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Iron sites with high intrinsic activity for oxygen evolution reaction (OER) can effectively enhanced the performance of perovskite oxide as electrocatalyst for water electrolysis. However, doping of iron in perovskite LaCoO 3 remains a challenge owing the strong Co–O bond and robust structure of LaCoO 3. Herein, the lattice doping of Ni in LaCoO 3 has been adopted to promote the interaction between iron ions and Co site in LaCoO 3. Firstly, molten salt of Ni(NO 3) 2 provides free-moving Ni ions to substitute Co sites in the lattice of LaCoO 3 forming LaCo 1-x Ni x O 3 at the optimized Ni doping condition. Then, iron ions can easily be absorbed to LaCo 1-x Ni x O 3 due to the strong interaction between Ni and Fe by electrochemical activation at room temperature. The prepared LaCo 1-x-y Ni x Fe y O 3 nanoparticles keep the coarse surface for maximizing the exposure of active sites. The high-valence Co and oxygen vacancy from LaCo 1-x-y Ni x Fe y O 3 contribute to the better intrinsic activity for OER, demonstrating the overpotential of ƞ 10 of approximately 315 mV and good stability. The strategy of by introducing the lattice doping of other metal ion can realize the facile and effective construction of iron doped perovskite oxide for water oxidation. [Display omitted] • Molten salt of Ni(NO 3) 2 provides Ni ions to substitute Co sites in the lattice of LaCoO 3. • Iron ions are absorbed to LaCo 1-x Ni x O 3 with the strong interaction Ni–Fe by electrochemical activation. • Ni/Fe doping can expose more active site sites and adjust the electronic structure of Co sites. • LaCo 1-x-y Ni x Fe y O 3 exhibits the motivated OER activity and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ce-CoNH with nanorods architecture is constructed through molten salt method. • Incorporation of Ce could generate oxygen vacancy thus boosting alkaline water oxidation. • Ce doping could optimize local electronic structure of Co sites. • The catalyst has excellent OER performance in 1 M KOH. Rationalizing the development of highly active, non-precious electrocatalysts through facile and cost-effective synthesis methods for the oxygen evolution reaction (OER) constitutes a paramount research objective. In this study, we introduce an innovative molten salt approach to fabricate an arrayed nanorod architecture supported on a cobalt foam substrate denoted as Ce doped cobalt hydroxyl nitrate (Ce-CoNH). Cerium (Ce) is strategically employed to induce oxygen vacancies and effect localized electronic structure modifications of the cobalt (Co) sites. In comparison to individual CoNH catalysts, Ce-CoNH exhibits exceptional catalytic activity in alkaline water oxidation, achieving a notably low overpotential of 270 mV at a current density of 50 mA cm−2. Notably, the Ce-CoNH catalyst also demonstrates remarkable durability, sustaining a current density of 100 mA cm−2 for an impressive duration of 50 h, surpassing the performance of Ce-free CoNH samples, which can be attributed to the flexible influence of Ce doping and the robust nanorod structure. Collectively, our study underscores the viability of molten salt-synthesized heteroatom substitution, accompanied by the introduction of defect-rich structures, as an effective strategy for the rational design of advanced electrocatalysts tailored for water electrolysis applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zn2+ as strong Lewis acid act as an electron acceptor, accepting electrons from FeOOH. • Zn2+ is introduced into FeOOH with a looser structure by regulating EDL repulsion. • Leached Fe is compensated by Zn-induced redeposition to achieve self-healing. • The overpotential of optimized Zn 0.5 FeOOH is 250 mV at 100 mA cm−2 for OER. • Zn doping strategy is still applicable in alkaline seawater and AEM electrolyzers. The fast leaching of the Fe catalytic center and low conductivity of FeOOH have hindered the optimal stability and activity of Fe-based electrocatalysts for oxygen evolution reactions (OER). Here, Zn2+ is introduced into FeOOH with a looser nanosheet structure by regulating electric double layer (EDL) repulsion during electrodeposition. Meanwhile, as strong Lewis acids, Zn2+ in Zn x FeOOH could act as an electron acceptor, accepting electrons from FeOOH. The doping of Zn2+ shortens the bond length of Fe-O and enhances the covalency of Fe-O to improve electron transport rate and stability. The faster catalytic kinetics also been obtained by facilitating O* to form OOH* intermediates. At 100 mA cm−2, Zn 0.5 FeOOH requires overpotential of only 250 mV and maintains initial activity in 1 M KOH after 120 h. Notably, Zn-induced self-healing is achieved when the leaching and redeposition of Fe reach dynamic equilibrium. In 1 M KOH seawater, Zn 0.5 FeOOH requires overpotentials of 286 mV to produce current density of 100 mA cm−2. At 2.0 V, Zn 0.5 FeOOH can achieve 1000 mA cm−2 in anion exchange membrane (AEM) water electrolyzer at room temperature. This work provides an effective Zn-induced strategy for designing efficient and stable OER catalysts for industrial development. [ABSTRACT FROM AUTHOR]

