Long-Cycling Aqueous Organic Redox Flow Battery (AORFB) toward Sustainable and Safe Energy Storage

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• 作者：Bo Hu ; Camden DeBruler ; Zayn Rhodes ; T. Leo Liu
• 刊名：Journal of the American Chemical Society
• 出版年：2017
• 出版时间：January 25, 2017
• 年：2017
• 卷：139
• 期：3
• 页码：1207-1214
• 全文大小：538K
• ISSN：1520-5126

文摘

Redox flow batteries (RFBs) are a viable technology to store renewable energy in the form of electricity that can be supplied to electricity grids. However, widespread implementation of traditional RFBs, such as vanadium and Zn–Br₂ RFBs, is limited due to a number of challenges related to materials, including low abundance and high costs of redox-active metals, expensive separators, active material crossover, and corrosive and hazardous electrolytes. To address these challenges, we demonstrate a neutral aqueous organic redox flow battery (AORFB) technology utilizing a newly designed cathode electrolyte containing a highly water-soluble ferrocene molecule. Specifically, water-soluble (ferrocenylmethyl)trimethylammonium chloride (FcNCl, 4.0 M in H₂O, 107.2 Ah/L, and 3.0 M in 2.0 NaCl, 80.4 Ah/L) and N¹-ferrocenylmethyl-N¹,N¹,N²,N²,N²-pentamethylpropane-1,2-diaminium dibromide, (FcN₂Br₂, 3.1 M in H₂O, 83.1 Ah/L, and 2.0 M in 2.0 M NaCl, 53.5 Ah/L) were synthesized through structural decoration of hydrophobic ferrocene with synergetic hydrophilic functionalities including an ammonium cation group and a halide anion. When paired with methyl viologen (MV) as an anolyte, resulting FcNCl/MV and FcN₂Br₂/MV AORFBs were operated in noncorrosive neutral NaCl supporting electrolytes using a low-cost anion-exchange membrane. These ferrocene/MV AORFBs are characterized as having high theoretical energy density (45.5 Wh/L) and excellent cycling performance from 40 to 100 mA/cm². Notably, the FcNCl/MV AORFBs (demonstrated at 7.0 and 9.9 Wh/L) exhibited unprecedented long cycling performance, 700 cycles at 60 mA/cm² with 99.99% capacity retention per cycle, and delivered power density up to 125 mW/cm². These AORFBs are built from earth-abundant elements and are environmentally benign, thus representing a promising choice for sustainable and safe energy storage.