Photocatalytic Z-scheme water splitting is regarded as a promising approach for efficient conversion of solar energy into hydrogen. However, there is a considerable energy loss during the electron transfer process between two photosystems. How to cut down the energy loss becomes a critical issue for improving the solar energy conversion efficiency. Herein, we analyze and evaluate the maximal room for energy storage in photocatalytic water splitting systems and propose a strategy of integrating a redox flow battery (RFB) into a Z-scheme water splitting system to reduce the energy loss. Moreover, we construct a biohybrid photosystem II (PSII)–ZrO2/TaON Z-scheme system with an integrated quinone/ferricyanide RFB. The platform system can generate both electricity and hydrogen utilizing solar energy through photocatalytic charge and discharge processes of the RFB and the water splitting reaction, resulting in the enhancement of the solar energy conversion efficiency. This proof-of-concept work opens a new avenue to save the energy dissipated in Z-scheme water splitting for more efficient solar energy conversion.
