Outstanding Oxygen Evolution Reaction Research Articles

Fe-Co Co-Doped 1D@2D Carbon-Based Composite as an Efficient Catalyst for Zn-Air Batteries.

A Fe-Co dual-metal co-doped N containing the carbon composite (FeCo-HNC) was prepared by adjusting the ratio of iron to cobalt as well as the pyrolysis temperature with the assistance of functionalized silica template. Fe1Co-HNC, which was formed with 1D carbon nanotubes and 2D carbon nanosheets including a rich mesoporous structure, exhibited outstanding oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities. The ORR half-wave potential is 0.86 V (vs. reversible hydrogen electrode, RHE), and the OER overpotential is 0.76 V at 10 mA cm-2 with the Fe1Co-HNC catalyst. It also displayed superior performance in zinc-air batteries. This method provides a promising strategy for the fabrication of efficient transition metal-based carbon catalysts.

WC nanoparticles and NiFe alloy co-encapsulated in N-doped carbon nanocage for exceptional OER and ORR bifunctional electrocatalysis

Developing earth-abundant electrocatalysts with optimized intrinsic active sites is crucial for enhancing bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. In this study, we fabricated a hollow structured carbon framework utilizing NiFe Prussian Blue analogs (PBAs) as templates, while polypyrrole (PPy) and phosphotungstic acid (PW12). Pyrrole monomer underwent polymerization on the nanocubic PBA surface in the presence of PW12 (PBA@PPy-PW12). Subsequent carbothermal reduction created an N-doped carbon shell with embedded NiFe alloy and tungsten carbide (WC) nanoparticles. The polymeric PPy-PW12 nature can not only prevent the aggregation of PBA and WC structures but also enhance electrical conductivity by connecting neighboring nanospheres. Moreover, the introduction of WC can significantly enhance the bifunctional electrocatalytic activity of the carbon-based catalyst, which is attributed to synergism between the WC and NiFe materials within the NC layer. Consequently, NiFe/W0.3C@NC exhibited outstanding OER (overpotential = 290 mV for 10 mA/cm2; Tafel slope = 57 mV/dec) and ORR (half wave potential = 0.81 V; Tafel slope = 61 mV/dec) performances. This work presents a promising avenue for developing high-performance electrocatalysts for energy conversion systems that showcase remarkable efficiency, stability, and potential practicability.

Viologen-Cucurbit[7]uril Based Polyrotaxanated Covalent Organic Networks: A Metal Free Electrocatalyst for Oxygen Evolution Reaction.

Viologen-based covalent organic networks represent a burgeoning class of materials distinguished by their captivating properties. Here, supramolecular chemistry is harnessed to fabricate polyrotaxanated ionic covalent organic polymers (iCOP) through a Schiff-base condensation reaction under solvothermal conditions. The reaction between 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diium dichloride (DPV-NH2) and 1,3,5-triformylphloroglucinol (TPG) in various solvents yields an iCOP-1 and iCOP-2. Likewise, employing cucurbit[7]uril (CB[7]) in the reaction yielded polyrotaxanated iCOPs, denoted as iCOP-CB[7]-1 and iCOP-CB[7]-2. All four iCOPs exhibit exceptional stability under the acidic and basic conditions. iCOP-CB[7]-2 displays outstanding electrocatalytic Oxygen Evolution Reaction (OER) performance, demanding an overpotential of 296 and 332mV at 10 and 20mA cm-2, respectively. Moreover, the CB[7] integrated iCOP-2 exhibits a long-term stable nature for 30h in 1m KOH environment. Further, intrinsic activity studies like TOF show a 4.2-fold increase in generation of oxygen (O2) molecules than the bare iCOP-2. Also, it is found that iCOP-CB[7]-2 exhibits a high specific (19.48mA cm-2) and mass activity (76.74mAmg-1) at 1.59V versus RHE. Operando-EIS study evident that iCOP-CB[7]-2 commences OER at a relatively low applied potential of 1.5V versus RHE. These findings pave the way for a novel approach to synthesizing various mechanically interlocked molecules through straightforward solvothermal conditions.

Simultaneous Interface Engineering and Phase Tuning of CeO2-Decorated Catalysts for Boosted Oxygen Evolution Reaction.

