Boosting power density of photocatalytic fuel cells with integrated supercapacitive photoanode

The photocatalytic fuel cell (PFC) is a promising energy conversion technology for effective solar energy utilization, wastewater treatment, and electricity generation by photoelectrochemical reactions. Nevertheless, the discharging current output and stability of the PFC are still plagued by the low photoelectron conversion efficiency and time-varying light intensity, respectively. Herein, we integrated a RuO₂ capacitive layer and a TiO₂ photocatalytic layer into a capacitive photoanode, finally designing a PFC with the capacitive photoanode. Not only can the successful integration of the capacitive layer augment the discharging current, but it can also balance the solar intensity fluctuation by the ability of electron storage. The capacitive photoanode showed a high areal capacitance of 1040.7 mFcm^-2 at a current density of 0.5 mAcm^-2, was continuously charged and discharged for 1000 cycles, and maintained 87 % of the original capacitance after cycles. The superior rate capability, high capacitance, and good cycle performance of the capacitive photoanode originate from the "crack mud" structure in the capacitive layer. The discharging current of the capacitive photoanode was 32.0 mAcm^-2 under one sun illumination, and the electrochemical performance of the capacitive photoanode was better than that of the conventional TiO₂ photoanode. The capacitive photoanode PFC possessed a maximum short-circuit current of 300.0 μA⋅cm^-2 at the beginning of discharge, which is independent of the light intensity. The capacitive photoanode PFC adopts a new working mode and provides a unique solution for the practical application of PFC.