The effect of anode flow characteristics and temperature on the performance of a direct methanol fuel cell

An experimental direct methanol fuel cell (DMFC), designed and manufactured in-house, was used in this study. The cell is of standard filter-press con figuration with parallel rectangular single-pass anode channels. The membra ne electrode assembly (MEA), with a suitable Pt-Ru anode electrocatalyst, w as purchased from E-TEK Inc. A 1.0 M methanol in water solution was used as the fuel and pure oxygen was used as the oxidant in all experiments. Three graphite anode plates were machined with the same Bow channel configuratio n but each with different depth of channels. The cathode was kept the same for all experiments. Polarisation curves and ac impedance spectra were obta ined for varying temperatures and channel depths. To separate the contribut ion of the oxygen reduction reaction to the overvoltage from the: anode and membrane contributions, reference hydrogen electrode (RHE) measurements we re taken. By comparing the RHE polarisation with the methanol-oxygen polari sation experiments, it was: found that polarisation losses at the oxygen ca thode accounted for a 40-50% of the overpotential. The variation in the performance of the cell with flow of methanol/water mi x, with temperature and with current density was studied. Polarisation meas urements indicate that the medium channel depth flow channels performed bet ter than either the shallow depth or deep depth how channels indicating tha t there is a complex relationship between the effect of Bow velocity and th e influence of the: rate of production of product CO2. AC impedance spectro scopy measurements confirmed the observed polarisation results. This method proved to be able to provide a reliable indication of the performance of t he cell even when the cell had not yet achieved steady-state. In the case o f the shallow channel depth anode, ac impedance revealed that it required c onsiderably longer to achieve steady-state than the time required for the m edium and deep channel depths. (C) 2001 Elsevier Science B.V. All rights re served.