Degree

Doctor of Philosophy (PhD)

Department

Cain Department of Chemical Engineering

Document Type

Dissertation

Abstract

Hydrogen fuel cell and separation technologies such as proton exchange membrane fuel cells (PEMFCs) and electrochemical hydrogen pump (ECHP) offer a profound advantage in the transition to a low-carbon economy. An imperative hitch in hydrogen fuel cells and ECHP technology has been the electrocatalyst poisoning by carbon monoxide (CO) and other contaminants in the reactant mixture. By operating, hydrogen fuel cells and ECHPs at high temperatures (>200 °C), the effect of CO adsorption on the electrocatalyst surface could be curtailed. The high-temperature operation of devices necessitates a proton exchange membrane (PEM) to operate under anhydrous conditions.

In this work, a new class of anhydrous high-temperature proton exchange membrane (HT-PEM) based on H3PO4 doped PC-PBI membrane blends were examined, and the optimal blend (50:50 ratio) exhibited remarkably high conductivity in a wide temperature range (-70 °C to 240 °C), while also displaying excellent thermal stability and resiliency to water vapor. The new class of HT-PEM enables the operation of hydrogen fuel cells and ECHPs under a wide temperature range, concurrently promoting a better performance by reducing the ASR. The newly developed HT-PEM yielded high-temperature proton exchange membrane fuel cells (HT-PEMFCs) operating with a peak power density of 680 mW cm-2 at 220 ºC. For further advancement in performance, the kinetic and mass transport resistances of the liquid H3PO4 electrode ionomer binders needed to be addressed, for which liquid H3PO4 free – phosphonic acid-functionalized high-temperature polymer electrolytes were explored. The thin-film characterization of the newly synthesized polymer electrolytes was carried on using interdigitated electrode (IDE) platforms decorated with nanoscale platinum electrocatalysts.

The enhanced reaction kinetics and gas permeability of liquid H3PO4 free binder enabled an excellent ECHP performance of 1 A cm-2 at 55 mV under pure H2 anode feed and improved fuel cell performance of >0.9 W cm-2 of power density with H2/O2 at 220 °C. The high-temperature operation of ECHP under varying anode hydrogen-hydrocarbon-contaminant mixtures yielded better tolerance to CO and other contaminants in the anode feed, revealing that the performance was driven by hydrogen concentration rather than the concentration of CO in the anode feed mixtures.

Date

4-14-2021

Committee Chair

Arges, Christopher G.

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