High-performance BiVO4 photoanodes : elucidating the combined effects of Mo-doping and modification with cobalt polyoxometalate

Abstract

Bulk doping of BiVO4 with molybdenum combined with surface modification with a cobalt polyoxometalate water oxidation catalyst (CoPOM = Na10[Co4(H2O)2(PW9O34)2]) is reported. The best-performing Mo–BiVO4/CoPOM photoanode exhibits a photocurrent density of 4.32 mA cm−2 at 1.23 V vs. RHE under AM 1.5G (1 sun) illumination and an applied-bias photoconversion efficiency (ABPE) of ∼0.73%, which is an improvement by a factor of ∼24 with respect to pristine BiVO4. Mechanistic analyses are used to prove the contributions of Mo-doping and CoPOM modification. Mo-doping is shown to result in enhanced electronic conductivity and passivation of surface states, whereby these beneficial effects are operative only at relatively high applied bias potentials (>0.9 V vs. RHE), and at lower bias potentials (<0.7 V vs. RHE) they are counterbalanced by strongly detrimental effects related to increased concentration of electron polaronic states induced by the Mo-doping. CoPOM deposition is related to the enhancement of water oxidat