Low-cost Oxygen Evolution Reaction Catalysts Research Articles

Fe-Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media.

NiFe-based oxo-hydroxides are highly active for the oxygen evolution reaction but require complex synthesis and are poorly durable when deposited on foreign supports. Herein we demonstrate that easily processable, Earth-abundant and cheap Fe-Ni alloys spontaneously develop a highly active NiFe oxo-hydroxide surface, exsolved upon electrochemical activation. While the manufacturing process and the initial surface state of the alloys do not impact the oxygen evolution reaction performance, the growth/composition of the NiFe oxo-hydroxide surface layer depends on the alloying elements and initial atomic Fe/Ni ratio, hence driving oxygen evolution reaction activity. Whatever the initial Fe/Ni ratio of the Fe-Ni alloy (varying between 0.004 and 7.4), the best oxygen evolution reaction performance (beyond that of commercial IrO2) and durability was obtained for a surface Fe/Ni ratio between 0.2 and 0.4 and includes numerous active sites (high NiIII/NiII capacitive response) and high efficiency (high Fe/Ni ratio). This knowledge paves the way to active and durable Fe-Ni alloy oxygen-evolving electrodes for alkaline water electrolysers.

Phosphate-modified cobalt silicate hydroxide with improved oxygen evolution reaction

Oxygen Evolution Reaction (OER) has gained significant attention due to its crucial role in renewable energy systems. The quest for efficient and low-cost OER catalysts remains a challenge of significant interest and importance. In this work, phosphate-incorporated cobalt silicate hydroxide (denoted as CoSi-P) is reported as a potential electrocatalyst for OER. The researchers first synthesized hollow spheres of cobalt silicate hydroxide Co3(Si2O5)2(OH)2 (denoted as CoSi) using SiO2 spheres as a template through a facile hydrothermal method. Phosphate (PO43−) was then introduced to layered CoSi, leading to the reconstruction of the hollow spheres into sheet-like architectures. As expected, the resulting CoSi-P electrocatalyst demonstrated low overpotential (309 mV at 10 mA·cm−2), large electrochemical active surface area (ECSA), and low Tafel slope. These parameters outperform CoSi hollow spheres and cobaltous phosphate (denoted as CoPO). Moreover, the catalytic performance achieved at 10 mA cm−2 is comparable or even better than that of most transition metal silicates/oxides/hydroxides. The findings indicate that the incorporation of phosphate into the structure of CoSi can enhance its OER performance. This study not only provides a non-noble metal catalyst CoSi-P but also demonstrates that the incorporation of phosphates into transition metal silicates (TMSs) offers a promising strategy for the design of robust, high-efficiency, and low-cost OER catalysts.

Role of Electrode Thickness in NiFe Nanogranular Films for Oxygen Evolution Reaction

Nanostructured materials may provide a route to overcome the electrode-limiting performance in water splitting, the oxygen evolution reaction (OER), within the framework of low-cost catalysts search. However, for alloyed NiFe nanostructures, the relationship among the OER efficiency and the electrode physical characteristics (morphology, porosity, size, thickness, or mass loading) is largely unknown. This work introduces a new type of alloyed NiFe (90/10% at) nanogranular electrodes obtained by supersonic cluster beam deposition and investigates the dependence of their catalytic activity toward the OER on the film morphological and stoichiometric properties. The synthesized alloyed NiFe nanoparticles with 0.3–3.8 nm size assemble from the gas phase to form ultrathin film electrodes with thickness in the 15–88 nm range, corresponding to 5–30 μg/cm2 mass loading. The fitting of the optical spectroscopic data by an effective medium approximation model suggests that, independent of the thickness, the films have a 20% porosity and are completely hydroxydated. The resulting catalytic efficiency is independent on the film thickness, while the turnover frequency decreases with increasing electrode loading. These data suggest that an excess of catalyst mass with respect to the OER active sites is deposited in the case of thicker electrodes and sets the 15 nm film as an upper loading limit to maximize the electrocatalyst efficiency. This study represents a crucial step toward thickness optimization of NiFe electrodes to fabricate low-cost OER catalysts.

