Hydrogen Evolution from Pt/Ru-Coated p-Type WSe2 Photocathodes

Crystalline p-type WSe2 has been grown by a chemical vapor transport method. After deposition of noble metal catalysts, p-WSe2 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 similar to 1 mu m, which limited the attainable photocurrent densities in the samples to similar to 15 mA cm(-2) under 100 mW cm(-2) of Air Mass 1.5G illumination.