Date of Award

January 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Michael Mann

Abstract

Proton exchange membrane fuel cells (PEMFCs) have a unique property of zero (ultra-low) emission and provide significant technical and overall cost advantages compared to other types of fuel cells. As a result, PEMFCs have attracted considerable attention as an alternative power source for stationary and mobile applications. However, the PEMFCs are yet to realize mass-market commercialization hindered mainly by its poor durability. Therefore, numerous research efforts have been devoted to studying the durability of PEMFCs, motivated by the desire to improve its lifetime without unduly increasing cost or compromising performance.

The catalyst support largely determines the stability of supported platinum group metal (PGM) catalysts, overall electrochemical activity and durability of the catalyst layer in PEMFCs. This research was motivated by the desire to improve the stability and durability of the PEMFCs by utilizing the novel silica supported platinum (Pt/Silica) catalyst support. The purpose of this study was to develop a membrane electrode assembly (MEA) from Pt/Silica catalyst and to investigate/analyze the effects of Pt/Silica on the performance and durability of PEMFC. The primary hypothesis of this work is that the Pt/Silica catalyst would enhance the performance and durability of PEMFCs compared to ���������� − ���� − ��ℎ�� − ������ carbon-supported platinum (Pt/Carbon) catalysts.

In this dissertation work, two types of MEA’s were prepared using a hot-pressed GDE method. Type-A MEA was prepared using a state − of − the − art Pt/Carbon commercial catalyst and serve as a baseline MEA. Type-B MEA was prepared using novel Pt/Silica in-house fabricated catalyst, and was used as the basis to prove the hypothesis of this work. Finally, the MEA prepared during this research work were mounted in a 25 cm2 unit-cell PEMFC fixture for its ���� − �������� evaluation. The evaluation of both of Type-A and Type-B MEA was performed using Polarization (IV) and Cyclic Voltammetry (CV) electrochemical techniques. The performance and durability data was then compared to test the hypothesis of this research. The maximum power density of Pt/Silica catalyst was found to be 52 % of the commercial Pt/Carbon catalyst under the identical experimental setup and operating conditions. Similar results were demonstrated in CV testing, where the calculated ECASA of Pt/Silica catalyst was found to be 75 % of the commercial Pt/Carbon catalyst. Electrode flooding and low conductivity of silica support were experimentally found as the cause of the reduced performance of the Pt/Silica catalyst. When operated under conditions to eliminate flooding for Pt/Silica, its performance improved, with its maximum power density found to be 62 % of the commercial Pt/Carbon catalyst. When operated under the conditions to eliminate flooding for Pt/Silica, its performance improved, with its maximum power density found to be 62 % of the commercial Pt/Carbon catalyst. When the conductivity of Pt/Silica-based MEA was improved by adding carbon black in the catalyst ink, and operated under the conditions to eliminate flooding for Pt/Silica, its performance improved, with its maximum power density found to be 82 % of the commercial Pt/Carbon catalyst.

The durability study showed that the loss in ECASA of the novel Pt/Silica catalyst at the end of the 24-hour potential hold test was 27 % from its baseline condition. The corresponding loss in commercial Pt/Carbon catalyst was found to be 55 %. The Pt/Carbon catalyst deterioration was also more severe during 10,000-cycle potential cycling durability test compared to the baseline ECASA. The Pt/Carbon catalyst was able to retain only 27 % of the active Pt surface area compared to 68 % retained by the Pt/Silica catalyst after the 10,000-cycle test.

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