Modification of surface electronic structure via Ru-doping: Porous Ru–CoFeP nanocubes to boost the oxygen evolution reaction

Electrocatalysts for oxygen evolution reaction (OER) with excellent activity and favorable stability are received much attention, due to the urgent requirement for green energy. Herein, we report a low-cost, highly efficient and stable electrocatalyst, Ru–CoFeP (Ru doped CoFeP nanocubes). The superior OER performance of Ru–CoFeP is ascribed to the synergistic effects of the Ru doping, porous structure and exposed active sites. Ru–CoFeP catalyst owns a small overpotential of 185 mV at 10 mA cm−2, a Tafel slope of 67.6 mV dec−1 and a Cdl value of 9.1 mF cm−2, which is much better than those of undoped CoFeP catalyst. Density functional theory (DFT) calculations reveal that the electrons would move toward to Ru after the Ru doping on the active CoFeP (111) surface and the adsorption capacity to H2O molecules is also strengthened to elongate and break O–H bond. The Ru–CoFeP + Pt/C based rechargeable Zn-air battery exhibits excellent stability with slightly increased/decreased potential after 450 cycles at the current density of 5 mA cm−2, which shows a much better performance than that of RuO2+Pt/C battery. This work not only provides an efficient low-cost OER catalyst, but also demonstrates that Ru-doping would be a feasible strategy to enhance OER performance.

Manganese-doped nickel-iron bimetallic hydroxide catalyst for efficient electrocatalytic oxygen evolution reaction

<p indent="0mm">Hydrogen energy has many advantages such as wide source, high calorific value, clean and renewable energy, which is considered ideal secondary energy. Under the background of “carbon peak” and “carbon neutral”, the development of hydrogen energy has become the strategic deployment of all countries in the world. Renewable energy is converted into electric energy, and hydrogen production from water electrolysis is further realized through electric energy, which is currently considered as one of the safe and green way of hydrogen production. However, in the actual process of hydrogen production by electrolysis of water, there are problems such as high reaction overpotential and low energy conversion efficiency, which seriously restrict the cost of hydrogen production. During water electrolysis, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) occur at negative and positive electrodes respectively. Compared with the HER process of the two-electron reaction, the four-electron OER process requires a higher overpotential. Therefore, the four-electron OER process becomes the decisive step of the reaction. In order to achieve high efficiency and low energy consumption of hydrogen production process, it is urgent to use cheap, efficient and stable OER catalyst. At present, the search for efficient and low-cost OER catalyst is still the “holy grail” of water splitting. Among many non-noble metal catalysts, NiFe-layered double hydroxides (NiFe-LDHs) are considered as an ideal OER electrocatalyst in alkaline conditions due to their low raw material cost and adjustable structure. However, for NiFe-LDHs laminates, it is generally believed that the edge metal sites have higher catalytic activity than the internal metal sites, which leads to the insufficient utilization of the metal sites inside the laminates and reduces the catalytic activity of the OER reaction. In order to solve the above problems, based on the microstructural regulation of NiFe-LDHs, some methods have been used to improve its catalytic activity and stability in the OER process. Heterogeneous element doping is considered to be an effective method to regulate the electronic structure and electrochemical activity of catalysts. Metal ion doping (Cr, Cu, V, etc.) can optimize the electronic structure of nickel metal active site, reduce reaction overpotential, and improve catalytic efficiency. However, the high biotoxicity of traditional transition metals (Cr, V, Cu, etc.) limits their industrial application. Mn (Mn²⁺<inline-graphic specific-use="online" href="./online/TB-2021-1323-c1.png" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="./online/TB-2021-1323-c1.png"/><inline-graphic specific-use="print" href="./print/TB-2021-1323-c1.pdf" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="./print/TB-2021-1323-c1.pdf"/>Mn³⁺<inline-graphic specific-use="online" href="./online/TB-2021-1323-c1.png" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="./online/TB-2021-1323-c1.png"/><inline-graphic specific-use="print" href="./print/TB-2021-1323-c1.pdf" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="./print/TB-2021-1323-c1.pdf"/>Mn⁴⁺) with rich variation characteristics has a potential role in regulating lamellar charge characteristics. Herein, in order to fully improve the utilization of NiFe-LDHs laminates, this study introduces manganese ions with variable valence characteristics into NiFe-LDHs laminates (Mn-NiFe-LDHs), and utilizes the variable valence characteristics of manganese ions to fully enhance the carrier mobility and promote electron transfer in the laminate. At the same time, due to the electronegativity characteristics of manganese ions, part of the electrons will be transferred from the vicinity of the nickel site to the vicinity of the manganese site, causing the nickel site to exhibit electron-deficient characteristics, which enhance the overall capture of the electron-rich oxygen-containing functional groups of the laminate, thereby effectively enhancing the OER catalytic activity. According to the results of the catalytic reaction, the Mn-NiFe-LDHs electrode exhibits an overpotential of only 332 mV at a current density of <sc>10 mA/cm²,</sc> which is lower than the initial NiFe-LDHs of 384 mV. The reasonable doping of manganese ions can effectively adjust the Ni²⁺ site activity and enhance its electrocatalytic activity. And to further clarify the effect of doping on the activity of LDHs laminates to provide experimental facts support.

