The intrinsic hydrogen evolution performance of 2D molybdenum carbide

Abstract

Molybdenum carbide (Mo₂C), a member of transition metal carbides (TMCs), has shown promise in water splitting. Although excellent hydrogen evolution reaction (HER) performance of Mo₂C has been achieved both in acid and basic media, the intrinsic hydrogen evolution ability of two-dimensional (2D) Mo₂C is still not clear due to the difficulty of calculating the actual active surface area involved in the HER. In this work, the HER activity of Mo₂C nanosheets is measured on single 2D Mo₂C, which is synthesized through low-temperature carbonization of 2D molybdenum dioxide (MoO₂) nanosheets on a SiO₂/Si substrate. The edge sites of Mo₂C exhibit high catalytic activity with a small Tafel slope of 40.2 mV dec⁻¹ and an overpotential of 152 mV for 10 mA cm⁻² in alkaline media. Theoretical analyses reveal that the energy barriers for cleaving the OH–H bond in H₂O on the edge of Mo₂C are much smaller than those on the basal plane of Mo₂C and the Mo site of the edge of Mo₂C displays the optimal ΔG_H for the H absorption.