Efficient Oxygen Evolution Reaction Catalysts Research Articles

Recent progress in energy-saving electrocatalytic hydrogen production via regulating the anodic oxidation reaction.

Hydrogen energy with its advantages of high calorific value, renewable nature, and zero carbon emissions is considered an ideal candidate for clean energy in the future. The electrochemical decomposition of water, powered by renewable and clean energy sources, presents a sustainable and environmentally friendly approach to hydrogen production. However, the traditional electrochemical overall water-splitting reaction (OWSR) is limited by the anodic oxygen evolution reaction (OER) with sluggish kinetics. Although important advances have been made in efficient OER catalysts, the theoretical thermodynamic difficulty predetermines the inevitable large potential (1.23 V vs. RHE for the OER) and high energy consumption for the conventional water electrolysis to obtain H2. Besides, the generation of reactive oxygen species at high oxidation potentials can lead to equipment degradation and increase maintenance costs. Therefore, to address these challenges, thermodynamically favorable anodic oxidation reactions with lower oxidation potentials than the OER are used to couple with the cathodic hydrogen evolution reaction (HER) to construct new coupling hydrogen production systems. Meanwhile, a series of robust catalysts applied in these new coupled systems are exploited to improve the energy conversion efficiency of hydrogen production. Besides, the electrochemical neutralization energy (ENE) of the asymmetric electrolytes with a pH gradient can further promote the decrease in application voltage and energy consumption for hydrogen production. In this review, we aim to provide an overview of the advancements in electrochemical hydrogen production strategies with low energy consumption, including (1) the traditional electrochemical overall water splitting reaction (OWSR, HER-OER); (2) the small molecule sacrificial agent oxidation reaction (SAOR) and (3) the electrochemical oxidation synthesis reaction (EOSR) coupling with the HER (HER-SAOR, HER-EOSR), respectively; (4) regulating the pH gradient of the cathodic and anodic electrolytes. The operating principle, advantages, and the latest progress of these hydrogen production systems are analyzed in detail. In particular, the recent progress in the catalytic materials applied to these coupled systems and the corresponding catalytic mechanism are further discussed. Furthermore, we also provide a perspective on the potential challenges and future directions to foster advancements in electrocatalytic green sustainable hydrogen production.

The dual-functional role of carboxylate in a nickel-iron catalyst towards efficient oxygen evolution.

The efficiency of the oxygen evolution reaction (OER) is severely limited by the sluggish proton-coupled electron transfer processes and inadequate long-term stability. Herein, we introduce a carboxylate group (TPA) to modify NiFe layered double hydroxide (NiFe LDH@TPA), resulting in notable improvements in both activity and stability. A combination of spectroscopic and theoretical investigations reveals the dual-functional role of incorporated TPA. It facilitates the deprotonation of OER intermediates while strengthening the Fe-O bond and acting as a molecular fence, ensuring superior OER kinetics and anti-dissolution properties. NiFe LDH@TPA delivers a low overpotential of 200 mV at 10 mA cm-2 and an impressive long-term stability of 500 h at 150 mA cm-2, significantly outperforming its unmodified counterpart. Furthermore, operating in an anion exchange membrane water electrolyzer, it affords prolonged stability at an industrial-scale current density of 1 A cm-2, sustaining performance for over 120 hours. This strategy offers a promising avenue for the development of durable and efficient OER catalysts.

Transient-covering iridium species with ultrathin carbon shell via joule-heating for robust acidic water oxidation

Designing efficient and stable oxygen evolution reaction (OER) catalyst to boost the performance of the proton exchange membrane water electrolyzer is of paramount significance for the development of green hydrogen....

Modified photoanode by in situ growth of covalent organic frameworks on BiVO4 for oxygen evolution reaction.

The development of efficient oxygen evolution reaction (OER) catalysts is of great significance because the water oxidation reaction at the photoanode is the rate-determining step in photoelectrocatalytic (PEC) water splitting. Herein, two hybrid photoanodes named BiVO4/COF-Azo and BiVO4/COF-Ben were prepared by in situ solvothermal growth on a modified BiVO4 photoanode. Characterization results revealed that the Azo and Ben COFs could match with BiVO4 well to form heterojunctions, which could effectively enhance the separation efficiency of photogenerated carriers. Also, the smaller impedance of the composite photoanodes and faster kinetics of the water oxidation reaction promoted the charge transmission and enhanced the reaction efficiency of the surface-reaching holes, respectively. As a result, the composite photoanodes exhibited a larger photocurrent and more negative onset potential compared to the pristine BiVO4. This work not only provides a new strategy to construct efficient hybrid photoanodes, but also expands the applications of COFs.

