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

为了发展磷酸燃料电池，提高气体扩散电极的性能和寿命是至关重要的。我们提出了一种新型的电极，它的概念是电极中的电催化剂层的功能完全分配给亲水性的铂/炭黑(PT/CB)作为电解液网络，而氟化聚乙烯(FPE/CB)强防湿的CB作为供气网络。在本研究中，我们研究了1)高防潮性能FPE/CB的制备，2)电极性能与其组成的关系，3)电极加速寿命试验方法的建立。1.用QCM研究了F_2气体对聚乙烯薄膜的氟化作用，确定了制备FPE/CB的最佳反应条件，并在小型旋转KILM反应器上成功制备了FPE/CB。2.考察了Pt/CB、FPE/CB和粘结剂聚四氟乙烯(Teflon)的混合比对正极性能的影响。与传统的PTFE阴极相比，采用新型FPE/CB结构优化的阴极具有更高的氧还原性能，这是由于提高了催化剂的利用率和气体的渗透性。3.我们开发了一种新的电极中电解液填充水平的电化学评估方法，并建立了一套自动加速寿命测试系统。结果表明，优化后的新型阴极在加速试验期内的催化剂利用率和气体渗透性均优于传统阴极，相当于正常运行时间为几千小时。

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.