The Effects of Membrane Thickness on the Performance and Impedance of the Direct Methanol Fuel Cell

The purpose of this work is to investigate the effect of membrane thickness on direct methanol fuel cell (DMFC) performance and impedance under various operating conditions including operating temperature, methanol concentration, cathode flowrate, and cathode backpressure. The experiments were conducted by using three membranes of NRE-212 (50.8 m), N-115 (127 m), and N-117 (183 m) loading Pt—Ru (4 mg/cm²) and Pt-black (4 mg/cm²) at the anode and the cathode, respectively. The DMFC performance was analysed in terms of a polarization curve expressed by measuring voltage and current density and power—current density. In order to analyse performance losses such as activation loss and ohmic loss, the real and imaginary components of impedance were measured by AC impedance measurement system at various frequencies. Also, the crossover current at the open circuit was measured by using humidified nitrogen at the cathode and power supply. It was shown that DMFC performance was improved by the reduction of resistance for proton transport at the thinner membrane under the same test conditions. The comparison of open circuit voltage shows that using of a thicker membrane results in a larger value than that of using a thin membrane due to the decrease in methanol crossover.