Electrocatalytic Performance For Oxygen Evolution Reaction Research Articles

Lead‐Induced Microstrain in Synthesis and Manipulation of Porous Pyrochlore for Boosting Oxygen Evolution Reaction

AbstractPyrochlore ruthenates are highlighted as candidates to replace iridium oxide as oxygen evolution reaction (OER) electrocatalyst, but their designable geometric configurations and composition modulations are hampered by the high‐temperature (≈1100 °C) and long‐time calcination (more than 12 h), which further decreases the technical and economic feasibility. In this work, an energy‐ and time‐saving approach is proposed to prepare pyrochlore yttrium ruthenate at a much lower calcination temperature (600 °C) and shorter calcination time (6 h) just by inducing A‐site substitutions of lead ions (YPRO). The local microstrain derived from Pb provides the surficial compression and extra driving force to overcome the strain energy of phase‐transition resistances and the obtained low‐temperature YPRO exhibits enriched pores, deficient geometries, shortened Ru─O bond, and enlarged Ru─O─Ru bond angle, which further modify the electronic structure, involving of the rearranged band alignment and the eliminated bandgap. The regulated morphologic, geometric, and electronic structures in YPRO synergically boost the electrocatalytic OER performance (4.8‐fold and 30.0‐fold enhancements compared with pyrochlore yttrium ruthenate and commercial iridium dioxide (IrO2), respectively) in universal pH conditions. This substitution‐induced strain engineering on phase transition should also be effective for other high‐temperature materials and trigger their diverse intriguing properties.

Heterogeneous high-entropy catalyst nanoparticles for oxygen evolution reaction: Impact of oxygen and fluorine introduction

High-entropy catalysts attract rising attention for promoting oxygen evolution reaction (OER) due to the advantages of multiple catalytic active sites, unique lattice distortion effect, interatomic d-band ligand effect, etc. However, it still needs to design new high-entropy catalysts with low cost and high efficiency to meet the requirement of large-scale applications. In this study, AlNiCuCoFeY amorphous alloy ribbon is prepared by melt spinning method. Then, the ribbon is etched in HF solution to form a nanoparticle modified ribbon, whose superficial species are further conversed to high-entropy oxides/Al alloy (HEO/Al alloy) or high-entropy fluorides/Al alloy (HEF/Al alloy) heterogeneous nanoparticles with a diameter of ∼20 nm by subsequent oxidization or fluorination process. Herein, the oxidized metallic elements with high valence state can promote the adsorption of OER. Due to the large surface area, multiple active sites, and the synergistic effect of different species, the HEO/Al alloy or HEF/Al alloy composite only need 293 and 261 mV overpotential to afford 10 mA cm−2 current density. This work discusses the design of high-entropy electrocatalysts and demonstrated a promising route to improve their OER electrocatalytic performance.

Nickel phosphide nanoarrays decorated on amorphous NiPOx/Fe(OH)3: A stable core–shell electrocatalyst for efficient oxygen evolution at large current density

Severe reconstruction of transition-metal phosphides occurring in the oxygen evolution reaction (OER) process suffers from catalyst activity and long-term stability challenges. Herein, we develop a facile preoxidation tactic to fabricate an amorphous NiPOx/Fe(OH)3 protective layer on the surface of NiP nanoarrays and investigate the effect of the NiPOx/Fe(OH)3 layer thickness on electrocatalytic OER performance. We find the optimized NiP@NiPOx/Fe(OH)3 electrode achieves a promising OER performance, with a low overpotential of 270.7 mV and an ultralong durability for 500 h at 500 mA cm−2, predominantly originating from the synergy of the highly conductive NiP core and the NiPOx/Fe(OH)3 layer. Post-OER characterizations demonstrate that the NiPOx/Fe(OH)3 layer protects NiP from oxidation during the OER process and thus avoids the severe reconstruction of NiP adverse to the catalyst stability. This work opens an avenue for enhancing OER performance in water splitting via rational control of surface reconstruction of metal phosphides at the desired point.

Constructing Nanoporous Ir/Ta2 O5 Interfaces on Metallic Glass for Durable Acidic Water Oxidation.

