Investigation of Manufacturing Defects (Catalyst layers & pinholes) in PEMFC Electrode

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) is promising as an emissions-free energy system with high efficiency and reduced greenhouse gas effects. However, durability and cost are two major factors limiting its commercialization into the market. For a reliable mass production of fuel cell stacks, advance quality control testing methods are required to address the issues associated with the PEMFC materials (catalyst layers(CL), membranes, gas diffusion layer (GDL) electrodes and membrane electrode assemble (MEAs))1. One significant issue effecting the long-term stability of fuel cell stacks are defects that develop during the mass production of catalyst coated membranes (CCMs) and fabrication of MEAs2. Previous work has been done on various real defects existing in CCM production line. These defects were investigated and classified (missing/empty catalyst layers, voids, delamination and cracks) based on shape, size and orientation. Although various studies are conducted in order to measure the impact of some defects on overall performance of the cell, these techniques are limited to particular effects3-4. Here we are presenting a detailed investigation of defects associated with MEA components. An incomplete catalyst layer defect (fig.1b), that is transformed from decal substrate to CCMs and a pinhole, developed across the sealant during the fabrication of MEA is studied under by acceleration stress test (AST)5-6. Propagation of defects at different RH cycling periods (80% RH to 20% RH) on the cathode is performed at open circuit voltage (OCV). During the cyclic OCV, In-situ analysis including down polarization, linear sweep voltammetry (LSV) and Impedance is conducted to measure the degradation of electrode. MEA is also constantly examined using IR camera after 100 RH cycles (fig.1a). It is found that degradation of the defected MEA’s OCV was higher (2.84 mV/h) during short delay in RH cycling (5 mins 80% RH to 5 mins 20% RH) than under long delay in RH cycling (1.80mV/h operated at 5 mins 80% RH to 30 mins 20% RH). AST on cathode shows various levels of chemical degradation rates, leading to an increase in hydrogen gas crossover current (fig.1d) and impedance resistance (fig.1e). The growth of pinhole is studied with respect to hydrogen crossover. Fluctuation in the impedance curve at 7.58 mHz shows the charge transfer effect due to pinhole developed in the membrane. In addition, fluoride ion rate is examined to estimate the degradation of the polymer membrane causing this decrease in OCV. This study helps the fuel cell manufacturer better understand the impact of manufacturing defects and their effect developed during the fabrication process of the electrodes.