Electrocatalysis In Alkaline Media And Anion Exchange Membranes For Alkaline Fuel Cells

John, Jimmy

Electrocatalysis In Alkaline Media And Anion Exchange Membranes For Alkaline Fuel Cells

Abstract

The central theme of this thesis is the investigations of fundamental processes of relevance to the operation of fuel cells in alkaline media. In this respect, broadly speaking, aspects of electrocatalysis in alkaline media and phenomena active in hydroxide-conducting anion exchange membranes were explored. Specifically, the electrocatalytic oxidation of formate on platinum in alkaline media was examined in detail. Results from a suite of electrochemical measurements, complemented with in situ mass-spectrometric measurements in the form of differential electrochemical mass spectrometry (DEMS), revealed a highly adsorbate-mediated reaction mechanism of formate oxidation. In a comparative analysis of results, the relative inactivity of formate towards oxidation, vis-à-vis formic acid in acidic media, is inferred to be due to the slow kinetics associated with the rate-determining steps of the formation of an electro-active adsorbate from formate and its subsequent oxidation. This mechanistic study is detailed in Chapter 3. A prototypical quaternary-ammonium based anion exchange membrane material was the subject of electroanalytical investigations into the processes relevant to the application of anion exchange membranes in fuel cells. The uptake of carbonate ions, and any subsequent carbonate precipitation in the membrane, was studied using the electrochemical quartz crystal microbalance (EQCM) technique. The EQCM studies demonstrated reversible carbonate and formate (produced simultaneously with carbonate by the oxidation of methanol) exchange in the membrane. The studies, further, established that the membranes exhibit a finite capacity of carbonate/formate uptake which would preclude any precipitation. On an associated aspect, acoustic impedance measurements showed the membranes to undergo swelling on hydration. Further, during the EQCM measurements, the extent of swelling in the membrane changed ii dynamically in response to the electrochemically driven anion exchange process in the membrane. The results from these studies are documented in Chapter 4. Physical and charge transport in the membrane were probed by employing redox active molecules which are neutral and negatively charged, respectively, and the applicable transport mechanisms inferred from the electrochemical studies. Preliminary results from ex-situ microscopic/spectroscopic studies targeting a more detailed physicochemical understanding of the membrane phenomena are also documented. These studies are intended to be a prelude to a comprehensive in situ characterization of the membrane in the future that will be needed to critically address the form-function relationships in these material systems. The transport and the ex-situ studies form the subject matter of Chapter 5. As for the methodologies employed in this work, the theoretical and the experimental aspects of the DEMS and the EQCM techniques are presented in Chapter 2. On a related note, the development of advanced in situ FTIR setups is described in Chapter 6. The preliminary testing of these setups is also reported. It is expected that, in the future, these advanced spectroscopic tools would be an invaluable aid in examining electrochemical interfaces. The final chapter deals with the rotating disc electrode voltammteric studies of the oxidation of hydrogen in the presence of carbon monoxide on platinum lead (PtPb) intermetallic in acidic media. This study was motivated by the promising electrocatalytic activity of the PtPb intermetallic for formic acid and methanol oxidation in acidic media. iii

Date Issued

2013-08-19

Keywords

Formate Electro-oxidation; EQCM; DEMS; Viscoelasticity; PM-IRRAS; ATR-SEIRAS; PtPb intermetallic; Carbonation; IRRAS

Committee Chair

Abruna, Hector D

Committee Member

Hennig, Richard G.
Disalvo, Francis J

Degree Discipline

Chemistry and Chemical Biology

Degree Name

Ph. D., Chemistry and Chemical Biology

Degree Level

Doctor of Philosophy

Types

dissertation or thesis