Solar Redox Flow Batteries: Mechanism, Design, and Measurement

The increasing public awareness of the energy crisis since the 1970s has promoted the ongoing development of energy conversion and storage systems. As a supplement to photovoltaics, photoelectrochemical cells (PECs) are among the promising solar electricity generation systems. However, the intrinsic intermittence of sunlight can never guarantee continuous electricity supply. Therefore, PECs are being developed to convert solar energy to chemical energy in the forms of fuels such as H-2 and other organic chemicals. However, this technology requires massive storage systems for the solar fuels/chemicals, and complementary conversion systems for electricity generation from the solar fuels. Redox flow batteries (RFBs) are capable of large-scale real-time electricity storage and conversion. Both PECs and RFBs have been investigated for more than three decades, yet the integration of these two systems has not reached maturity. Hence, this review aims to give a critical overview of the state-of-the-art progress in solar redox flow batteries, from the aspects of the working mechanism, device engineering, and performance evaluation.