Doctoral Dissertations

Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Feng-Yuan Zhang

Committee Members

Matthew M. Mench, Zhili Zhang, Lloyd M. Davis

Abstract

In electrochemical energy devices, including fuel cells, electrolyzers and batteries, the electrochemical reactions occur only on triple phase boundaries (TPBs). The boundaries provide the conductors for electros and protons, the catalysts for electrochemical reactions and the effective pathways for transport of reactants and products. The interfaces have a critical impact on the overall performance and cost of the devices in which they are incorporated, and therefore could be a key feature to optimize in order to turn a prototype into a commercially viable product. For electrolysis of water, proton exchange membrane electrolyzer cells (PEMECs) have several advantages compared to other electrolysis processes, including greater energy efficiency, higher product purity, and a more compact design. In addition, the integration of renewable energy sources with water electrolysis is very attractive because it can be accomplished with high efficiency, flexibility, and sustainability. However, there is a lack in fundamental understanding of rapid and microscale electrochemical reactions and microfluidics in PEMECs. This research investigates the multiscale behaviors of electrochemical reactions and microfluidics in a PEMEC by coupling an innovative design of the PEMEC with a high-speed and microscale visualization system (HMVS). The results of the investigation are used to aid in revealing the electrochemical reaction mechanisms and the microfluidics behavior including bubble generation, growth and detachment, which all together play a very important role in the optimization of the design of PEMECs. The effects of operating parameters such as current density, temperature and pressure on the electrochemical reactions and the microfluidics are determined and analyzed by mathematical models of PEMECs, which also match the experimental results. Improved understanding of the electrochemical reactions and microfluidics in PEMECs can not only help to optimize their designs, but can also help advance many other applications in energy, environment and defense research fields.

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