Mitigation of Performance Degradation of Cathodes for Polymer Electrolyte Membrane Fuel Cells

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are green energy conversion devices that convert chemical energy to electrical energy. Compared to other types of fuel cells, PEMFCs have various advantages including the low operating temperature, high power density, and short start-up times [1, 2]. However, the limited durability and high cost of platinum catalysts are the primary obstacles to the large scale commercialization of PEMFCs. Hence, a variety of scientific approaches have tried to improve the durability of Pt electrocatalysts as a main component of PEMFC membrane electrode assemblies (MEAs) [3]. Studies reported that the performance degradation of the catalyst layer in MEAs can be divided into the reversible and irreversible degradation processes. The first case is the permanent degradations caused by the platinum dissolution or corrosion of carbon support. It is well known results in PMEFC MEAs that carbon corrosion mainly occurs at operating conditions of higher than 1.0 V, whereas platinum agglomeration/dissolution happen at 0.6‒1.0 V. That is, the deterioration of platinum in the cathode is unavoidable under general PEMFC operating conditions of 0.6‒1.0 V [4, 5]. Numerous studies, such as tuning of platinum alloy composition and use of highly durable Pt-alloy catalysts have been conducted to suppress irreversible performance degradation [6-8]. In the reversible degradation phenomena, oxygen or hydroxyl groups are bonded to platinum in the cathode, which interferes with oxygen reduction reactions and reduces performance. However, even reversible degradation can result in permanent performance decay if not removed for a long time. Hence, researches on the strategies to mitigate reversible degradation are necessary to extend the lifetime of PEMFC MEAs. In particular, Pt-O film generated during operation is reversible and can be easily recovered by the periodical reduction of cathode potential [9, 10]. In this research, we develop the mitigation method to prevent performance degradation of MEAs during constant current operation. In addition, we quantitatively analyze the mitigation mechanism of MEAs via various physicochemical and electrochemical analysis tools.