High-entropy materials (HEMs) with unique electronic structures and diverse elemental compositions have emerged, however, HEMs are complicated to prepare. Here, we prepared an amorphous FeCoNiMoW high-entropy oxide (FCNMWO) catalyst by simple one-pot hydrothermal preparation, based on a method that used polyoxometalate clusters as metal cation linkers. The FCNMWO with amorphous structure exhibited better oxygen evolution reaction, as confirmed by a series of characterization and electrochemical experiments, which exhibited a low overpotential of 313 mV at a current density of 10 mA cm−2 with a Tafel slope of 40.95 mV dec−1, indicating excellent charge transfer capability. Moreover, the presence of polyoxometalate clusters modulated the electronic structure and accelerated charge transfer processes, promoting OER property. In addition, analysis of the results before and after OER stability revealed that the leaching of Mo induced reconstruction on the catalyst surface, and the MOOH were actual active species. This work is instructive for further design and development of efficient high entropy electrocatalysts with admirable OER properties. [Display omitted] • Simple a one-pot hydrothermal is used to synthesize amorphous high entropy oxide. • The synergistic effect of various metals improves the performance of OER. • The surface reconstruction of Fe sites realizes real active substance. • FCNMWO shows a remarkably stability after a 24 h stability test. [ABSTRACT FROM AUTHOR]

Developing low-cost and high performance catalysts for oxygen evolution reaction (OER) is a vital way to promote the effective cost and industrial applications of water splitting. In this work, we synthesize the hierarchical structure of NiFe(OH) x /VS/NF nanosheets using vanadium sulfide (VS) layer coating on the nickel foam (NF) as substrate. VS on the surface of NF can make effect on the distribution and morphology of NiFe(OH) x. The vertical NiFe(OH) x nanosheets supported VS/NF can not only provide abundant active sites for OER but also have the advantages of excellent conductivity substrate. The three dimensional skeleton structure of NF can also faster oxygen diffusion process, which suggests outstanding electrocatalytic activity in alkaline medium. Employing it for water splitting with a current density of 200 mA cm−2 is achievable at a low voltage of 1.506 V vs. RHE with remarkable long-term stability. Moreover, the synergistic hybridization of layered VS/NF with layered double hydroxides (LDH) materials enlightens the design and fabrication of promising hybrid materials. This work may offer a viable route to design the advanced electrode materials for OER electrocatalysts. Unlabelled Image • The hierarchical structure of NiFe(OH) x /VS/NF nanosheets was prepared. • VS on of NF makes effect on the distribution and morphology of NiFe(OH) x. • The vertical NiFe(OH) x nanosheets provide abundant active sites and good conductivity. • The synergistic hybridization of NiFe(OH) x /VS/NF is a promising way for efficient OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag doping is realized on the lattice surface of CoMoO 4 nanorods by molten salt method. • Ag doping causes the Co 1−x Ag x MoO 4 to produce more oxygen vacancies. • The stability of Co 1−x Ag x MoO 4 is enhanced by doping Ag with ion polarization. • DFT reveals that Ag doping modulates the electronic structure. Spinel type oxides including CoMoO 4 are promising catalysts for water electrolysis. However, MoO 4 2− is easy to dissolve during oxygen evolution reaction (OER), resulting in the poor performance. The lattice modulation of CoMoO 4 may be an effective strategy for better activity and stability. In our work, molten salt method has been adopted to realize the incorporation of Ag into the lattice surface of CoMoO 4 nanorods. The physical characterizations show that Ag is uniformly distributed in the surface lattice of optimized Co 1−x Ag x MoO 4. Lattice Ag doping stabilizes the structure of Co 1−x Ag x MoO 4 by adjusting the electron distribution state to form a high-valence Co. Moreover, the incorporation of low-valence Ag+ causes the Co 1−x Ag x MoO 4 to produce more oxygen vacancies, which reduces the charge transfer resistance by about 15 times compared to CoMoO 4. The electrochemical measurements demonstrate that Co 1−x Ag x MoO 4 exhibits a lower OER overpotential (330 mV) at 10 mA cm−2 and the 2.7 longer time than CoMoO 4 during chronopotentiometry test. DFT calculation reveals that Ag doping with ion polarization optimizes the electron distribution of Co-O and enhances the covalency of Mo-O to slow down the solubility of Co 1−x Ag x MoO 4. This work shows that lattice doping of metal ions may be a great choice for excellent electrocatalysts for OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Partially amorphous structures are designed by rapid microwave