Oxygen Evolution Reaction Performance Research Articles

Computational screening of transition metal atom doped ZnS and ZnSe nanostructures as promising bifunctional oxygen electrocatalysts.

The design of bifunctional oxygen electrocatalysts showing high catalytic performance for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for developing new renewable energy storage and conversion technologies. Herein, based on the first principles calculations, we systematically explored the electrocatalytic activity of a series of transition metal atom (Fe, Co, Ni, Cu, Pd and Pt)-doped ZnS and ZnSe nanostructures for OER and ORR. The calculated results revealed that Ni- and Pt-doped ZnS and ZnSe nanostructures exhibit promising electrocatalytic performance for both OER and ORR in comparison to the pristine ZnS and ZnSe nanostructures. Especially, the OER/ORR overpotentials of Ni-doped ZnS and ZnSe nanostructures are estimated to be 0.28/0.30 and 0.31/0.31 V, respectively, disclosing their great potential as bifunctional oxygen electrocatalysts. Moreover, it is found that Ni-doped ZnS and ZnSe nanostructures for OER and ORR are on the top of the volcano plots, evincing promising catalytic performance. Our results provide theoretical insights into a feasible strategy to synthesize highly efficient ZnS- and ZnSe-based bifunctional oxygen electrocatalysts in the future.

Factorial Optimization of CoCuFe-LDH/Graphene Ternary Composites as Electrocatalysts for Water Splitting.

The layered double hydroxides (LDHs) have demonstrated significant potential as non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Their unique compositional and structural properties contribute to their efficiency and stability as catalysts. In this study, CoCuFe-LDH composites were grown on graphene (G) via a cost-effective and straightforward one-step hydrothermal process. A 2-level full-factorial model was employed to determine the impact of Co (1.5, 3, and 4.5 mmol) and graphene (10, 30, and 50 mg) concentrations on the onset potential of OER and HER, which were the chosen response variables. OER and HER activity variabilities were assessed in triplicate using Co[3]Cu[3]Fe[3]-LDH/G[30] (central point), which were determined at 0.01% and 0.02%, respectively. Statistical analyses demonstrated that Co[4.5]Cu[3]Fe[3]-LDH/G[10] and Co[1.5]Cu[3]Fe[3]-LDH/G[10] showed the lowest onset potential at 1.52 V and -0.32 V (V vs RHE) for the OER and HER, respectively, suggesting that a high cobalt concentration enhances OER performance, while optimal HER catalysis was achieved with lower cobalt concentrations. Moreover, the trimetallic composites exhibited good stability with negligible loss of catalytic activity over 24 h.

Impact of graphene incorporation on the oxygen evolution reaction of Co-Fe-based electrocatalysts synthesized via one-step electrodeposition

The oxygen evolution reaction (OER) presents a major challenge for water splitting due to its slow kinetics. In this study, Co-Fe-Gr nanocomposite coatings were developed on carbon steel via electrodeposition using graphene (Gr) at concentrations of 0.02, 0.04, and 0.06 g/L to enhance OER performance. The sample with 0.02 g/L Gr exhibited a unique cauliflower-like morphology with aligned cobalt, as revealed by FE-SEM, leading to an increased electrochemical surface area. This optimal nanocomposite (Co-Fe-Gr (0.02 g/L)) demonstrated a low overpotential of 88 mV at 10 mA cm2, high stability (4.2 mF cm⁻2), and low resistance (R = 7.5 Ω cm⁻2). Additionally, it showed a small Tafel slope of 6.6 mV/dec and maintained stability after 12 h. A turnover frequency (TOF) of 73.6 s⁻1 indicated that graphene doping significantly reduced the adsorption energy of intermediates, greatly enhancing OER activity for efficient water splitting applications.

