Enhanced bulk and interfacial charge transfer in Fe:VOPO4 modified Mo:BiVO4 photoanodes for photoelectrochemical water splitting

Abstract

Bismuth vanadate (BiVO₄) is a promising photoanode material for photoelectrochemical (PEC) water oxidation. However, its performance is greatly hindered by poor bulk and interfacial charge transfer. Herein, to address this issue, iron doped vanadyl phosphate (Fe:VOPO₄) was grafted on molybdenum doped BiVO₄ (Mo:BiVO₄) for significantly enhancing charge transfer and oxygen evolution kinetics simultaneously. Consequently, the resultant Fe:VOPO₄/Mo:BVO₄ photoanode exhibits a remarkable photocurrent density of 6.59 mA cm⁻² at 1.23 V versus the reversible hydrogen electrode (V_RHE) under AM 1.5G illumination, over approximately 5.5 times as high as that of pristine BiVO₄. Systematic studies have demonstrated that the hopping activation energy of small polarons is significantly reduced due to the Mo doping, resulting in accelerated bulk charge transfer. More importantly, the deposition of Fe:VOPO₄ promotes the interfacial charge transfer between Mo:BiVO₄ and Fe:VOPO₄ via the construction of V−O−V and P−O bonds, in addition to facilitating water splitting kinetics. This work provides a general strategy for optimizing charge transfer process, especially at the interface between photoanodes and cocatalysts.