Water and air management systems for a passive direct methanol fuel cell

In this paper water and air management systems were developed for a miniature, passive direct methanol fuel cell (DMFC). The membrane thickness, water management system, air management system and gas diffusion electrodes (GDE) were examined to find their effects on the water balance coefficient, fuel utilization efficiency, energy efficiency and power density. Two membranes were used, Nafion^® 112 and Nafion^® 117. Nafion^® 117 cells had greater water balance coefficients, higher fuel utilization efficiency and greater energy efficiency. A passive water management system which utilizes additional cathode gas diffusion layers (GDL) and a passive air management system which makes use of air filters was developed and tested. Water management was improved with the addition of two additional cathode GDLs. The water balance coefficients were increased from −1.930 to 1.021 for a cell using a 3.0 mol kg⁻¹ solution at a current density of 33 mA cm⁻². The addition of an air filter further increased the water balance coefficient to 1.131. Maximum power density was improved from 20 mW cm⁻² to 25 mW cm⁻² for 3.0 mol kg⁻¹ solutions by upgrading from second to third generation GDEs, obtained from E-TEK. There was no significant difference in water management found between second and third generation GDEs. A fuel utilization efficiency of 63% and energy efficiency of 16% was achieved for a 3.0 mol kg⁻¹ solution with a current density of 66 mA cm⁻² for third generation GDEs.