Enhancing Hydrogen Evolution Reaction via Synergistic Interaction between the [Mo₃S₁₃]^2- Cluster Co-Catalyst and WSe₂ Photocathode

A thiomolybdate [Mo₃S₁₃]^2- nanocluster is a promising catalyst for hydrogen evolution reaction (HER) due to the high number of active edge sites. In this work, thiomolybdate cluster films are prepared by spin-coating of a (NH₄)₂Mo₃S₁₃ solution both on FTO glass substrates as hydrogen evolving electrodes and on highly 00.1-textured WSe₂ for photoelectrochemical water splitting. As an electrocatalyst, [Mo₃S₁₃]^2- clusters demonstrate a low overpotential of 220 mV at 10 mA cm^-2 in 0.5 M H₂SO₄ electrolyte (pH 0.3) and remain structurally stable during the electrochemical cycling as revealed by in situ Raman spectroscopy. Moreover, as a co-catalyst on WSe₂, [Mo₃S₁₃]^2- clusters enhance the photocurrent substantially by more than two orders of magnitude (from 0.02 to 2.8 mA cm^-2 at 0 V vs RHE). The synergistic interactions between the photoelectrode and catalyst, i.e., surface passivation and band bending modification by the [Mo₃S₁₃]^2- cluster film, promoted HER catalytic activity of [Mo₃S₁₃]^2- clusters influenced by the WSe₂ support, are revealed by intensity-modulated photocurrent spectroscopy and density functional theory calculations, respectively. The band alignment of the WSe₂/[Mo₃S₁₃]^2- heterojunction, which facilitates the electron injection, is determined by correlating UV-vis with photoelectron yield spectroscopy results. © 2022 The Authors. Published by American Chemical Society.