Importantly, the beneficial effect of CoPOM deposition is unambiguously demonstrated to be related to the enhancement of water oxidation catalysis, whereby the borate electrolytes show a more beneficial effect on the stability of PEC performance as compared to phosphate-based electrolytes. Furthermore, the experimental evidence shows that under the PEC operating conditions the molecular CoPOM is, at least partially, disintegrated and converted to cobalt oxide, and is therefore best conceived as a pre-catalyst. Taken together, our work establishes CoPOM-derived catalysts as effective water oxidation catalysts at BiVO4 photoanodes, provides new insights into the combined effects of Mo-doping and modification with molecular cobalt polyoxometalates on the PEC performance of BiVO4, and suggests that further progress in the development of BiVO4 photoanodes depends critically on devising alternative doping strategies to overcome the negative polaronic effects associated with bulk doping of BiVO4, since these detrimental effects set fundamental limits to the maximum achievable photovoltage and thus compromise the overall photoconversion efficiency.