Thermomechanical Stability of Low and High-Temperature Pem Fuel Cell Sealants

Abstract

Sealants are vital components in Polymer electrolyte membrane fuel cell or PEM fuel cell that prevent the leakage of reactant gases from the perimeter of the cell. The sealants also help to avoid the direct mixing of reactant gases in the cell and provide insulation between the anode and cathode electrode of the cell. The present thesis emphasizes the physical and chemical characteristics of commercial sealant materials silicone rubber, ethylene propylene diene monomer (EPDM) rubber, fluoroelastomer (FKM) rubber, and polytetrafluoroethylene (PTFE). In addition, the time-dependent viscoelastic property, particularly the creep characteristics of PTFE sealant is investigated. In PEM fuel cell, the components are subjected to an assembly pressure of 1–5 MPa, leading to compressive stress in the components. Therefore, the creep response of PTFE sealant is explored at various temperatures in the range of 25–65ºC, at three stress levels of 2 MPa, 3 MPa, and 4 MPa. The time-temperature superposition (TTS) method is employed to construct the creep compliance master curve at a reference temperature of 25°C, and thereby, to predict the long-term creep behavior of PTFE sealant. The creep compliance master curve obtained offers the prediction for 4.5 hours. The present thesis further investigates in detail the influence of PTFE sealants’ accelerated creep on the performance of a 1cm2 active area PEM fuel cell. It is reported that at the cell voltage of 0.4V, the current density for case 1 (without creep) and case 2 (sealants’ accelerated creep) are 1.309655 and 1.041806 Acm-2, respectively. Furthermore, an experimental investigation is carried out to examine the collective impact of relative humidity (RH) and temperature on the dynamic viscoelastic characteristics of EPDM, FKM, and PTFE sealants in PEMFCs. These three sealants are subjected to four different RH conditions of 0, 50, 70, and 90% during the temperature sweep test from room temperature (RT) up to 90°C. Similarly, these sealants are exposed to four different temperatures of 30, 45, 60, and 80°C, during the RH sweep test conducted from 5 to 90% RH. The findings from the dynamic properties, which include the storage modulus (E’), and loss modulus (E”) of the sealants indicate that the degradation of PTFE sealant is the least, while that of FKM sealant is highest, under the combined temperature and RH environmental conditions of PEMFC.