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Hydrogen is considered a promising clean energy vector with the features of high energy capacity and zero-carbon emission. Water splitting is an environment-friendly and effective route for producing high-purity hydrogen, which contains two important half-cell reactions, namely, the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). At the heart of water splitting is high-performance electrocatalysts that efficiently improve the rate and selectivity of key chemical reactions. Recently, perovskite oxides have emerged as promising candidates for efficient water splitting electrocatalysts owing to their low cost, high electrochemical stability, and compositional and structural flexibility allowing for the achievement of high intrinsic electrocatalytic activity. In this review, we summarize the present research progress in the design, development, and application of perovskite oxides for electrocatalytic water splitting. The emphasis is on the innovative synthesis strategies and a deeper understanding of structure–activity relationships through a combination of systematic characterization and theoretical research. Finally, the main challenges and prospects for the further development of more efficient electrocatalysts based on perovskite oxides are proposed. It is expected to give guidance for the development of novel non-noble metal catalysts in electrochemical water splitting. [ABSTRACT FROM AUTHOR]

• Mo is successfully doped into SrCo 0.5 Fe 0.5 O 3-δ perovskite oxides using a modified sol-gel method. • SrCo 0.5 Fe 0.4 Mo 0.1 O 3-δ requires ∼200 and ∼310 mV overpotentials to reach 10 mA cm−2 for HER and OER. • A current density of 10 mA cm−2 could be achieved by applying a potential of 1.68 V vs. RHE in the SCFM10||SCFM10 electrolyzer. • SrCo 0.5 Fe 0.4 Mo 0.1 O 3-δ exhibits remarkable stability for HER and OER in alkaline electrolyte. Perovskite oxides with high electrocatalytic activities and cost-effectiveness can be developed by rational doping. Here, we fabricate a series of perovskite oxides comprising SrCo 0.5 Fe 0.5-x Mo x O 3-δ (x = 0, 0.05, 0.10, 0.15) doped with different proportions of Fe and Mo elements to enhance the long-term stabilities and electrocatalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among them, SrCo 0.5 Fe 0.4 Mo 0.1 O 3-δ (SCFM10) exhibits the optimum electrocatalytic activity for water splitting, exhibiting overpotentials at −10 mA cm−2 and 10 mA cm−2 of ∼200 mV for HER and ∼310 mV for OER, respectively, generating a current density of 10 mA cm−2 using only 1.68 V in a two-electrode electrolytic cell. Additionally, SCFM10 demonstrates outstanding stability, maintaining continuous operation for 100 h without visible decay. These results give some new points of view into the development of bifunctional catalysts for the purpose of efficient water splitting in a sensible way. [Display omitted] [ABSTRACT FROM AUTHOR]

Antimony (Sb) as a low-toxic and cost-effective metal is a promising material to catalyse CO 2 electroreduction to formate with practical viability. However, monometallic Sb suffers from intrinsically low catalytic activity and the competing hydrogen evolution. Here, we report nanoporous Sb-Bi alloys for substantially improving the catalytic activity of Sb and suppressing hydrogen evolution. The optimal Sb-Bi alloy exhibits a maximum Faradaic efficiency of 95.8 % toward formate production, surpassing the 11.6 % of monometallic Sb counterpart. Operating the catalyst in the flow cell demonstrates a formate partial current density of 734 mA cm−2 and cathodic energy efficiency of 59 % at a moderate overpotential of 800 mV, representing a record formate-production performance so far. Experimental and theoretical studies indicate that the Sb-Bi interactions activate Sb sites to selectively stabilize *OCHO intermediates, facilitating CO 2 -to-formate conversion. This work offers insights in manipulating bimetallic interactions to transform inert materials into active catalysts for efficient electrocatalysis. [Display omitted] • Sb-Bi interactions induce electrocatalytic switching from HER to CO 2 ER. • Sb 2 Bi 6 exhibits a maximum formate selectivity of 95.8 % in an H-type cell. • Sb 2 Bi 6 achieves a record formate activity of 734 mA cm−2 in a flow cell. • Sb-Bi interactions facilitate Sb sites to stabilize *OCHO for formate formation. [ABSTRACT FROM AUTHOR]

Advancing the development of economical, high-performance, and durable non-precious metal electrocatalysts for oxygen evolution reaction (OER) holds critical significance. This study presents a self-supporting ternary metal phosphide (NiCoFe–P/NF) electrode developed by direct phosphating metal-organic frameworks (MOFs) precursor. Benefiting from a three-dimensional hierarchical porous structure, optimized electronic configuration, high electrical conductivity, and synergistic effect of multiple elements, the synthesized NiCoFe–P/NF electrocatalyst exhibits exceptional catalytic performance compared to the monometallic or bimetallic phosphides, achieving a low overpotential of 209 mV and a Tafel slope of 29 mV dec−1 at 10 mA cm−2 in 1 M KOH solution. In addition, the prepared catalyst exhibits superior stability and durability, as evidenced by its well-preserved morphology after 48 h of stability test. Furthermore, at a high current density of 100 mA cm−2, the long-term efficiency remains >90% even after 96 h. Density functional theory (DFT) calculations reveal that the high catalytic performance of the NiCoFe–P/NF catalyst is ascribed to modified electronic states and lower adsorption energy to the related species. This study not only presents the synthesis of extremely stable and active OER catalysts but also offers a novel and practical method for the development of new catalysts. [Display omitted] • Self-supporting trimetallic phosphide was investigated for OER. • NiCoFe–P/NF electrode provides superior OER activity and stability. • DFT calculations explain the origin of the high catalytic activity. • A chemically uniform trimetallic two-dimensional MOF served as the precursor. [ABSTRACT FROM AUTHOR]