Although proton exchange membrane water electrolyzers (PEMWE) are considered as a promising technique for green hydrogen production, it remains crucial to develop intrinsically effective oxygen evolution reaction (OER) electrocatalysts with high activity and durability. Here, a flexible self-supporting electrode with nanoporous Ir/Ta2O5 electroactive surfaceis reported for acidic OER via dealloying IrTaCoB metallic glass ribbons. The catalyst exhibits excellent electrocatalytic OER performance with an overpotential of 218mV for a current density of 10mA cm-2 and a small Tafel slope of 46.1mV dec-1 in acidic media, superior to most electrocatalysts. More impressively, the assembled PEMWE with nanoporous Ir/Ta2 O5 as an anode shows exceptional performance of electrocatalytic hydrogen production and can operate steadily for 260h at 100mA cm-2 . In situ spectroscopy characterizations and density functional theory calculations reveal that the modest adsorption of OOH* intermediates to active Ir sites lower the OER energy barrier, while the electron donation behavior of Ta2 O5 to stabilize the high-valence states of Ir during the OER process extended catalyst's durability.

Earth-Abundant Electrocatalysts for the Oxygen Evolution Reaction Supported on Layered Zirconium Phosphate Nanomaterials

Recently, we have demonstrated improved electrocatalytic activity of layered zirconium phosphate (ZrP) nanomaterials loaded with earth-abundant metal ions suitable as catalysts for the oxygen evolution reaction (OER). We compared the catalytic efficiency of ZrP nanoparticles ion-exchanged with transition metals (Fe, Ni, Co) in the interior of the layers as well as in the external surface to a system in which the metal catalysts are confined exclusively on the external ZrP surface. Linear sweep voltammetry revealed that the electrocatalytic systems with metal catalysts on the external ZrP nanomaterials’ surface had improved OER activity compared to systems with metals intercalated in the ZrP interlayers. This result prompted us to study a system of exfoliated ZrP particles which provide only external surfaces to the electrocatalytic metal ions. A comparison between adsorbed Co or Ni catalysts on ZrP nanoparticles and those same catalysts on exfoliated ZrP nanoplatelets proved that the later systems were more active, with diminished overpotentials and reduced Tafel plot slopes. Comparison between Co and Ni catalyst on ZrP particles with different morphologies (hexagonal platelets, rods, cubes, and spheres) revealed that the more active Co catalysts are those on hexagonal ZrP platelets, whereas the best Ni catalysts are those on ZrP spheres. More recently, efficient OER catalysts were obtained with cobalt porphyrin molecular electrocatalysts both intercalated in ZrP and adsorbed on exfoliated ZrP nanoplatelets. Mixed metal NiFe-intercalated ZrP electrocatalysts at 90% Fe metal content proved to have superior OER electrocatalytic performance (decreased overpotentials, increased mass activities, reduced Tafel slopes) compared to adsorbed counterparts. We are exploring OER activities of other mixed-metal catalysts on ZrP, bifunctional catalysts, and operando synchrotron X-ray absorption spectroscopy studies to elucidate the nature of the active species.

In-situ construction of pomegranate-like nickel-vanadium nitride for hydrogen production through urea-assisted water-splitting

To accelerate the promotion of hydrogen energy utilization, the research of efficient and stable catalysts has been the priority, and the combination of multifunctional catalytic performance for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is needed. Transition metal nitrides (TMNs) is considered as an inexpensive alternative to noble metal-based catalysts. However, NH3 is mostly used in TMNs synthesis method, which is contrary to the original intention of environmental protection. Herein, nickel-vanadium nitride (VN) with pomegranate nanostructure grown on Ni foam (NF) is obtained by hydrothermal and following environmental-friendly urea nitridation approach (Ni/VN/NF). Remarkably, Ni/VN/NF exhibits excellent electrocatalytic performances for HER, OER and UOR. Remarkably, the electrolyzer can be driven to produce hydrogen through intermittent energy sources, such as wind, solar, and thermal energy, proving its potential applications on storing the renewable energies. This work provides a strategy for the development of high-performance TMNs for urea-assisted water-splitting.

