Physiochemical properties of positive deposits in the lead fluoroborate flow batteries with tartaric acid additive

Abstract

In this work, tartaric acid is used as an additive to investigate its effect on the physiochemical properties of positive deposits in lead fluoroborate flow batteries since it can react with boric acid, which is produced by the hydrolysis of fluoroboric acid, to produce boron-tartaric acid with a π-conjugated structure. With increasing the concentration of tartaric acid, the charge transfer resistance is lowered. The size of particle electrodeposited on the positive electrode is significantly decreased. The nonstoichiometric ratio of oxygen in the positive sediment PbOx is characterized by XPS. The value of x is gradually enhanced with increasing the content of tartaric acid, 1.73 at 50 mmol·L−1. However, the oxygen evolution reaction is serious at the high content of tartaric acid due to a large amount of OH· near the positive electrode surface. The flow cells are cycled at 25 mA·cm−2 for 2 h in the electrolyte with different concentrations of tartaric acid. The overall efficiency of the cell containing 10 mmol·L−1 tartaric acid is much higher than that without any additive. Its average cycle efficiency is >96 %, and the energy efficiency is >80 %.