PEMFC Development at Asahi Glass Co., Ltd.
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Abstract Perfluorinated ion exchange membranes were studied and the membrane technology for PEMFC has been developed. Thermal stability, mechanical strength, water content, AC specific resistance and gas permeability were measured. The influence of membrane thickness on gas permeability and the influence of incorporation of cations on water content and AC specific resistance of Flemion® and Nafion® 117 were estimated. Gas permeation rates of the membranes decreased in inverse proportion to the increase of the membrane thickness and gas permeability coefficients were nearly constant and independent of the thickness. Hydrogen permeation rates of Flemion®S at 70'C were converted to 2.1 mA/cm2 as cunent density. Flemion®R-electrode assembly showed to maintain stable perfonnance for over 3,500hr. Furthermore, it was found that usage of thinner membranes or one with higher ion-exchange capacity gave not only lower intemal cell voltage but also higher iR-free cell voltage. PTFE-yam embedded type membrane (Flemion®Mc and Sc) and PTFE-flbril dispersed type (Flemion®R12) was examined to afford improvement in mechanical strength at moist and high temperature atmosphere. Flemion®Sc (80!am) was examined to give high cell performance of 0.67V at 0.5A/cm2, 80-C, I ata. FlemiorNMc-electrode assembly was examined to keep stable performance during the life test of over 1,500hr.
Introduction Asahi Glass Co., Ltd. has participated in the NEDO's PEFC program and evaluated the characteristics of Flemion® for fuel cells 1-6).
In the first phase, mechanical strength, gas permeation,
AC specific resistance and single cell performance were measured and a new method for binding gasdiffusion electrodes and membrane, "adhesion method" was developed 1,2). Now in the second stage of this program which got under way in the fiscal year 1996, three kinds of Flemion® membranes (cation exchange capacity: 1.0 meqJg) which had different thickness were selected as the candidate membranes for PEFC. In order to clarify the properties of membranes required for PEFC, the influence of membrane thickness on gas permeability and the influence of incorporation of cations on water content and AC specific resistance of Flemion® and Nafionsl 17 in wet state were estimated. The
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applicability of the reinforcement with PTFE yams was investigated, also. The effect of the ionexchange capacity of the resin impregnated in cathode was studied in life test of membrane-electrode assemblies. EXPERIMENT Membranes Perfluorosulfonic acid type cation exchange membranes, such as various kinds of Flemion® membranes and Nafion® membranes, were studied. Ion exchange capacity and thickness of these membranes were summarized in Table 1. These membranes were made firom perfluorinated non-
crosslinked polymer and it was known that characteristics of membranes such as water content were changed by the history of membrane treatment [7,8]. So standard pretreatment conditions were decided as shown in Fig. 1. In
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