Construction of Ni2P-NiFe2O4 heterostructured nanosheets towards performance-enhanced water oxidation reaction

Water electrolysis represents a promising option for clean hydrogen production, but its overall efficiency is hindered by the sluggish oxygen evolution reaction (OER) with a complex electron transfer process. The construction of heterostructure has emerged as an effective approach to enhance the electrocatalytic performance for OER because of the improvement of exposed active surface and mass/charge transfer. In this work, we report the synthesis of hierarchical nanosheet-structured Ni2P-NiFe2O4 as a robust OER catalyst via an annealing treatment and followed by in-situ phosphating process. The Ni2P-NiFe2O4 electrocatalyst exhibits an overpotential of 305 mV to realize 100 mA cm−2 in 1.0 M KOH. Density functional theory calculations further confirm that the construction of heterostructure could optimize adsorption energy of oxygen-containing intermediates and reduce energy barrier during the OER process. This work may provide insights into the electrocatalytic activities of non-noble-metal-based catalysts and present an effective method for the preparation of complex structures.

Engineering S, N-doped carbon nanosheets derived from thiazolothiazole-based conjugated polymer for efficient electrocatalytic oxygen evolution and Zn-air battery

Electrochemical oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) by using metal-free electrocatalysts is an emerging research interest for clean energy due to its cost affordability and eco-friendliness. However, only a few metal-free electrocatalysts are reported to exhibit robust OER and ORR performances, although OER and ORR are very important in various energy technology like metal-air batteries, fuel cells, etc. Herein, we have developed a rigid thiazolo [5,4-d] thiazole-based organic conjugated polymer, P-TzTz, and its polymer-derived N and S-doped carbon nanosheets for metal-free electrocatalytic OER and ORR. The polymer possesses a unique two-dimensional nanosheet structure with a moderate surface area of 72.6 m2/g and a wide range of pore sizes. The synthesized P-TzTz displayed a reasonable electrocatalytic OER performance with excellent long-term stability. The OER performance was further enhanced by pyrolyzing the P-TzTz at 800 °C to prepare the N and S-doped carbon nanosheet, P-TzTz-CNS800. The elevated surface area (228 m2/g) with uniform mesopores, enhanced electrical conductivity of P-TzTz-CNS800, and the presence of N, and S as the dopants for improving active sites made the P-TzTz-CNS800 a promising OER/ORR electrocatalyst as it showed the OER overpotential of 347 mV@10 mA/cm2 current density with more than 45 h long-range durability and 98% Faradic efficiency of oxygen evolution. Finally, to utilize the good OER efficacy of P-TzTz-CNS800-based metal-free electrocatalyst, a rechargeable Zn-air battery was fabricated as a proof of concept by taking P-TzTz-CNS800 as the air cathode. The Zn-air battery revealed a constant open circuit potential of 1.44 V and high charging/discharging stability over 40 h with a minimal loss in round trip frequency. Thus, the report corroborates the promising potential of P-TzTz derived N and S-doped carbon nanosheets as an efficient metal-free electrocatalyst as an air cathode for Zn-air battery for clean energy conversion.

A novel Ni3S2/MnO2@N,F-CQDs composite with spherical-chain-like morphology for efficient oxygen evolution reaction in aqueous alkaline solutions

Developing earth-abundant transition metal-based oxygen evolution reaction (OER) electrocatalysts is extremely essential for accomplishing efficient electrocatalytic overall water splitting. Herein, we synthesized a Ni3S2/MnO2@N,F-CQDs catalyst with a microstructure composed of interlaced nanowires in a spherical-chain shape by treating a nickel foam substrate with sulfur and co-regulating the morphology and properties of manganese dioxide with carbon dots. The catalyst exhibited excellent OER electrocatalytic performance and stability under alkaline conditions, requiring only a low overpotential of 226 mV at 10 mA cm-2 and a Tafel slope of 105.76 mV dec-1. Furthermore, the catalyst remained stable after 3000 cycles of Cyclic Voltammetry (CV) testing and multistep chronopotentiometric (CP) measurements at the current density of 10, 50 and 100 mA cm−2 for 12 h, respectively. The enhanced performance of Ni3S2/MnO2@N,F-CQDs catalyst was mainly attributed to the practical improvement of charge interface transport performance induced by carbon dots and interface layer Ni3S2 which increased active catalytic sites of the electrode and reduced charge transfer resistance. These results suggest a promising approach for developing efficient OER electrocatalysts.

