Effects of water transport on performance behaviors of hydrogen bromine redox flow batteries

Abstract

The H2/Br2 redox flow batteries (RFBs) have exhibited to be a promising high-power energy storage system in which proton-exchange membranes are used as the ion carriers like the fuel cells. The membrane transport properties are highly influenced by water and hydrogen bromide (HBr) distributions inside a cell, which have a significant impact on charge/species transport efficiency and overall cell performance. In particular, the membrane is in close contact with the aqueous Br2/HBr electrolyte solution and thus the hydrogen electrode is prone to flooding, which makes removal of liquid water and HBr in the hydrogen side more challenging, particularly during charge process. In this study, we present a two-phase H2/Br2 RFB model to accurately capture key performance loss factors, i.e., hydrogen electrode flooding and HBr accumulation. The present model which rigorously accounts for the two-phase flow in the hydrogen side and variation of water uptake of membrane as a function of HBr accumulation, is successfully validated against experimental polarization curves and water crossover flux data measured during charge and discharge. The simulation results highlight that severe flooding in the hydrogen electrode occurs during charge, i.e., accompanied by the high level of HBr accumulation. However, the level of electrolyte dehydration due to the high HBr accumulation is not as serious as the activation overpotential increase due to hydrogen electrode flooding.