Efficient charge transfer at a homogeneously distributed (NH4)2Mo3S13/WSe2 heterojunction for solar hydrogen evolution

Abstract

Highly (00.1)-textured polycrystalline WSe₂ films are developed as hydrogen evolving photoelectrodes and improved through deposition of a thin ammonium thiomolybdate (NH₄)₂Mo₃S₁₃ catalyst film. This semiconducting thiomolybdate forms a heterojunction with the p-type WSe₂ film passivating recombination centers of excited electron–hole pairs at the edges of the (00.1) textured WSe₂ nanoflakes. In addition, thiomolybdate acts as a photoelectrocatalyst at the electrode – aqueous electrolyte interface during light-driven hydrogen evolution. Whereas the photoelectrochemical activity of pure WSe₂ is dominated by charge carrier recombination processes at edge states of the hexagonal nanoflakes, we obtain homogeneous charge transfer across the van der Waals planes concomitant with the passivation of these edge states. A photocurrent density of up to 5.6 mA cm⁻² at 0 V vs. RHE is obtained with the proposed homogeneously distributed (NH₄)₂Mo₃S₁₃/WSe₂ heterojunction system under AM 1.5 illumination in the 0.5 M H₂SO₄ electrolyte. We conclude that homogeneously distributed semiconducting catalysts on the van der Waals planes of WSe₂ nano-crystallites are a feasible strategy towards solar hydrogen evolution with large-area photoelectrocathodes.