Transition metal doped into layered double hydroxide as efficient electrocatalysts for oxygen evolution reaction: A DFT study

The doping of transition metal (TM) into layered double hydroxide (LDH) is a widely used method for developing efficient and durable electrocatalysts for the oxygen evolution reaction (OER). In this study, a series of TM-doped bimetallic LDH (TMII/TMIII@M3N-LDH(110)) models were constructed and their OER properties were systematically evaluated using density functional theory (DFT) calculations. Furthermore, the overall volcano plot was constructed, from which seven potential OER catalysts were screened out. Among them, PtIII@Co3Fe-LDH(110) and RuII@Co3Fe-LDH(110) were identified as the most promising candidates, exhibiting excellent OER performance with a theoretical overpotential (ηOER) of 0.20 V, and were analyzed for the doping effect of TM by electronic structure. The results demonstrated that TM doped into M3N-LDH(110) plays a crucial role in the OER process. These theoretical studies not only pave the way for further exploration of efficient OER catalysts but also illustrate the potential of trimetallic LDH as high-performance catalysts.

Facile synthesis of Co-doped In2O3 integrated with tubular g-C3N4 heterostructure and their synergistic effect on the enhanced photocatalytic degradation of tetracycline and oxygen evolution reaction

In this work, we developed cost-effective and environmentally friendly bifunctional catalysts for energy and environmental applications. Tubular graphitic carbon nitrides (TCN), In2O3, In2O3/TCN, and x% cobalt (Co) doped In2O3/TCN (x = 1 %, 3 %, and 5 wt% of Co) composite materials synthesized by polymerization and hydrothermal methods. The photocatalytic activity of these materials was tested for tetracycline (TC) removal under sunlight and visible light illumination. Among them, 5 % Co-In2O3/TCN composite exhibited the highest photocatalytic efficiency, achieving 100 % and 94 % TC degradation under sunlight and visible light, respectively. PL analysis indicated that the 5 % Co-In2O3/TCN composite exhibited superior charge separation efficiency. Scavenging tests confirmed that holes (h+) and superoxide radicals (O2•−) play important roles in the photocatalytic process. The electrochemical performance of the prepared materials was investigated in 1.0 M KOH. Among the catalysts, the 5 % Co-In2O3/TCN@nickel foam (NF) composite showed the best oxygen evolution reaction (OER) performance with low overpotential (240 mV) and Tafel slope (95 mV/dec) and maintained stability for more than 24 h at 10 mA/cm2. An electrolyzer using 5 % Co-In2O3/TCN@NF||Pt/C@NF catalyst achieved cell voltages of 1.73 V and 2.23 V at 10 mA/cm² and 100 mA/cm², respectively. In this study, we developed low-cost photo and electrocatalysts that exhibited excellent environmental remediation and energy production capabilities.

Synergistic effect of nanocrystalline NiCo2S4 and NiCo alloy embedded in N-doped carbon fibers towards high-performance electrocatalysts for oxygen evolution reaction

Developing oxygen evolution reaction (OER) electrocatalysts with high efficiency, low cost and good stability for water splitting is significant to relieve the energy crisis and environmental pollution. Herein, NiCo alloy (NC) nanoparticles (NPs) embedded N-doped carbon fibers (NCF) were prepared by electrospinning and carbonization. The surfaces of the NC@NCF were anchored with nanocrystalline NiCo2S4 (NCS) in a following solvothermal process to form NCS-NC@NCF composite. Synergistic effect of the alloy (NC) and the semiconductor (NCS) was successfully stimulated, i.e., rapid charge separation and transfer was achieved during the OER process. In addition, the carbon fibers substrate is beneficial for good dispersion of the NC and NCS NPs as well as the conductivity improvement of the as-prepared NCS-NC@NCF catalyst. The prepared NCS-NC@NCF catalyst electrode owns good OER performances of a low overpotential of 291 mV, 342 mV and 376 mV to respectively deliver current densities of 10 mA cm−2, 50 mA cm−2 and 100 mA cm−2, which are respectively 19 mV, 82 mV and 116 mV lower than those of the RuO2 electrode (310 mV, 424 mV and 492 mV), indicating the great potential of the catalyst in water splitting. Moreover, good durability of current density retention of 90.7 % is observed after 60 h of continuous OER polarization for the catalyst. Additionally, a two-electrode system composed of commercial Pt/C and the NCS-NC@NCF electrodes only needs a driven voltage of 1.51 V to afford 10 mA cm−2 for water splitting, which is superior to that (1.69 V) of the Pt/C||RuO2 system.

