Highly (001)-textured p-type WSe₂ Thin Films as Efficient Large-Area Photocathodes for Solar Hydrogen Evolution

Highly (001)-textured, photoactive WSe₂ 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 WSe₂ films can be improved significantly. However, these as-crystallized WSe₂ films are only weakly photoactive in a 0.5 М H₂SO₄ electrolyte under AM 1.5 solar irradiation which we attribute to an inefficient photogenerated charge transfer across the WSe₂/electrolyte interface via the prevailing van der Waals planes of the WSe₂ crystallites. In this work photochemically deposited platinum on the p-type WSe₂ photocathode is used for an efficient electron transfer thus inducing the hydrogen evolution reaction. Upon illuminating the WSe₂ 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 WSe₂, i.e. at the grain boundaries of the WSe₂ 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 WSe₂ thin films.