Highly (001)-textured p-type WSe(2) Thin Films as Efficient Large-Area Photocathodes for Solar Hydrogen Evolution

Highly (001)-textured, photoactive WSe(2) thin films have been prepared by an amorphous solid-liquid-crystalline solid process promoted by palladium. By increasing the thickness of the Pd promoter film (≥10 nm) the structure and texture of the WSe(2) films can be improved significantly. However, these as-crystallized WSe(2) films are only weakly photoactive in a 0.5 М H(2)SO(4) electrolyte under AM 1.5 solar irradiation which we attribute to an inefficient photogenerated charge transfer across the WSe(2)/electrolyte interface via the prevailing van der Waals planes of the WSe(2) crystallites. In this work photochemically deposited platinum on the p-type WSe(2) photocathode is used for an efficient electron transfer thus inducing the hydrogen evolution reaction. Upon illuminating the WSe(2) photocathodes in a Pt-ion containing electrolyte, the photogenerated electrons reduce Pt(+) to Pt leading to the precipitation of Pt islands, preferentially at edge steps of the WSe(2), i.e. at the grain boundaries of the WSe(2) crystallites. The increasing amount of Pt islands at the grain boundaries linearly enhances the photocurrent density up to 2.5 mA cm(−2) at 0 V(RHE) in sulfuric acid, the highest reported value up to now for WSe(2) thin films.