Evidently, for both CoPOM-free photoanodes (red and blue line), the photocurrent spikes after switching on the light and negative current overshoots after switching off the light (see insert in Fig. ) are significantly more pronounced, demonstrating that in the absence of water oxidation catalyst the charge carriers are prone to intense surface recombination. In other words, in the absence of the CoPOM co-catalyst, the photogenerated holes do not react fast enough with water but accumulate in the surface layer of BiVO4 or Mo-BiVO4, enhancing thus the probability of recombination with electrons. The intense recombination of surface-accumulated holes and electrons leads to a rapid decrease of the photocurrent immediately after switching on the light, and continues even after the light is switched off, as apparent from the negative current overshoot after switching off the light. In contrast, the current spikes are less pronounced and the overshoots are nearly absent at the Mo-BiVO4/CoPOM photoanode, which clearly demonstrates that the CoPOM co-catalyst efficiently extracts the holes photogenerated in the Mo-BiVO4 layer and channels them to water molecules in the electrolyte solution. This explains the significant photocurrent enhancement upon the deposition of CoPOM shown in Fig. and. In this context, we also note that the addition of polyethyleneimine (PEI) as a cationic linker has no effect on the performance of the photoanodes (Fig. ), which highlights the intrinsically good electronic communication between the CoPOM and BiVO4.