"Double-Use" Strategy for Improving the Photoelectrochemi-cal Performance of BiVO4 Photoanodes using a Cobalt-Functionalized Polyoxotungstate

ABSTRACT: A ‘Double-Use’ strategy for the development of high-performance bismuth vanadate (BiVO4) photoanodes for solar water splitting is reported, where a molecular cobalt-phosphotungstate (CoPOM = Na10[Co4(H2O)2(PW9O34)2]) is used both as a bulk doping agent as well as a surface-deposited water oxidation co-catalyst. The use of CoPOM for bulk doping of BiVO4 is shown to enhance the electrical conductivity and improve the charge separation efficiency, resulting in the enhancement of the maximum applied-bias photoconversion efficiency (ABPE) by a factor of ~18 to 0.54% at 0.87 V vs. RHE, as compared to pris-tine BiVO4 (0.03% at 1.04 V vs. RHE). In addition, modification of CoPOM-doped BiVO4 with CoPOM as a surface co-catalyst enhances the hole extraction and improves the water oxidation kinetics, resulting in the overall enhancement of the ABPE to 0.79% (at 0.82 V vs. RHE), i.e. by a factor of ~26 with respect to pristine BiVO4. This study establishes the ‘double-use’ strategy involving CoPOMs as an effective, straightforward and easily scalable approach for the development of high-quality photoanodes for solar water splitting, and highlights the future potential of utilizing well-designed polyoxometalates as precursors for the syn-thesis of energy materials.