Experimental Study on the Degradation Mechanisms of Proton Exchange Membrane Fuel Cells Using the Accelerated Stress Test Method

Abstract

Long-term durability of a Polymer Electrolyte Membrane Fuel Cell (PEMFC) is the main bottleneck to a wide-scale of commercialization for the power sources of various devices. Over the last several decades focused researches have been conducted to investigate its mechanism but still isolated facts and mechanisms have been found. In this thesis, in-situ electrochemical measurements and scanning electron microscope (SEM) which belongs to ex-situ measurement were conducted to investigate the systematic analysis for degradation mechanisms of PEMFC under three modes of Accelerated Stress Test (AST)methods. The objectives of the thesis are to determine the causes of degradations and mechanisms by identifying microstructural changes in the PEMFC especially in MEA. To achieve the goals, we made the MEA and prepare other components of PEMFC to setup the PEMFC single cell system. Three different modes of AST were applied to study degradation behaviors in fast time. Polarization curve, high frequency resistance (HFR) and cyclic voltammetry (CV) were conducted to estimate the changes of performance of cell which indicates the whole reaction rate of single cell, the contacts between the components of MEA and electrochemical surface area (ECSA) which indicates the active Pt surface area. Activation overvoltage and the Tafel slope take a role to identify degradation mechanism related to characteristics of Pt. Limiting current density and contribution of mass transport overvoltage feeding low concentration reactants show the direct trends of mass transport of reactants. Our results indicate that the collapse of carbon support and the subsequent local environment which surrounds carbon support is the major factors controlling the long-term durability of a PEMFC at AST on carbon support materials. Contact loss of ionomer with support and catalyst degradation simultaneously occur at AST on catalyst materials. With relatively high temperature and low relative humidity (RH) conditions, pinhole formations may be the reason of membrane/ionomer degradation. ⓒ 2014 DGIST