Improving the photoelectrocatalytic efficiency of CuWO4 through molybdenum for tungsten substitution and coupling with BiVO4†

Abstract

A systematic investigation on the photoelectrocatalytic (PEC) performance of a series of CuW_1−xMo_xO₄ materials with different Mo for W substitution (x = 0–0.8), successfully synthesized as single, transparent photoactive layers, allowed us to identify copper molybdo-tungstate with x = 0.5 (CuW_0.5Mo_0.5O₄) as the best performing Mo-containing CuWO₄-based material for photoanodes fabrication. For 250 nm thick material, the CuW_0.5Mo_0.5O₄ exhibits a 6-fold photocurrent increase at 1.23 V vs. RHE with respect to pure CuWO₄. Both PEC analyses in the presence of NaNO₂ as sacrificial agent and intensity modulated photocurrent spectroscopy (IMPS) measurements, here applied to this class of materials for the first time, demonstrate that the superior PEC performance of CuW_0.5Mo_0.5O₄ stems from a more efficient separation of photoproduced charges with respect to CuWO₄, while the charge injection efficiency is close to 100% for both materials. Further enhanced separation of photoproduced charges, resulting in increased PEC performance of the CuW_0.5Mo_0.5O₄ electrode in the 400–480 nm wavelength range, can be achieved by coupling it with BiVO₄, to form a type II heterojunction system.