Unveiling the Role of Surface Self‐Reconstruction of Metal Chalcogenides on Electrocatalytic Oxygen Evolution Reaction

AbstractTransition metal chalcogenides are an important class of electrocatalysts with broad application prospects in alkaline oxygen evolution reactions. Many researchers are focusing on the in situ conversion of metal cations in catalysts, but have rarely considered the contribution of oxidation, leaching, and re‐absorption of chalcogenides to the catalytic activity. Herein, multiple characterization approaches are used to monitor the evolution mechanism and origin CoTe@CoS‐electrocatalyzed oxygen evolution reaction (OER) activity. The research results reveal that the electro‐oxidative dissolution of Te and S on the electrode surface forms TeO32− and SO32−, which are adsorbed on the electrode surface. Moreover, TeO32− and SO32− species will further transform into TeO42− and SO42−. As expected, the extra addition of mixed tellurite and sulfate ions to the Co (OH)2 electrolyte produces a synergistic effect that can significantly boost OER activity. Selenites reveal the analogous effect, indicating that the adsorption of chalcogenates the electrode surface has a universal effect on improving OER performance. The findings of this work provide unique insights into the species conversion of catalytic materials and the mechanism of enhancing catalytic activity during OER processes.

Unveiling the Role of Electrocatalysts Activation for Iron‐Doped Ni Oxyhydroxide in Enhancing the Catalytic Performance of Oxygen Evolution Reaction

Water electrolysis using renewable electricity is a promising strategy for high‐purity hydrogen production. To realize the practical application of water electrolysis, an electrocatalyst with high redox properties and low cost is essential for enhancing the sluggish oxygen evolution reaction. Herein, we fabricated Fe‐doped nickel oxalate (Fe‐NiC2O4) directly grown on nickel (Ni) foam as an efficient electrocatalyst for the alkaline oxygen evolution reaction using a facile one‐step hydrothermal method. Fe‐NiC2O4 served as a precursor for obtaining highly active Fe‐doped Ni oxyhydroxide (Fe‐NiOOH) via in situ electrochemical oxidation. Consequently, 0.75Fe‐NiOOH was demonstrated to be the optimal electrocatalyst, exhibiting outstanding oxygen evolution reaction activity with a low overpotential of 220 mV at a current density of 100 mA cm−2 and a Tafel slope of 20.5 mV dec−1. Furthermore, Fe‐NiOOH maintained its oxygen evolution reaction activity without performance decay during long‐term electrochemical measurements, owing to the phase transformation from nickel oxyhydroxide (NiOOH) to γ‐NiOOH (gamma nickel oxyhydroxide). These performances significantly surpass those of recently reported transition‐metal‐based electrocatalysts.

Cr dopant mediates hydroxyl spillover on RuO2 for high-efficiency proton exchange membrane electrolysis

Simultaneously improving the activity and stability of catalysts for anodic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE) remains a notable challenge. Here, we report a chromium-doped ruthenium dioxide with oxygen vacancies, termed Cr0.2Ru0.8O2-x, that drives OER with an overpotential of 170 mV at 10 mA cm−2 and operates stably over 2000 h in acidic media. Experimental and theoretical studies show that the synergy of Cr dopant and oxygen vacancy induces an unconventional dopant-mediated hydroxyl spillover mechanism. Such dynamic hydroxyl spillover from Cr dopant to Ru active site changes the rate-determining step from OOH* formation to O2 formation and thus greatly improves the OER performance. Moreover, the Cr dopant and oxygen vacancy also play a crucial role in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif. When assembled into the anode of a practical PEMWE device, Cr0.2Ru0.8O2-x enables long-term durability of over 200 h at an ampere-level current density and 60 degrees centigrade.

