A 25 cm2 single Si-based solar redox flow battery with aqueous iodine-bromine redox couples

Abstract

Solar redox flow battery (SRFB) technology offers a compelling strategy for the efficient conversion and storage of solar energy, mitigating the intermittency challenges associated with renewable energy sources. This study presents an experimental investigation into the performance of a 25 cm2 SRFB employing a single-junction silicon photo-device coupled with a neutral pH aqueous iodine-bromine redox couple. The iodine-bromine redox couple was selected through a preliminary screening process, considering its compatibility with the photovoltaic device's current-voltage performance and desirable electrochemical properties. Experimental results demonstrate the successful integration of a 25 cm2 photoactive-area device with the SRFB system, showcasing efficient solar charging capabilities. The integrated SRFB presented in this study reaches a solar-to-chemical (STC) conversion efficiency of 9.54 %. Subsequent discharge of the stored chemical energy yielded a maximum solar-to-output electricity efficiency (SOEE) of 3.11 %, with an average efficiency of 2.44 % over a continuous 360-hour cycling period. Furthermore, the electrochemical characterisation of the iodine-bromine redox couple confirmed desirable reversibility and stability. These findings underscore the potential of neutral pH aqueous iodine-bromine redox couples for scalable and sustainable solar energy storage applications, providing valuable insights for the further scale-up of SRFB systems. © 2025 The Authors