Characterization of electrode structures and the related performance of direct methanol fuel cells

The performance of membrane electrode assemblies (MEAs) in fuel cells is substantially affected by the structures of the electrodes. An increase of about 25% in power performance was achieved merely by controlling the pressure of hot press in the MEA fabrication process for a given Pt loading, instead of by employing pore formers and heat treatment-a widely accepted method-to modify the structures of the electrode. The microstructures of the different hot-pressed electrodes were examined by transmission electron microscopy, scanning electron microscopy, and small angle X-ray scattering to assess the effect of the pressure on the structures of the electrodes. Based on experimental observations, the improved performance of the MEA is attributed to the porosity of the cathode electrode, in which a network of macrofissures and sub-microfissures allows air to penetrate the electrode. Emphasis is also placed on the relationship between the total porosity of the electrodes and the MEA performance. Results of this study demonstrate that the specific power density nearly doubles when the total porosity increased from 57% to 76%. Also, the MEAs mounted in an air-breathing DMFC small pack were fabricated in-house to supply power for a mobile phone.