Sr-Stabilized IrMnO2 Solid Solution Nano-Electrocatalysts with Superior Activity and Excellent Durability for Oxygen Evolution Reaction in Acid Media.

The development of cost-effective catalysts for oxygen evolution reaction (OER) in acidic media is of paramount importance. This work reports that Sr-doped solid solution structural ultrafine IrMnO2 nanoparticles (NPs) (≈1.56nm) on the carbon nanotubes(Sr-IrMnO2/CNTs) are efficient catalysts for the acidic OER. Even with the Ir use dosage 3.5 times lower than that of the commercial IrO2, the Sr-IrMnO2/CNTs only need an overpotential of 236.0mV to drive 10.0mA cm-2 and show outstanding stability for >400.0 h. Its Ir mass activity is 39.6 times higher than that of the IrO2 at 1.53V. The solid solution and Sr-doping structure of Sr-IrMnO2 are the main origin of the high catalytic activity and excellent stability of the Sr-IrMnO2/CNTs. The density function theory calculations indicate that the solid solution structure can promote strong electronic coupling between Ir and Mn, lowering the energy barrier of the OER rate-determining step. The Sr-doping can enhance the stability of Ir against the chemical corrosion and demetallation. Water electrolyzers and proton exchange membrane water electrolyzers assembled with the Sr-IrMnO2/CNTs show superb performance and excellent durability in the acid media.

Dinitrosyl Iron Complex-Derived Nanosized Zerovalent Iron (NZVI) as a Template for the Fe-Co Cracked NZVI: An Electrocatalyst for the Oxygen Evolution Reaction.

Nanosized zerovalent iron (NZVI) Fe@Fe3O4 with a core-shell structure derived from photocatalytic MeOH aqueous solution of dinitrosyl iron complex (DNIC) [(N3MDA)Fe(NO)2] (N3MDA = N,N-dimethyl-2-(((1-methyl-1H-imidazole-2-yl)methylene)amino)ethane-1-amine) (1-N3MDA), eosin Y, and triethylamine (TEA) is demonstrated. The NZVI Fe@Fe3O4 core shows a high percentage of zerovalent iron (Fe0 %) and is stabilized by a hydrophobic organic support formed through the photodegradation of eosin Y hybridized with the N3MDA ligand. In addition to its well-known reductive properties in wastewater treatment and groundwater remediation, NZVI demonstrates the ability to form heterostructures when it interacts with metal ions. In this research, Co2+ is employed as a model contaminant and reacted with NZVI Fe@Fe3O4 to result in the formation of a distinct Fe-Co heterostructure, cracked NZVI (CNZVI). The slight difference in the standard redox potentials between Fe2+ and Co2+, the magnetic properties of Co2+, and the absence of surface hydroxides of Fe@Fe3O4 enable NZVI to mildly reduce Co2+ and facilitate Co2+ penetration into the iron core. Taking advantage of the well-dispersed nature of CNZVI on an organic support, the reduction in particle size due to Co2+ penetration, and Fe-Co synergism, CNZVI is employed as a catalyst in the alkaline oxygen evolution reaction (OER). Remarkably, CNZVI exhibits a highly efficient OER performance, surpassing the benchmark IrO2 catalyst. These findings show the potential of using NZVI as a template for synthesizing highly efficient OER catalysts. Moreover, the study demonstrates the possibility of repurposing waste materials from water treatment as valuable resources for catalytic energy conversion, particularly in water oxidation processes.

