Gas diffusion electrodes and operating conditions for electrochemical energy storage applications

The world today faces two contradictory challenges: climate change and energy security. Interestingly, both challenges can be potentially addressed by targeting atmospheric CO2. The global demand for energy has increased due to population growth and most of this demand is met by the dwindling resource of fossil fuels. Consequently, the concentration of atmospheric CO2 has risen past the upper safety limit of 350 ppm, and has even reached as high as 404 ppm. This is believed to be a major cause of several undesirable climate effects such as global warming and increased occurrence of erratic weather. Multifaceted efforts have been made to curb atmospheric CO2 levels and decrease reliance on fossil fuels by seeking out clean, affordable and reliable energy sources. Renewable energy sources (i.e., wind, tide, and solar) are increasingly competitive due to their natural, clean and carbon-free nature. However, renewable energy sources are intermittent, limited by geography and seasons, and often unpredictable. To overcome these limitations and supply energy generated by renewable energy sources more efficiently and continuously, a suitable form of large-scale storage for on-demand utilization is needed. This thesis researches two energy storage technologies that show promise to help address both challenges: electrochemical reduction of CO2 into useful feedstock chemicals or fuels, and lithium air battery. Electrochemical reduction of CO2 into value-added chemicals is expected to play an important role in reducing CO2 emissions and dependence on fossil fuels as well as in utilizing excess, otherwise wasted energy from intermittent renewable sources. However, to be a viable technology, performance levels of CO2 electrolyzers need to be raised by making electrodes and catalyst efficient enough for commercialization. This dissertation starts with discussing the interplay between cathode performance and CO2 concentration in the feed as well as electrolyte pH (Chapter 2). Use of diluted feed elevates the utilization of CO2 up to 31 % with high Faradaic efficiency for CO (>80%). This work highlights the importance of mass transport and indicates that the direct use of flue gas as a feed for electroreduction of CO2 has promise. This dissertation also reports a detailed investigation of the relationship between the physical structure of electrodes and electrochemical activity (Chapter 3) as well as further improvement of electrodes by incorporating carbon nanotubes for electroreduction of CO2 (Chapter 4). Optimized gas diffusion electrodes (GDEs) outperform commercially available GDEs and exhibit no decay in performance during continuous operation. In addition, micro-porous layers (MPLs) composed of carbon powder exhibit better durability leading to high cathode performance compared to MPLs composed of carbon nanotubes for electroreduction of CO2. Lithium air (Li-air) battery can be a promising candidate for effective storage of renewable energy and has applications ranging from portable electronics to electric vehicles because of its extremely high theoretical energy density. However, several fundamental challenges such as poor round-trip efficiency, unsatisfactory durability and safety must be overcome to realize the promise of Li-air battery. This dissertation employs the design and fabrication of a non-aqueous Li-air battery with flowing ionic liquid (Chapter 5). The flow configuration exhibits a substantial increase in discharge capacity compared with the non-flowing battery. Also, this dissertation reports experimental and computational investigations on optimizing the gas diffusion-based cathode to produce higher discharge current densities particularly for Li-air flow batteries (Chapter 6).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Kim, Byoungsu

Contributors dc:contributor

• Kenis, Paul J.A.
• Yang, Hong
• Flaherty, David W.
• Rodríguez-López, Joaquín

• Carbon Dioxide Reduction
• Lithium Air Battery
• Gas Diffusion Electrodes
• Electrocatalysis

Statement dc:rights

• Copyright 2017 Byoungsu Kim

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/100419

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/100419