Methanol Cross-over in Direct Methanol Fuel Cells

Transport rates of methanol in ionomer membranes exposed to methanol aqueous solutions were determined electrochemically in cells identical to direct methanol fuel cells (DMFCs) and by NMR measurements on the membrane equilibrated with the methanol solutions. We will compare the electrochemical and NMR results and discuss them in the context of temperature and membrane thickness effects on methanol cross-over in DMFCs. In addition, we show results for CO 2 emission from the cathode of an operating DMFC as a function of cell current and methanol concentration in the feed stream, that indicate (1) at low concentrations, methanol cross-over can be lowered by methanol consumption in the anode; and (2) at higher concentrations, methanol is carried across the cell significantly by electroosmosis.