MoO42− doped Ni-Fe-Se nanospheres electrodeposited on nickel foam as effective electrocatalysts for oxygen evolution reaction

Arming Amorphous NiMoO4 on Nickel Phosphide Enables Highly Stable Alkaline Seawater Oxidation

Seawater electrolysis holds tremendous promise for the generation of green hydrogen (H2). However, the system of seawater-to-H2 faces significant hurdles, primarily due to the corrosive effects of chlorine compounds, which can cause severe anodic deterioration. Here, a nickel phosphide nanosheet array with amorphous NiMoO4 layer on Ni foam (Ni2P@NiMoO4/NF) is reported as a highly efficient and stable electrocatalyst for oxygen evolution reaction (OER) in alkaline seawater. Such Ni2P@NiMoO4/NF requires overpotentials of just 343 and 370 mV to achieve industrial-level current densities of 500 and 1000 mA cm-2, respectively, surpassing that of Ni2P/NF (470 and 555 mV). Furthermore, it maintains consistent electrolysis for over 500 h, a significant improvement compared to that of Ni2P/NF (120 h) and Ni(OH)2/NF (65 h). Electrochemical in situ Raman spectroscopy, stability testing, and chloride extraction analysis reveal that is situ formed MoO4 2-/PO4 3- from Ni2P@NiMoO4 during the OER test to the electrode surface, thus effectively repelling Cl- and hindering the formation of harmful ClO-.

Adjusting the valence band center of Co-Ni-bimetallic sulfides through lattice expansion and stacking faults triggered by strain engineering to boost oxygen evolution reaction

Stress engineering can improve catalytic performance by straining the catalyst lattice. An electrocatalyst, Co₃S₄/Ni₃S₂-10%Mo@NC, was prepared with abundant lattice distortion to boost oxygen evolution reaction (OER). With the assistance of the intramolecular steric hindrance effect of metal-organic frameworks, slow dissolution by MoO₄^2- of the Ni substrate and recrystallization of Ni²⁺ was observed in the process of Co(OH)F crystal growth with mild temperature and short time reaction. The lattice expansion and stacking faults created defects inside the Co₃S₄ crystal, improved the material conductivity, optimized the valence band electron distribution of the material, and promoted the rapid conversion of the reaction intermediates. The presence of reactive intermediates of the OER under catalytic conditions was investigated using operando Raman spectroscopy. The electrocatalysts exhibited super high performance, a current density of 10 mA cm^-2 at an overpotential of 164 mV and 100 mA cm^-2 at 223 mV, which were comparable to those of integrated RuO₂. Our work for the first time demonstrates that the dissolution-recrystallization triggered by strain engineering is a good modulation approach to adjust the structure and surface activity of catalyst, suggesting promising industrial application.

Tunable d-band center of a NiFeMo alloy with enlarged lattice strain enhancing the intrinsic catalytic activity for overall water-splitting

Developing efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) under alkaline conditions is prospective for reducing energy consumption during water electrolysis. In this work, we successfully synthesized nanocluster structure composites composed of NiFeMo alloys with controllable lattice strain by the electrodeposition method at room temperature. The unique structure of NiFeMo/SSM (stainless steel mesh) facilitates the exposure of abundant active sites and promotes mass transfer and gas exportation. The NiFeMo/SSM electrode exhibits a low overpotential of 86 mV at 10 mA cm^-2 for the HER and 318 mV at 50 mA cm^-2 for the OER, and the assembled device reveals a low voltage of 1.764 V at 50 mA cm^-2. Moreover, both the experimental results and theoretical calculations reveal that the dual doping of Mo and Fe can induce the tunable lattice strain of nickel, which in turn changes the d-band center and electronic interaction of the catalytically active site, and finally enhances the HER and OER catalytic activity. This work may provide more options for the design and preparation of bifunctional catalysts based on non-noble metals.

