Electrochemical cycling and beyond: unrevealed activation of MoO3 for electrochemical hydrogen evolution reactions

Abstract

We demonstrate electrochemical cycling-induced reduction of MoO₃ to monoclinic molybdenum dioxide and molybdenum sub-oxides (MoO_3−x), which exhibit excellent electrochemical hydrogen evolution reaction (HER) activity. The conversion of MoO₃ during cycling was probed; after 250 cycles, the redox peaks were found to diminish with an onset potential shift and increased HER current density. At 400 cycles, the insertion/deinsertion processes observed in the initial cycles are completely absent and the HER current density is enhanced to the maximum. The effect of MoO₃ morphology and size on the electrochemical reduction of MoO₃ was also studied.