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

[Image: see text] 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.