Fast solvent evaporation of phase pure CuBi2O4 photocathodes for photoelectrocatalytic water splitting

P-type metal oxide semiconductor CuBi₂O₄ exhibits excellent energy band structures and photoelectric response characteristics, which are critical for photoelectrocatalytic water splitting. However, the photocurrent densities are still well below the theoretical limit due to poor charge carrier separation and transport properties. In this work, we report a synthetic method for the preparation of phase-pure CuBi₂O₄ photocathode films via spray pyrolysis by adjusting the evaporation rate of the atomized droplets. An increase in the evaporation rate of the solvent may fix the structure of the deposited film faster and decrease the time available for the establishment of the segregation gradient, thus producing phase-pure semiconductor films. This method reduces process complexity and cost, and the applicability of spray pyrolysis for the preparation of phase-pure CuBi₂O₄ films is also confirmed. In addition, the photoelectrochemical evaluation of the samples prepared under different treatment conditions reveals that hole transport critically affects the photoelectrocatalytic performance of CuBi₂O₄ photocathodes. CuO can be used as a hole transport layer to promote the collection and transfer of holes and reduce the recombination of photogenerated carriers.