Metal-organic framework-derived boron-doped iron-cobalt tannate nanoparticles as a high-efficiency electrocatalyst for oxygen evolution reaction

Electrocatalytic oxygen evolution reaction (OER) is an important half reaction for energy conversion and storage, which possesses low OER efficiency due to the multistep proton-coupled electron transfer. Herein, B-doped iron-cobalt tannate nanoparticles (B-doped FeCoTA) are synthesized by one-step hydrothermal method. It is proved that the optimized B-doped FeCoTA exhibits excellent electrocatalytic performance for OER with a low overpotential of 306 mV at a current density of 10 mA cm−2, a small Tafel slope of 28 mV dec−1, a high double-layer capacitance of 6.31 mF cm−2 and excellent OER stability with a low potential of 1.55 V (vs RHE) at 10 mA cm−2, which is ascribed to the synergistic effect between bimetallic and heteroatom doping. The B incorporation can greatly enhance the electrical conductivity between metals, facilitate electron transfer and material exchange, thus greatly reducing reaction dynamics and strengthening OER performance. This work can provide a good strategy for the design and development of new efficient and stable OER electrocatalysts.

Single‐Source‐Precursor‐Derived Binary FeNi Phosphide Nanoparticles Encapsulated in N, P Co‐Doped Carbon as Electrocatalyst for Hydrogen Evolution Reaction and Oxygen Evolution Reaction

Water‐splitting processes require advanced catalysts for the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). A facile and cost‐effective approach using single‐source precursors (SSPs) to prepare active and durable bifunctional electrocatalysts consisting of core–shell structured transition metal phosphide (TMPs) nanoparticles dispersed and immobilized in a highly defective N‐, P‐codoped carbon matrix. The bimetallic FeNi phosphide supported on N‐, P‐codoped carbon is synthesized through pyrolysis at 900 °C under an argon atmosphere (FeNiP@NPC‐900), displaying promising electrocatalytic performance for both HER and OER, with low overpotentials of 191 and 278 mV, respectively. Furthermore, FeNiP@NPC‐900 exhibits remarkable durability in both acidic and alkaline electrolytes. The excellent catalytic and long‐term performance is attributed to several factors, including the novel SSP approach, which prevents the agglomeration of active TMPs particles, the in situ formation of exposed nanopores during the carbonization of the precursor without using surfactants, and the heterostructure between highly defective carbon and TMPs, which positively influences the electronic structure at the interface and facilitates charge transfer. The unique core–shell nanostructure protects the catalytically active phase from corrosion and synergistically promotes the activity performance. Therefore, a new strategy for designing active and stable heterostructured TMPs@carbon‐based electrocatalysts is provided.

Copper-cobalt bimetallic conductive metal–organic frameworks as bifunctional oxygen electrocatalyst in alkaline and neutral media

The preparation of low cost bifunctional electrocatalysts that efficiently catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a crucial step towards realizing high-performance Zn–air batteries. Herein a bimetallic CuCo-HITP (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) conductive metal-organic frameworks (MOFs) was synthesized as a bifunctional electrocatalyst for OER and ORR through an effective and facile ammonia-assisted method. Structural characterization showed that the metal ions coordinated with HITP ligands through strong coordination bonds of M − N4 to construct a two-dimensional (2D) porous structure. The electrochemical tests demonstrated that CuCo-HITP had superior bifunctional OER and ORR electrocatalytic performance in both alkaline and neutral media. It should be attributed to the bimetallic synergistically effect, which lead to more active sites, faster charge transfer rate and improvement of the catalytic reaction kinetics.

High-efficiency oxygen electrocatalyst for Zn-air batteries on CoMn alloy encapsulated in N-doped carbon architectures

A low-cost efficient electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently required for the commercialization of Zn-air batteries. Herein, CoMn nanoalloys encapsulated in nitrogen-doped hollow carbon architectures (CoMn@NHC) as dual electrocatalysts for Zn-air batteries were developed successfully. The obtained CoMn@NHC nanohybrid expresses excellent electrocatalytic performances for ORR (E1/2 = 0.87 V) and OER (Ei=10 = 1.51 V). More encouragingly, a homemade aqueous Zn-air battery using CoMn@NHC catalyst delivers a larger peak power density of 92.3 mW cm−2 and excellent stability of nearly 300 h, outperforming the commercial Pt/C + RuO2. The remarkable electrocatalytic performances are owing to the unique microstructure and the synergistic effect between CoMn alloy and N-doped carbon substrate. This study opens a new way for designing high-efficient bifunctional electrocatalysts for application in renewable energy facilities.

