Exploring the potential of transition metal tungstates for photoelectrochemical water oxidation: a combined experimental and computational approach

Abstract

The combination of experimental and computational methodologies offers a reliable strategy to not only discover new materials but also rationalize their performance and their intrinsic limitations. Following this concept, fourth-period metal tungstates (RWO₄, R = Mn, Fe, Co, Ni, Cu or Zn) have been explored for their application as photoanodes for solar water oxidation. The theoretical screening of these materials reveals large effective masses for both electron and hole carriers, while the density of states (DOS) profiles indicate that only Fe and Cu tungstates show adequate features to be photoanodes. This agrees with experimental data showing that they yield the best photocurrents in the series. In fact, FeWO₄ reaches over 0.04 mA cm⁻² at 1.23 V_RHE under one sun, a value 67% higher than the current record. The still low photoactivity is partly linked to the fact that the electrode deviates from the band edge pinning regime over a wide potential range. Under the same conditions, CuWO₄ delivers a photocurrent over 0.3 mA cm⁻², in line with the best results found in the literature. Overall, the exploratory analysis performed in this paper not only identifies the parameters that limit the photoelectrochemical response of a wide range of metal tungstates, but it enables the identification of iron and copper tungstates as promising photoanodes for solar water oxidation whose performance may be enhanced by the implementation of some modification strategies.