Optimization of Membrane Electrode Assembly in Air-Breathing Direct Methanol Fuel Cell

Abstract

The structure and performance of MEA were optimized by tailoring the catalyst layer,cathodic microporous layer ( MPL) ,anodic MPL and membrane,with the considerations of unique characteristics of airbreathing direct methanol fuel cell ( DMFC) such as methanol crossover and cathode flooding. It was found that high catalyst loading could suppress the methanol crossover effectively,but too high catalyst loading can lead to high mass transport resistance. Hydrophobic anodic MPL with 30% ( by mass) PTFE could facilitate the CO2 bubble detachment,which decreased the methanol concentration gradient and suppressed the methanol crossover accordingly. When Nafion 115 was used as membrane,methanol crossover was severe,while Nafion 117 was used, the water in cathode could not be effectively back-flowed to the anode by hydraulic pressure. For considerations of complicated interactions and trades-off between the water and methanol crossover effects,the optimized MEA showed peak power density of 33 mW·cm-2 at ambient conditions,the best working methanol concentration was 4 mol·L-1.