Biomimetic Amino Acid Functionalized Phenazine Flow Batteries with Long Lifetime at Near‐Neutral pH

Aqueous organic redox flow batteries (AORFBs) are a promising electrochemical technology for large‐scale energy storage. We report a biomimetic, ultra‐stable AORFB utilizing an amino acid functionalized phenazine (AFP). A series of AFPs with various commercial amino acids at different substituted positions were synthesized and studied. 1,6‐AFPs display much higher stability during cycling when compared to 2,7‐ and 1,8‐AFPs. Mechanism investigations reveal that the reduced 2,7‐ and 1,8‐AFPs tend to tautomerize and lose their reversible redox activities, while 1,6‐AFPs possess ultra‐high stability both in their oxidized and reduced states. By pairing 3,3′‐(phenazine‐1,6‐diylbis(azanediyl))dipropionic acid (1,6‐DPAP) with ferrocyanide at pH 8 with 1.0 M electron concentration, this flow battery exhibits an OCV of 1.15 V and an extremely low capacity fade rate of 0.5 % per year. These results show the importance of molecular engineering of redox‐active organics for robust redox‐flow batteries.