Recent advantages on mass transfer structure construction in transition metal‐based cost‐effective catalyst toward alkaline oxygen evolution

The electrochemical oxygen evolution reaction (OER) can be combined with various reactions to fabricate electrochemical energy conversion and storage devices while the slow kinetics and poor mass transfer capability at high current densities were the key constraints to its large‐scale application. Therefore, this review primarily focuses on design and optimization of mass transfer structures of TM‐metal‐based OER catalysts. Nanostructuring, porous design, and the creation of hierarchical architectures have been applied during catalyst synthesis to enhance the surface area and accessibility, thereby improving mass transfer and catalytic OER efficiency. Strategies including doping, substrate invitation, soft/hard templating has been utilized to accelerate mass transfer as well as the ion/electron conduction efficiency for the overall improvement of OER performance of the catalysts. These developments underline the critical role of advanced material design in achieving high‐performance OER catalysts and highlight the potential of TM‐based materials in cost‐effective and scalable applications.

Insulator-Transition-Induced Degradation of Pyrochlore Ruthenates in Electrocatalytic Oxygen Evolution and Stabilization through Doping.

Ru-based pyrochlores (e.g., Y2Ru2O7-δ) are promised to replace IrO2 in polymer electrolyte membrane (PEM) electrolyzers. It is significant to reveal the cliff attenuation on the oxygen evolution reaction (OER) performance of these pyrochlores. In this work, we monitor the structure changes and electrochemical behavior of Y2Ru2O7-δ over the OER process, and it is found that the reason of decisive OER inactivation is derived from an insulator transition occurred within Y2Ru2O7-δ due to its inner "perfecting" lattice induced by continuous atom rearrangement. Therefore, a stabilization strategy of the Ir-substituted Y2Ru2O7-δ is proposed to alleviate this undesirable behavior. The double-exchange interaction between Ru and Ir in [RuO6] and [IrO6] octahedra leads the charge redistribution with simultaneous spin configuration adjustment. The electronic state in newly formed octahedrons centered with Ru 4d3 (with the state of eg'↑↑a1g ↑ eg 0) and Ir 5d6 (eg'↑↓↑↓a1g ↑↓ eg 0) relieves the uneven electron distributions in [RuO6] orbital. The attenuated Jahn-Teller effect alleviates atom rearrangement, represented as the mitigation of insulator transition, surface reconstruction, and metal dissolution. As results, the Ir-substituted Y2Ru2O7-δ presents the greatly improved OER stability and PEM durability. This study unveils the OER degradation mechanism and stabilization strategy for material design of Ru-based OER catalysts for electrochemical applications.

RuO2/FeCo2O4 as an efficient oxygen evolution reaction catalyst in alkaline medium

The oxygen evolution reaction (OER) is a four-electron-proton reaction requiring a large overpotential. In order to improve the electrocatalytic activity of iron-based OER electrocatalysts, the overpotential must be reduced in order to improve the efficiency and cost-effectiveness. Herein, FeCo LDH, FeCo2O4, RuO2/FeCo2O4, and Ru/CoFe LDH are synthesized on carbon cloth (CC) by a simple hydrothermal and annealing technique. The materials are characterized systematically, and their electrocatalytic OER properties are evaluated in detail. RuO2/FeCo2O4 delivers superior OER performance in 1 M KOH, such as a low onset potential 1.55 V at a current density of 10 mA/cm−2, a Tafel slope of 85.2 mV/dec−1, as well as robust stability. The Mott-Schottky analysis reveals that the built-in electric field accelerates charge transfer and enhances the catalytic activity of RuO2/FeCo2O4.

