The performance of all three photoanodes was also examined by repeated linear sweep voltammetry (LSV) under chopped illumination in aqueous borate electrolyte at pH 9.0 (Figure , Supporting Information). For the modified Composite 1 and Composite 2 electrodes, we noticed slightly increasing photocurrents between the 1 st and 2 nd LSV scan. We suggest that this might be due to the oxidation of the Co from Co 2+ to Co 3+ in the surface layer, accompanied by partial conversion of CoPOM into cobalt oxide. This was verified by performing the identical experiment with the individual, Co-, W-or P-doped BiVO4 (Figure , Supporting Information), where a similar initial photocurrent increase was only observed for the Co-doped BiVO4 sample, while samples doped only with W or P did not show this initial increase of photocurrents. Notably, after the initial increase, photocurrents of the Co-doped BiVO4 then dropped (Figure , Supporting Information), suggesting that this sample is not stable under the operational conditions. Note that in the presence of both dopants, Co and W (Figure and S13g, Supporting Information), we observe the characteristic behaviour observed for the CoPOM-doped sample, i.e. initial increase of the photocurrent between LSV run 1 and run 2, and stable photocurrents afterwards. These data again corroborate our hypothesis of a combined beneficial synergistic effect of doping with both Co and W on the BiVO4 photoanode performance.