Surface Roughening of Electrolyte Membrane for Pt- and Ru-Sputtered Passive Direct Methanol Fuel Cells

Platinum (Pt) and ruthenium (Ru) were sputtered on an electrolyte membrane and it was used as a membrane-electrode assembly for passive direct methanol fuel cells (DMFCs) operating with high concentration methanol solution (4 M). Thick (Pt of 300 nm and Ru of 150 nm) and thin (Pt of 150 nm and Ru of 75 nm) sputtered catalysts were prepared and their performance was first evaluated to find out the best sputtering conditions showing higher performance. Subsequently, four electrolyte membranes with different surface roughness were prepared to investigate its influence on the performance. As a result, the performance of the passive DMFC showed increasing tendency as the roughness is low, while the performance was decreased as the roughness was high, indicating there exists an optimal roughness of the electrolyte membrane. It was further investigated through morphological study through electron microscopy that such performance variation is attributed to the surface of sputtered Pt–Ru catalyst on the rough electrolyte membrane that adequate roughness induces the increase of reactive area while a too rough surface bears the poor contact of it with gas-diffusion layer.