Date of Award

Spring 2018

Project Type

Thesis

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Xiaowei Teng

Second Advisor

Nivedita Gupta

Third Advisor

Nan Yi

Abstract

Direct ethanol fuel cells (DEFCs) are a promising technology for the generation of electricity via the direct conversion of ethanol into CO2, showing higher thermodynamic efficiency and volumetric energy density than hydrogen fuel cells. However, implementation of DEFCs is hampered by low selectivity of CO2 generation at the anode where the ethanol oxidation reaction (EOR) happens. Therefore, anode catalysts with high reactivity for the EOR and high selectivity for CO2 generation via breaking C-C bond are highly needed. To evaluate the catalysts’ capability of splitting C-C bond of the ethanol molecule, highly sensitive CO2 detection technique was developed in this research using a CO2 microelectrode. Such an in situ CO2 measurement tool enabled the real time detection of the partial pressure of CO2 during the EOR using linear sweeping voltammetry measurements, through which electro-kinetic details of CO2 generation could be obtained. Electro-kinetics of CO2 generation were studied on the PtRh/SnO2 core-shell catalysts made by a ‘surfactant-free’ method. The results showed that Pt and Rh components located in the core were partially oxidized and therefore improved the CO2 generation at low electrical potential. In addition, in situ CO2 measurements provided the mechanistic understanding of potentiodynamics of the EOR, particularly the influence of *OH adsorbates on CO2 generation rate and CO2 selectivity. Our results showed that at low potential, inadequate *OH adsorbates impaired the removal of reaction intermediates, and thus Pt/Rh/SnO2 exhibited the best performance toward CO2 generation due to its strong ability to dissociate water molecules forming *OH oxidants, while at high potential, Rh sites were overwhelmingly occupied (poisoned) by *OH adsorbates, and thus Pt/SnO2 exhibited the best performance toward CO2 generation.

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