In conclusion, we have demonstrated a novel 'Double-Use' strategy for fabrication of high-performance BiVO4 photoanodes for solar water splitting in which a single precursor, a molecular cobalt polyoxometalate (CoPOM), is used both as a doping agent and as a co-catalyst for water oxidation. Doping BiVO4 by CoPOM significantly enhances the conductivity and improves the charge separation efficiency, resulting in the enhancement of the maximum applied-bias photoconversion efficiency (ABPE) by a factor of ~18 as compared to pristine BiVO4. Further surface modification of CoPOM-doped BiVO4 with CoPOM as a co-catalyst enhances the hole extraction and improves the water oxidation kinetics, yielding the overall enhancement of the ABPE as high as by a factor of ~26 with respect to pristine BiVO4. Interestingly, with respect to the doped BiVO4 photoanodes, we found systematic differences in the surface composition and PEC performance of samples doped with CoPOM as compared to samples with identical elemental composition but doped with metal salts. While these differences are not fully understood yet, they point to possible advantages of using molecularly well-defined precursors, such as CoPOM, in fabrication of high-performance photoelectrodes. Taken together, our results establish the 'Double-Use' strategy involving CoPOMs as a remarkably effective, straightforward and easily scalable approach for the development of high-quality photoanodes for solar water splitting and highlight the future potential of utilizing well-designed polyoxometalates as precursors for the synthesis of energy materials.