Date of Award

2018-01-01

Degree Name

Doctor of Philosophy

Department

Engineering

Advisor(s)

Dr. Cristian E. Botez

Abstract

The solid acid CsH2PO4 (CDP), exhibits a sudden increase in its proton conductivity as it’s heated above a certain temperature (around T~235oC), which makes it a very attractive candidate to be used as an electrolyte in intermediate temperature fuel cells. Unfortunately, at these temperatures the sample is not stable, as starts to dehydrate; which causes a dramatic drop in the proton conductivity over a short period of time (less than one hour). In order to inhibit, or at least delay, the dehydration process, the solid acid it’s put under a saturated water vapor atmosphere. Another method to stabilize the highly conductive phase is to subject the solid acid to a pressure of ~1GPa. However, none of these methods are practical approaches for making full scale and operational fuel cells. The main purpose of this research is to find an alternative to stabilize the proton conductivity of CDP at intermediate temperatures, by using hermetically sealed chambers filled with different gases above temperatures of the heated induced high proton conductivity. Also, we mixed CDP with nano-silica (1-x)CsH2PO4 / xSiO2 (0≤x≤0.3) for the same purpose. In this study, we used the following characterization techniques: temperature- and time-resolved electrochemical impedance spectroscopy (EIS), x-ray powder diffraction, and thermal analysis methods to analyze the composite (1-x)CsH2PO4 / xSiO2 (0≤x≤0.3). EIS data was collected at different temperatures (200oC-260oC) using both, a dry and humid (PH2O ~ 0.38 atm) atmospheres. EIS was also obtained by using a different volume hermetically sealed chambers filled with Argon, Helium, air, Nitrogen , dry air (with no humidity) and under vacuum.

Language

en

Provenance

Received from ProQuest

File Size

80 pages

File Format

application/pdf

Rights Holder

Israel Martinez

Download

Share

COinS