Three-Dimensional Bicontinuous BiVO₄/ZnO Photoanodes for High Solar Water-Splitting Performance at Low Bias Potential

A photoanode capable of high-efficiency water oxidation at low bias potential is essential for its practical application for photocathode-coupled tandem systems. To address this issue, a photoanode with low turn-on voltage for water oxidation and high charge separation efficiency at low bias potential is essential. In this study, we demonstrate the photoanode of the BiVO4/ZnO three-dimensional (3D) bicontinuous (BC) structure. ZnO has a relatively cathodic flat-band potential, which leads to low turn-on potential; the BiVO4/ZnO 3D BC photoanode shows an onset potential of 0.09 V versus the reversible hydrogen electrode (VRHE). Moreover, we achieve remarkably high charge separation efficiency at low bias potential (78% at 0.6 VRHE); this is attributed to the application of thin-film BiVO4 shells by high light-scattering properties of the 3D BC structure. As a result, the BiVO4/ZnO 3D BC photoanode generates a high water oxidation photocurrent of up to 3.4 ± 0.2 mA cm–2 (with CoPi catalyst coating). This photocurrent value is reproducible, and the photocurrent-to-O2 conversion efficiency is over 90%. To the best of our knowledge, this is the highest value among the values of the photocurrent at 0.6 VRHE in previous BiVO4-based heterojunction photoanodes.