Date of Award

Summer 2020

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Ralph E. White

Second Advisor

Kevin Huang

Abstract

Until recently the world’s main source of energy has been fossil fuels, such as coal and petroleum. However, these energy sources are polluting our planet, becoming scarce and increasingly inaccessible, and are costly to extract. Therefore, much attention has been directed to harvesting clean, abundant, and renewable energy, such as solar rays and wind. However, the intermittency of solar and wind power generation requires an effective energy buffering solution (aka energy storage) to become efficient and reliable. With high efficiency and energy density, rechargeable batteries and reversible fuel cells are two of the best methods for this purpose. Unfortunately, a broader and deeper implementation of these two technologies is currently hindered by their poor performance, specifically the sluggish electrode kinetics.

The overarching objective of this Ph.D. work is to fill this technical and scientific gap by investigating the fundamentals of oxygen electrolysis (oxygen reduction reaction and oxygen evolution reaction) mechanisms of non-noble metal-based oxygen electrode materials operating in alkaline electrochemical cells, such as metal-air batteries. The overall approach employed is two-fold: experimentation and theoretical modeling. The oxygen electrode material studied is a mixture of model perovskite structured complex oxide, La0.6Sr0.4CoO3-δ (LSCO) and Vulcan carbon (XC-72) in different ratios. Standard linear sweep voltammetry (LSV) under rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) is the primary tool used to collect electrochemical data, from which the multiphysics models are validated.

A 1-D RDE multiphysics model is first established from multi-step, multi-electron (4 or 2 electron transfer), sequential and parallel elementary electrode reactions in conjunction with a peroxide-involving chemical reaction. The governing equations are derived from basic charge transfer and mass transport theories with appropriate boundary conditions. The model is then validated by the RDE LSV data collected from the LSCO/XC-72 oxygen electrode. The validated model is able to project partial current densities for each elementary electrode reaction considered along with the peroxide production rate of the chemical reaction, which cannot be done by “classical” approaches. The 1-D RDE model is further expanded into a 2-D RRDE model to quantify the peroxide intermediates vs applied potential. The new 2-D model is validated with a glassy carbon electrode and it is found that the addition of a parallel, series 1e- reduction of oxygen, incorporating a superoxide intermediate, is necessary.

Rights

© 2020, Victoria F. Mattick

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