MORPHOLOGICAL VARIATION OF PLATINUM CATALYSTS IN PHOSPHOTUNGSTIC ACIDFUEL-CELL

Morphological modifications occurring on platinum catalysts during ope ration in a phosphotungstic acid fuel cell were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scann ing electron microscopy-energy dispersive atomic X-ray (SEM-EDAX) anal yses. An increase of platinum particle size was observed on both anode s and cathodes with the time of operation in fuel cell. This phenomeno n was significantly larger on the cathode. The uptake of electrolyte b y the catalyst layers increased during cell operation. Concurrently, a n increase of cell performance was recorded. On the basis of physicoch emical characterizations, the growth mechanism of platinum particles w as attributed to a dissolution-redeposition phenomenon involving small er crystallites. Whereas, the increase of cell performance during the first period of operation is likely due to an increase of the three-ph ase reaction zone at the electrode-electrolyte interface whose positiv e contribution to the cell polarization prevails over the effects of p latinum crystallite growth. (C) 1998 Elsevier Science S.A.