Date of Award

5-2011

Embargo Period

12-4-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor(s)

John Kitchin

Comments

Gas separation processes have received extensive interest over the past few years due to concerns over global carbon dioxide emissions. Most of these processes have inherently low efficiencies which need to be solved before carbon dioxide can be captured in the volumes necessary from point sources such as coal plants. To accomplish this, new technological advancements will be made.

In this work, an electrochemical gas separation process is used which separates carbon dioxide and oxygen from various feed sources including air and simulated flue gas streams. When capturing carbon dioxide from more concentrated feed gas streams, large amounts of carbon dioxide can be captured for every mole of oxygen, up to 3.56:1 moles of carbon dioxide to oxygen. Cell potentials lower than 1.23 V were used to carry out this separation. An anion exchange membrane is used in this device which lowers cell resistive losses over previous oxygen electrochemical separation cells. An energy analysis was conducted which showed that cell potentials of 0.5 V will need to be reached if this separation process is to be used in conjunction with carbon dioxide capture from a pulverized coal plant.

To lower the cell potentials necessary for this separation further, catalyst development into lowering the reaction barriers is necessary at both the anode and the cathode used in this process. The oxygen evolution reaction taking place at the anode was examined, and an investigation into lowering the potential requirements of this reaction was carried out. Perovskite catalysts of the formula La0.7Sr0.3BO3 B = [Ni, Co, Fe, Mn] were synthesized using an evaporation- vi induced self-assembly process (EISA) which resulted in surface areas between 4-32 m2/g. Catalysts were then tested for their oxygen evolution capability at overpotentials up to 0.7 V. Perovskite catalysts were found to be active for oxygen evolution but the overpotentials of reaction were in excess of those found previously for NiO.

Transition metal oxides and mixed oxides were examined for the oxygen evolution reaction (OER). NiO, Co3O4, and Fe2O3 as well as mixed oxides of Ni-Fe and Ni-Co were investigated. Catalysts were synthesized using the EISA synthesis process and catalysts with surface areas between 7-31 m2/g were made. A synergistic effect towards oxygen evolution previously shown by other researchers between Ni and Fe was shown here with these higher surface area EISA catalysts. A peak in activity at 10 mol% Fe in the mixed Ni-Fe oxide system was found. Mixed Ni-Co oxide catalysts showed no synergistic effect towards oxygen evolution. Co3O4 had the highest activity of the catalysts in this system.

Surface spectroscopy of the mixed Ni-Fe oxide catalysts using XPS showed a mixed surface of NiO and Fe oxide. No identification of the exact Fe oxide phase could be made due to the low signal readings. No evidence of alloying between Ni and Fe was found to be present meaning separate phases of these oxides are found on the surface of this high surface area powder. XAS analysis showed phases of NiO and Fe2O3 present in these mixed catalysts. in situ EXAFS showed further oxidation under oxygen evolution conditions occurring on Fe sites while NiO sites remained unchanged.

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