An N-defective graphitic carbon nitride-supported Ir/Fe catalyst with low Ir-content as highly efficient oxygen evolution reaction catalyst for acidic water splitting

To develop a low-cost acidic water electrolysis catalyst with high efficiency and stability and low Ir content, a catalyst with highly dispersed Ir/Fe complex sites (∼ 5 wt% Ir) was synthesized by a simple carbonization and oxidation process. N-defective g-C3N4 (NCN) was introduced to enhance the support effect between metal nanoparticles and CN bases and the intrinsic catalytic activity for the oxygen evolution reaction (OER). NCN provided more active sites and adjusted the electronic structure of CN. Compared with the original single Ir catalyst, the electrons of the Ir-Fe metal catalyst were transferred from the base to the metal, which maintained the high OER performance and stability of the catalyst. Density functional theory calculations demonstrated that the Gibbs free energy of Ir/Fe@NCN was greatly reduced during O*→OOH* as the rate-determining step. The overpotential of the Ir/Fe@NCN catalyst was 242 mV at 10 mA/cm2, and its mass activity (612.6 A/g) was much higher than that of IrO2 (88.6 A/g), showing excellent OER performance. This study provides a new strategy for the design and optimization of highly efficient and low-cost acidic Ir/transition metal OER catalysts.

Direct Capturing and Regulating Key Intermediates for High-Efficiency Oxygen Evolution Reactions.

Developing efficient oxygen evolution reaction (OER) electrocatalysts can greatly advance the commercialization of proton exchange membrane (PEM) water electrolysis. However, the unclear and disputed reaction mechanism and structure-activity relationship of OER pose significant obstacles. Herein, the active site and intermediate for OER on AuIr nanoalloys are simultaneously identified and correlated with the activity, through the integration of in situ shell-isolated nanoparticle-enhanced Raman spectroscopy and X-ray absorption spectroscopy. The AuIr nanoalloys display excellent OER performance with an overpotential of only 246mV to achieve 10mA cm-2 and long-term stability under strong acidic conditions. Direct spectroscopic evidence demonstrates that * OO adsorbed on IrOx sites is the key intermediate for OER, and it is generated through the O-O coupling of adsorbed oxygen species directly from water, providing clear support for the adsorbate evolution mechanism. Moreover, the Raman information of the * OO intermediate can serve as a universal "in situ descriptor" that can be obtained both experimentally and theoretically to accelerate the catalyst design. It unveils that weakening the interactions of * OO on the catalysts and facilitating its desorption would boost the OER performance. This work deepens the mechanistic understandings on OER and provides insightful guidance for the design of more efficient OER catalysts.

Lanthanide Vanadate: An Efficient and Stable Oxygen Evolution Reaction Catalyst for Enhanced Water-Splitting Applications

Hydrogen fuel production through water-splitting reactions offers a sustainable approach to store renewable energies. However, the efficiency of this process is impeded by the oxygen evolution reaction (OER), a complex four-electron oxidation half-reaction. In this study, we present a highly active and stable OER catalyst, lanthanide vanadate (LnVO4 - Ln = La to Lu), synthesized using a straightforward hydrothermal method. Comprehensive characterization of the electrocatalysts was performed employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis. When applied to nickel (Ni) foam, lanthanide vanadate achieved a current density of 10 mA cm-2 at an overpotential of +280 mV in a 1.0 M KOH electrolyte. Furthermore, exceptional stability was demonstrated for over 5 hours of continuous operation. These findings highlight the potential of lanthanide vanadate-based materials as promising catalysts for efficient and stable overall water-splitting processes.

Advanced and Scalable Polyol-Mediated Synthesis Route for Highly Active Ni Metal Sulfides (M = Fe, Mn, Cr, Mo) As Efficient Electrocatalysts for Sea/Saline Water Oxidation

