Time-resolved photo-electrochemical measurements to study band bending of BiVO4 photoanodes

The oxide semiconductor BiVO4 is a promising photoanode for the oxygen evolution reaction (OER) under visible light. It is a well-suited model photo-anode for the time-resolved investigation of light-pulse-induced space charge layer reorganization and electron-transfer chemistry at BiVO4-electrolyte interfaces. In order to study the different timescales of the photo-capacitive and photo-chemical processes including the effect of defect states, a time-resolved photo-electrochemical rotating ring-disk electrode setup with a time-resolution of better than 1 ms is developed. Measurements were performed under dark, continuous and chopped illumination using a LED array that simulates the AM 1.5G spectrum. Cyclic voltammetry measurements revealed four different regions for the photocurrents which can be associated with different states of band bending and allow for the determination of the flat band potential. The photocurrent transients during switch-on and -off of the LED array shows an exponential time evolution with three time-constants that are attributed to (1) fast reorganization of the space charge layer, (2) slower onset / relaxation of the photocatalytic OER and (3) very slow photo-corrosion. These findings help to understand the interplay between photo-induced space charge reorganization and OER related charge transfer in the electrochemical double layer during photocatalytic water splitting.