Date of Award

12-14-2015

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Branko N. Popov

Abstract

The major barriers in the commercialization of the fuel cell technology for automotive applications are the cost and durability of the Pt catalyst and the support stability at high potentials. The U.S. Department of Energy (DOE) targets direct hydrogen fuel cell systems for transportation to meet 65% peak-efficiency, 5,000 hour durability with a mass production cost of $40/kW by 2020. Currently in 2015, the system can be operated at peak energy efficiency of 60% for 3,900 hours with cost of $55/kW. To meet these targets, precious metal loadings must be greatly reduced without altering the catalyst stability. The primary objective of this dissertation is to develop highly active and durable hybrid cathode catalysts (HCC) with ultra-low Pt loading for Proton Exchange Membrane Fuel Cells (PEMFC) through interaction of highly active and stable Pt and compressive Pt-lattice (Pt*) catalyst deposited on catalytically active and highly stable carbon composite catalyst (CCC) support and active carbon composite catalyst (A-CCC) support. The HCC activity is enhanced by by the synergistic effect of catalytic active sites for ORR present in the supports and those in Pt and Pt*. The stability of Pt-based catalyst can be greatly improved by doping with transition metal (TM), which weakens interactions between Pt and adsorbents such as OHads and Hupd. Highly active and durable HCC is developed in this study through: (i) synthesis of highly catalytically active and stable Co-containing CCC and A-CCC supports, (ii) surface functionalization and uniform Pt deposition on CCC and A-CCC supports, (iii) performance optimization of Co-doped Pt catalysts by using protective coating to inhibit particle agglomeration and growth during the pyrolysis step, (iv) optimization of Pt/Co ratio and annealing temperature and (v) chemical leaching to remove excess metal used to dope the support. T The support stability has been enhanced through optimization of: (i) Brunauer-Emmett-Teller (BET) surface, (ii) the support structural properties (amorphous/crystalline ratio), and (iii) the hydrophilic/hydrophobic ratio of the supports. During the past five years, the performance and durability of the catalysts were continuously studied. Stability of the catalyst was tested under U. S. DRIVE Fuel Cell Tech Team suggested protocols (a) potential cycling between 0.6 and 1.0 V for 30,000 cycles, (b) potential holding at 1.2 V for 400 h, and (c) potential cycling between 1.0 and 1.5 V for 5,000 cycles. The mass activity, H2-air polarization curve, ECSA, and power density were measured at regular intervals. Detailed results of this work will be discussed in this dissertation.

Rights

© 2015, Tianyuan Xie

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