Dual functions of heterometallic FeCo oxyhydroxides in borate-treated BiVO4 photoanodes toward boosted activity and photostability in photoelectrochemical water oxidation

Decorating a semiconductor photoanode with an oxygen evolution cocatalyst is an effective strategy for promoting the utilization efficiency of surface charge for oxygen evolution. Herein, a new hybrid catalyst i.e. heterometallic FeCo oxyhydroxides (FexCo1-xOOH) decorated on borate-treated BiVO4 photoanode (B-BiVO4), is prepared via a simple immersion procedure. The obtained photoanode serves as a water oxidation catalyst capable of accelerating the transportation of the photo-generated holes from the B-BiVO4 photoanode to the surface active sites of FexCo1-xOOH nanoparticles, while the Fe and Co species in the FexCo1-xOOH serve as hole shuttling mediators beneficial to the oxygen evolution reaction. Particuarly, introducing Co into BiVO4 lattice boosts the photostability by inhibiting the photooxidation-coupled dissolution of V5+ from BiVO4 lattice. The B-BiVO4/FexCo1-xOOH photoanode displays an extremely excellent photocurrent density of 5.21 mA cm−2 at 1.23 VRHE, with a 60% increase over the B-BiVO4 (3.26 mA cm−2). Particularly, the photocurrent density of the B-BiVO4/FexCo1-xOOH photoanode during consecutive illumination for 10 h shows a negligible decay, corresponding to more 95% of the initial photocurrent density. The improved PEC performance is attributed to the accelerated charge separation/transfer and surface water oxidation reaction occurring in the photoanode matrix and/or at the photoanode/electrolyte interface due to the synergistic effect of bifunctional FexCo1-xOOH and B-BiVO4.