INVESTIGATION OF THE MICROSTRUCTURE IN THE CATALYST LAYER AND EFFECTSOF BOTH PERFLUOROSULFONATE IONOMER AND PTFE-LOADED CARBON ON THE CATALYST LAYER OF POLYMER ELECTROLYTE FUEL-CELLS

Effects of a perfluorosulfonate ionomer (PFSI) and of a polytetrafluor oethylene (PTFE) loaded carbon (PTFE-C) on the catalyst layer in the e lectrode of a polymer electrolyte fuel cell (PEFC) prepared by a new m ethod based on the process of PFSI-colloid formation were investigated by electrochemical techniques and a mercury pore sizer. The microstru cture of the catalyst layer and its effect on the PEFC performance wer e affected by the contents of both PFSI and PTFE-C. The catalyst layer has two distinctive pore distributions with a boundary of ca. 0.04 mu m. The volume of larger pore (secondary pore) deceased with an increa se of the PFSI content and increased with an increase of the PTFE-C co ntent. The volume of the smaller pore (primary pore) was independent o f the content of both PFSI and PTFE-C. The PFSI as well as the PTFE ex isted only in the secondary pore. The content of PFSI affected the per formance of PEFC in the whole current density range. On the other hand , the content of PTFE-C influenced it greatly at high current density due to its gas feeding faculty. in the PEFC, reaction sites were found to exist in the secondary pore coated with the macromolecule PFSI. Th e hydrophobic PTFE-C works to supply the reaction gas to the reaction sites covered with the PFSI in the secondary pore, and to exhaust the product water from there. The high performance of PEFC at high current density was achieved with the best mixture of the PFSI and the PTFE-C .