The Role of Ion Exchange Membrane in Vanadium Oxygen Fuel Cell

The effect of membrane properties on the vanadium-oxygen fuel cell performance was studied on a series of commercially available ion exchange membranes of different thickness and ion exchange capacity by selected characterization techniques including electrochemical impedance spectroscopy (ohmic and charge transfer resistance), steady load curves (performance stability) and galvanostatic charge-discharge cycles (efficiencies and capacity decay). Performance stability of the fuel cell was studied under defined conditions (state of charge, temperature, air flow rate) using continuous charging of vanadium electrolyte. In contrast to the previous studies, our results revealed that the membrane affects the fuel cell performance mainly via water management in the catalytic layer of gas diffusion cathode, while vanadium permeation across the membrane has only a minor impact. Generally, the fuel cell shows improved performance stability for more conductive membranes (thinner and with higher ion-exchange capacity), partially due to reduced ohmic losses, but more significantly due to the better ability of the membrane to drain water from the cathode via osmosis, which prevents the flooding of the cathodic catalytic layer. With the optimized membrane, we achieved stable fuel cell performance at the highest current and power density values reported (75 mA cm-2 and 57 mW cm-2 in 50% state of charge).