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There is a growing interest in the development of active, durable, and cost-effective electrocatalysts for oxygen evolution reactions (OER). In this study, we synthesized a self-reconstruction iron-doped sulfide-regulated nickel molybdate catalyst using wet chemical sulfuration and electrodeposition techniques. The core-shell nanorods (SC@NMO) were produced through rapid sulfuration. We investigated the effects of sulfur leaching on rapid and extensive electrochemical self-reconstruction. Our approach utilized the phase change of Fe3+ and electrodeposition-induced restructuring to enhance the catalyst's OER activity and stability in an alkaline electrolyte. Notably, iron ions establish a precipitation-dissolution dynamic equilibrium at the interface between the catalyst surface and the electrolyte, which minimizes iron loss and results in a more efficient and stable catalyst. The prepared sample, SC-Fe(Ni)OOH@NMO, demonstrated exceptional oxygen evolution performance and long-term stability in a 1 M KOH solution, achieving an overpotential of only 279 mV at a current density of 100 mA cm−2. It maintained stable operation for 200 h in a high-concentration 6 M KOH solution. The above data prove that this work provides a feasible strategy to enhance the OER catalytic capacity of metal oxides by the two modification methods of co-doping of metal and non-metal and reconstruction. [Display omitted] • The core-shell nanorods were obtained by wet sulfuration. • The dynamic reconstruction of Fe3+ improves the catalyst's activity and stability. • SC-NiFeOOH@NMO has long-term stability in high concentration alkaline medium. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal organic framework (MOF) is currently-one of the key catalysts for oxygen evolution reaction (OER), but its catalytic performance is severely limited by electronic configuration. In this study, cobalt oxide (CoO) on nickel foam (NF) was first prepared, which then wrapped it with FeBTC synthesized by ligating isophthalic acid (BTC) with iron ions by electrodeposition to obtain CoO@FeBTC/NF p-n heterojunction structure. The catalyst requires only 255 mV overpotential to reach a current density of 100 mA cm−2, and can maintain 100 h long time stability at 500 mA cm−2 high current density. The catalytic properties are mainly related to the strong induced modulation of electrons in FeBTC by holes in the p-type CoO, which results in stronger bonding and faster electron transfer between FeBTC and hydroxide. At the same time, the uncoordinated BTC at the solid–liquid interface ionizes acidic radicals which form hydrogen bonds with the hydroxyl radicals in solution, capturing them onto the catalyst surface for the catalytic reaction. In addition, CoO@FeBTC/NF also has strong application prospects in alkaline electrolyzers, which only needs 1.78 V to reach a current density of 1 A cm−2, and it can maintain long-term stability for 12 h at this current. This study provides a new convenient and efficient approach for the control design of the electronic structure of MOF, leading to a more efficient electrocatalytic process. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of the oxygen evolution reaction (OER) limits the development of water electrolysis technology and the long-term efficiency of hydrogen energy production. In addition, it is important to evaluate the reconstruction performance of OER catalysts for actual water electrolysis. We created a self-supported electrode with FeS film coated Fe foam as a substrate, ordered resoluble molybdate (MoO 4 2−) anions in interlayers, and Co-doped as a catalytically active phase for the OER. The catalyst is capable of electrochemical self-reconstruction (ECSR). With the dissolution of molybdate and sulfur ions, the catalyst surface cobalt iron oxide (CoFe 2 O 4) forms an active amorphous FeCoOOH, which is favorable for alkaline OER. We realized the introduction of new active sites in the catalyst reconstruction process. Finally, the composite CoFeO x catalyst increased the specific surface area, promoted bubble transport, and enhanced electron mass transfer. The synergistic coupling effect of the catalyst makes it have excellent OER activity and stability. Remarkably, Co–Mo/FeS nanosheets afforded an electrocatalytic OER with a current density of 100 mA cm−2 at a low overpotential of 321 mV. These discoveries open up new opportunities for the application of doping and template-directed surface reconfiguration, which holds promise as an effective electrocatalyst for the OER. [Display omitted] • Hydrothermal and electroactivation methods to synthesis Co–Mo/FeS. • Doping Co to increase active sites. • Rapid dissolution of MoO 4 2− facilitates deep surface reconstruction of CoFe 2 O 4. • The synergistic effect of MoO 4 2− and Co increases the FeS intrinsic activity. [ABSTRACT FROM AUTHOR]

Inverse spinels with characteristic structures are one of the most popular electrocatalytic materials, but typically have limited intrinsic activities for oxygen evolution reactions (OER). Here, taking the conventional inverse spinel Fe 3 O 4 as an example, a series of M (M = Ni, Co, Mn) and S co-doped Fe 3 O 4 OER catalysts are selected by the guidance from theoretical simulations, and then experimentally verified by hydrothermally growing M and S co-doped Fe 3 O 4 on iron foams (M,S-Fe 3 O 4 /IF). Based on experimentally and theoretically investigating their OER performance, M,S-Fe 3 O 4 /IF are considered to follow mixed OER mechanisms including adsorbate evolution mechanism and lattice oxygen mechanism, and Ni,S-Fe 3 O 4 /IF and Co,S-Fe 3 O 4 /IF display low overpotentials of 276 and 300 mV at 100 mA cm-2, respectively. Particularly, the Co atoms into S-Fe 3 O 4 /IF serve as promoters for in-situ Fe dissolution and redeposition of electrochemical reconstruction during alkaline OER processes. This work contributes new avenues for designing spinel-type materials with mixed OER mechanisms. [Display omitted] • M,S-Fe 3 O 4 (M = Ni, Co, Mn) were prepared guided by theoretical simulations. • M and S atoms into Fe 3 O 4 lattice cause lattice distortion and electronic modulation. • The introduction of Co promotes the in-situ redeposition of Fe during alkaline OER. • An AEM electrolyzer using the catalyst delivers a 1 A cm-2 current density at 1.94 V. • A mixed OER mechanism including both AEM and LOM is innovatively proposed. [ABSTRACT FROM AUTHOR]

