Methanol diffusion rates through the anode diffusion layer in direct methanol fuel cells from limiting current measurements

Metal foams may be used in direct methanol fuel cells to feed reactants to the catalyst layer and to collect current from the resulting electrochemical reaction. Although the mass transfer from the metal foam to the underlying gas diffusion layer (GDL) is diffusion-dominated, it is found that at a fixed methanol concentration, the limiting current density increases with increasing methanol flow rates. This unexpected result is attributed to the more efficient removal of product CO2 from the GDL. A methodology is developed to estimate the effective diffusion coefficient of methanol in the anode diffusion layer from limiting current density measurements, and to extract the fraction of GDL volume occupied by CO2.