Molecular Design of Fused-Ring Phenazine Derivatives for Long-Cycling Alkaline Redox Flow Batteries

Abstract

The utilization of redox-active organic species in aqueous redox flow batteries holds great promise for large-scale and sustainable energy storage. Herein, we report the low-temperature green synthesis of three different phenazine derivatives and investigate their performances in alkaline organic redox flow batteries. Electrochemical characterizations reveal that the ortho-substituents of the hydroxyl groups in phenazine derivatives have significant influences on the battery performances. By introducing an additional phenyl group adjacent to the hydroxyl group in the phenazine motif and a carboxyl group with strong solubilizing effect, the redox flow battery based on fused-ring benzo­[a]­hydroxyphenazine-7/8-carboxylic acid with 1.0 M electron concentration exhibits greatly improved capacity retention rate of 99.986% cycle–1 (99.92% day–1) and stable average energy efficiency of ∼80% for over 1300 cycles. Moreover, a combinatorial library of hydroxyphenazine derivatives with varying substituent groups was built, and their redox properties were simulated to guide further molecular structure design of phenazine-derived electroactive compounds.

New insights into phenazine-based organic redox flow batteries by using high-throughput DFT modelling

“…34 However, there are only a few examples where phenazine compounds have been used for redox ow batteries. [35][36][37] In the rst example, a bipolar redox active molecule containing phenazine and TEMPO moieties acting as anolyte and catholyte redox centers, respectively, was synthesized and employed in a symmetric RFB. 35 Following a similar strategy to the quinone family, 24,38 Hollas et al performed a virtual screening on several phenazine derivatives with hydroxo, carboxylate and sulfonate groups in aqueous solutions and modied the molecular structure of the pristine phenazine with hydroxo and sulfonate groups to increase the solubility and tune the redox potential.…”

“…36 In a similar fashion, Wang et al characterized phenazines containing amino and hydroxo groups in aqueous RFBs with experimental and computational techniques. 37 They also performed a systematic computational investigation of various multi-hydroxyl substituted phenazines and showed how the redox potentials depend on the number and position of the hydroxo groups. However, a systematic computational screening of phenazine derivatives with functional groups of different nature is still highly needed, considering that more than 100 different phenazine structural derivatives have been identied in nature, and over 6000 compounds that contain phenazine as a central unit have been synthesized.…”

Material Design of Aqueous Redox Flow Batteries: Fundamental Challenges and Mitigation Strategies

“…www.advmat.de www.advancedsciencenews.com , which operated over 500 cycles at 67 Ah L −1 (10.2 Wh L −1 ) with 0.0195% capacity decay per cycle and 0.169% per day (Figure 15c). Recently, Wang et al [144] introduced an electron-donating phenyl group adjacent to the hydroxyl group in phenazine to further enhance the stability. As a result, benzo[a]hydroxyphenazine-7/8-carboxylic acid (3.4c, BHPC) demonstrated a low decay rate (0.014% per cycle and 0.08% per day) at a 1.0 m electron concentration for 1300 cycles when coupled with a Fe(CN) 6 3−/4− catholyte, achieving an energy density of 7.3 Wh L −1 (Figure 15d).…”

“…The choice of membrane is a critical component for determining the power capability and stability of RFBs. Water uptake (W U ) reflects the hydrophilicity of the ion exchange membrane (IEM), which could be measured via the weight change of dry (W d ) and wet states (W w ) [50b,149] 100% 1300 (0.5 m, 0.014%/cycle, 0.08%/day) [144] 7. 100 (0.24 m, 0.01%/cycle, 0.16%/day) [147] 3.2 99% ≈80% (@80 mA cm [Fe(CN) 6 ] 3−/4− (catholyte)…”

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

“…[18] They developed 7,8-dihydroxyphenazine-2-sulfonic acid (DHPS) which shows acapacity fade rate of 0.68 % per day.Recently,W ang et al reported aseries of phenazine derivatives which have both good solubility and chemical stability,a nd the AORFB based on benzo-[a]hydroxyphenazine-7/8-carboxylic acid (BHPC) presents alow capacity fade rate of 0.08 %per day. [19] Thedegradation mechanisms of phenazines in AORFBs is not clear.D HPS and BHPC were both operated in alkaline cells at high pH values,w hereas the operability at lower pH that potentially enables corrosion resistance with less expensive electrolytecontacting materials is more desired. Thef ew examples of phenazine flow batteries make it difficult to fully understand the structure-activity relationship (SAR): the effects of different functional groups at different substituent positions of phenazine derivatives in the aspect of the electrochemical redox properties and battery performance.Thus,the synthesis and SAR study of more structurally and functionally diverse phenazine derivatives for AORFBs to understand the degradation mechanism of phenazines and further improve the capacity retention rate at near-neutral pH are waiting to be explored.…”