Devrelopment of new gas diffusion electrodes and materials for high performance and long-life phosphoric acid fuel cells

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In order to develop phosphoric acid fuel cells (PAFCs), it is essential to improve performance and lifetime of gas diffusion electrodes. We have proposed a new type of electrode, which is based on the concept that the functions of the electrocatalyst layr in the electrode are allotted completely to hydrophilic Pt/carbon black (Pt/CB) as the electrolyte network and CB strongly wet-proofed by fluorinated polyethylene (FPE/CB) as the gas supplying network. In this research, we investigated 1) the preparation of FPE/CB with high wet-proofing property, 2) the relation between the performances of the proposed electrode and its composition, and 3) an establishment of the method of accelerated life-time test for the electrodes. We have obtained the following results.1.Fluorination of polyethylene films with F_2 gas was examined by using QCM.Based on the kinetic data obtained, we have determined the optimum condition for preparing FPE/CB and have succeeded to fabricate it by a bench-scale rotary-kilm reactor.2.We examined the cathode performances as a function of the mixing ratio of Pt/CB,FPE/CB and binder PTFE (Teflon). The cathode optimized in the structure with the new FPE/CB exhibited a high performance for oxygen reduction compared with the conventional one using PTFE owing to the improved catalyst utilization and gas permeability.3.We have developed a new method for electrochemical evaluation of fill-level with electrolyte in the electrode in PAFCs, and also an automatic accelerated life-time testing system. It was demonstrated using this system that the optimized new cathode exhibited better properties of catalyst utilization and gas permeability than the conventional one over the accelerated test period, corresponding to a normal operation time of several thousands hours.