Significance of diffusion layers on the performance of liquid and vapor feed passive direct methanol fuel cells

Passive direct methanol fuel cell (pDMFC) has attracted the attention of scientists due to its high energy density. Under passive operating conditions, the properties of the diffusion layer significantly affect cell performance. In this study, the effect of the surface morphology, structure, permeability of diffusion layers (PTFE-treated carbon paper (CP) or carbon cloth (CC)) on the catalyst utilization, methanol, water fluxes, Faraday efficiency, and current discharge in pDMFC were investigated in liquid and vapor feed pDMFCs. Although catalyst utilization using the CP was higher than that using CC, the performance using the latter was enhanced in both liquid and vapor methanol feed. In liquid feed pDMFC, the optimum methanol concentration in the case of CC was 4 M, giving a power of 31 mW/cm2 compared to an optimum of 2 M and a power of 27 mW/cm2 in the case of CP. Although CP and CC have the same hydrophobicity, water droplet detachment from the cathode surface was easier in the case of CC compared to CP. In vapor feed pDMFC, using 100 wt% methanol at 0.25 V, the steady-state performance (29 mW/cm2) using CC was 190% of that using CP. Under active operation conditions, the performance of cell using CP is better than that using the CC due to the high catalyst utilization and the limited mass transfer effect.