Synergistic Sr Activation and Cr Buffering Effect on RuO2 Electronic Structures for Enhancing the Acidic Oxygen Evolution Reaction.

The oxygen evolution reaction (OER) performance of ruthenium-based oxides strongly correlates with the electronic structures of Ru. However, the widely adopted monometal doping method unidirectionally regulates only the electronic structures, often failing to balance the activity and stability. Here, we propose an "elastic electron transfer" strategy to achieve bidirectional optimization of the electronic structures of Sr, Cr codoped RuO2 catalysts for acidic OER. The introduction of electron-withdrawing Sr intrinsically activates the Ru sites by increasing the oxidation state of Ru. Simultaneously, Cr acts as an electron buffer, donating electrons to Ru in the presence of Sr in the as-prepared catalysts and absorbing excess electrons from Sr leaching during the OER. Such a bidirectional regulation feature of Cr prevents overoxidation of Ru and maintains its high oxidation state during the OER. The optimal Ru3Cr1Sr0.175 catalyst exhibits a low overpotential (214 mV @ 10 mA cm-2) and excellent stability (over 300 h).

Superhydrophilic and Underwater Superaerophobic Dual-Function Peony-Shaped Selenide Micro-nano Array Self-Supported Electrodes for High-Efficiency Overall Water Splitting Driven by Renewable Energy.

With the intensification of global environmental pollution and resource scarcity, hydrogen has garnered significant attention as an ideal alternative to fossil fuels due to its high energy density and nonpolluting nature. Consequently, the urgent development of electrocatalytic water-splitting electrodes for hydrogen production is imperative. In this study, a superwetting selenide catalytic electrode with a peony-flower-shaped micronano array (MoS2/Co0.8Fe0.2Se2/NixSey/nickel foam (NF)) was synthesized on NF via a two-step hydrothermal method. The optimal catalytic activity of cobalt-iron selenide was achieved by adjusting the Co/Fe ratio. The intrinsic catalytic activity of the electrodes was enhanced by incorporating transition metal selenides, which then served as a precursor for the subsequent loading of MoS2 nanoflowers on the surface to fully expose the active sites. Furthermore, the superwetting properties of the electrode accelerated electrolyte penetration and electron/mass transfer, while also facilitating bubble detachment from the electrode surface, thereby preventing "bubble shielding effect". This resulted in superior oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance, as well as overall water splitting capabilities. In a 1.0 M KOH solution, the electrode required only 166 and 195 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. When functioning as a bifunctional catalytic electrode, only 1.60 V of voltage was necessary to drive the electrolyzer to reach a current density of 10 mA cm-2. Moreover, laboratory simulations of wind and solar energy-driven water splitting validated the feasibility of establishing a sustainable energy-to-hydrogen production chain. This work provides new insights into the preparation of low-overpotential, high-catalytic-activity superhydrophilic and underwater superaerophobic catalytic electrodes by rationally adjusting elemental ratios and exploring changes in electrode surface wettability.

Tailoring the Compositions and Nanostructures of Trimetallic Prussian Blue Analog-Derived Carbides for Water Oxidation.

The electrochemical splitting of water for hydrogen production faces a major challenge due to its anodic oxygen evolution reaction (OER), necessitating research on the rational design and facile synthesis of OER catalysts to enhance catalytic activity and stability. This study proposes a ligand-induced MOF-on-MOF approach to fabricate various trimetallic MnFeCo-based Prussian blue analog (PBA) nanostructures. The addition of [Fe(CN)6]3- transforms them from cuboids with protruding corners (MnFeCoPBA-I) to core-shell configurations (MnFeCoPBA-II), and finally to hollow structures (MnFeCoPBA-III). After pyrolysis at 800°C, they are converted into corresponding PBA-derived carbon nanomaterials, featuring uniformly dispersed Mn2Co2C nanoparticles. A comparative analysis demonstrates that the Fe addition enhances catalytic activity, while Mn-doped materials exhibit excellent stability. Specifically, the optimized MnFeCoNC-I-800 demonstrates outstanding OER performance in 1.0mKOH solution, with an overpotential of 318mV at 10mAcm-2, maintaining stability for up to 150h. Theoretical calculations elucidate synergistic interactions between Fe dopants and the Mn2Co2C matrix, reducing barriers for oxygen intermediates and improving intrinsic OER activity. These findings offer valuable insights into the structure-morphology relationships of MOF precursors, advancing the development of highly active and stable MOF-derived OER catalysts for practical applications.