Heterogeneous catalysts have attracted extensive attention among various emerging catalysts for their exceptional oxygen evolution reaction (OER) capabilities, outperforming their single-component counterparts. Nonetheless, the synthesis of heterogeneous materials with predictable, precise, and facile control remains a formidable challenge. Herein, a novel strategy involving the decoration of catalysts with CeO2 is introduced to concurrently engineer heterogeneous interfaces and adjust phase composition, thereby enhancing OER performance. Theoretical calculations suggest that the presence of ceria reduces the free energy barrier for the conversion of nitrides into metals. Supporting this, the experimental findings reveal that the incorporation of rare earth oxides enables the controlled phase transition from nitride into metal, with the proportion adjustable by varying the amount of added rare earth. Thanks to the role of CeO2 decoration in promoting the reaction kinetics and fostering the formation of the genuine active phase, the optimized Ni3FeN/Ni3Fe/CeO2-5% nanoparticles heterostructure catalyst exhibits outstanding OER activity, achieving an overpotential of just 249mV at 10mAcm-2. This approach offers fresh perspectives for the conception of highly efficient heterogeneous OER catalysts, contributing a strategic avenue for advanced catalytic design in the field of energy conversion.

Short-time potentiostatic assisted borate to induce the generation of ultrathin NiFe LDH active phase for industrial-level water oxidation

Self-supported NiFe-based oxygen evolution reaction (OER) catalysts with high activity and durability are essential for the industrialization of green hydrogen. Herein, Boron-interfered NiFe LDH nanosheets (B2-NiFe-(a-10)) with abundant wrinkle structure are prepared by introducing nonmetallic sources into the surface reconstruction of layered double hydroxide (NiFe LDH) through a novel short-time potential constant activation strategy. It enhances interactions with the electrolyte, decreases Arrhenius activation energy (Ea), accelerates efficient charge transfer and O2 escape rate. The as-reconstructed B2-NiFe-(a-10) exhibits outstanding alkaline OER activity with an ultralow overpotential of 290 mV at 100 mA cm−2 and excellent durability (100 h). Additionally, density functional theory calculations further reveal that the interaction optimizes the adsorption of oxygenated intermediates (*OH→*O), induces the center of the d-band toward the Fermi energy level, and lowers the dissociation barrier of H2O. Moreover, the anion-exchange membrane water electrolyzer (AEMWE) achieves a current density of 1 A cm−2 at 1.97 V.

Template-assisted strategy for synthesizing transition metal oxyhydroxide for high-efficiency oxygen evolution reaction

Oxyhydroxides have been widely recognized as the true active species for oxygen evolution reaction (OER), while most of them are created via the complicated and time-consuming electrochemical activation process. Here, we develop a facile template-mediated method for directly synthesizing highly active oxyhydroxides toward OER. The optimal FeCoOOH prepared via using Cu2O as a sacrificial template could exhibit outstanding electrocatalytic OER performance, delivering a current density of 10 mA cm−2 with the overpotential of merely 320 mV, and a corresponding Tafel slope of 77.5 mV dec−1. Detailed mechanism study outlines that the extraordinary OER performance of such FeCoOOH originated from the intrinsically high OER activity of oxyhydroxide and the high specific surface area of the particular architecture. This work demonstrates a simple and direct route for the successful fabrication of highly active oxyhydroxides, which may open a new way for the synthesis of other active species.

Hollow-structured cobalt sulfide electrocatalyst for alkaline oxygen evolution reaction: Rational tuning of electronic structure using iron and fluorine dual-doping strategy