Double etch strategy induced morphologic transformation engineering of Fe–Ni hydroxide for the efficient and stable oxygen evolution

Developing high-efficiency and steady nickel-iron based catalysts are of great significance for oxygen evolution reaction (OER). However, the rarity of active sites exposed to electrolytes is difficult, limiting their OER properties. Herein, an innovative double-etch strategy has been developed to synthesize Fe–NiOH@NF nanosheet supported on nickel foam. Where NH4+ was applied to change the morphology of precursor (NiNH4PO4) from one-dimensional (1D) to two-dimensional (2D) to expose a larger solution contact area and the etch of OH− thinned the layered structure in the process of transforming Fe–NiNH4PO4 for Fe-β-Ni(OH)2. And the double etching strategy makes Fe–NiOH@NF-5 possess excellent electrocatalytic OER performance, when reaching the current densities of 100 and 1000 mA cm−2, the obtained catalytic materials only required a low overpotential of 260 and 320 mV, respectively. Meanwhile, the stability of the structure was also verified in strong corrosion environment (1 M KOH), and the catalytic activity presents unattenuated after stable operation at 100 mA cm−2 for 80 h. Density functional theory (DFT) confirmed that the optimized adsorption intermediates and conductivity were the keys to the better performance. The morphology control strategy of this work provided a significant reference for the improved OER properties of transition metal-based catalysts.

Microwave solvothermal synthesis of Component-Tunable High-Entropy oxides as High-Efficient and stable electrocatalysts for oxygen evolution reaction

Transition-metal-based high-entropy oxides (HEOs) are appealing electrocatalysts for oxygen evolution reaction (OER) due to their unique structure, variable composition and electronic structure, outstanding electrocatalytic activity and stability. Herein, we propose a scalable high-efficiency microwave solvothermal strategy to fabricate HEO nano-catalysts with five earth-abundant metal elements (Fe, Co, Ni, Cr, and Mn) and tailor the component ratio to enhance the catalytic performance. (FeCoNi2CrMn)3O4 with a double Ni content exhibits the best electrocatalytic performance for OER, namely low overpotential (260 mV@10 mA cm−2), small Tafel slope and superb long-term durability without obvious potential change after 95 h in 1 M KOH. The extraordinary performance of (FeCoNi2CrMn)3O4 can be attributed to the large active surface area profiting from the nano structure, the optimized surface electronic state with high conductivity and suitable adsorption to intermediate benefitting from ingenious multiple-element synergistic effects, and the inherent structural stability of the high-entropy system. In addition, the obvious pH value dependable character and TMA+ inhibition phenomenon reveal that the lattice oxygen mediated mechanism (LOM) work together with adsorbate evolution mechanism (AEM) in the catalytic process of OER with the HEO catalyst. This strategy provides a new approach for the rapid synthesis of high-entropy oxide and inspires more rational designs of high-efficient electrocatalysts.

Silver nanoparticles embedded in phosphorus and nitrogen-doped hierarchical hollow porous carbon for efficient supercapacitor and electrocatalytic water oxidation

Supercapacitor (SC) and oxygen evolution reaction (OER) require highly efficient multifunctional catalysts prepared from non-noble metals and heteroatoms. In this work, we have developed silver (Ag) decorated on phosphorus (P), nitrogen (N) -doped hollow porous carbon (HPC) prepared through hydrothermal followed by pyrolysis method. The prepared bifunctional electrocatalyst was studied through different characterization techniques. As-prepared HPC-UD, P-HPC-UD, and Ag@P-HPC-UD integrate high-level P-doping, large specific surface areas (up to 1452, 1247, and 528 m2 g−1), and hierarchical multipores of cross-linked micro and mesopore channels. As a result, the Ag and P modified the active sites and electronic structure of the HPC bifunctional catalyst, which is beneficial for the electrocatalytic process. As a result, the Ag@P-HPC-UD catalyst provides an outstanding specific capacitance value of 388 F g−1 at 0.5 A g−1 when used as a SC electrode. Furthermore, the Ag@P-HPC-UD electrocatalyst exhibited efficient OER behavior with a lower overpotential of 165 mV at 10 mA cm−2 current density and a lower Tafel value of 55.46 mV dec−1, which is remarkably superior to commercial RuO2 electrocatalyst. Therefore, the Ag@P-HPC-UD electrocatalyst pathway for a new revolution in developing a highly impressive carbon-based electrode towards both SC and electrocatalytic OER performance.

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS2/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm−2 for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS2/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.