Recent studies have made significant progress in addressing oxygen evolution (OER), a bottleneck reaction in water electrolysis, by utilizing innovative electrode materials and catalysts to enable low-grade and saline water splitting, thus offering promising prospects for advancing sustainable hydrogen production systems.1 This study applied a modified polyol-mediated strategy2 to describe an advanced procedure for synthesizing NiMSx where M = (Fe, Mn, Cr, Mo). Several physical and chemical characterization tools are applied to investigate the obtained saline/seawater oxidation electrocatalysts, including XRD, SEM, TEM, and electrochemical characterization. The outcomes of these characterizations were displayed as graphs. The catalysts reveal nanoclusters morphologies. The figure below depicts the preliminary findings, illustrating the electrochemical performance and the physical characterizations. Figure 1 (a) and (b) represent the polarisation curves of the oxygen evolution activity of the synthesized MNiSx electrocatalysts on Carbon cloth and Ni foam working electrodes, respectively, in a three-electrode configuration with Pt wire serving as the counter and Hg/HgO serving as the reference electrode in 1M KOH plus natural seawater from the Galway Bay Ireland. The catalysts obtained a high current exchange density of above and close to the 200 mAcm-2. Figure 1(c) displays the images of the catalyst-coated working electrodes prepared via dip coating, both Ni foam and carbon cloth, while Figures 1(d) and 1(e) reveal the nanostructure-based clusters of the produced materials with the scanning and transmission electron microscopy, respectively. In addition, we are evaluating the efficacy of this high-performance anode electrocatalyst in a single cell with a working electrode area of 3 cm2 for the oxygen evolution reaction (OER) and Pt/C as a cathode for hydrogen evolution reaction (HER). Our research project aims to develop highly efficient Oxygen Evolution Reaction (OER) catalysts.We will employ various ex-situ and in-situ characterization techniques, including, Impedance spectroscopy, chronopotentiometry/chronoamperometry, Powder X-ray diffraction (XRD), Raman spectroscopy, and FTIR spectroscopy. Impedance spectroscopy determines the system's impedance as a function of frequency and offers insights into electrochemical behavior, such as resistance, capacitance, and charge transfer resistance. Chronopotentiometry/chronoamperometry will be applied to check the long-term stabilities of catalysts. X-ray diffraction (XRD) will examine the crystal structure of the stimuli in real-time during OER. X-ray photoelectron spectroscopy (XPS) will be applied to analyze the materials' surface chemistry and elemental composition by measuring the energies of emitted photoelectrons from X-ray irradiation. In-situ Raman spectroscopy will enable us to study changes in the catalysts' electronic structure and coordination environment during the reaction providing valuable insights into the underlying mechanism of OER. FTIR spectroscopy will reveal information about the response intermediates and mechanisms during OER. We can obtain a detailed understanding of the reaction pathway by monitoring the changes in the vibrational spectra of the reactants and products. Finally, post-mortem analysis of the catalysts will be performed after electrochemical testing to assess their degradation. Above all will help us optimize the catalysts' design for long-term stability and high-performance OER. Acknowledgments The authors acknowledge the ANEMEL Project funded by the Horizon Europe (European Innovation Council) Grant agreement 101071111. References Tong, W.; Forster, M.; Dionigi, F.; Dresp, S.; Sadeghi Erami, R.; Strasser, P.; Cowan, A. J.; Farràs, P., Electrolysis of low-grade and saline surface water. Nature Energy 2020, 5 (5), 367-377. Zhang, H.; Hyun, B.-R.; Wise, F. W.; Robinson, R. D., A generic method for rational scalable synthesis of monodisperse metal sulfide nanocrystals. Nano letters 2012, 12 (11), 5856-5860. Figure 1

Catalytic Active Sites Determination and Charge Transport of Transition Metal Oxides for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a key process that enables the storage of renewable energies in the form of chemical fuels.[1] Unraveling the catalytic mechanism is of paramount significance for the rational design of efficient electrocatalysts.[1] Here, we use well-defined crystalline cobalt oxyhydroxides CoOOH nanorods and nanosheets as model catalysts to investigate the geometric catalytic active sites.[2] We disclose a linear correlation of catalytic activities with their lateral surface areas, suggesting that the active sites are exclusively located at lateral facets rather than basal facets. Theoretical calculations show that the coordinatively unsaturated cobalt sites of lateral facets upshift the O 2p-band center closer to the Fermi level, thereby enhancing the covalency of Co-O bonds to yield the reactivity. Following this, we develop a eutectic dealloying strategy to activate the porous spinel NiFe2O4 nanowires with up to four metal cation substitutions.[3] Spinel oxide of NiFeXO4 (X= Fe, Ni, Al, Mo, Co, Cr, ~195 mV@10mA·cm-2) outperforms most spinel phase OER electrocatalysts and comparable to the state-of-the-art NiFe hydroxides. This work elucidates the geometrical catalytic active sites and enlightens the surface engineering for efficient OER catalysts. Besides, we studied the dependence of catalytic performances on electrical conductivities and unveils that charge transportability, to our surprise, regulates the reaction kinetics of the electronically accessible active sites.[4] Remarkably, the regulation extent correlates with the electrical conductivities, suggesting the strong coupling of the electrocatalytic process with electronic transport. Furthermore, we argue the origin of Ov-promoted catalytic activities of NiFe-based (oxy)hydroxides.[5] We uncover the pivotal role of charge transport for their electrocatalytic OER and propose that the superficial Ov imposes electron donation to the conductive band of NiFeOOH and therefore enables the regulation of electronic transport to switch on/off OER catalysis. The work highlights the pivotal role of electronic transportability in unfolding catalytic potential, holding both fundamental and technical implications for electrocatalysts. Fang Song, ..., and Xile Hu*. Am. Chem. Soc. 2018, 140, 7748; Fang Song, Xile Hu*. Nat. Commun. 2014, 5, 4477; Fang Song, Xile Hu*, J. Am. Chem. Soc. 2014, 136, 16481-16484; Fang Song, ..., Hao Ming Chen,* Clemence Corminboeuf,* Xile Hu *. ACS Cent. Sci. 2019, 5, 558; Chen, Wenshu; Gu, Jiajun*; Du, Yongping*; Song, Fang*; ...; Zhang, Di. Adv. Funct. Mater. 2019, 30, 2000551; Bowen Liu, ..., Fang Song,* Qinglei Liu.* ACS Nano 2022, 16, 9, 14121.Sihong Wang, Qu Jiang, ..., and Fang Song,* Commun. 2022, 13, 6650;Qiwen Zhang, ..., Fang Song*, Mingwei Chen, and Pan Liu*. ACS Nano 2023, 17, 1485.Haoyue Zhang,# Lingling Wu,# ..., and Fang Song*., ACS Appl. Mater. Interfaces, In revision.Haoyue Zhang,# Lingling Wu,# ..., and Fang Song*. ACS Catal. In press.

