Ultrastable aqueous phenazine flow batteries with high capacity operated at elevated temperatures

Aqueous organic redox flow batteries (AORFBs) permit us to utilize renewable energy through organic redox-active materials. While long cell-cycling lifetime has been aspired in AORFBs at room temperature, the exploration of robust organic molecules with thermal stability for energy storage, especially in sunlight-rich areas with elevated temperature, is of vital importance. In the present work, we demonstrate an extremely stable AORFB with high capacity based on propionic-acid-functionalized phenazine (PFP) at both room and elevated temperatures. The full redox-flow battery based on 1,8-PFP with 2.0 M electron concentration in 1.0 M KOH against ferrocyanide presents an OCV of 1.15 V, and no capacity fade is observed when cycled at 45°C for 53 days, which is among the best capacity retention reported so far. These results demonstrate great promise of PFPs for future energy-storage technology in tough conditions with high temperature and strong alkaline solutions.