Synergetic Nanostructure Engineering and Electronic Modulation of a 3D Hollow Heterostructured NiCo2O4@NiFe-LDH Self-Supporting Electrode for Rechargeable Zn–Air Batteries

Developing electrocatalysts that integrate the merits of the hollow structure and heterojunction is an attractive but still challenging strategy for addressing the sluggish kinetics of oxygen evolution reaction (OER) in many renewable energy technologies. Herein, a 3D hierarchically flexible self-supporting electrode with a hollow heterostructure is intentionally constructed by assembling thin NiFe layered double hydroxide (LDH) nanosheets on the surface of metal-organic framework-derived hollow NiCo2O4 nanoflake arrays (NiCo2O4@NiFe-LDH) for rechargeable Zn-air batteries (ZABs). Theoretical calculations demonstrate that the interfacial electron transfer from NiFe-LDH to NiCo2O4 induces the electronic modulation, improves the conductivity, and lowers the reaction energy barriers during OER, ensuring high catalytic activity. Meanwhile, the 3D hierarchically hollow nanoarray architecture can afford plentiful catalytic active sites and short mass-/charge-transfer pathways. As a result, the obtained catalyst exhibits remarkable OER electrocatalytic performance, showing low overpotentials (only 231 mV at 10 mA cm-2, 300 mV at 50 mA cm-2) and robust stability. When assembling liquid and flexible solid-state ZABs with NiCo2O4@NiFe-LDH as the OER catalyst, the ZABs achieve excellent power density, high specific capacity, superior cycle durability, and good bending flexibility, exceeding the RuO2 + Pt/C benchmarks and other previously reported self-supporting catalysts. This work not only constructs an advanced hollow heterostructured catalyst for sustainable energy systems and wearable electronic devices but also provides insights into the role of interfacial electron modulation in catalytic performance enhancement.

Electrocatalytic behavior of Ni-Co-Fe3O4 nanospheres for efficient oxygen evolution reaction

Herein, a simple hydrothermal approach has been used to synthesize nickel and cobalt co-doped ferric oxide (Ni-Co-Fe3O4) nanospheres and tested for electrocatalytic oxygen evolution reaction (OER). The different characterization outcomes verify the successful co-doping of Ni and Co into Fe3O4. The as-synthesized Ni-Co-Fe3O4 nanospheres demonstrated better electrochemical properties as compared to its counterparts Fe3O4, Co-Fe3O4, and Ni-Fe3O4. At a define current density of 10 mA cm−2, the Ni-Co-Fe3O4 electrocatalyst obtained a smaller overpotential of 243 mV and the tafel value of about 54.84 mV dec-1. In addition, Ni-Co-Fe3O4 acquired efficient electrochemical stability for 25 h duration reaching current density of 10 mA cm−2 in 1 M potassium hydroxide solution. Furthermore, it is determined that the outstanding electrocatalytic OER activity of the prepared material as a result of its distinct morphology. Analyses using the density functional theory revealed that less hydroxyl ions adhesion energy is very beneficial for the OER of crystalline Ni-Co-Fe3O4 nanospheres. The least adhesive energy for adsorption of hydroxyl ion at the top of the Fe atom in Ni-Co-Fe3O4 further confirmed their outstanding results in improving electrocatalytic OER performance. Our work gives a decent option for future transition metal oxides based electrode nanomaterials for water electrolysis applications.

Solution combustion synthesis of hierarchical porous CoNiFeCu0.1 medium-entropy alloy: A highly efficient and robust electrocatalyst for water oxidation

The development of efficient and stable oxygen evolution reaction (OER) electrocatalysts with nonprecious materials is still a great challenge for the hydrogen-based energy industry. Here, we report the rational design and effective synthesis of hierarchical porous medium-entropy alloys (MEAs) as promising electrocatalysts for OER via a solution combustion method. Owing to the compositional advantages and unique hierarchical porous structure, the as-prepared CoNiFeCu0.1 MEA on nickel foam (CoNiFeCu0.1 @NF) shows superior electrocatalytic performance for OER with an overpotential of about 255 mV at 10 mA cm−2 and a small Tafel slope of 42.7 mV dec−1 in 1.0 M KOH solution. Moreover, it is revealed that the alloying of element Cu in CoNiFe MEA can significantly enhance the charge transfer ability for OER electrocatalysis. The present work shows the hierarchical porous MEAs prepared by solution combustion method have great potential as efficient and robust electrocatalysts for water oxidation in alkaline medium.