Membrane-Less Hydrogen Iron Redox Flow Battery

In this study, a new type of redox flow battery (RFB) named “membrane-less hydrogen-iron RFB” was investigated for the first time. The membrane is a cell component dominating the cost of RFB, and iron is an abundant, inexpensive, and benign material, and thus, this iron RFB without the membrane is expected to provide a solution to the challenging issues of current battery systems such as high cost and safety concerns. The research focus in this study was placed on defining key design parameters to make this new system promising as an RFB. Crossing rate of reactants over carbon porous electrode (CPE) was controlled by modifying its pore structure with Teflon impregnation, and the effects of the Teflon on crossover, kinetic, Ohmic, and mass transfer was investigated by cell-based test and one-dimensional computational model. It was found that the cell performance (i.e., charge and discharge polarization) of the new membrane-less system was equivalent to that of the conventional membrane-system (i.e., RFB having a membrane). Especially, the Ohmic properties of the new system were constant and stable, while in the conventional membrane system, they were significantly varied and deteriorated as cell tests were continued, indicating that degradation or contamination of membrane affecting Ohmic properties could be mitigated effectively in the membrane-less system, which was found first in this research. The modeling analysis provided insight into the system, showing that the effect of reactant crossover on performance decay was not significant, and Teflon impregnation in the CPE caused significant kinetic and Ohmic losses by impeding ion transport and reactant access to reaction sites. From this study, it was found that the membrane-less H₂-iron system is feasible and promising in resolving the challenge issues of the conventional systems. And the results of this study are expected to provide guidelines for research and development of flow battery systems without having a membrane.