Taken together, all these findings indicate that the 'Double-Use' of CoPOM as both a dopant and a surface co-catalyst can effectively promote the charge separation and hole transfer carrier dynamics at BiVO4 photoanodes, respectively, in line with the established knowledge on the effects of doping and co-catalysts in the literature. To confirm the actual oxygen evolution performance of the photoanodes, we performed photoelectrocatalytic OER measurements (Figure ) in an aqueous borate solution (pH 9.0) under AM 1.5G (1 sun) illumination at E = 0.80 V vs. RHE. Under these conditions, we observed O2 evolution rates of 104.1 ± 18.5 µmol L -1 h -1 (BiVO4), 504.7 ± 26.7 µmol L -1 h -1 (Composite 1) and 856.9 ± 33.3 µmol L -1 h -1 (Composite 2) during a 20 min illumination experiment. The corresponding faradaic efficiencies are comparable for the three systems (BiVO4:102.7% ± 13.2%; Composite 1: 97.5% ± 9.5%, Composite 2: 102.3% ± 12.2%), indicating the nearly quantitative oxygen evolution at all BiVO4 photoanodes. Finally, the applied-bias photoconversion efficiency (ABPE) was also determined. As shown in Figure , the maximum photoconversion efficiencies are 0.03% (at 1.04 V vs. RHE) for BiVO4, 0.54% (at 0.87 V vs. RHE) for Composite 1, and 0.79% (at 0.82 V vs. RHE) for Composite 2. Two points are noteworthy. Firstly, the fact that the maximum power point is shifted to more negative bias potentials after doping and surface modification with CoPOM is highly beneficial in view of potential construction of tandem tandem solar-driven water splitting systems in which photoanodes for O2 evolution are combined with photocathodes for H2 evolution. Secondly, the maximum ABPE of 0.79% (at 0.82 V vs. RHE) for the Composite 2 is not only higher by a factor of ~26 as compared to pristine BiVO4, but even slightly higher than the best performing Mo-doped BiVO4 photoanode modified with CoPOM cocatalyst (ABPE of 0.73% at 0.86 V vs. RHE) we investigated recently. This highlights the beneficial effect of the 'Double-Use' strategy employing CoPOM on the fabrication of BiVO4 photoanodes with improved performance.