Utilizing renewable electricity for water electrolysis offers a promising way for generating high-purity hydrogen gases while mitigating the emission of environmental pollutants. To realize the water electrolysis, it is necessary to develop highly active and precious metal-free electrocatalyst for oxygen evolution reaction (OER) which incurs significant overpotential due to its complicated four-electron transfer mechanism. Hence, we propose a facile preparation method for hollow-structured Fe and F dual-doped CoS2 nanosphere (Fe-CoS2-F) as an efficient OER electrocatalyst. The uniform hollow and porous structure of Fe-CoS2-F enlarge the specific surface area and increase the number of exposed active sites. Furthermore, the Fe and F dual-dopants synergistically contributed to the adjustment of electronic structure, thereby promoting the adsorption/desorption of oxygen-containing reaction intermediates on active sites during the alkaline OER procedure. As a result, the prepared Fe-CoS2-F exhibits outstanding OER activity, characterized by a low overpotential of 298 mV to achieve a current density of 10 mA cm−2 and a Tafel slope as small as 46.0 mV dec−1. Based on computational theoretical calculations, the introduction of the dual-dopants into CoS2 structure reduce the excessively strong adsorption energy of reaction intermediate in the rate determining step, leading to effectively promoted electrocatalytic cycle for OER in alkaline environment. This study presents an effective strategy for preparing noble metal-free OER electrocatalysts with promising potential for large-scale industrial water electrolysis.

Activity trends of Pd clusters supported on C2N for oxygen evolution and reduction reactions

Developing highly efficient electrocatalysts for the oxygen evolution reaction (OER) and reduction reaction (ORR) is crucial for future renewable energy technology. Here, we use first-principles calculations combined with genetic algorithm to determine the structures of various Pd clusters supported on experimentally available C2N monolayer and evaluate the OER and ORR performance. Our findings show that the activity of the supported Pd clusters is closely linked to the local geometrical and electronic structure of the active site. Furthermore, we establish the activity trends of the clusters based on the adsorption free energies of intermediates. In particular, C2N supported Pd7 and Pd8 clusters exhibit outstanding OER activity with low overpotentials. We identify a volcano relation for the OER on the clusters, suggesting that the high activity of the cluster is related to the moderate adsorption strength of intermediates. Mechanistic analysis indicates that the second water formation is the potential-determining step for ORR on the clusters due to the strong adsorption of *OH. Additionally, we identify a linear scaling relationship between the ORR overpotentials and adsorption free energies of *OH, demonstrating that reducing the adsorption strength of reaction intermediates on Pd clusters can improve the activity. This work unravels the activity trends of cluster catalysts and provides strategies for the rational design of highly efficient single-cluster catalysts for OER and ORR.

A solution-based oxidation–reduction approach for spontaneous construction of nanowire architectures on copper metals

Copper (Cu) is a critically important functional material with widespread applications in catalysis, battery technology, and sensing. The oxidation–reduction approach serves as an efficient means to modify Cu metals, enabling the creation of nanowire architectures that expand their specific surface area and facilitate the engineering of catalytic active sites. However, the crucial issue is that the reduction process typically requires high-temperature treatment in an H2 atmosphere, which is laborious and demanding. Here using the dimethylamine methyl borane (C2H10BN) as an efficient reduction reagent, we report a facile solution-based oxidation–reduction approach at room temperature for the direct formation of the nanowire architectures on commercial Cu foams (CF), resulting in a unique three-dimensional (3D) hierarchically skeleton architecture. Moreover, as a typical application, cobalt hydroxide (Co(OH)2) is electrodeposited on the CF with nanowires (CFNW) to form a CFNW/Co(OH)2 electrode for oxygen evolution reaction (OER). The obtained results indicate the nanowire structure significantly increases the contact area between Co(OH)2 and CFNW substrate, resulting in an outstanding OER performance with an overpotential of 175 mV at 10 mA cm−2 in 1 M KOH. Importantly, this study presents a straightforward modification approach applicable to Cu metals, enabling large-scale production of advanced 3D skeleton Cu materials with diverse applications.

Fabrication and characterisation of CrMnFeCoNi high entropy alloy electrocatalyst for oxygen evolution reaction

Water electrolysis is attracting increasing attention in becoming the main method for green energy production, which has long been hindered by the sluggish kinetics of oxygen evolution reaction (OER) and high cost of noble-metal (NM) containing electrodes. Template replication technique has been employed to fabricate porous CrMnFeCoNi high entropy alloy (HEA) bulk foams with > 95 % porosity. High entropy led to the formation of a single-phase solid solution of transition metals in the as-fabricated porous HEA bulk foam, and the lattice distortion brings about the outstanding OER performance that is close to that of the RuO2 reference sample. Effective electrochemically active surface area and amount of exposed active sites are increased by grinding into nanoparticles, which produced superior OER performance with a near-record low overpotential of ∼ 245 mV to drive a current density of 10 mA/cm2, a low Tafel slope of 73.6 mV/dec, a double layer capacitance of 102.3 mF, and excellent long-term stability over 24 h. This work demonstrates a cost-effective way to fabricate NM-free HEA electrocatalyst with complex structure and excellent stability in OER, which could help in advancing the research for alkaline water electrolysis.

