Abstract
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 VRHE in sulfuric acid, the highest reported value up to now for WSe2 thin films.
Highlights
(001)-textured, photoactive WSe2 thin films have been prepared by an amorphous solid-liquidcrystalline solid process promoted by palladium
In the present work we demonstrate the highly textured crystallization of WSe2 films on a conductive back contact and that the photodeposition of Pt islands improves the photoactive properties of polycrystalline WSe2 thin films significantly, allowing the application of these films for solar hydrogen generation
With increasing thickness of the Pd-promoter film the crystalline quality of the WSe2 films is considerably improved, which is obvious from the increase of the (002 l)-peak (l = 1–5) intensities by several orders of magnitude, and the corresponding decrease of the full widths at half maximum (FWHM) of the (002) diffraction peaks
Summary
(001)-textured, photoactive WSe2 thin films have been prepared by an amorphous solid-liquidcrystalline solid process promoted by palladium. McKone et al showed that a p-type, niobium-doped WSe2 single crystal, coated with a Pt/ Ru catalyst, splits water with a solar-to-hydrogen conversion efficiency of more than 7%15. A thin catalytically active Pt/Ru metal film on the WSe2 crystal surface significantly promoted the charge (electron) transfer from the cathode into the electrolyte, leading to a photocurrent density of up to 25 mA cm−2 at 0 VRHE in an acidic solution
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