Tailoring CoAl2O4 inversion degree-driven photocarrier separation and injection for photoelectrochemical water splitting

Highly efficient photoanodes are highly desirable for hydrogen production to construct photoelectrochemical (PEC) water oxidation devices. This work used the spinel-structured CoAl2O4 (CAO) as the cocatalysts to BiVO4(BVO), delivering the high photocurrent density of 3.85 mA/cm2 at 1.23 VRHE. Interestingly, their PEC performance depended on the CAO's inversion degree (δ). When δ = 0.2, the oxygen evolution process on CAO can cooperatively adsorb *OOH and dissociate the O2, then the *OH absorbs on the re-exposed active site again, leading to an improved charge separation on the surface. Meanwhile, the n-p heterojunction was formed at the interface of BVO/CAO, with the most robust built-in field strength at δ = 0.2, and the charge separation in bulk was greatly improved. Additionally, the CAO can also retard the photo corrosion of BVO by effectively extract and reservoir the photoholes, achieving over 10 h of long-term durability on BVO/CAO-450. This work illustrates the roles of CAO, clarifies the effect of inversion degree on PEC water oxidation, offers fresh insights into constructing highly efficient and stable OER catalysts, and provides fundamentals for developing high-efficiency PEC devices.