Proton exchange membrane fuel cells convert chemical energy into electrical energy at high efficiencies with few to no emissions. From a chemistry and materials standpoint, phenomena associated with the electrolyte and catalysts are key to improving the performance and lowering the cost of these devices. Towards this end, atomic force microscopy (AFM) was used to probe the chemical domains responsible for proton transport. Phase imaging was used to gain quantitative information regarding the size and distribution of proton conducting domains and it was found that the nature of tip-sample interaction forces strongly affects the resolution and subsequent interpretation of such domains. For a Nafion perfluorosulfonic acid electrolyte, dramatic differences in domain morphology were observed at hydrated and dehydrated conditions. Novel AFM current imaging was performed on a half fuel cell in which a platinum coated tip served as a nanoscale cathode to probe the electrochemical activity at the surface of a polymer electrolyte. Comparison of current and phase images of a Nafion membrane revealed that not all aqueous surface domains are electrochemically active to the same extent. Phase images and point-by-point current-voltage measurements suggest that large domains (>100 nm2) with a high degree of surface connectivity are most active. Electrochemical pulse deposition was used to localize platinum catalysts at these domains, resulting in a device with a platinum loading of 2 μg/cm2 and a maximum power density of 120 mW/cm2.
|Advisor:||Buratto, Steven K.|
|Commitee:||Bowers, Michael T., Chmelka, Bradley F., Metiu, Horia|
|School:||University of California, Santa Barbara|
|School Location:||United States -- California|
|Source:||DAI-B 72/01, Dissertation Abstracts International|
|Keywords:||Ion conductance, Platinum catalysts, Proton exchange membrane fuel cells|
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