Constructing the Fe/Cr double (oxy)hydroxides on Fe3O4 for boosting the electrochemical oxygen evolution in alkaline seawater and domestic sewage

Developing the electrocatalysts which can be directly performed in sewage and seawater without further treatment kills two birds with one stone since it can turn waste into raw materials and produce H2. Herein, the heterointerface between Fe(Cr)OOH and Fe3O4 is constructed through a scalable method. Systematic experiments and theoretical calculations confirmed that the Fe(Cr)OOH coupling with Fe3O4 can significantly decrease the oxygen evolution reaction (OER) overpotential (η500 = 241 mV in 1 M KOH) and promote the mass and electron transfer. Impressively, this electrode could work efficiently and maintain 100 mA cm−2 for 100 h in both alkaline seawater and domestic sewage. The electrolyzer using such electrode as anode could deliver a current density of 500 mA cm−2 in 5 M KOH at a small cell voltage of 1.62 V. This work provides a facile route to prepare efficient and low-cost OER catalysts, which has important implications for energy conversion.

Structural design of cobalt phosphate on nickel foam for electrocatalytic oxygen evolution

The elaborate design and synthesis of low-cost, efficient and stable electrocatalysts for the oxygen evolution reaction (OER), which may alleviate the current energy shortage and environment pollution, is still a great challenge. Herein, metal phosphonate precursors with controllable morphologies were synthesized in situ on the surface of nickel foam with different solvents, and could be easily converted into carbon- and nitrogen-doped cobalt phosphate through a calcination method. The OER catalytic performance of the final products was studied in detail. The results showed that the nanowire shaped samples of CoPiNF-800 synthesized with deionized water under hydrothermal conditions had the strongest electrochemical performance. They exhibited extraordinary catalytic activity with a very low overpotential of 222 mV at 100 mA cm−2, the smallest impedance and excellent electrochemical stability. These results not only demonstrate the possibility of preparing low-cost OER catalysts based on transition metal phosphate, but also aid our understanding of the controllable synthesis process of different morphologies.

