Unraveling compositional effects on the light-induced oxygen evolution in Bi(V–Mo–X)O4 material libraries

Abstract

The influence of co-deposited transition metals X (X = Ta, W, Nb) with various relative concentrations on the photoelectrochemical performance of BiVO₄ is investigated. Thin film material libraries with well-defined composition gradients of Bi, V and two transition metals are fabricated by combinatorial sputter co-deposition. Materials with the highest photoelectrochemical performance are identified by high-throughput characterization of the Bi(V–Mo–X)O₄ material libraries using an optical scanning droplet cell. Bi(V–Mo–W)O₄ and Bi(V–Mo–Nb)O₄ material libraries show the highest improvement in the photocurrent, with ten times higher photocurrents of up to 1 mA cm⁻² compared to a BiVO₄ reference material library. Deviations from the V : Bi equiatomic ratio lead to a decrease in the photocurrent for pristine monoclinic BiVO₄. By the addition of transition metals this effect is minimized and no significant decrease in the photocurrent occurs up to 10 at% variation from the equiatomic V : Bi ratio. Excellent photoelectrochemical performance is reached under these conditions in regions with a V : Bi atomic ratio of 70 : 30 and co-deposited Nb concentrations of >10 at%. Scanning photoelectrochemical microscopy allows the evaluation of the correlation between the generated oxygen at a photoanode and the measured photocurrent.