Firstly, in order to gain insight into the role of the individual doping elements (Co, W, P) present in CoPOM, we prepared also doped BiVO4 samples where NaWO4•2H2O, Na2HPO4•7H2O, and Co(NO3)2•6H2O were used as sources of the respective elements, and identical molar amounts were incorporated as in the case of Composite 1 photoanodes, see Figure and Figure , Supporting Information. Notably, Co-doping of BiVO4 exerts the positive influence on the photocurrent density also at lower electrode potentials (leading to the significant cathodic shift of the onset potential), while W-doping of BiVO4 enhances photocurrents significantly only at higher bias potentials (> 0.7 V vs. RHE). Interestingly, there is a clear beneficial synergistic effect when both Co-and Wdoping of BiVO4 are used. Furthermore, the photocurrent at the Composite 1 photoanode is slightly higher than that of Composite 3 photoanode in the full potential range. The possible reason is that the ratio of W/Co on the surface of BiVO4 detected by XPS is different (2.29 for the Composite 1 photoanode, 1.08 for the Composite 3 photoanode), as shown in Table , Supporting Information. We hypothesize that this difference in the ratio of W/Co on the surface of the Composite 1 and Composite 3 photoanodes might be due to the different forms of the doping substances. For example, the structure of CoPOM is expected to be partially disintegrated but will still retain its core structure in the acid precursor solution, while the doping solution used for preparation of the reference Composite 3 photoanode is fully homogenous. Apparently, such small differences in the precursor chemistry can influence the ratio of W/Co on the surface and impact the photocurrent generation.