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Abstract:
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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 . |