FeCoNi molybdenum-based oxides for efficient electrocatalytic oxygen evolution reaction

The search for highly efficient and inexpensive electrocatalysts is crucial to the advancement of environmentally friendly and sustainable energy sources. Here, adopting a one-step hydrothermal method, we have effectively fabricated a self-supported multi-metal molybdenum-based oxide (FeCoNi-MoO4) on nickel foam (NF). In addition to changing the catalyst's microstructure, the introducing of Fe and Co, enhanced its active center count, improved its electronic structure, and in turn reduced the difficulty for high-valence Ni and Fe species to form, which accelerates the oxygen evolution reaction (OER) kinetics by promoting the development of the actual active materials, NiOOH and FeOOH. FeCoNi-MoO4 has outstanding OER performance, requiring just 204 mV overpotentials at 10 mA cm−2 and 271 mV at 100 mA cm−2. Its exceptional OER kinetics at both low and high currents are indicated by a Tafel slope of 50.6 mV dec−1, which is attributed to the combined effect of its multi-metal composition and a higher number of active sites. Moreover, the FeCoNi-MoO4 electrode was operated continuously for over 48 h. Furthermore, the density functional theory (DFT) results demonstrated that the introducing of Fe and Co, which quickens the rate of electron transfer during the electrocatalytic process, improves the ability of oxygen intermediate species to adsorb, and ultimately lowers the overpotential, is responsible for the increased electrocatalytic activity of FeCoNi-MoO4. This work offers hope for further developments in the sector by proposing an efficient approach for creating multi-active electrocatalysts that are stable, economical, and efficient.

Metal‐Organic Frameworks: Direct Synthesis by Organic Acid‐Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts

AbstractMetal‐organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure‐activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid‐etching strategy (AES). Using π‐conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc‐MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X‐ray diffraction and low‐dose transmission electron microscopy, which is quasi‐lattice‐matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc‐MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d‐band center, high M−O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm−2) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

Metal-Organic Frameworks: Direct Synthesis by Organic Acid-Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts.

Metal-organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure-activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid-etching strategy (AES). Using π-conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc-MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X-ray diffraction and low-dose transmission electron microscopy, which is quasi-lattice-matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc-MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d-band center, high M-O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm-2 ) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

Superaerophilic/Superaerophobic NiFe-LDHs Electrode for Enhancing Overall Water Splitting in Alkaline Media.

Overall water splitting, as a critical approach to producing green hydrogen, is greatly impeded by the mass transfer of gaseous bubbles and dissolved gas molecules. Herein, a bifunctional superaerophilic/superaerophobic (SAL/SAB) NiFe layered-double-hydroxides (LDHs) electrode has been developed, which can drive H2 and O2 bubbles out of the reaction system by asymmetric Laplace pressure and accelerate dissolved gases diffusion through reducing their diffusion distance. Consequently, the SAL/SAB NiFe-LDHs electrode exhibits excellent HER activity with an overpotential of -76 mV at -10 mA cm-2 and outstanding oxygen evolution reaction activity with an overpotential of 253 mV at 100 mA cm-2. The bifunctional SAL/SAB NiFe-LDHs electrode is further utilized in overall water splitting, which can achieve 10 mA cm-2 with a cell voltage of 1.54 V. This work provides an efficient strategy to improve the efficiency of overall water splitting and can stimulate new electrode design in various gas-involved processes.

