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 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 in situ topotactic reduction transformation from NiMoO4·xH2O/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 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 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.