The dual gain strategy of introducing nickel doping and anchoring amorphous iron oxyhydroxide nanosheets on ZIF-67 achieves an efficient oxygen evolution reaction

A ZIF-67@Ni@FeOOH composite material was synthesized using nickel-doped ZIF-67 as a precursor and was electrochemically characterized as an efficient oxygen evolution reaction (OER) catalyst. The results indicated that Ni doping preserved the polyhedral structure of ZIF-67 while enhancing its OER activity. The introduction of amorphous FeOOH nanosheets allowed ZIF-67@Ni@FeOOH to not only retain its original polyhedral structure but also develop a hollow interior and self-remodeling surface, resulting in numerous defects. These features contribute to improved charge transfer efficiency and enhanced conductivity of the material. The dual enhancement effect is achieved by combining the doping strategy with structural defect engineering. The synergistic effects of Co, Ni, and Fe species further boost OER performance. The ZIF-67@Ni@FeOOH catalyst exhibited remarkable OER efficacy, with the lowest overpotential at a current density of 10 mA cm−2 being 329 mV and a low Tafel slope of 42.95 mV dec−1. In situ Raman spectroscopy revealed that high-valence hydroxyl oxides, specifically NiOOH and CoOOH, present on the composite surface were the active species for OER. This study offers a promising approach for developing economically viable electrocatalysts with superior efficiency for OER.

Surface Reconstruction Regulation of Co3N Through Heterostructure Engineering Toward Efficient Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) electrocatalysts generally experience structural and electronic modifications during electrocatalysis. This phenomenon, referred to as surface reconstruction, results in the formation of catalytically active species that act as real OER sites. Controlling surface reconstruction therefore is vital for enhancing the OER performance of electrocatalysts. In this study, a new approach is introduced of heterostructure engineering to facilitate the surface reconstruction of target catalysts. Using MnCo carbonate hydroxide (MnCo─CH)@Co3N as a demonstration, it is discovered that the surface reconstruction occurs more readily and rapidly on MnCo─CH@Co3N than on Co3N. More interestingly, during the reconstruction process, Mn species migrate to the surface, enabling the in situ formation of highly active Mn-doped CoOOH. Consequently, the MnCo─CH@Co3N catalyst after reconstruction exhibits a low overpotential of 257mV at 10mAcm-2, compared to 379mV of individual Co3N. This work offers fresh perspectives on understanding the enhanced OER performance of heterostructure electrocatalysts and the role of heterostructure in promoting surface reconstruction.

An Investigation of the Interface between Transition Metal Oxides (MnOx, FeOx, CoOx and NiOx)/MoO3 Composite Electrocatalysts for Oxygen Evolution Reactions

This study presents the synthesis of a multicomponent metal oxide electrocatalyst that increases the activity of the oxygen evolution reaction (OER). We synthesized transition metal oxides (MnOx, FeOx, CoOx, and NiOx) with MoO3 heterostructures through a solid-state reaction approach at low cost. In comparison to the other compositions, CoOx garnered higher attention and demonstrated superior performance on account of its large surface area and varied crystal facets. The MnOx-MoO3, FeOx-MoO3, CoOx-MoO3, and NiOx-MoO3 compositions attained an overpotential of 390 mV, 350 mV, 310 mV, and 340 mV, respectively, at a current density of 10 mA cm−2 in alkaline solution. The performance of OER was enhanced in CoOx-MoO3 at 10 mA cm−2, while FeOx-MoO3 exhibited a lower current density at 100 mA cm−2 than other metal oxides. The CoOx-MoO3 material exhibited a favorable crystal interface transition due to the presence of MoO3 oxide. For the first time, we report on the MoO3-to-(MnOx, FeOx, CoOx, and NiOx) interface crystal transition and the active surface area for OER catalytic activity in water-splitting processes. This investigation intends to develop an electrocatalyst that is capable of producing hydrogen with the use of heterostructure metal oxides.

