Effects of CO2 concentration and electric current on the ionic conductivity of anion exchange membranes for fuel cells

Abstract

The dependences of the CO2 concentration and the effects of electric current on the ionic conduction properties of anion exchange membranes (AEMs) in fuel cells were investigated. The ionic conductivity of AEMs was measured by AC impedance method at 40°C in various atmospheres. After the initial ion exchange process, contact with air containing 38 % CO2 caused the ionic conductivity of AEMs to decrease to 40 % of the value measured immediately after the initial ion exchange process. However, exposing the AEMs in a CO2-free air atmosphere increased the ionic conductivity to 50 % of the value measured immediately after the initial ion exchange process. Then 89 C cm-2 of direct current (DC) was applied in a CO2-free atmosphere to the AEMs. The ionic conductivity increased close to the value measured immediately after the initial ion exchange process. These results are discussed by assuming that bicarbonate (HCO3-) is produced in the AEMs.