Efficient charge transfer at a homogeneously distributed (NH 4 ) 2 Mo 3 S 13 /WSe 2 heterojunction for solar hydrogen evolution

Highly (00.1)-textured polycrystalline WSe 2 films are developed as hydrogen evolving photoelectrodes and improved through deposition of a thin ammonium thiomolybdate (NH 4 ) 2 Mo 3 S 13 catalyst film. This semiconducting thiomolybdate forms a heterojunction with the p-type WSe 2 film passivating recombination centers of excited electron–hole pairs at the edges of the (00.1) textured WSe 2 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 WSe 2 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 (NH 4 ) 2 Mo 3 S 13 /WSe 2 heterojunction system under AM 1.5 illumination in the 0.5 M H 2 SO 4 electrolyte. We conclude that homogeneously distributed semiconducting catalysts on the van der Waals planes of WSe 2 nano-crystallites are a feasible strategy towards solar hydrogen evolution with large-area photoelectrocathodes.