A Universal Process: Self-Templated and Orientated Fabrication of XMoO₄ (X: Ni, Co, or Fe) Nanosheets on MoO₂ Nanoplates as Electrocatalysts for Efficient Water Splitting

Abstract

Fabrication of superior nonprecious electrocatalysts is essential for water electrolysis. Herein, the epitaxial growth of the XMoO₄ (X = Ni, Co, Fe) nanosheets on the hexagonal MoO₂ nanoplates are carried out. The preoxidation of MoO₂ nanoplate is fatal to the epitaxial growth of a nanosheets array on MoO₂ nanoplates. The hierarchical heterostructure of the vertically aligned NiMo nanosheets on MoO₂ nanoplate (NiMo/MoO₂) is well-maintained in the process of <i>in situ</i> topotactic reduction transformation from NiMoO₄·<i>x</i>H₂O/MoO₂. Attributing it to the rich electroactive sites from nanosheets array, together with the intrinsic electrocatalytic performance of NiMo alloy, the as-engineered NiMo/MoO₂ as electrocatalyst exhibits admirable hydrogen evolution reaction (HER) activity with a small onset potential of -12 mV <i>vs</i> RHE (1 mA cm^-2) and a tafel value of 43.6 mV dec^-1 at alkaline media. Furthermore, the obtained CoMoO₄/MoO₂ possesses excellent oxygen evolution performance, which is verified by an ultralow overpotential of 230 mV@10 mA cm^-2, small Tafel slope (51 mV dec^-1), and robust durability. The developed NiMo/MoO₂ and CoMoO₄/MoO₂ electrocatalysts are assembled into an alkaline electrolyzer, which affords a cell potential of 1.51 V at 10 mA cm^-2, as well as outstanding operational durability, which is superior to the typically constructed 20 wt % Pt/C-RuO₂ system (1.59 V at 10 mA cm^-2). Hence, the universal strategy using MoO₂ nanoplates as Mo source and epitaxial substrate may be extended to explore and construct economical and superior Mo-based electrocatalysts for water electrolysis.