activation and borate doping. • Borate species and microwave treatment synergically promote the formation of OER active species FeOOH. • Partially amorphous feature regulates the electronic structure and abundant of active sites. • Partially amorphous m-B-FeNiNH/IF exhibits excellent OER activity and long-term stability. Metal nitrate hydroxides (MNHs) show great potential in the field of electrocatalytic water splitting, especially for oxygen evolution reaction (OER). The conversion of crystalline transition metal-based catalysts into partially amorphous counterparts is considered to be a promising but challenging strategy for improving OER performance of MNH S. Here, a simple and rapid microwave method is reported to synthesize partially amorphous borate doped iron-nickel nitrate hydroxide nanoarray uniformly grown on conductive iron foam (m-B-FeNiNH/IF) for OER. The microwave activation can promote the formation of the partial amorphous structure, leading to optimize geometric, electronic structure, and produce more high intrinsic activity. Moreover, with the addition of borate, synergistically promoted FeOOH (Fe 4 (NO) 3 (OH) 11 → FeOOH) as active species may significantly improve OER performance with a low overpotentials of only 246 mV at 100 mA cm−2 and a 26.5 mV dec−1 Tafel slope, outperforming most of the non-noble metal based catalysts reported. The partially amorphous and self-supported m-B-FeNiNH/IF maintain catalytic durability and structural integrity for 100 h at 100 mA cm−2 large-current-density. This work may provide insights into improving electrocatalytic performance by introducing partially amorphous structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • The short-time room-temperature electrochemical activation is adopt to realize the S doping. • S-doped NiFe-LDH provides the large surface area and long-term robustness. • The synergistic effect between NiFe-LDH and S species is helpful for OER. • A facile electrochemical activation strategy can be used for anion doping of the catalysts. Anion doping shows promising potential in optimizing the adsorption and desorption of reaction intermediates on the surface of NiFe-based layered double hydroxide (NiFe-LDH) for oxygen evolution reaction (OER). However, conventional doping methods are meticulous and complex. Hence, S-doped NiFe-LDH (S-NiFe-LDH- t -A) driven by short-time room-temperature electrochemical activation procedure is synthesized. The NiFe-LDH prefabricated by spontaneous substrate corrosion ensures large active surface area, exposed active sites and long-term robustness. Then moderate S doping electrochemically motivated is applied to the regulation of NiFe-LDH, which not only improves the bonding between metals and reaction intermediates but also induces decreased free energy, thus enhancing OER performance. Electrochemical measurements verified the low overpotential of 270 mV at 50 mA cm−2 and favorable durability for optimized S-NiFe-LDH-9-A benefited from the synergistic effect between NiFe-LDH and S species. This work provides a facile electrochemical activation strategy for anion doping, which show implications for the design of advanced catalysts. [ABSTRACT FROM AUTHOR]

Designing and exploring efficient and stable Fe-based nanostructures catalyst is playing a critical role in the industrial application of water splitting. Herein, amorphous Fe–Ni bimetallic hydroxides film on the conductive FeS nanosheets supported by three-dimensional iron foam (IF) (denoted as FeNi(OH) x /FeS/IF) has been successfully synthesized by an ultrafast surface modification process (30 s). The fast surface reaction using FeS/IF as substrate in nickel nitrate solution facilitates the formation of bimetallic ultrathin film of FeNi(OH) x with enhanced performance oxygen evolution reaction (OER). Owing to the excellent conductivity, FeS nanosheets supported by IF may improve the dispersion and conductivity of FeNi(OH) x as active sites for OER. The physical characterizations confirm the closed interaction of FeNi(OH) x /FeS/IF, which suggests the validity of this facile surface modification. The electrochemical measurements show that FeNi(OH) x /FeS/IF only need a low overpotential of 273 mV to reach the 100 mA cm−2 (geometric current density) towards OER. The excellent catalytic performance can be attributed to the improved conductivity of substrate, a greater number of active sites and strong the synergistic effect of the Fe–Ni bimetallic hydroxides. The great long-term stability has been obtained. This work provides a simple route to produce advanced hierarchical nanostructure as electrocatalysts for OER. Image 1 • Amorphous Fe–Ni bimetallic hydroxides film on the conductive FeS nanosheets was prepared. • The fast surface reaction using FeS/IF as substrate is the key for amorphous hydroxides. • The bimetallic ultrathin amorphous film of FeNi(OH) x has the enhanced intrinsic activity. • This work provides a simple route for hierarchical nanostructure for OER. [ABSTRACT FROM AUTHOR]