In-situ hydrothermal roasting of Ni-based oxide as efficient oxygen evolution reaction catalysts

Oxygen evolution reaction (OER) is the key reaction in the water splitting and CO2 electrochemical reduction. However, the current catalysts for OER still suffer from high potentials and poor stability. Herein, hierarchical self-supporting Ni-based oxides (NiMOx)/Ni–V/Ni foam (NF) (M = Fe, Co, Cu, Mo) catalysts are directly grown on NF by in-situ hydrothermal roasting method. The OER activity of a series of Ni-based oxide catalysts doped with different metal are investigated. The results demonstrate that the NiFeOx/Ni–V/NF exhibits the best OER activity. At the current density of 10 mA cm−2, a smaller overpotential for OER of 270 mV is achieved in 1.0 M KOH electrolyte. No obvious decay in performances is observed after constant electrolysis of about 25 h, demonstrating its outstanding stability. The formation of new oxides compounds and the structure changes due to the addition of Fe, Co, Cu, Mo to the NiOx contribute to the improvements in activity.

Simultaneously Improved Activity and Stability for Acidic Water Oxidation of IrRu Oxides by a Dual Role of Tungsten Doping.

Acidic oxygen evolution reaction (OER) remains a significant challenge due to the low activity and/or poor stability of the catalysts, even with state-of-the-art catalysts such as IrO2 and RuO2. Herein, we propose a strategy to enhance both the catalytic activity and stability of IrRu oxides for acidic OER by doping non-noble metal W. The W-doped IrRu3Ox (W-IrRu3Ox) undergoes a process of W leaching and reconstruction during the OER, leading to a more uniform distribution of elements, while the electronegative nature of W influences the electronic structures of Ir and Ru in W-IrRu3Ox. The dual role of W in promoting the formation of active site Ir5+ and inhibiting the concentration of soluble Ru>4+ ions results in a synergistic enhancement of both the activity and stability of acidic OER. Remarkably, W-IrRu3Ox exhibits outstanding catalytic activity for the OER in 0.5 M H2SO4, with a high stability of more than 500 h. This work presents a novel and feasible strategy for the development of efficient and stable catalysts for acid OER, shedding light on the design of advanced electrocatalysts for energy conversion and storage applications.

Co-Adjusting d-Band Center of Fe to Accelerate Proton Coupling for Efficient Oxygen Electrocatalysis.