A one-stone-three-birds strategy to construct Mo-FeS2/Ni3S2@C electrocatalyst with strong interfacial coupling effect to achieve efficient oxygen evolution reaction

The development of high-performance oxygen evolution reaction (OER) electrocatalysts is quite pivotal to facilitate hydrogen production. In this work, we integrate the synergistic effects of heterogeneous interface engineering, multiscale engineering and doping engineering to greatly improve the catalytic activity of the electrocatalyst. Specifically, with a Anderson-type polymetallic oxonate (NH4)3[NiMo6O24H6]·7H2O as a precursor, the Mo-FeS2/Ni3S2@C nanowire arrays that uniformly grown on nickel foam (NF) surfaces were prepared by a simple hydrothermal process followed by calcination. The as-prepared Mo-FeS2/Ni3S2@C exhibits excellent alkaline OER performance with a low overpotential of 196 mV to achieve a current density of 10 mA cm−2 and maintain high stability for over 100 h at 100 mA cm−2. Theoretical calculations and experimental results indicate that the high activity of Mo-FeS2/Ni3S2@C is mainly attributed to the charge interaction at the multiple interfaces of FeS2, Ni3S2 and porous carbon layers. The Mo facilitates inducing the formation of high-valent Ni, Fe, thus forming of the Ni(Fe)OOH phase that contributes to the intrinsic OER active site of the Mo-FeS2/Ni3S2@C electrode. In addition, the surface of Mo-FeS2/Ni3S2@C nanowire is composed of ordered nanosheets, exhibiting a unique hierarchical multi-scale structure, which is conducive to exposing more active sites. This hierarchical structure gives it superhydrophilic and superoxyphobic properties, ensuring the stability during continuous electrolysis. This study showcases the importance of multi-engineering synergies and foresees the avenue of designing novel OER electrocatalysts.

Role of active redox sites and charge transport resistance at reaction potentials in spinel ferrites for improved oxygen evolution reaction

Fe and Ni oxide-based systems are often investigated as electrocatalysts for the oxygen evolution reaction (OER) in water electrolysis and the improvement in OER activity is explained by two main reasons, (i) improving bulk electrical conductivity and (ii) synergic effect between Ni and Fe. Among the two factors, the identification of the dominant factor for OER is very important for catalyst engineering in the right direction. In order to have a better understanding, spinel-structured ZnFe2O4 nanoparticles have been synthesized and its bulk conductivity is studied by progressively varying Ni doping. The conductivity of the synthesised compounds follows the order of ZnFe2O4 > Ni0.3Zn0.7Fe2O4 > Ni0.5Zn0.5Fe2O4 > Ni0.7Zn0.3Fe2O4 > NiFe2O4. The oxygen evolution studies reveal that NiFe2O4 is highly active with an onset potential of 1.57 V versus reversible hydrogen electrode (RHE) and Tafel slope of 102 mV/dec. With the increase in Ni doping, the structure changes from spinel to inverse spinel as confirmed by X-ray diffraction and Raman spectra. Further, the contribution from Ni redox sites in addition to Fe ion sites and FexNi1−xOOH species formation, causes improved OER performance. This study uniquely proves that the OER activity majorly relies on redox/active metal sites, FexNi1−xOOH species and charge transfer resistance at OER potential rather than the bulk electrical conductivity of spinel ferrites. This conclusion is supported by voltammetry and impedance studies of five different spinel ferrites.