimental optimization of bilayer OER electrode processing with improved electrochemical and mechanical performance. References A. Hauch, R. Küngas, P. Blennow, A. B. Hansen, J. B. Hansen, B. V. Mathiesen and M. B. Mogensen, Science, 2020, 370, eaba6118.B.-K. Park, Q. Zhang, P. W. Voorhees and S. A. Barnett, Energ Environ Sci, 2019, 12, 3053-3062.Y. Li, R. Gemmen and X. Liu, J Power Sources, 2010, 195, 3345-3358.A. V. Virkar, Int J Hydrogen Energ, 2010, 35, 9527-9543.S. N. Rashkeev and M. V. Glazoff, Int J Hydrogen Energ, 2012, 37, 1280-1291.K. Chen and S. P. Jiang, Int J Hydrogen Energ, 2011, 36, 10541-10549.M. Gong, R. S. Gemmen and X. Liu, J Power Sources, 2012, 201, 204-218.J. Fleig, Phys Chem Chem Phys, 2005, 7, 2027-2037.D. S. Mebane and M. Liu, J Solid State Electr, 2006, 10, 575-580.D. S. Mebane, Y. Liu and M. Liu, J Electrochem Soc, 2007, 154, A421. Figure 1

(Invited) Highly Active OER Electrodes Derived from Fe-Doped Ni Oxyfluoride Formed by Anodizing of NiFe Electrodeposits

Because of the limited availability of fossil fuels and pertinent global environmental issues, hydrogen production via electrochemical water splitting using renewable resources is an important alternative for future energy economies. For efficient alkaline water electrolysis to produce hydrogen, we need to develop highly active and durable electrocatalysts, particularly for oxygen evolution reaction (OER) because of high overpotential. Anodizing of metals and alloys is a promising means of directly fabricating an OER electrocatalyst on a metallic current collector. Binder-free electrocatalysts are readily formed by anodizing. Since Fe-doped Ni oxyhydroxides and hydroxides are recently reported as highly active OER electrocatalysts in alkaline media. Here, we report anodizing of NiFe electrodeposits in fluoride-containing ethylene glycol electrolyte and the conversion of resultant nanoporous Fe-doped Ni oxyfluoride to highly OER active hydroxide during OER (1).NiFe alloy films containing 7.2 – 21.1 at% Fe were obtained by electrodeposition on Ni substrate. Then, the alloys were anodized at 10 V in ethylene glycol electrolyte containing ammonium fluoride and water. The anodizing developed a porous layer consisting of crystalline NiF2 phase. XPS analysis revealed the presence of Fe and O as well as Ni and Fe. Thus, porous Fe-doped Ni oxyfluoride was developed by anodizing. The as-anodized NiFe alloys were initially less active for OER in 1.0 mol dm-3 KOH, but during potential cycling to OER potential, the OER activity was gradually enhanced. The enhancement was dependent upon Fe content, and the highest activity was obtained for the Ni-11.8 at% Fe. After activation, the porous layer was converted to amorphous hydroxide, and the fluoride content was highly reduced. Thus, anodically formed Fe-doped oxyfluoride on the NiFe electrodeposits is a suitable precursor of highly active OER electrocatalyst. The galvanostatic durability test exhibited the stable overpotential, disclosing the high durability of this electrocatalyst.Reference N. Yamada, S. Kitano, Y. Yato, D. Kowalski, Y. Aoki and H. Habazaki, ACS Applied Energy Materials, in press, doi.org/10.1021/acsaem.0c02362.

Understanding and Enhancing Catalyst Performance in AEM Electrolyzers Using a Statistical Approach

The behavior of the anode electrode in the Anion Exchange Membrane Water Electrolyzer (AEMWE) – where the oxygen evolution reaction (OER) occurs – is complex and influenced by several factors. Very few studies have been performed to understand OER electrode performance by optimizing contributing individual factors that influence the performance. This study highlights the individual effects of: catalyst loading, catalyst selection, gas diffusion layer (GDL) type and conductive additive content. The influence of each factor is elucidated through a Design of Experiments (DoE) approach with a full statistical analysis. Electrochemical data, alongside Pareto charts, parametric trends and their mutual interactions will be presented. Such a DoE approach is also helpful in making useful predictions, allowing new combinations to be discovered and tested. The end result is very high performance with a current density of 1 A/cm2 at 1.64 V in 0.1 M KOH being achieved. Furthermore, we extend our understanding from this electrolyzer work, coupled with our previous electrode engineering for AEM fuel cells [1-3] to design electrodes for an AEM-based Unitized Regenerative Fuel Cell (URFC). Good baseline performance was achieved, including a round trip efficiency of 40.7 % at 500 mA/cm2. This study will serve as a guide for optimal electrode design with insights into design-performance compromises, which can be especially helpful when making design choices and performing techno-economic analyses.

Rationally Designed Ni–Ni3S2 Interfaces for Efficient Overall Water Electrolysis

High‐performance water‐splitting electrocatalysts are needed by the energy sector for sustainable hydrogen production. Herein, it is demonstrated that the surface decoration of a nickel foam (NF) with porous Ni/Ni3S2 microsheets yields an electrode with high electrical conductivity and an abundance of accessible Ni0–Ni3S2 interfaces as active sites for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In 1 m potassium hydroxide, Ni–Ni3S2/NF exhibits outstanding HER activity (an overpotential of 57 mV at a current density of 10 mA cm−2) and similarly impressive OER activity (a low overpotential of only 295 mV at a current density of 20 mA cm−2). A water electrolyzer constructed using Ni–Ni3S2/NF as the HER and OER electrodes exhibits a low cell voltage of only 1.57 V with no obvious performance loss over 30 h, outperforming devices based on expensive Pt/C and RuO2 catalysts. To the best of the author's knowledge, Ni–Ni3S2/NF is one of the best non‐precious metal electrocatalysts reported to date for overall water splitting.

