The serpentine germanate materials are promising oxygen evolution reaction (OER) electrocatalysts due to their unique layered crystal structure and electronic structure. However, the catalytic activities still need to be improved to satisfy the practical applications. Adjusting the d-band center of metal active site to balance the adsorption and desorption of intermediates is considered an effective approach to improve the OER activity. In this work, an element dopant strategy was proposed to optimize the d-band state of Ni3Ge2O5(OH)4 serpentine to improve the OER activity. The density functional theory calculations revealed that Fe3+ doping increased the d-band center of the Ni3Ge2O5(OH)4 serpentine, which optimized the adsorption strength of intermediates on surface Ni and Fe atoms so that the Fe3+ doped Ni3Ge2O5(OH)4 (Ni2.25Fe0.75Ge2O5(OH)4) exhibited much reduced Gibbs free energy changes in the rate-determining step compared with pristine serpentine. Inspired by the theoretical calculations, the Ni x Fe3–x Ge2O5(OH)4 nanosheets with different amounts of doped Fe3+ were designed and synthesized. The structural characterizations indicated that Fe3+ was successfully doped into Ni3Ge2O5(OH)4 and replaced the Ni2+. The Fe3+ doped Ni x Fe3–x Ge2O5(OH)4 nanosheets showed greatly improved OER activity than Ni3Ge2O5(OH)4 and Fe3Ge2O5(OH)4. Further electrochemical analysis illustrated that Fe3+ doping reduced the adsorptive/formative resistance of intermediates and the charge transfer resistance and facilitated the kinetic process of OER. The in situ Raman spectra indicated that the Fe3+ doped Ni3Ge2O5(OH)4 possesses a more active Ni–O bond than pristine Ni3Ge2O5(OH)4. This work provides an effective strategy to tune the d-band center of serpentines for efficient electrocatalytic OER.

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Transition-metal-based layered serpentine materials are promising as cheap and active electrocatalysts for the oxygen evolution reaction (OER). However, the serpentine materials have poor conductivity and chemical stability, which induce that the activity and stability of these materials are not favorable. Herein, Ni3Ge2O5(OH)4 nanosheets are designed to grow on highly conductive porous Mo2N materials to form composite catalysts for the electrochemical OER. The fabrication of Mo2N/Ni3Ge2O5(OH)4 is achieved via facile hydrothermal methods, and a series of characterizations show that the Ni3Ge2O5(OH)4 nanosheets are anchored on porous Mo2N. The as-synthesized composite materials show a remarkably reduced OER overpotential and improved durability compared to pure Ni3Ge2O5(OH)4 in an alkaline electrolyte. The electrochemical impedance spectroscopy and in situ Fourier transform infrared spectra reveal that Mo2N can efficiently promote the charge transmission and act as a stable substrate to maintain the electrochemical activity. This study provides a facile strategy to design composite-layered serpentine catalysts for an efficient OER.

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