Insight into CoPi-mediated heterointerfaces for highly efficient photoelectrochemical water splitting

The coupling of photoanode (Pho) and oxygen evolution catalyst (OEC) is an ideal approach to enhance the photoelectrochemical (PEC) activity. Nevertheless, the anticipated photocurrent density has not been reached due to slow charge transfer dynamics and severe charge recombination at the interface. Herein, a novel “killing two birds with one stone” approach was discovered by employing CoPi as an interface mediator, which shifts its charge transfer behavior from conventional hole storage or passivation to hole transporter. The optimized BiVO₄/CoPi/FeOOH photoanode achieves a noteworthy photocurrent density of 5.4 mA/cm² and exhibits long term stability (13 h). The dynamic analysis and electrochemical characterization reveal that CoPi can rapidly and directly transfer more photogenerated holes to the surface of OEC in comparison to traditional slow holes transfer behavior, resulting in highly efficient interface charge separation. Interestingly, the strong interfacial interactions can also be extended to OEC/electrolyte interface, specifically by promoting the surface reaction dynamics. Moreover, this innovative approach of altering behavior of CoPi can also be utilized to design other photoanodes, like BiVO₄/CoPi/NiOOH, aimed at efficient PEC water splitting. This finding affords a smart strategy to develop highly efficient and stable photoelectrodes for water splitting.