Leaching Studies of Assembly Aids for Balance of Plant of PEM Fuel Cells

Study of the deteriorative effect of contaminants o n a system performance is important for its design. The choice of balance of plant (BOP) materials will str aightly influence on the cost of PEM fuel cells [1]. Thus t he studies have been rigorously conducted for years [1 ~7]. The effects have been analyzed by both in-situ and ex-situ techniques. The leaching rates of materials such as assembly aids have been also studied, and it has be en presented that the amount and its composition depen d on the materials [2]. For examples according to their study for assembly aids, there has been a trend that almost no organic or inorganic compounds have been leached out from fluorocarbon type materials though the other uretha ne, silicone, and epoxy type materials have had more compounds in soaking water. In the soaking water in urethane type assembly aids, among six different materials, the TOC has varied more than ten times f rom 100ppm to 1800ppm. Some organic compounds have been identified as methyl diamine, diethyl glycol monoethyl ether acetate, diethyl glycol monoethyl e ther, benzyl alcohol in those urethane’s solutions. But t he ratio of these compounds in the solution has varied from different materials [2]. In this presentation, we have studied the leaching rates of six assembly aids with different protocols . The materials was coated on Teflon sheet and soaked in DI water. TOC, pH, and solution conductivity has been measured. The results indicate that the extraction rate of organic or inorganic compounds depends on the mater ials. In Figure 1, the number from 50A01 to 50A06 represents the solutions where different assembly a id materials have been soaked. The difference between S ts A and C is the protocol of soaking. For both sets, total volume of solutions was always the same. However, i n Set A, only small volume of the soaking water has b een replaced with new DI water at each stated date thou g in Set C, whole solution has been replaced with new DI water at each stated date. As shown in Figure 1, al though all six tested assembly aids seem to become at the equilibrated state in two days in the test of Set A , leaching of some compounds from Set C was also observed continuously after two days. We assume the decrease of pH for 50A03 might be caused by permeation of carbo n dioxide through the bottle since TOC and solution conductivity of Set A did not change much. (The dat a is not shown in this abstract.) There were two trends. One trend was like the result of 50A04 and 50A05 soluti ns in which all compounds would leach out in two days and only less of compounds would come out after the dat . (The pH would come or stay close to pH=7, and the conductivity would go close to zero.) For BOP, thes e two materials are better than the other four. The other four assembly aids may continuously release contaminants to the FC system if they will be used in the system. We will continue this study and will provide the analysis to discuss how these two trends could be determined. The behavior of each compounds how to leach out might be affected by the other compounds, and combination effect might exist. The data may includ e GCMS and ICP-MS analysis, and the pH might be one key for the understanding.