Increased electrolyte flow resistance and blockage due to hydrogen evolution in a flow battery single cell under stack electrolyte feeding conditions

Abstract

In a flow battery stack, individual cells are typically fed with electrolyte in a parallel configuration, resulting in identical pressure drops across each cell. In this parallel liquid supply system, the distribution of electrolyte flow is closely related to the flow resistance in each branch. During operation, gas bubbles generated by chemical and physical processes tend to accumulate in the electrode pores, obstructing electrolyte flow and leading to uneven electrolyte distribution. Previous studies have mainly focused on single-cell experiments using constant flow pumps, which differ significantly from the nearly constant pressure difference liquid supply within the stack electrodes. To investigate the effects of gas evolution on liquid flow under constant pressure difference conditions, we propose a gravity-driven electrolyte feeding system for testing in a single cell, which simulates the flow conditions encountered in real stack applications. Under the interaction between gas bubbles and liquid flow, hydrogen evolution reactions at the scale of “mA cm^-2” significantly reduce the electrolyte flow through the porous electrode. When the pressure difference drops below a critical threshold, the electrolyte flow rate continues to decrease significantly and may even stop entirely. And a sufficient feeding pressure difference is essential for enhancing bubble removal efficiency.