Electrocatalytic O2 conversion and water-splitting hold great promise to enable the chemicals–electricity inter-transition in many renewable-energy initiatives. Enhancing the kinetics of the oxygen reduction reaction (ORR) is challenging. Here, we present that Zn3(VO4)2/Ni(OH)2/rGO (reduced graphene oxide) nanosheet arrays-a Zn3(VO4)2/Ni(OH)2 composite in the form of nanometre-thick nanosheets on an rGO substrate-serve as an efficient and stable electrocatalyst for the ORR in alkaline electrolytes. The thin-sheet structure and smaller free energy of Zn3(VO4)2/Ni(OH)2, as well as the excellent conductivity of the rGO substrate, enable a large electrochemically-active surface area and a high electron transport, contributing to the superior electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Furthermore, Zn3(VO4)2/Ni(OH)2/rGO and Zn3(VO4)2/Ni(OH)2 samples exhibit remarkable long-term water-splitting stability of 48 h. Density functional theory (DFT) calculations reveal the optimized intermediate affinity ability at the Ni(OH)2 side, due to electrons transferring from Ni(OH)2 to Zn3(VO4)2. Additionally, the higher hybridization degree of density of states (DOS) boosts electron transfer in the electrocatalytic process. More broadly, this work provides new inspiration for the construction of a novel noble metal-free electrocatalyst that could show great promise in energy electrocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru-doped SrFe 1-x Ru x O 3-δ perovskite oxides were successfully fabricated through a modified sol–gel method. • The SrFe 0.7 Ru 0.3 O 3-δ exhibits significantly enhanced bifunctional electrocatalytic activities for HER and OER in alkaline electrolytes. • The DFT studies demonstrate Ru doping optimizes the electronic structure of SrFe 0.7 Ru 0.3 O 3-δ and thus improves the charge transfer efficiency. • An electrolyzer with SFR30 as both the anode and cathode catalysts requires only a cell voltage of 1.58 V vs. RHE to drive a current density of 10 mA cm−2 in an alkaline medium. Recently, perovskite oxides have acquired a rapidly growing research interest in energy storage and conversion systems, especially the electrolysis of water. Rational doping is an extremely effective strategy to enhance the hydrogen evolution reaction/oxygen evolution reaction (HER/OER) of the perovskite oxides. Herein, a series of novel bi-functional electrocatalysts were synthesized by doping Ru in SrFeO 3-δ perovskite oxide (SrFe 1-x Ru x O 3-δ , x = 0, 0.15, 0.30, 0.45) which exhibit remarkable enhancements of HER/OER activities and long-term stabilities in the alkaline solution (1.0 M KOH). Among them, SrFe 0.7 Ru 0.3 O 3-δ (SFR30) shows the best electrocatalytic activities for overall water splitting, exhibiting low overpotentials for HER (∼41 mV) and OER (∼334 mV) at −10 and 10 mA cm−2, respectively, generating current densities of 10 mA cm−2 in alkaline electrolytic cell using the potential of 1.58 V. In addition, the SFR30 electrocatalyst exhibits remarkable stability which can be operated continuously for 96 h without significant delay. Density functional theory (DFT) calculations indicate that Ru doping can effectively modulate the adsorption of intermediates on the active sites to achieve excellent electrocatalytic performance. Many new prospects have been opened for the development of bi-functional electrocatalysts for overall water splitting. [ABSTRACT FROM AUTHOR]

Given its superior structure, the abundance of surface functional groups, and low cost, cotton fiber filtration paper can be used as the support for hydrogen evolution reaction (HER) and oxygen evolution reaction catalysts (OER) instead of copper foam (CF), nickel foam (NF), or carbon cloth (CC). Herein, the chemical plating method was used to create thin self-supporting electrodes based on cotton fiber filtration paper (FP). The Co-Ni-P amorphous nanospheres can be uniformly dispersed on the self-supporting FP due to its porous structure and oxygen functional groups. The Co-Ni-P/FP electrode has an overpotential as low as 125 mV for HER and 320 mV for OER at the current density of 10 mA cm−2. Additionally, according to density functional theory (DFT) calculations, the Co atom added to the Ni-P nanosphere can lead to considerably more charge accumulation around the Co and Ni active sites, which greatly encourages the HER and OER processes. The novel porous support, FP, provides a fresh way the preparation of self-supporting electrodes. [Display omitted] • Filter paper is used to prepare the self-supporting electrode as the substrate. • The preparation method is simple and the properties are stable. • Rich oxygen-containing functional groups of FP promote deposition and dispersion. • Explore the excellent electrochemical performance of amorphous Co-Ni-P/FP by DFT. [ABSTRACT FROM AUTHOR]

• Co 3 V 2 O 8 -T (T = temperature/°C) are prepared as bifunctional electrocatalysts. • Co 3 V 2 O 8 -400 nanofibers show small Tafel slopes of 43 and 63 mV dec−1 for ORR and OER. • The Co 3 V 2 O 8 -400 nanofiber has the best catalytic activities for ORR and OER. • The mechanism of Co 3 V 2 O 8 -400 nanofiber is simulated by DFT. Highly active and stable bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are necessary for practical fuel cells, metal-air batteries, and water splitting. Herein, we report a series of bifunctional Co 3 V 2 O 8 -T (T = temperature/°C) electrocatalysts by using Co-carbon electrospun nanofiber as a template, followed by a one-step calcination process. As expected, the developed Co 3 V 2 O 8 -400 nanofiber electrocatalyst shows a very small Tafel slope of 43 and 63 mV dec−1 for the ORR and OER in the alkaline solution, respectively. In addition, density functional theory (DFT) calculations reveal that the metallic conductivity and interface V-Co interaction of Co 3 V 2 O 8 -400 nanofiber boost ORR and OER electrocatalytic reactions. [ABSTRACT FROM AUTHOR]