Mechanistic Insights on Enhanced Activity of Cu-Deposited Fibrous Electrocatalyst for Oxygen Evolution Reaction

Water electrolysis is an ideal method for producing hydrogen, which is expected as a next-generation energy carrier. However, the sluggish reaction kinetics of the oxygen evolution reaction (OER) limits the overall energy efficiency.1,2 Therefore, designing efficient electrocatalyst for the OER is crucial and has been studied extensively for more than a few decades.3 Precious metal catalysts such as RuO2 and IrO2 exhibit high activity,4,5 but are expensive, and transition metals have been attracted as alternative catalysts.6 In this study, a fibrous Cu catalyst was synthesized as a highly active and low-cost OER catalyst. An electrospinning method was selected to synthesize a fibrous polymer substrate, which was subsequently coated with Cu by electroless deposition. We applied Cu, which is a low cost and has excellent electrical conductivity as an electrocatalyst. As a geometric structure, fiber shape was adopted to increase the specific surface area and improving the diffusion efficiency of the catalyst. We selected PVdF-HFP as catalyst support, to promote the diffusion of the ions in the electrolyte and enhance the activity as a catalyst by its ferroelectricity.In order to clarify the effect of geometric structure on the OER activity, Cu catalysts were synthesized by various methods, including drop-casting, impregnation, and electrospinning. It was found that the fibrous Cu catalyst exhibited the best OER activity amongst all the geometric structures tested in this study, probably due to the increased active surface area as well as better mass transport and diffusion. Furthermore, the effect of the dielectric properties of PVdF-HFP on the OER activity was clarified. The molecular orientation of PVdF-HFP was evaluated by infrared (IR) spectroscopy, which indicates that the stretching and annealing treatment can effectively increase its electric polarizability. Linear sweep voltammetry (LSV) confirmed that the fibrous Cu catalyst with stretching and annealing treatment showed superior OER activity compared to the pristine fibrous Cu catalyst, indicating the large electric polarizability also enhanced the OER.Based on these results, it was clarified that the improvement of the OER activity of the fibrous Cu catalyst was due to the following reasons; (i) improvement of mass transport by fibrous structure, and (ii) optimization of the OER reaction energetics by catalyst(Cu)-support(PVdF-HFP) interaction. Optimizing both geometry and electronic structure of the electrocatalyst provides a new design strategy to achieve improved activity towards oxygen evolution reaction.1 Seh, W. Z. et al., Science. 2017, 355, eaad4998.2 Fabbri, E. et al., Catal. Sci. Technol. 2014, 4, 3800–3821.3 Jiao, Y. et al., Chem. Soc. Rev. 2015, 44, 2060–2086.4 Lee, Y. et al., J. Phys. Chem. Lett. 2012, 3, 399–404.5 Paoli, A. E. et al., Chem. Sci., 2015, 6, 190–196.6 Hong, T. W. et al., Energy Environ. Sci. 2015, 8, 1404–1427.

Crystalline state transformation strategy for improving the catalytic performance of oxygen evolution reaction at high current density

Because the oxygen evolution reaction (OER) greatly limits the large-scale application of electrolyzed water, it is crucial to develop and synthesize effective electrocatalysts. Herein, we report a solvent substitution strategy to prepare the iron-naphthalenedicarboxylic acid (Fe-NDC) coordination complex. Through the crystalline state transformation of Fe-NDC from the crystalline to the amorphous phase, the catalytic performance of the prepared catalyst for OER at high current density can be significantly improved under alkaline conditions. Profiting from exposed metal active sites and expanded electron transport channels, amorphous-phase Fe-NDC (AP-Fe-NDC) exhibits stable electrocatalytic activity, with 225 and 333 mV overpotentials at 10 and 500 mA/cm2, respectively. Moreover, AP-Fe-NDC displays high oxygen yield and faraday efficiency. This rapid and facile strategy will be of immediate benefit to guide the preparation of other high-performance and low-cost OER catalysts.

