Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Mechanical and Materials Engineering


Dr. Xueliang Sun

Second Advisor

Dr. Jun Yang


Low temperature fuel cells, including proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), are now attracting enormous interest as a promising power generation device. However, high cost and low durability of the catalysts limit their wide-spread commercialization. This thesis is focused on increasing the electrocatalytic activity and durability of Pt catalysts on supports. Due to the drawbacks of commercially-used carbon black supports, carbon nanotubes (CNT) and nitrogen-doped carbon nanotubes (CNx) are synthesized as the catalyst supports by the chemical vapor deposition method. The electrocatalytic activities and electrochemical durability of the catalysts on these novel supports are evaluated. And the single H2/02 fuel cell performances are tested. CNT and CNx are compared as the supports of Pt nanoparticles. Smaller size and more uniformly dispersed Pt nanoparticles are deposited on CNx than on CNT without pretreatment. Pt supported on CNx (Pt/CNx) exhibits a larger electrochemical surface area (ECSA) and higher catalytic activity toward oxygen reduction reaction (ORR), in comparison with Pt supported on CNT (Pt/CNT). Pt catalysts supported on CNT and CNx of different nitrogen contents are examined for their electrochemical stabilities with accelerated durability tests for the first time. Based on the loss of ECSA and TEM images of the Pt nanoparticles, Pt/CNx exhibited much higher stabilities than Pt/CNT, and the stability increases with the iii increase of nitrogen contents in the CNx supports. SnO2 nanoparticles are deposited on CNx with the atomic layer deposition (ALD) technique as a co-catalyst of Pt. A three-dimensional Pt-SnO2/CNx/carbon paper composite electrode demonstrates higher electrocatalytic activities over ORR and methanol oxidation reaction (MOR) than Pt/CNx/carbon paper. The pre-deposited SnO2 also increases the electrochemical stability of Pt catalysts. Polycrystalline SnO2 is more effective than the amorphous form in stabilizing Pt catalysts. Pt alloys such as Pt-Ni supported on functionalized CNT are studied. A volcano-shape relationship is observed between the electrocatalytic activities toward ORR and the Ni contents in the PtNi alloy catalysts with different atomic ratios, with Pt75Ni25 exhibiting the highest activity. A geometric effect of Pt-Pt interatomic distance and electronic effect are proposed to explain the enhancement Ofelectrocatalytic activity with Ni introduction.



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