The problem in d-band center modulation of transition metal-based catalysts for the rate-determining steps of oxygen conversion is an obstacle to boost the electrocatalytic activity by accelerating proton coupling. Herein, the Co doping to FeP is adopted to modify the d-band center of Fe. Optimized Fe sites accelerate the proton coupling of oxygen reduction reaction (ORR) on N-doped wood-derived carbon through promoting water dissociation. In situ generated Fe sites optimize the adsorption of oxygen-related intermediates of oxygen evolution reaction (OER) on CoFeP NPs. Superior catalytic activity toward ORR (half-wave potential of 0.88V) and OER (overpotential of 300mV at 10mA cm-2) express an unprecedented level in carbon-based transition metal-phosphide catalysts. The liquid zinc-air battery presents an outstanding cycling stability of 800h (2400 cycles). This research offers a newfangled perception on designing highly efficient carbon-based bifunctional catalysts for ORR and OER.

Activating Commercial Nickel Foam to a Highly Efficient Electrocatalyst for Oxygen Evolution Reaction through a Three-Step Surface Reconstruction.

It is highly desired to directly use commercial nickel foam (CNF) as an electrocatalyst for the oxygen evolution reaction (OER) via simple surface reconstruction. In our research, a simple three-step preactivation process was proposed to reconstruct CNF as an efficient OER catalyst, including calcination, high-voltage treatment, and immersing in electrolyte. The optimal CNF after three-step activation reaches an excellent OER performance of 228 and 267 mV at η10 and η100 in alkaline media and can tolerate long-term tests under a large current density of 500 mA·cm-2. The promotion of each step was explored. The calcination step leads to a reconstructive surficial morphology with an enlarged active surface, providing a prerequisite for the following construction steps. The high-voltage treatment changes the valence of surface Ni species, generating phases with higher catalytic activity, and the immersing process introduces Fe heteroatoms into the surface of CNF, boosting the catalytic performance of CNF through Ni-Fe interactions. This research provides a simple method of making high-performance catalysts with accessible nickel foam, a potential for large-scale application in practical industry, and new thinking for the manipulation of Ni-based catalysts.

In-situ synthesis of conductive Fe-MOFs on the carbon nanotubes/carbon cloth as high-performance catalyst for alkaline oxygen evolution

In the electrolysis of water, the efficiency is heavily constrained by the slow kinetic process of the oxygen evolution reaction (OER) at the anode. Herein, by a simple hydrothermal method for the in-situ growth of Fe3(HHTP)2 on the open three-dimensional nanostructured substrate, Co-anchored carbon nanotubes/carbon cloth (Co/CNT/CC), Fe3(HHTP)2@Co/CNT/CC was prepared and acted as an OER electrocatalyst. The combination of carbon nanotubes (CNTs) and carbon cloth not only enhanced the substrate conductivity, but also facilitated the uniform loading of Fe3(HHTP)2. The in-situ growth, on the other hand, allowed the Fe3(HHTP)2 to connect with the conductive substrate tightly, thus enhancing the stability of the interfacial contact, improving the electron transfer efficiency and providing enough catalytically active sites. In addition, the construction of self-supported electrodes could effectively avoid the use of binders and improve the stability of the composites during electrolysis. The Fe3(HHTP)2@Co/CNT/CC displayed excellent properties in alkaline electrolytes as an efficient OER catalyst, achieving a current density of 50 mA cm−2 at an overpotential of only 1.60 V and perfect stability in long-term tests. Herein, the present work provides a rational tactics for developing self-supporting electrodes with plentiful active sites and high stability to enhance the electrochemical efficiency of water splitting.

1D mesoporous NiFe2O4 nanorods fabricated by electrospinning for efficient oxygen evolution reaction

Designing and preparing efficient and stable oxygen evolution reaction (OER) catalysts is crucial to improve water splitting performance. One-dimensional (1D) structural catalysts have received increasing attention for the OER due to their unique structural characteristics. In this study, 1D mesoporous NiFe2O4 (NFO) spinel nanorods are fabricated by electrospinning, and the differences in physical structure and electrochemical performance of NFO nanorods prepared by different electrospinning precursors are investigated. It is found that the NFO nanorods prepared by precursor of nickel-iron hydroxide particles (denoted as NFOH) exhibit a diameter of approximately 200 nm and a surface area of 26.4 m2 g−1. In 1 M KOH solution, NFOH nanorods achieve low overpotentials of respective 316 mV and 396 mV to obtain current densities of 10 mA cm−2 and 50 mA cm−2, as well as a low Tafel slope of 67.2 mV dec−1, even lower than commercial NFO. Notably, the nanorods also demonstrate excellent long-term stability. The high OER activity can be attributed to the small nanoparticle size, abundant electrochemical active sites provided by the 1D mesoporous nanostructure, and increased conductivity, which promote charge/electron transfer and enhance the conversion of active species, thereby improving the efficiency of water electrolysis. This work may broaden the perspective and approach for the structural design of OER catalysts.