Core-Shell NiO/C@NiFe-LDH Nanocomposite as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Highly efficient and low-cost oxygen evolution reaction (OER) electrocatalysts have been urgently needed for the development of renewable hydrogen energy via water electrolysis. Herein, a core-shell NiO nanoparticles decorated carbon sphere (NiO/C) and NiFe-layered double hydroxide (NiFe-LDH) nanocomposite (NiO/C@NiFe-LDH) was prepared by a calcination-hydrothermal synthesis approach. In this nanocomposite, NiO/C as the core were derived from Ni based metal organic frameworks (Ni-MOFs), which not only provide a porous and conductive carbon support for NiFe-LDH nanosheets to expose active sites, but also offer a synergistic active site for NiFe-LDH nanosheets. The structure and morphology of NiO/C@NiFe-LDH were mainly characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption test. The OER catalytic activity of NiO/C@NiFe-LDH was optimized by adjusting the ratio between NiO/C and NiFe-LDH and adding bridging agents. Under the optimum conditions, the overpotential at 10 mA cm−2 for NiO/C@NiFe-LDHs is only 299 mV(vs RHE), lower than that of commercial RuO2 (330 mV). Besides, the NiO/C@NiFe-LDH exhibits a good stability in 10-hour testing. These results show that the ingenious combination of different OER catalysts may be an effective strategy to prepare low-cost OER catalysts with good performance.

Improving catalytic activity of metal telluride by hybridization: An efficient Ni3Te2-CoTe composite electrocatalyst for oxygen evolution reaction

Development of high-performance electrocatalysts for oxygen evolution reaction (OER) is the key to improve the efficiency of many energy conversion process. Metal telluride is a type of low-cost OER catalyst with promising activity. To improve the OER performance of metal telluride, we propose herein the design of composite metal telluride OER catalyst that fully utilizes the advantages of each component in the composite. The developed Ni 3 Te 2 -CoTe/CC composite electrocatalyst has a high OER performance than its Ni 3 Te 2 and CoTe counterpart. The improved OER performance of the composite Ni 3 Te 2 -CoTe electrocatalyst can be on one hand ascribed to the high density of state near Fermi level in Ni 3 Te 2 phase, as suggested by DFT analysis. On the other hand, the introduction of CoTe phase in the composite effectively enlarges the electrochemical surface area of the catalyst, thus improving the activity of the composite. • A novel Ni 3 Te 2 -CoTe/CC catalyst is developed. • The Ni 3 Te 2 -CoTe/CC catalyst combines advantages of Ni 3 Te 2 and CoTe. • The Ni 3 Te 2 -CoTe/CC catalyst shows high OER activity and stability.

In situ growth of ultrathin NiFe layered double hydroxide nanosheets on reduced oxide graphene as an enhanced oxygen evolution electrocatalyst

It is highly essential but challengeable to explore the earth-abundant and low-cost oxygen evolution reaction catalysts to replace Ir- or/and Ru-based ones. In this article, we report an in situ growth of ultrathin NiFe layered double hydroxide nanosheets on reduced graphene oxide in formamide aqueous solution followed by simple chemical reduction. These ultrathin layered double hydroxide nanosheets in the composite occur in single- or multi-layer forms on reduced graphene oxide matrix. Consequently, the obtained catalyst exhibits the enhanced BET surface area and electrochemically active surface area, and low mass transfer resistance. This electrocatalyst displays the excellent OER activity with a small onset potential of 233 mV. Additionally, it only requires an overpotential of 254 mV to achieving current density of 10 mA cm−2, and can gives a current density of 70.60 mA cm−2 at overpotential of 300 mV in 0.1 M KOH. It also demonstrates the robust long-time electrochemical durability.

High OER performance Ni(OH)2 with hierarchical structure

A stable, efficient, and low-cost oxygen evolution reaction catalyst is very momentous to deal with energy crisis and achieve sustainable energy conversion and storage. Herein, the composite of Ni(OH)2 and reduced graphene oxide were obtained by a hydrothermal method at a high temperature and high pressure in a one-step hydrothermal process. SEM images showed that a multilayer sandwich structure with reduced graphene oxide in the middle of two layers of Ni(OH)2 was achieved for the electrode. This unique hierarchical catalyst exhibited remarkable oxygen evolution reaction (OER) electrochemical activity in 1 M KOH media: a 313-mV overpotential at 10 mA cm−2, a small Tafel slope of 46 mV dec−1, and excellent stability for a 22-h chronopotentiometry test. In addition, the overpotential of our catalyst is much lower than that of RuO2, i.e., 20 mV lower at 50 mA cm−2. This work demonstrates a new type of excellent OER catalyst with a hierarchical structure.

