Insight into the PEC and interfacial charge transfer kinetics at the Mo doped BiVO(4) photoanodes

BiVO(4) is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency. Herein, we have investigated the effect of Mo doping on SnO(2) buffer layer coated BiVO(4) for PEC water splitting. SnO(2) and Mo doped BiVO(4) layers are coated with layer by layer deposition through a precursor solution based spin coating technique followed by annealing. At 5% doping of Mo, the sample (SBM5) shows a maximum current density of 1.65 mA cm(−2) at 1.64 V vs. RHEl in 0.1 M phosphate buffer solution under AM 1.5 G solar simulator, which is about 154% improvement over the sample without Mo (SBM0). The significant improvement in the photocurrent upon Mo doping is due to the improvement of various bulk and interfacial properties in the materials as measured by UV-vis spectroscopy, electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis, and open-circuit photovoltage (OCPV). The charge transfer kinetics at the BiVO(4)/electrolyte interface are investigated to simulate the oxygen evolution process in photoelectrochemical water oxidation in the feedback mode of scanning electrochemical microscopy (SECM) using 2 mM [Fe(CN)(6)](3−) as the redox couple. SECM investigation reveals a significant improvement in effective hole transfer rate constant from 2.18 cm s(−1) to 7.56 cm s(−1) for the hole transfer reaction from the valence band of BiVO(4) to [Fe(CN)(6)](4−) to oxidize into [Fe(CN)(6)](3−) with the Mo doping in BiVO(4). Results suggest that Mo(6+) doping facilitates the hole transfer and suppresses the back reaction. The synergistic effect of fast forward and backward conversion of Mo(6+) to Mo(5+) expected to facilitate the V(5+) to V(4+) which has an important step to improve the photocurrent.