4,4′-Hydrazobis(1-methylpyridinium) as a Two-Electron Posolyte Molecule for Aqueous Organic Redox Flow Batteries
H. Lebel, Dominic Rochefort, Calvine Lai, Thomas Boulanger, Alizée Débiais, Louis Hamlet, Meysam Maleki, Marc‐Antoni Goulet
Abstract
Aqueous organic redox flow batteries (AORFBs) are a safe and sustainable solution for the storage of intermittent renewable energy. While several highly soluble two-electron organic molecule negolytes have been developed for AORFBs, most reported organic posolyte species exchange only one electron. Herein, readily available 4,4′-hydrazobis(1-methylpyridinium) dichloride (HydBPyMeCl) is described as a novel two-electron posolyte molecule for AORFBs. The synthesis of HydBPyMeCl was accomplished by a three-step process, yielding multiple grams of the compound. HydBPyMeCl exhibited a reversible two-electron transfer at high redox potential (+0.64 V vs Ag/AgCl reference electrode, pH = 0). When evaluated at 1 M concentration and low pH (2 M HCl) with V 3+ /V 2+ on the negative side, HydBPyMeCl showed high stability. A capacity retention of 99.997% per cycle (99.980% per day measured over 70 days) was achieved, coupled with a high volumetric specific capacity of 47.1 Ah/L (87.2% of capacity utilization at 80 mA/cm 2 ).