A facile synthesis of hierarchical CoFe2O4 nanosheets for efficient oxygen evolution in neutral medium

It is of great significance to develop electrocatalysts that are abundant in Earth's crust, highly efficient, and exceptionally durable for the oxygen evolution reaction (OER), particularly in neutral medium. Herein, the hierarchical CoFe2O4 nanosheets supported on iron foam (CoFe2O4/IF) were prepared by the ambient spontaneous redox reaction between iron foam and Co2+ at room temperature. The chemical composition and structure of as-prepared CoFe2O4/IF nanosheets were characterized by XRD, XPS, SEM and TEM. The CoFe2O4/IF. The as-obtained CoFe2O4/IF electrode presents excellent electrocatalytic OER activity with an overpotential of 429 mV at 10 mA cm−2 and maintains the stability of 50 h in 1 M PBS. The outstanding electrocatalytic OER activity of CoFe2O4/IF can be credited to the decreased transfer resistance and unique structural features. In addition, the CoFe2O4/IF presented here holds promise for noble-metal-free OER electrocatalyst.

A high-efficiency NiFeSe4/NiSe2 bifunctional electrocatalyst with outstanding oxygen evolution reaction and overall water splitting performance

NiFeSe4/NiSe2-8 h had good overall water splitting performance. The heterostructure of the prepared NiFeSe4/NiSe2-8 h promoted the redistribution of electrons and improved the conductivity of the material.

Synergistic effect of a bamboo-like Bi2S3 covered Sm2O3 nanocomposite (Bi2S3-Sm2O3) for enhanced alkaline OER.

The availability of hydrogen energy from water splitting through the electrocatalytic route is strongly dependent on the efficiency, durability, and cost of the electrocatalysts. Herein, a novel Bi2S3-covered Sm2O3 (Bi2S3-Sm2O3) nanocomposite electrocatalyst was developed by a hydrothermal route for the oxygen evolution reaction (OER). The electrochemical properties were studied in 1.00 mol KOH solution after coating the target material on the stainless-steel substrate (SS). Physical analysis via XRD, FTIR, IV, TEM/EDX, and XPS revealed that the Bi2S3-Sm2O3 composite possesses metallic surface states, thereby displaying unconventional electron dynamics and purity of phases. The Bi2S3-Sm2O3 composite shows outstanding OER activity with a low overpotential of 197 mV and a Tafel slope of 74 mV dec-1 at a 10 mA cm-2 current density as compared to pure Bi2S3 and Sm2O3. Meanwhile, the composite catalyst retains high stability even after 100 h of the chronoamperometry test. Thus, this work unveils a new avenue for the speedy flow of electrons, which is attributed to the synergetic effect between Bi2S3 and Sm2O3, as well as enriched interfacial defects, which exhibit greater oxygen adsorption capability with improved electronic assemblies in the active interfacial region. In addition, the introduced porous structure in core-shell Bi2S3-Sm2O3 provides extraordinary electrical properties. Thus, this article offers a realistic framework for electrochemical energy generation.

Boosting oxygen evolution reaction rates with mesoporous Fe-doped MoCo-phosphide nanosheets.

Transition metal-based catalysts are commonly used for water electrolysis and cost-effective hydrogen fuel production due to their exceptional electrochemical performance, particularly in enhancing the efficiency of the oxygen evolution reaction (OER) at the anode. In this study, a novel approach was developed for the preparation of catalysts with abundant active sites and defects. The MoCoFe-phosphide catalyst nanosheets were synthesized using a simple one-step hydrothermal reaction and chemical vapor deposition-based phosphorization. The resulting MoCoFe-phosphide catalyst nanosheets displayed excellent electrical conductivity and a high number of electrochemically active sites, leading to high electrocatalytic activities and efficient kinetics for the OER. The MoCoFe-phosphide catalyst nanosheets demonstrated remarkable catalytic activity, achieving a low overpotential of only 250 mV to achieve the OER at a current density of 10 mA cm-2. The catalyst also exhibited a low Tafel slope of 43.38 mV dec-1 and maintained high stability for OER in alkaline media, surpassing the performance of most other transition metal-based electrocatalysts. The outstanding OER performance can be attributed to the effects of Mo and Fe, which modulate the electronic properties and structures of CoP. The results showed a surface with abundant defects and active sites with a higher proportion of Co2+ active sites, a larger specific surface area, and improved interfacial charge transfer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the catalyst's high activity originates from the presence of Mo6+/Mo4+ and Co2+/Co3+ redox couples, as well as the formation of active metal (oxy)hydroxide species on its surface.

