The influence of cathode flow field surface properties on the local and time-dependent performance of direct methanol fuel cells

The influence of cathode flow field wettability on the local and time-dependent performance of DMFCs was investigated by galvanostatic measurements of local current distribution, cell voltage and pressure drop along the cathode channels. The cathode flow fields made of graphite were either untreated, hydrophobic or hydrophilic. Drop shape analysis yielded contact angles in the descending order hydrophobic (126.8°), untreated (115.9°) and hydrophilic (26.2°). Especially at low air stoichiometry (λ_air = 2), hydrophilic cathode flow fields are advantageous with regard to higher power densities, suppression of local current fluctuations and substantial reduction of pressure drop along the cathode channels.