Date of Award

1-1-2012

Document Type

Campus Access Thesis

Department

Chemical Engineering

First Advisor

John W Weidner

Abstract

A gas-phase sulfur dioxide (SO2) depolarized electrolyzer has been investigated for the large scale production of hydrogen. One issue that negatively affects electrolyzer operation is the diffusion of SO2 from the anode to cathode. A viable method to reduce crossover is to use a thin, low-permeability anode prelayer (LPAP) film with significant resistance to SO2 transport supported on a membrane with high proton conductivity. However, it is difficult to measure the properties of the LPAP film since this layer is not free standing. Hence, we have developed a model that allows us to obtain the gas transport properties (i.e., diffusion coefficient and gas solubility) of a prelayer knowing the gas transport properties of the primary supporting membrane using the electrochemical monitoring technique (EMT). We experimentally verified our two-layer model via EMT experiments using membrane electrode assemblies (MEAs) made of single layers of Nafion 115 (N115) and Nafion 212 (N212), and an MEA of N115 and N212 laminated together. That is, the Nafion 212 membrane served as a pseudo-LPAP film where the two-layer model was used to extract the parameters for N212 knowing those of N115. We then applied our model to a two-layer MEA consisting of an LPAP film on a N115 membrane to obtain the SO2 transport parameters in the LPAP film. Although this study was used to develop MEAs that reduce SO2 crossover in a gas-phase sulfur dioxide (SO2) depolarized electrolyzer, it is applicable for the analysis of gas transport in any two-layer material (e.g. proton exchange membrane).

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