The TPC shows, at certain potentials, that there are two time constants. The faster component is associated with charge transfer while the slow one is related to the charge accumulation at the RuOx catalyst (the latter one not being visible in the EIS as the stabilization time at each potential step was long enough to allow the catalyst to reach equilibrium at a certain DC potential). The charge transfer time is also close to the value determined by intensitymodulated photocurrent spectroscopy in the previously reported Sb2Se3 photocathode with the same device configuration (Au/Sb2Se3/TiO2/RuOx, ~ 3 ms at 0.1 VRHE). The time constants obtained by other methods verify that the R-C element in our model at the lowest frequency range before and shortly after the actual onset of the photocurrent is associated with the charge transfer reaction of electrons from the RuOx catalyst to the electrolyte solution.