Anode structure design for generating high stable power output for direct ethanol fuel cells

Three anode structures, one without a microporous layer (MPL), one with a hydrophilic MPL, and one with a hydrophobic MPL, were tested for direct ethanol fuel cells. The quick-scan polarization curve obtained from the membrane electrode assembly (MEA) without MPL exhibited a higher performance than those with MPL. From the anode potential measurement, electrochemical impedance spectroscopy (EIS) analysis and constant-current discharge measurement, it was proven that the existence of MPL at the anode diffusion layer could limit ethanol mass transport in the flow channel to the anode catalyst layer (CL), resulting in a low ethanol concentration in the anode CL, especially at higher current density operation. Moreover, the MEA with hydrophilic MPL showed lower cell performance than the one with hydrophobic MPL. The swelling of the Nafion ionomer at full hydration decreased pore size and porosity in the anode MPL, which then hindered the ethanol transport to the anode catalyst layer. Finally, it can be concluded that the negative effect from ethanol crossover seems to be less significant than the positive influence when keeping ethanol concentration high in the anode catalyst layer.