Session: 09-01: Photovoltaic & Electrochemical Technologies

Paper Number: 132456

132456 - Mass Transport Loss Due to Gas Diffusion Layer Degradation of Pem Fuel Cell Under Wet/dry Cycles 

Abstract: 

 Polymer electrolyte membrane fuel cell (PEMFC) experiences repetitive variations in relative humidity (RH) during start-up and shutdown processes. It is known that these RH variations lead to swelling and shrinkage of polymer resulting in mechanical stresses on catalyst coated membrane. These stresses cause the deterioration of performance and durability of PEMFC. Most previous research related to the mechanical degradation due to the RH variations focused on the membrane and catalyst layer like pinhole formation, and Pt/C agglomeration/dissolution. However, there is lack of studies examining the effect of RH variations on gas diffusion layer (GDL), a crucial component for the mass transport in PEMFC. In this study, the changes of GDL, which plays a significant role in mass transport, under wet/dry cycle in PEM single cell were investigated.

 A single cell having an active area of 25 cm² was employed to conduct an in-situ accelerated stress test (AST) along with the electrochemical characterization. In this experiment, the mechanical degradation was induced thorough a wet/dry cycle as a AST. The AST protocol involved alternating of 2-min wet (RH 60% inlet gas) and 2-min dry (RH 0% inlet gas) with N₂ flows of 500 mL/min on both the anode and cathode sides. The surface morphologies of GDL before and after wet/dry cycle were compared using a field emission scanning electron microscope (FE-SEM). The static contact angles on GDL surface and the water penetration pressure through the GDL pores were also compared before/after the AST. The electrochemical characteristics during the AST were assessed by polarization curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). In addition, the mass transport loss was obtained using the Nernst equation with the polarization curves measured by switching O₂ and air at the cathode.

 The mean voltage decreased from 0.621 to 0.583 V at the current density of 1.4 A/cm² and the peak power density was reduced from 1.15 to 0.98 W/cm² after undergoing 5,000 cycles of AST. The electrochemical surface area determined by CV curves, which is equal to the catalyst reaction area, decreased 22.1%. The wet/dry AST cycles caused the agglomeration of polytetrafluoroethylene (PTFE) in GDL. The water penetration pressure showed that the breakthrough pressure decreased, and the range of pressure fluctuation widened with the decrease of water discharge frequency. This indicates the increase variability in water saturation and a deterioration in water management ability of GDL. EIS represented that the increases of ohmic and charge transfer resistance were relatively small, and the mass transfer resistance significantly increased after wet/dry cycles. The mass transport loss calculated by Nernst equation increased 6.9% at 1.4 A/cm². In this study, it was identified that not only catalyst coated membrane degraded by wet/dry cycles, but GDL degraded under repetitive RH variations, resulting in the increase in mass transport loss and the deterioration of water removal ability.

Presenting Author: HanBeen Seo Chosun University

Presenting Author Biography: I am in master course at Chosun University, Republic of Korea. My reserach area is the topic of "Performance comparison and analysis by degradation of polymer electrolyte membrane fuel cell".

Authors:

HanBeen Seo Chosun University
Sung Yong Jung Chosun University