Reversible electron storage in tandem photoelectrochemical cell for light driven unassisted overall water splitting.

• A tandem photoelectrochemical cell was designed for bias-free overall solar water splitting. • ZIF-67 decorated WO 3 photoanode exhibited superior photoelectrochemical performance. • Z-scheme black phosphorus/BiVO 4 photocathode was presented. • The pseudo-capacitive WO 3 photoanode makes it possible to realize round-the-clock hydrogen production. Photoelectrochemical (PEC) cell, representing as one of the most promising candidates to implement solar-driven unassisted overall water splitting, still remains a bottleneck in the construction of technology strategies for efficient solar energy utilization due to the intermittent nature of sunlight. Herein, we demonstrate an approach to realize round-the-clock hydrogen production by a solar rechargeable tandem PEC cell with two photoactive electrodes, where the photoanode is composed of a pseudocapacitive WO 3 nanoflakes film sensitized with visible-light responsive zeolitic-imidazolate-framework-67 (ZIF-67), and the photocathode is constituted with a Z-scheme BiVO 4 -black phosphorus (BP) heterojunctions that can broaden the light absorption to near-infrared (NIR) region as well as maintain the strong redox ability to fasten hydrogen evolution reactions by the effective charge separation. Deliberately, the alignment of Fermi level between the as-prepared WO 3 -ZIF-67 photoanode and BiVO 4 -BP photocathode permits us to realize a tandem PEC cell with reversible electron storage property, enabling light-induced charge storing and on-demand release in the dark, for the application of unassisted overall water splitting. The formed tandem PEC cell shows a promising strategy for the conversion of solar power into hydrogen fuel by integrating pseudocapacitive materials into man-made photovoltaic cells, and provides a new guidance for the design of multi-functional PEC device. [ABSTRACT FROM AUTHOR]