The effect of nanocatalyst size on performance and degradation in the cathode of proton exchange membrane fuel cells

Abstract

This thesis discusses the role of initial particle size on the mechanisms of surface area loss of carbon-supported platinum (Pt) electrocatalysts in the cathode of proton exchange membrane fuel cells. Electrocatalyst decay protocols were used to accelerate cathode performance loss for Pt catalysts. Four cathodes with mean platinum particle sizes of 2.1, 3.5, 6.7 and 11.3 nm were evaluated to elucidate the impact of particle size on initial performance and subsequent degradation, when subjected to identical potential cycles. The degradation of Pt electrochemically active surface area (ECA) was significantly greater for 2.1 and 3.5 nm initial sizes compared to 6.7 and 11.3 nm initial sizes. As expected, the ECA loss of the cathodes shows an inverse proportionality with initial particle size. However, the initial performance of the 11.3 nm initial particle size electrode was significantly lower than the three smaller sizes. Thus, an initial Pt particle size of 6.7 nm was identified to offer the ideal balance performance and durability. The current state of standardization in characterizing particle size by transmission electron microscopy (TEM) is also investigated. The result is a standardized protocol for image acquisition and analysis.