UC Irvine

Polymer electrolyte fuel cells (PEFCs) provide a promising way to mitigate global warming since these power sources produce no emissions of greenhouse gases. PEFCs convert chemical energy of hydrogen and air to electricity via electrochemical pathway. For broad deployment of PEFCs in transportation sector cost and durability need to be addressed. At the heart of the fuel cell is the catalyst layer, where platinum (Pt) catalyst is used to catalyze oxygen reduction reaction (ORR). Pt is typically dispersed on carbon support and with ionomer (such as Nafion) to enable ORR. Understanding Pt-ionomer interface is critical to enable PEFCs with low Pt content. Therefore, in this work Pt- ionomer interfacial and transport properties within the catalyst layers were examined using variety of electrochemical diagnostic techniques.

Optimizing electrode morphology with a more uniform ionomer distribution is key to reducing ohmic losses and increasing electrocatalyst utilization in PEFCs. For ionomer transport properties, we determined three different methods including direct current (DC) hydrogen pump (HP), HP electrochemical impedance spectroscopy (EIS) and H2/N2 EIS to investigate catalyst layer ionic conductivity, and it was the first and unique study to compare each method. Apart from that, we developed an 1D H2/N2 EIS impedance fitting model, which enable us to evaluate catalyst layer ionic conductivity with good accuracy. For Pt ionomer interfacial properties study, we first studied performance and electrochemical characterizations for MEAs containing novel high oxygen permeability ionomers (HOPIs) synthesized by Giner, and a comparison was made between novel ionomer and commercial Nafion ionomer. After that, we investigated some possible factors which influence cell performance and catalyst/ionomer interfacial properties using 3M materials including Pt loading, ionomer content and carbon support types, which would bring thoughts and inspirations to community regarding the design of optimal catalyst layer. Finally, we studied Pt ionomer transport and interfacial properties change during carbon corrosion accelerated stress tests (ASTs). We performed both in-situ and ex-situ measurements on MEAs containing different types of carbon support, which enable us to better understand the causes for drop of performance from ionomer interfacial properties perspective.