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.

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 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 in situ topotactic reduction transformation from NiMoO4·xH2O/MoO2. Attributing 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 vs. 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@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@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.