Enhancing Hydrogen Evolution Reaction via Synergistic Interaction between the [Mo 3 S 13 ] 2- Cluster Co-Catalyst and WSe 2 Photocathode.

A thiomolybdate [Mo 3 S 13 ] 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 (NH 4 ) 2 Mo 3 S 13 solution both on FTO glass substrates as hydrogen evolving electrodes and on highly 00.1-textured WSe 2 for photoelectrochemical water splitting. As an electrocatalyst, [Mo 3 S 13 ] 2- clusters demonstrate a low overpotential of 220 mV at 10 mA cm -2 in 0.5 M H 2 SO 4 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 WSe 2 , [Mo 3 S 13 ] 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 [Mo 3 S 13 ] 2- cluster film, promoted HER catalytic activity of [Mo 3 S 13 ] 2- clusters influenced by the WSe 2 support, are revealed by intensity-modulated photocurrent spectroscopy and density functional theory calculations, respectively. The band alignment of the WSe 2 /[Mo 3 S 13 ] 2- heterojunction, which facilitates the electron injection, is determined by correlating UV-vis with photoelectron yield spectroscopy results.