The manganese doped Co 3 O 4 (Mn-Co 3 O 4) with hollow sphere framework exhibited superior OER activity in a wide pH range. Mn atom substitution increased the ratio of Co3+/Co2+, and enhanced the covalency of metal-oxygen (M−O) bonds. The increased high valency of Co led to the d-band center modification of Mn-Co 3 O 4 , which decreased the adsorption energy in RDS. [Display omitted] • The target catalyst Mn-Co 3 O 4 exhibited superior OER activities in wide-pH range. • Mn atom substitution increased the ratio of Co3+/Co2+, and enhanced the covalency of metal-oxygen (M−O) bonds. • The increased high valency of Co led to the d-band center modification of Mn-Co 3 O 4 , which decreased the adsorption energy in RDS. • Hollow sphere structure enabled the catalyst with large surface area and excellent mass transport properties for superior OER dynamics. Heteroatomic substitution of spinel oxides can theoretically optimize oxygen evolution reaction (OER) via redistribution of charges and modification of d-band center. However, the wide pH range of electrocatalysis and catalytic mechanism are still great challenges. Herein, we successfully construct heteroatom Mn-substituted spinel Co 3 O 4 (Mn-Co 3 O 4) with porous hollow sphere structure for highly efficient and wide pH range OER. Benefiting from the atomic Mn-substitution and charge transfer, the Co site in Mn-Co 3 O 4 displays an increased ratio of Co3+/Co2+. Electrochemical measurements demonstrate that Mn-Co 3 O 4 exhibited superior OER activities with small overpotentials of only 305, 520 and 460 mV to afford a current density of 10 mA cm−2 in alkaline, neutral and acidic media, respectively. Meanwhile, Mn-Co 3 O 4 also possesses favorable long-term stability in wide-pH electrolyte. The improved reaction kinetics of Mn-Co 3 O 4 are mainly attributed to the unique hollow sphere structure with high specific surface area, and the increased high valency of Co, which can introduce the d-band center modification of Mn-Co 3 O 4 , and reduce the adsorption energy of oxygen intermediates in rate-determining step (RDS). [ABSTRACT FROM AUTHOR]

[Display omitted] • S, Fe-CoP@IF porous nanoneedle structures based on precipitation dissolution equilibrium. • S, Fe dual doping strategy precisely regulates the crystal structure of CoP. • The excellent stability and activity of S, Fe-CoP@IF shows potential for industrialization. • DFT reveals that dual doping promotes H* adsorption on CoP and facilitates the charge transfer rate. Transition metal phosphides (TMPs) have been proved as promising catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, CoP has a strong hydrogen adsorption energy, resulting in a slow Heyrovsky step in the HER. Herein, the solid phase FeS is ionized into S and Fe ions and doped into cobalt precursor during the hydrothermal process based on the precipitation dissolution equilibrium principle, and the doping strategy precisely regulated the atomic ratio of metal/P. The optimized S, Fe-CoP@IF one-dimensional porous nanoneedles structure exhibit excellent HER performance, which only required 82.3 mV and 200.1 mV to achieve 100 mA cm−2 and 3 A cm−2 together with high currents stability for 100 h. It also has better OER performance, with 260 mV reaching 100 mA cm−2. Further simulated industrial test for S, Fe-CoP@IF in alkaline anion-exchange membrane (AEM) cells show that only 1.75 V is required to attain 500 mA cm−2. Density functional theory (DFT) calculations confirmed that the dual-doping further modulates the electronic structure of CoP, reduces the Gibbs free energy for hydrogen adsorption. This work provides the possibility to further improve the catalytic activity of cobalt phosphide and apply it to industrial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfur doping NiFe 2 O 4 nanocones arrays on iron foam (S-NiFe 2 O 4 /IF) are obtained. • Low-valence Ni in tetrahedron sites are more actives sites than high-valence Fe atom. • S introduction optimizes the adsorption of OER intermediates on Ni sites. • S-NiFe 2 O 4 /IF achieves an industrial 500 mA cm−2 at overpotential of 310 mV for 100 h. • An AEM electrolyzer using S-NiFe 2 O 4 /IF delivers a 1 A cm−2 current density at 1.79 V. The microstructure of active centers in bimetallic/multimetallic catalysts is under a long-time debate toward oxygen evolution reaction (OER). Here, sulfur doping NiFe 2 O 4 nanocone arrays on iron foams (S-NiFe 2 O 4 /IF) is prepared via a scalable hydrothermal method. The favorable 3D nanocone arrays can offer large electrochemical surface area and allow for effective electrolyte access and O 2 escape. Physical characterizations confirm low-valence Ni atoms in tetrahedron sites are more actives sites than high-valence Fe atoms in this S-doped bimetallic catalyst. Meanwhile, DFT calculations further verify the S introduction enhances the adsorption and dissociation of water, and optimizes the adsorption of OER intermediates on Ni sites. Therefore, the optimal S-NiFe 2 O 4 /IF achieves industrial-level 500 mA cm−2 at an overpotential of only 310 mV and maintains for 100 h in an alkaline medium. In addition, integrating S-NiFe 2 O 4 /IF into an anion-exchange membrane water electrolyzer can deliver a current density of 1.0 A cm−2 at 1.79 V. [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]

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]