In Situ Fabrication of Mn-Doped NiMoO4 Rod-like Arrays as High Performance OER Electrocatalyst

The slow kinetics of the oxygen evolution reaction (OER) is one of the significant reasons limiting the development of electrochemical hydrolysis. Doping metallic elements and building layered structures have been considered effective strategies for improving the electrocatalytic performance of the materials. Herein, we report flower-like nanosheet arrays of Mn-doped-NiMoO₄/NF (where NF is nickel foam) on nickel foam by a two-step hydrothermal method and a one-step calcination method. The doping manganese metal ion not only modulated the morphologies of the nickel nanosheet but also altered the electronic structure of the nickel center, which could be the result of superior electrocatalytic performance. The Mn-doped-NiMoO₄/NF electrocatalysts obtained at the optimum reaction time and the optimum Mn doping showed excellent OER activity, requiring overpotentials of 236 mV and 309 mV to drive 10 mA cm^-2 (62 mV lower than the pure NiMoO₄/NF) and 50 mA cm^-2 current densities, respectively. Furthermore, the high catalytic activity was maintained after continuous operation at a current density of 10 mA cm^-2 of 76 h in 1 M KOH. This work provides a new method to construct a high-efficiency, low-cost, stable transition metal electrocatalyst for OER electrocatalysts by using a heteroatom doping strategy.

Electro-enhanced sulfamethoxazole degradation efficiency via carbon embedding iron growing on nickel foam cathode activating peroxymonosulfate: Mechanism and degradation pathway

The combination of peroxymonosulfate (PMS) activation by hetero-catalysis and electrolysis (EC) attracted incremental concerns as an efficient antibiotics degradation method. In this work, carbon embedding iron (C@Fe) catalysts growing on nickel foam (NF) composite cathode (C@Fe/NF) was prepared via in-situsolvothermal growth and carbonization method and used to activate PMS toward sulfamethoxazole (SMX) degradation. The EC-[C@Fe/NF(II)]-PMS system exhibited an excellent PMS activation, with 100% SMX removal efficiency achieving within 30 min. Reactive oxygen species (ROS) generation and their roles in SMX degradation were confirmed by quenching experiments and electron paramagnetic resonance. It was found that singlet oxygen (¹O₂) and surface-bound radicals were responsible for SMX degradation, and ¹O₂ contributed the most. Furthermore, the possible SMX degradation pathways were proposed on the base of the detected degradation intermediates and density functional theory (DFT) calculation. Toxicity changes were also assessed by the Ecological Structure Activity Relationships (ESAR). This work provides a practicable strategy for synergistically enhancing PMS activation efficiency and promoting antibiotics removal.

Construction of superhydrophilic metal-organic frameworks with hierarchical microstructure for efficient overall water splitting

Metal-organic frameworks (MOFs) display promising potential due to their exquisite structural advantages. Carboxylate-based MOFs, such as MIL-53 structures, attract a lot of attention among MOF families because of their remarkable stability in water and even alkaline condition. Hence, the delicate hierarchical microstructure is constructed by introducing MoO₄^2- into NH₂-MIL-53(NiFe) using a straightforward solvothermal strategy. The NiFeMo-MOF/NF electrode manifests a superior OER performance, producing an overpotential of 239 mV at 50 mA cm^-2 and a decent Tafel slope of 87.0 mV dec^-1. Furthermore, in a typical electrodeposition equipment, NiFeMo-MOF/NF is applied as the working electrode and the composite electrode named as (M) Ni-NiOOH/NF is generated by electrodeposition and electrooxidation process to assess HER performance, producing an overpotential of 119 mV at 50 mA cm^-2 and a decent Tafel slope of 58.3 mV dec^-1. The integrated electrolysis device delivers an extraordinarily low cell voltage of 1.50 V at 10 mA cm^-2 while applying NiFeMo-MOF/NF as the anode, (M)Ni-NiOOH/NF as the cathode for overall water splitting, exceeding the noble RuO₂/NF||Pt-C/NF (1.60 V@10 mA cm^-2). This study provides a promising design strategy for future electrolysis catalysts.

Synergistic coupling of FeOOH with Mo-incorporated NiCo LDH towards enhancing the oxygen evolution reaction

FeOOH-modified NiCoMo LDH/NF with excellent OER activity and stability was successfully prepared using a hydrothermal method combined with electrodeposition.