Interface-coupling of CoFe-LDH on MXene as high-performance oxygen evolution catalyst

Oxygen evolution reaction (OER) is the bottleneck reaction of the overall water splitting process despite the intensive research in the past decades. Efficient yet stable low-cost OER catalysts have been widely explored but further improvement is still highly demanded. Herein, a type of hybrid OER catalyst was prepared by the growth of CoFe-LDH (layered double hydroxide) on the surface of Ti3C2 MXene nanosheets, which exhibits superior OER performance than the state-of-the-art RuO2. The enhancement of the OER performance could be attributed to the combination of oxygen-breaking ability of CoFe-LDH and metallic conductivity of Ti3C2 MXene substrate. Meanwhile, the direct growth of CoFe-LDH on the hydroxyl-rich surface of MXene effectively prevents itself from aggregation, exposing more CoFe-LDH edge active sites. What's more important is that the intimate interface between CoFe-LDH and Ti3C2 MXene brings in efficient charge transfer and oxygen activation, which is supported by the DFT calculation results. The direct growth of CoFe-LDH on MXene endows the insulating LDH with metallic features with the O 2p states become distributed above the Fermi level which is mediated by the possible anionic redox process. This work demonstrates the great potential of MXene-based hybrid nanostructure for energy conversion applications.

Co2P Nanoparticles Wrapped in Amorphous Porous Carbon as an Efficient and Stable Catalyst for Water Oxidation.

Exploring highly active, enduringly stable, and low-cost oxygen evolution reaction catalysts continues to be a dominant challenge to commercialize renewable electrochemical water-splitting technology. High-active and earth-abundant cobalt phosphides are recently considered as promising candidates. However, the poor inherent electron transfer efficiency and instability hinder its further development. In this work, a novel approach was demonstrated to effectively synthesize Co2P nanoparticles wrapped in amorphous porous carbon framework (Co2P/C). Benefiting from extremely high specific surface area of porous carbon, plenty of active sites were adequately exposed. Meanwhile, unique anchoring structure between Co2P nanoparticles and amorphous carbon outerwear insured high charge transfer efficiency and superior stability of Co2P/C. Due to these favorable properties, low overpotential of 281 mV at 10 mA cm−2 and Tafel slope of 69 mV dec−1 were achieved in resultant Co2P/C catalyst. More significantly, it only exhibited a negligible overpotential increase after 30 h stability test, and these performances entirely preceded commercial RuO2 benchmark. In summary, we proposed a simple and feasible strategy to prepare metal phosphides wrapped with amorphous porous carbon outerwear for efficient and durable electrochemical water oxidation.

Grafting Cobalt Diselenide on Defective Graphene for Enhanced Oxygen Evolution Reaction

SummaryCobalt diselenide (CoSe2) has been demonstrated to be an efficient and economic electrocatalyst for oxygen evolution reaction (OER) both experimentally and theoretically. However, the catalytic performance of up-to-now reported CoSe2-based OER catalysts is still far below commercial expectation. Herein, we report a hybrid catalyst consisting of CoSe2 nanosheets grafted on defective graphene (DG). This catalyst exhibits a largely enhanced OER activity and robust stability in alkaline solution (overpotential at 10 mA cm−2: 270 mV; Tafel plots: 64 mV dec−1). Both experimental evidence and density functional theory calculations reveal that the outstanding OER performance of this hybrid catalyst can be attributed to the synergetic effect of exposed cobalt atoms and carbon defects (electron transfer from CoSe2 layer to defect sites at DG). Our results suggest a promising way for the development of highly efficient and low-cost OER catalysts based on transition metal dichalcogenides.

