Water/Oxygen Circulation-Based Biophotoelectrochemical System for Solar Energy Storage and Release.

Fabricating an artificial photoelectrochemical device to provide electric power on demand is highly desirable but remains a challenge. In response to the intermittent nature of sunlight, we develop a water/oxygen circulation-based biophotoelectrochemical system (BPECS) by integrating a polypyrrole (PPy) capacitor electrode into a photobiofuel cell (PBFC). Unlike traditional PEC devices, the modular and integrated system design of BPECS can not only improve compatibility among PEC cells, BFCs, and capacitor devices, but also offers a feasible way for tackling the intermittent nature of sunlight. In this system, the molecules of water and oxygen can form a self-circulation, thus making this device intrinsically safe and cost-effective. Through the alternate two-step energy conversion (i.e., solar-to-chemical/electric and chemical-to-electric), this conceptual model obtains maximum power output densities of 0.34 ± 0.01 and 0.19 ± 0.02 mW cm-2 in light and dark conditions, respectively, and presents stable long-term cycling performance for solar energy storage and release. Our results demonstrate that such a BPECS achieves high-effective solar energy utilization, which carries great significance to the development of artificial BPECS and provides research opportunities to explore a deployable route for grid-scale photovoltaic energy storage.