Influence of Mo doping on interfacial charge carrier dynamics in photoelectrochemical water oxidation on BiVO4

Abstract

The understanding of interfacial charge transfer processes is vital to the design of efficient photoanodes in photoelectrochemical (PEC) water splitting. Bismuth vanadate (BiVO₄) is a promising photoanode material to drive the oxygen evolution reaction (OER). However, intrinsic BiVO₄ suffers from a slow charge carrier mobility and sluggish OER kinetics, which gives rise to a high charge carrier recombination rate and unsatisfactory photoelectrochemical performance. Although the impact of metal doping of BiVO₄ in the field of photocatalysis and photoelectrochemistry has been investigated in literature, a detailed understanding of the interfacial charge carrier dynamics in dependence of surface configuration is still required for further PEC device optimization. In this work, BiVO₄ film samples were prepared by a modified metal organic precursor decomposition method. Effects of molybdenum (Mo) doping on the photocurrent density, electrochemical impedance spectra and interfacial charge transfer kinetics of BiVO₄ were investigated. Our results indicate: (1) interfacial charge transfer resistances (R_ct) of BiVO₄ in 0.1 M phosphate buffer solution decrease 2 to 3 orders of magnitude under illumination. (2) Intensity of the photocurrent is predominantly limited by R_ct, rather than the semiconductor bulk resistance (R_bulk). (3) Mo doping does not only increase photovoltage, but also obviously decreases R_ct. (4) Compared to pristine BiVO₄, Mo doping leads to an enhancement of photocurrent density at 1.23 V vs. RHE to 25.3 μA cm⁻², i.e., by a factor 2.7.