One-step construction of porous Ni/Co metal/oxide nanocubes for highly efficient oxygen evolution

A one-step method to synthesize porous Ni/Co metal/oxide as highly efficient oxygen evolution reaction (OER) catalysts is presented. Using Ni-Co Prussian blue analogue as both the precursor and the template, a simple oxidation in air at low temperatures results in the formation of Ni/Co metal/oxide nanocubes with fine particles. The optimized porous NiCoOx-400 exhibits excellent OER activity with a low onset of 1.40 V (vs. RHE), an overpotential of 280 mV at 10 mA/cm2 and a small Tafel slope of 74 mV/decade in 0.1 M KOH solution, significantly superior to those of the state-of-the-art noble-metal OER catalyst IrO2/C. This approach offers the potential to generate highly active and low-cost OER catalysts on a large scale.

Phosphonate-Based Metal–Organic Framework Derived Co–P–C Hybrid as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Cobalt phosphate is considered to be one of the most active catalysts for the oxygen evolution reaction (OER) in neutral or near-neutral pH media, but only a few transition-metal phosphates are investigated in alkaline media, probably due to their poor intrinsic electrical conductivity and/or tendency to aggregate. Herein, in situ-formed cobalt phosphate decorated with N-doped graphitic carbon was prepared using phosphonate-based metal–organic frameworks (MOFs) as the precursor. It can serve as a highly active OER catalyst in alkaline media, affording a current density of 10 mA cm–2 at a small overpotential of 215 mV on the Ni foam. A combination of X-ray absorption spectroscopy and high-resolution XPS elucidates the origin of the high activity. Our observations unveil that cobalt diphosphate having the distorted metal coordination geometry with long Co–O and Co–Co distances is mainly responsible for the high OER activity. These results not only demonstrate the potential of a low-cost OER catalyst derived...

In Situ Activating Ubiquitous Rust towards Low-Cost, Efficient, Free-Standing, and Recoverable Oxygen Evolution Electrodes.

Developing effective ways to recycle rusted stainless steel and to promote the sluggish oxygen evolution reaction (OER), associated with water splitting and metal-air batteries, is important for a resource-sustainable and environment-friendly society. Herein, we propose a strategy to enable rusted stainless steel plate to be used as an abundant and low-cost OER catalyst, wherein a hydrothermal combined in situ electrochemical oxidation-reduction cycle (EORC) method is developed to mimic and expedite the corrosion process, and thus activate stainless steel into free-standing OER electrodes. Benefiting from the plentiful electrolyte-accessible Fe/(Ni) oxyhydroxides, high conductivity and mechanical stability, this electrode exhibits remarkable OER performances including low overpotential, fast kinetics, and long-term durability. The slight degradation in current after long-term use can be repaired immediately in situ by an EORC.

A mini review on nickel-based electrocatalysts for alkaline hydrogen evolution reaction

High gravimetric energy density, earth-abundance, and environmental friendliness of hydrogen sources have inspired the utilization of hydrogen fuel as a clean alternative to fossil fuels. Hydrogen evolution reaction (HER), a half reaction of water splitting, is crucial to the low-cost production of pure H2 fuels but necessitates the use of electrocatalysts to expedite reaction kinetics. Owing to the availability of low-cost oxygen evolution reaction (OER) catalysts for the counter electrode in alkaline media and the lack of low-cost OER catalysts in acidic media, researchers have focused on developing HER catalysts in alkaline media with high activity and stability. Nickel is well-known as an HER catalyst and continuous efforts have been undertaken to improve Ni-based catalysts as alkaline electrolyzers. In this review, we summarize earlier studies of HER activity and mechanism on Ni surfaces, along with recent progress in the optimization of the Ni-based catalysts using various modern techniques. Recently developed Ni-based HER catalysts are categorized according to their chemical nature, and the advantages as well as limitations of each category are discussed. Among all Ni-based catalysts, Ni-based alloys and Ni-based hetero-structure exhibit the most promising electrocatalytic activity and stability owing to the fine-tuning of their surface adsorption properties via a synergistic nearby element or domain. Finally, selected applications of the developed Ni-based HER catalysts are highlighted, such as water splitting, the chloralkali process, and microbial electrolysis cell.