High-Voltage Metal-Free Disproportionation Flow Batteries Based on 9,10-diphenylanthracene

Abstract

Several metal-free, nonaqueous, disproportionation redox-flow-battery chemistries based on electrochemically active organic molecules are presented. The electrochemistry of 9,10-diphenylanthracene (DPA), a polycyclic aromatic compound, involves two reversible redox couples separated by more than 3 V, which are associated with electrochemical disproportionation of the neutral molecule. Nonaqueous solvents are investigated with the dual aims of realizing this high voltage in a battery cell and maximizing active-species solubility. Functionalized DPA analogues are synthesized and shown to exhibit electrochemical responses similar to pristine DPA; appending diethyleneglycoxy esters on each phenyl group to form DdPA (9,10-Bis(4-(2-(2-methoxyethoxy)ethoxy)carbonyl-phenyl)anthracene) improves solubility over DPA by a factor of 20 in acetonitrile and 5 in dimethoxyethane. The 0.21 M maximum concentration of DdPA in dimethoxyethane suggests an energy density of 8 Wh l−1, which begins to approach the energy density of state-of-the-art aqueous RFBs. Charge/discharge of a stagnant one-dimensional cell delivers the highest cell voltages from an organic single-active-species RFB chemistry yet reported. Energy and power efficiencies for DPA in dimethoxyethane and DdPA in acetonitrile are similar to nonaqueous vanadium acetylacetonate in cells of similar construction.