Rational design of bimetal phosphide embedded in carbon nanofibers for boosting oxygen evolution

The development of non-precious metal electrocatalysts for oxygen evolution reaction (OER) is crucial for generating large-scale hydrogen through water electrolysis. In this work, bimetal phosphides embedded in electrospun carbon nanofibers (P-FeNi/CNFs) were fabricated through a reliable electrospinning–carbonization–phosphidation strategy. The incorporation of P-FeNi nanoparticles within CNFs prevented them from forming aggregation and further improved their electron transfer property. The bimetal phosphides helped to weaken the adsorption of O intermediate, promoting the OER activity, which was confirmed by the theoretical results. The as-prepared optimized P-Fe1Ni2/CNFs catalyst exhibited very high OER electrocatalytic performance, which required very low overpotentials of just 239 and 303 mV to reach 10 and 1000 mA cm−2, respectively. It is superior to the commercial RuO2 and many other related OER electrocatalysts reported so far. In addition, the constructed alkaline electrolyzer based on the P-Fe1Ni2/CNFs catalyst and Pt/C delivered a cell voltage of 1.52 V at 10 mA cm−2, surpassing the commercial RuO2||Pt/C (1.61 V) electrolyzer. It also offered excellent alkaline OER performance in simulated seawater electrolyte. This demonstrated its potential for practical applications across a broad range of environmental conditions. Our work provides new ideas for the ration design of highly efficient non-precious metal-based OER catalysts for water electrolysis.

Nickel-cobalt phosphide nanowires as precatalysts for surface reconstruction to prepare durable and efficient OER catalysts

The investigation of transition metal phosphides (TMPs) as efficient electrocatalysts for water splitting has garnered significant attention in academic research. Nevertheless, limited research has been conducted on the alteration of the structural and morphological properties of TMPs resulting from the unavoidable surface reconstruction during the oxygen evolution reaction (OER). This study introduces a newly developed catalyst, namely nickel–cobalt phosphide nanowires (NiCoP), which facilitates the in-situ growth of nickel–cobalt oxide (NiCo2O4) through surface reconstruction during anodic potential cycling in alkaline electrolytes. The catalyst's extensive modification can be observed through ex-situ characterization techniques. The catalyst undergoes a significant transformation that ultimately yields a phosphide scaffold, leading to the formation of a spinel oxide surface. This transformation enhances the catalytic environment for the OER, making it highly efficient and potent. The transformed catalyst demonstrates comparable catalytic performance to the precious RuO2 catalyst across various current densities. Importantly, it exhibits remarkable long-term stability, as demonstrated by its ability to sustain continuous operation for 72 h at a current density of 50 mA while maintaining stable catalytic performance.

High negative voltage activating perovskite oxide with bi-vacancy synergistic regulation for water oxidation

Oxygen vacancy engineering is a strategy to design efficient oxygen evolution reaction (OER) catalysts, but it may lower the band center of O 2p and result in high energy barrier. Here, La0.6Sr0.4Co0.9Fe0.1O3‑δ (LSCF) perovskite catalyst with O and Sr vacancies were prepared by high reduction voltage treatment. The bi-vacancy facilitates the synergistic regulation by providing the inverse movement the d-band center and p-band center to enhance M−O covalency, thus activating lattice oxygen of LSCF. The synergistic effect of Sr and O vacancy reduces the OH adsorption energy on the surface of LSCF, which makes OH adsorption and desorption easier. By optimizing the reduction voltage and time, the overpotential (at 10 mA cm−2) of the high reduction voltage treated LSCF (LSCF- −2V-80 s) is reduced by 130 mV compared to LSCF. The LSCF- −2V-80 s still showed clear lattice fringes after stability test. Moreover, the stronger covalency of LSCF- −2V-80 s to produce O22– intermediates is inclined to be lattice oxygen mediated mechanism (LOM). The bi-vacancy strategy made LSCF- −2V-80 s produce a current density of 174 A/g at 2.50 Vcell in anion exchange membrane water electrolyzer. Bi-vacancy synergistic strategy derived from one-step high reduction voltage provides a new route for OER catalysts.