Iron Phosphates as Highly Efficient Precatalysts for Oxygen Evolution Reaction and Their in Situ Electrochemical Conversion

Current energy issues have prompted demand for the innovations in constructing a clean and sustainable energy platforms. One of examples for energy carrier to actualize a zero carbon society is hydrogen, which is a promising carbon-free fuel with an excellent weight energy density. Hydrogen production through alkaline water electrolysis using renewable energy resources (light and wind)-derived electricity is an attractive ecofriendly and cost-effective technology because cheap nonprecious electrocatalysts can be employed in alkaline media. However, oxygen evolution reaction (OER) at the anode side in the water electrolysis is basically slow and prevents the widespread applications of water electrolysis. Thus, highly efficient and cheap electrocatalysts for OER are highly desirable.Iron (Fe)-based compounds have recently received much attention as OER electrocatalysts because Fe is a quite earth-abundant metallic element that is a very cheap and non-toxic. Therefore, Fe is a promising candidate as electrocatalyst for OER. Due to the insufficient OER activity on simple Fe oxides, previous studies have attempted to enhance the activity by incorporating Fe and other metallic elements.[1,2] Recently, we established a novel comprehensive structural descriptor for the OER on Fe-based simple and multimetal oxides;[3] i.e., shorter minimum Fe–O bond length in the crystalline structures led to higher OER activity regardless of elemental composition, Fe–O coordination number, and crystal category. Thus, this descriptor enabled us to quickly develop excellent OER catalyst, Ba0.65Ca0.35Fe12O19, comprising extremely short Fe–O bond lengths.[4] Furthermore, we found that post-spinel CaFe2O4 catalyzes OER via "multi-iron-site mechanism" involving a reaction intermediate with O–O direct formation on multiple Fe atoms, and CaFe2O4 consequently displayed outstanding OER activity despite the long Fe–O bond length.[5] However, we speculate that OER activity of Fe-based oxides cannot be further enhanced based on crystal structures, and it necessitates to employ another type of compounds.In this study, we report the OER performances of Fe-based phosphates in alkaline media. We selected three kinds of Fe-based phosphates with distinct crystal structures: trigonal FePO4, trigonal Fe3O3(PO4), and monoclinic Fe4(P2O7)3. The electrochemical measurements and post-characterizations identified the Fe-based phosphates as efficient precatalysts that can be electrochemically converted into highly active Fe-based compounds. Notably, the OER performances of the electrochemically converted Fe-based compounds overcame those of the above-mentioned most active Fe-based multimetal oxides and any previously reported crystalline OER electrocatalysts. Therefore, the Fe-based phosphates are promising candidates as OER precatalysts, which can be in situ converted into excellent OER electrocatalysts, and have further advantages of low price, environmental friendliness, and easy production.[6] The part of this paper is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). This paper was funded in part by the JSPS KAKENHI Grant-in-Aid (18H01786), the JST PRESTO (JPMJPR15S3) and CREST (JPMJCR16P3) programs, the Tokuyama Science Foundation, and the “Creation of Life Innovative Materials for Interdisciplinary and International Researcher Development” program of the MEXT. The authors thank Dr. Takeshi Aihara in Tokyo Institute of Technology for fruitful discussions.

High Entropy Induced γ-NiOOH Formation in Layered Double Hydroxide as Highly-Active and Ultra-Stable Electrocatalyst for Oxygen Evolution Reaction

Developing a low-cost and highly efficient oxygen evolution reaction (OER) electrocatalyst and understanding the underlying reaction mechanism are critical for sustainable renewable energy conversion and storage. In this study, high entropy layered double hydroxide (LDH) was self-supported on nickel foam using a simple hydrothermal method. The resulting binder-free high entropy LDH consisting of five different transition metals of Fe, Ni, Co, Mn, and Cr exhibits an excellent OER activity in alkaline condition with a low overpotential of 218 mV at a current density of 50 mA cm-2. It is superior to the binary, ternary, and quaternary-metal LDH counterparts. We demonstrate that the high entropy LDH possesses ultra-stable electrochemical stability at a high current density of 400 mA cm-2 for 600 h. The modulation of electronic structure facilitates the formation of the highly active γ-NiOOH and the shifting of the d-band center, resulting the outstanding OER performance. The excellent catalytic activity and stability of the high entropy LHD make it is as a highly potential candidate for commercial use.