Hydrogen Evolution from Pt/Ru-Coated p-Type WSe_2 Photocathodes

Abstract

Crystalline p-type WSe_2 has been grown by a chemical vapor transport method. After deposition of noble metal catalysts, p-WSe_2 photocathodes exhibited thermodynamically based photoelectrode energy-conversion efficiencies of >7% for the hydrogen evolution reaction under mildly acidic conditions, and were stable under cathodic conditions for at least 2 h in acidic as well as in alkaline electrolytes. The open circuit potentials of the photoelectrodes in contact with the H^(+)/H_2 redox couple were very close to the bulk recombination/diffusion limit predicted from the Shockley diode equation. Only crystals with a prevalence of surface step edges exhibited a shift in flat-band potential as the pH was varied. Spectral response data indicated effective minority-carrier diffusion lengths of ~1 μm, which limited the attainable photocurrent densities in the samples to ~15 mA cm^(–2) under 100 mW cm^(–2) of Air Mass 1.5G illumination.

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