Yusuke Hiramitsu

Renewing Accelerated Stress Tests Correlated to Actual Deterioration in Proton Exchange Membrane Fuel Cells to Evaluate the Durability of Perfluorinated and Hydrocarbon Proton Exchange Membranes

Perfluorinated and hydrocarbon proton exchange membranes (PFSA and HC-PEM) have been developed for proton exchange membrane fuel cells (PEMFCs). Especially, an aromatic HC-PEM has high strength though inferior flexibility because of a hard molecular frame and high gas barrier of O2 and H2 compared with PFSA-PEM. Based on such characteristics of HC-PEM, thin types of HC-PEMs have been developed for practical use. As generally known, in case of increasing the ionexchange capacity aiming at obtaining the enough proton conductivity, the other characteristics such as membrane formability, mechanical strength, the dimensional stability, the resistance to water and the oxidation resistivity become insufficient. Nowadays, many HC-PEM developers have been challenging to overcome such problems, which leaded to the development of the HCPEM exceeding PFSA-PEM in the durability at the open circuit voltage (OCV) and for the relative humidity (RH) cycles introduced as the accelerated stress tests (ASTs) [1]. However, it is too early to conclude that HC-PEM is superior to PFSA-PEM for automobile use. Regarding ASTs of PEM for automobile use, a lot of data should be accumulated in order to decide the common protocols for both the PFSA-PEM and HC-PEM or the original protocols for the HC-PEM, alternating the present AST protocols which were developed based on the deterioration mechanism of a PFSA-PEM in PEMFC. In order to obtain the conditions of ASTs and the deterioration indexes from fuel cell that suit a chemical and mechanical deterioration of both the PEMs especially occurred in the PEMFC system for automobile use, the authors are examining the deterioration behavior of PEMs from the single cell test and the element test under the Cell Evaluation Project supported by New Energy and Industrial Technology Development Organization (NEDO) while obtaining the advice from Toyota Motor Corp., Nissan Motor Co., Ltd, Honda R&D Co., Ltd. and Fuel Cell Commercialization Conference of Japan (FCCJ). The chemical AST protocol for the single cell test proposed from FCCJ and DOE is OCV test at 90 °c of cell temperature (Tc) with 61 °c of anode and cathode humidifier temperature (Tha, Thc), presently. The mechanical AST protocol is RH cyclic test at 80 °c of Tc, 90 °c of Tha and Thc for 2 min. and dry for 2 min with air or N2 in anode and cathode [2, 3]. In this study, the following deterioration behaviors are hypothecated for HC-PEM in the single cell. Firstly, an oxidative decomposition with hydrogen peroxide by-product at the cathode and/or the hydrolysis with water of a main chain progress. Secondarily, the mechanical property of the HCPEM decreases with main chain decomposition. Finally, the HC-PEM is mechanically failed.