Enhancing Hydrogen Evolution Reaction via Synergistic Interaction Between [Mo_³S_¹³]^2- Cluster Co-catalyst and WSe_² Photocathode

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 (PEC) 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 (IMPS) and density functional theory (DFT) 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 (PYS) results.