A Study On The Membrane Electrode Assemblies And The Catalyst Of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are expected to find wideapplication as mobile, portable, and distributed stationary power sources owing totheir outstanding advantages, such as zero or low emission, high efficiency, highpower density, and rapid start-up. However, the high cost of production and the poordurability of membrane electrode assemblies (MEAs) obstruct the large-scalecommercialization of PEMFCs. In this dissertation, a series of research centered onPEMFCs was conducted, including the fabrication technique of MEAs, the structuraloptimization of the catalyst layer, and the synthesis of high catalytic activity and highdurability Pt electrocatalyst.By evaporating dilute catalyst ink on the gas diffusion layers directly to form thegas diffusion electrodes, a novel and simple MEA fabrication method was proposed.With this method, no special equipment was needed and the catalyst loading could beprecisely controlled. The MEAs that were obtained with the same preparationparameters exhibited almost coincident current-voltage curves, namely this MEAfabrication method has a good reproducibility. Peak power densities about900mW/cm2could be achieved with a Nafion content between30~40wt%inside thecatalyst layers.In order to improve the catalyst utilization and the mass transfers inside thecatalyst layers, structurally ordered catalyst layers (SOCLs) with aligned carbonnanotubes (CNTs) as the catalyst support were prepared. The alignment of the CNTswas realized by employing a perpendicular AC electric field on the Pt/CNTs catalystink while it was drying on the gas diffusion layers. With the alignment of the CNTssupport, the SOCLs were more favorable for mass transport and charge conductanceand had a higher catalyst utilization efficiency as compared with the randomlystructured catalyst layers. Consequently, the MEAs based on SOCLs showed up to30%increase in peak power output.Graphite nanoplatelets (GNPs), which have high electron conductivity, largespecific surface area, excellent chemical stability and easy availability, were used asthe support for the Pt/GNPs catalyst. By using1-pyrenecarboxylic acid as a linkingreagent, the Pt nanoparticles had a narrow size profile, which was centered at approximately2to3nm, and an even spatial distribution on the GNPs surface. Theresultant Pt/GNPs catalyst exhibited a noticeably higher durability andelectrochemical activity than the commonly used Pt/C catalyst.The effect of π-π stacking interaction energies and functionalities on thedeposition of Pt nanoparticles on the GNPs surface was studied by using a series ofdecorating reagents that had different aromatic rings and functionalities. Also, theaction mechanism of the decorating reagents was researched by changing thepreparation conditions of the catalysts. We concluded that when a decorating reagenthad a strong π-π stacking interaction energy with the GNPs and its functionality couldbe ionized in the reaction solution, its assistance on the Pt deposition would be moreefficient, and the decorating reagents had no effect on the crystal structure of the Ptnanoparticles and the durability of the catalysts.