Porphyrin-Based Posolytes: A Novel Approach to Advancing Aqueous Organic Redox Flow Battery Technology

Aqueous organic redox flow batteries (AORFBs) hold great promise for large-scale energy storage, particularly in integrating renewable energy into the grid. However, their development is constrained by the scarcity of efficient posolytes. This study opens a new pathway for advancing AORFBs by unlocking the potential of porphyrins as active electrolytes. Despite their promise, the electrochemical stability of porphyrins in aqueous environments has been a critical challenge. To address this issue, we propose the porphyrin metalation with Zn to allow the redox reaction within the water potential window and the optimization of the electrolyte to enhance the durability of porphyrin in lc-cations formed during oxidation. We introduce an efficient synthesis method for obtaining zinc porphyrin (ZnTPPS) and demonstrate that its stability and redox reversibility can be significantly improved in mildly acidic buffer solutions. When paired with 1,1 '-bis(3-sulfonatopropyl)-viologen as the negolyte, the resulting AORFB achieved a stable capacity of approximately 500 mAhL-1 over 100 cycles, with nearly 100 % coulombic efficiency, reflecting superior electrochemical performance. These findings position ZnTPPS as a novel and promising posolyte, paving the way for more efficient AORFB systems.