MOF-derived Co3O4 thin film decorated BiVO4 for enhancement of photoelectrochemical water splitting

Bismuth vanadate (BiVO₄) with narrow bandgap was considered as one of the most desirable matrices for photoanode in photoelectrochemical (PEC) water splitting system. However, the poor charge separation in BiVO₄ causes the practical PEC efficiency significantly lower than the theoretical value. Herein, we demonstrated an effective strategy for growing positively charged Co-MOF (ZIF-67) onto the surface of BiVO₄ photoelectrode via the electrostatic attraction with negatively charged BiVO₄. Then the Co-MOF-BiVO₄ photoelectrodes were annealed and a uniform Co₃O₄ thin film was formed on the BiVO₄ photoelectrode. Compared with the bare BiVO₄ photoanode, the best photocurrent density of Co₃O₄/BiVO₄ photoanode reached up to 2.35 mA/cm² (1.23 V vs RHE), with an incident photon to current conversion efficiency (IPCE) of 26% (360 nm). The PEC hydrogen production of Co₃O₄/BiVO₄ was 0.61 mmol/cm² in 5 h (100 mW/cm², 1.23 V vs RHE), which was almost 3.2 times higher than that of bare BiVO₄. The significant enhancement of PEC performance over Co₃O₄/BiVO₄ photoanodes could be attributed to the unique structure characteristics of the in-situ MOF-derived Co₃O₄ thin film, with extend surface area and increased number of active sites.