Synthesis, Characterization and Applications of Spinel Cobaltite Nanomaterials.

Recently, spinel structures (AB2O4) Nanoparticles (NPs) having binary and ternary mixtures of metal oxides have been established as promising redox catalysts. Due to the presence of two mixed valence metal cations, transport of electrons takes place easily between multiple transition-metal cations with relatively low energy of activation. Among these, spinel cobaltite (MCo2O4) is very attractive due to its low cost, non-toxicity, higher stability, higher electronic conductivity and electrochemical property. To date, MCo2O4 has been used in the fabrication of supercapacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. A variety of MMCo2O4materials have been synthesized, characterized, and utilized in the fabrication of super capacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. The progress in the field of the spinel MCo2O4 materials opens the door to novel and efficient applications in the nanoscience and nanotechnology, and elctrochemistry.

NiCo Nanoneedles on 3D Carbon Nanotubes/Carbon Foam Electrode as an Efficient Bi-Functional Catalyst for Electro-Oxidation of Water and Methanol

In this study, we report a 3D structured carbon foam electrode assembled from a bi-functional NiCo catalyst, carbon nanotubes (CNT), and a monolith 3D structured carbon foam (CF) as a highly active and stable electrode for oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). When the NiCo@CNTs/CF electrode was used as an anode in OER, after the anodization step, the electrode required a small overpotential of 320 mV to reach the current density of 10 mA cm−2 and demonstrated excellent stability over a long testing time (total 30 h) in 1 M KOH. The as-prepared NiCo@CNTs/CF electrode also exhibited a good performance towards methanol oxidation reaction (MOR) with high current density, 100 mA cm−2 at 0.6 V vs. Ag/AgCl, and good stability in 1 M KOH plus 0.5 M CH3OH electrolyte. The NiCo@CNTs/CF catalyst/electrode provides a potential for application as an anode in water electrolysis and direct methanol fuel cells.

Effects of Annealing Temperature on the Oxygen Evolution Reaction Activity of Copper-Cobalt Oxide Nanosheets.

Developing high performance, highly stable, and low-cost electrodes for the oxygen evolution reaction (OER) is challenging in water electrolysis technology. However, Ir- and Ru-based OER catalysts with high OER efficiency are difficult to commercialize as precious metal-based catalysts. Therefore, the study of OER catalysts, which are replaced by non-precious metals and have high activity and stability, are necessary. In this study, a copper–cobalt oxide nanosheet (CCO) electrode was synthesized by the electrodeposition of copper–cobalt hydroxide (CCOH) on Ni foam followed by annealing. The CCOH was annealed at various temperatures, and the structure changed to that of CCO at temperatures above 250 °C. In addition, it was observed that the nanosheets agglomerated when annealed at 300 °C. The CCO electrode annealed at 250 °C had a high surface area and efficient electron conduction pathways as a result of the direct growth on the Ni foam. Thus, the prepared CCO electrode exhibited enhanced OER activity (1.6 V at 261 mA/cm2) compared to those of CCOH (1.6 V at 144 mA/cm2), Co3O4 (1.6 V at 39 mA/cm2), and commercial IrO2 (1.6 V at 14 mA/cm2) electrodes. The optimized catalyst also showed high activity and stability under high pH conditions, demonstrating its potential as a low cost, highly efficient OER electrode material.

Iron doped nickel ditelluride hierarchical nanoflakes arrays directly grown on nickel foam as robust electrodes for oxygen evolution reaction

The highly applied cost effective electrocatalyst for the oxygen evolution reaction is pivotal to various energy storage and conversion devices. In this work, Fe-doped NiTe2 nanoflakes have been synthesized via facile one-step solvothermal approach. The hierarchical Ni0.4Fe0.6Te2 nanoflakes grwon on Nickel foam (NF) demonstrate the high electrochemical activity and stability towards Oxygen evolution reaction in 1 M KOH solution. The optimized Ni0.4Fe0.6Te2/NF needs only 190 mV overpotential to produce 10mAcm−2 and can afford the higher current densities for the OER of 400mAcm−2 and 500mAcm−2 at overpotential of 300 mV and 330 mV, respectively. The small Rct value for the Ni0.4Fe0.6Te2/NF suggests the reduced polarization resistance and electrode-electrolyte resistance. Moreover, it showed the extraordinary stability of 30 hours in controlled electrolysis experiment with no significant change in oxygen evolution reaction (OER) activity. The synergistic effect of bimetal atoms are considered mainly responsible for the high catalytic activity and stability, providing assistance in inducing the lattice distortion into the crystal structure of NiTe2 that activates the evolution of surface partial oxygen atoms, enabling lattice oxygen mechanism. Even after prolong activity of OER; formation of dynamic NiFeOOH(Te)/NF species sustains excellent OER activity. This work provides facile synthetic approach to develop highly applied low cost and binder free electrocatalyst.