Degradation of electrochemical active compounds in aqueous organic redox flow batteries

Aqueous organic redox flow batteries (AORFBs) represent a promising energy storage technology that may enable the grid-scale integration of intermittent renewable energy. The water-soluble, redox-active organic species that are utilized to reversibly store electricity are the most critical performance-determining components in AORFBs. To ensure affordability and competitiveness in practical installations, it is of vital importance to enhance the structural stability and long-term durability of organic electrolytes, ultimately decreasing their levelized cost. Herein, we summarize the proposed decomposition mechanisms for representative organic electrolytes, including quinones, viologens, nitroxide radicals, and ferrocene derivatives. By reviewing the influence of molecular engineering on the side reactions of electrolytes, we intend to provide a better understanding of the decisive factors and inspire further attempts to design structurally robust and cycling-stable electrolytes for AORFB. Finally, we provide possible directions and prospects for future AORFB research.