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

Abstract

Aqueous organic redox flowb atteries (AORFBs) are ap romising electrochemical technology for large-scale energy storage.W er eport ab iomimetic,u ltra-stable AORFB utilizing an amino acid functionalizedp henazine (AFP). A series of AFPs with various commercial amino acids at different substituted positions were synthesized and studied. 1,6-AFPs displaym uchh igher stability during cycling when compared to 2,7-and 1,8-AFPs.M echanism investigations reveal that the reduced 2,7-and 1,8-AFPs tend to tautomerize and lose their reversible redox activities,w hile 1,6-AFPs possess ultra-high stability both in their oxidized and reduced states.B yp airing 3,3'-(phenazine-1,6-diylbis(azanediyl))dipropionic acid (1,6-DPAP)w ith ferrocyanide at pH 8w ith 1.0 Melectron concentration, this flowbattery exhibits an OCV of 1.15 Vand an extremely lowcapacity fade rate of 0.5 %per year.These results show the importance of molecular engineering of redox-active organics for robust redox-flowb atteries.

Multielectron Organic Redoxmers for Energy-Dense Redox Flow Batteries

“…More recently, Ji et al suggested a tautomerization-based degradation mechanism for a series of amino acid-functionalized phenazine molecules (Figure c) . Flow cell tests demonstrate that the 2,7- and 1,8-disubstituted phenazine analogs display obvious capacity fades.…”

“…More recently, Ji et al suggested a tautomerization-based degradation mechanism for a series of amino acid-functionalized phenazine molecules (Figure 8c). 111 Flow cell tests demonstrate that the 2,7-and 1,8-disubstituted phenazine analogs display obvious capacity fades. NMR analysis of both the cycled anolytes and the aged electrolytes of reduced phenazine determines formation of tautomerized byproducts, indicating a major degradation pathway via dearomatization of the phenyl ring by receiving protons transferred from the ring N atoms.…”

“…(c) Tautomerization-based decomposition of amino acid-functionalized phenazine molecules. Reprinted with permission from ref . Copyright 2021 Wiley.…”

Modular TEMPO Dimerization for Water-in-Catholyte Flow Batteries with Extreme Energy Density, Power, and Stability

“…Vanadium redox flow batteries (VRFBs) have found commercial application due to their high capacity (1.6-3.0 M Vanadium ions electron concentration), energy density (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) Wh•L -1 ), and capacity rebalancing ability. 1 However, the resource constraints and volatile pricing of vanadium limit the widespread application of VRFBs 2 and have stimulated the development of aqueous organic redox flow batteries (AORFBs), [3][4][5][6][7][8][9][10] which employ water-soluble organic redox active molecules as the anolyte and catholyte.…”

“…Thus, new scientific approaches for designing redox molecules are needed to circumvent this seemingly inherent conflict between volumetric capacity and stable cycling in AORFBs. While a lot of research for AORFBs has been devoted to the development of anolyte (negolyte) redox molecules, such as quinones, 14,15,24,[16][17][18][19][20][21][22][23] viologens, [25][26][27][28][29][30][31][32][33][34] and phenazines, [35][36][37][38][39][40] stable catholyte (posolyte) species with high capacity are scarce yet equally important in full cells. 11 Among all the studied catholyte molecules, (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) derivatives represent one of the most promising redox cores due to its stable redox behavior, high redox potential (> 0.8 V vs. SHE), solubility as high as 2 M demonstrated cycling for TEMPTMA (N Me -TEMPO), 41 and low cost.…”