Proton exchange membrane fuel cells (PEMFCs) are a type of device that converts chemical energy into useful electrical work. A key component of PEMFC is membrane electrode assembly (MEA), which determines the power density and the service life of fuel cells. Current PEMFC technologies require high loadings of precious metal catalysts, such as Pt, in MEA to produce sufficient power densities for transport applications. The high cost and unsatisfactory durability of MEA still hinder the large-scale commercialization of fuel cell electric vehicles. This thesis aims to explore ways to enhance the performance and durability of MEA, while reducing the usage of precious metals. In tackling the activation loss during MEA operation, Pd@Pt core-shell catalyst is synthesized in gram-scale batches,...[ Read more ]

Proton exchange membrane fuel cells (PEMFCs) are a type of device that converts chemical energy into useful electrical work. A key component of PEMFC is membrane electrode assembly (MEA), which determines the power density and the service life of fuel cells. Current PEMFC technologies require high loadings of precious metal catalysts, such as Pt, in MEA to produce sufficient power densities for transport applications. The high cost and unsatisfactory durability of MEA still hinder the large-scale commercialization of fuel cell electric vehicles. This thesis aims to explore ways to enhance the performance and durability of MEA, while reducing the usage of precious metals. In tackling the activation loss during MEA operation, Pd@Pt core-shell catalyst is synthesized in gram-scale batches, and used as the cathode catalyst for oxygen reduction reaction. A novel post-treatment method is applied to the core-shell catalyst, allowing partial removal of the Pd core and hence improving of platinum group metal (PGM) mass activity of the catalyst. Using single cell MEA test, the post-treated core-shell catalyst demonstrates high mass activities of 0.98 A/mg_Pt and 0.53 A/mg_PGM, and the mass activity after 30000 square-wave potential cycles remains 63% of the begin-of-test value. In improving the mass transport properties of MEA, the effects of ionomer-to-carbon ratio (I/C), structure and hydrophobicity of carbon support, MEA fabrication method, and MEA conditioning parameters are investigated. Using commercially available Pt/C catalyst, at a cathode Pt loading of 0.1 mg/cm², only 1/3 of that used in the state-of-the-art MEAs, the mass-transport-optimized and well-conditioned MEA delivers a peak power density of 1.06 W/cm² in H₂/air feeds. When post-treated core-shell catalyst is used in optimized MEA, under H₂/air flows and the same Pt loading, a peak power density of 1.15 W/cm² can be delivered. Surface analysis is applied to examine the pore structure of carbon support, and when combined with MEA performance evaluation, guidelines to achieve high-power and durable low-Pt MEA are constructed. To identify the source of MEA performance loss, MEAs before and after accelerated stress test (AST) are characterized using XRD, TEM, EIS, cyclic voltammetry, crossover current tests, and cathode effluent water is collected at each stage of fuel cell operation and analyzed for fluoride and sulfate release.