Elucidating the role of surface states of BiVO4 with Mo doping and a CoOOH co-catalyst for photoelectrochemical water splitting

Bismuth vanadate (BiVO4) is a promising material for photoelectrochemical (PEC) water splitting, however, its PEC performance is limited by the high surface and bulk charge recombination rates. Here we present a comprehensive study to elucidate a recombination phenomenon of BiVO4 that arises with Mo doping. The Mo doping produces multiple effects including the formation of MoOx (reduced form of Mo6+) species and oxygen vacancies (V(O)s) on the surface of the BiVO4 that work in tandem with V4+ species (and MoOx) acting as surfaceactive intermediates (i-SS) providing improved hole transfer to the electrolyte. In contrast, in the absence of V4+ species, the V(O)s can act as recombination centers (r-SS). Further, CoOOH co-catalyst coating is used to minimize such recombination centers. Eventually, a photocurrent enhancement of similar to 37 times (1.1 mA/cm(2) at 1.23 V vs. RHE) and a cathodic shift in onset potential of similar to 500 mV compared to that of pristine BiVO4 (0.03 mA/cm(2) at 1.23 V vs. RHE) is obtained. We carried out in-depth PEC analysis using hole scavenger measurements, PEC impedance spectroscopy, and intensity-modulated photocurrent spectroscopy to elucidate the effect of the surface reduction process upon doping, the impact of Vos, MoOx species and CoOOH layer on the enhanced PEC performance.

Automated summary

This study provides a comprehensive analysis of the recombination phenomenon of BiVO4 with Mo doping, highlighting the importance of V4+ species, MoOx species, and CoOOH co-catalyst coating in enhancing the photoelectrochemical performance. By reducing charge recombination rates, the photocurrent of BiVO4 is significantly enhanced, demonstrating the potential for improved water splitting efficiency.