Durability and degradation of gas diffusion electrodes for the electroreduction of CO2 to fuels

Cofell, Emiliana R.

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https://hdl.handle.net/2142/115771 Copy

Description

Title

Durability and degradation of gas diffusion electrodes for the electroreduction of CO2 to fuels

Author(s)

Cofell, Emiliana R.

Issue Date

2022-04-22

Director of Research (if dissertation) or Advisor (if thesis)

Kenis, Paul J.A.

Doctoral Committee Chair(s)

Perry, Nicola

Committee Member(s)

• Gewirth, Andrew A.
• Dillon, Shen
• Evans, Christopher

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• CO2
• durability

Abstract

The electrochemical reduction of CO2 (CO2RR) is an emerging green technology that offers the dual benefits of recycling CO2 emissions and producing valuable fuels and chemicals in a carbon-neutral manner. Previous research has focused on the use of gas diffusion electrodes (GDEs) in CO2RR systems, which have enabled the conversion of CO2 into products at high, industrially relevant rates. However, the durability of GDEs has not been widely studied, although analyses suggest a lifetime of thousands of hours is needed for economically feasibility. In my work, I systematically probe the time-dependent performance of GDEs in a flow electrolyzer using alkaline electrolytes for high-throughput production of CO from CO2. Through a variety of physical and chemical materials characterization techniques, I elucidate degradation mechanisms and strategies for improving GDE durability for CO2RR. Initially, we were interested in the impact of electrolyte composition and concentration on the GDE, and studied the impact of operation in various molarities of KOH and CsOH on the GDE. By using a physiochemical characterization protocol consisting of SEM, EDS, Micro-CT, and XRD of electrode pre-and post-testing, we determined that carbonate deposits forming on the electrode surface have a rapidly deleterious effect on CO2RR performance, halting conversion of CO2 to CO by decreasing available catalyst active area. We found that switching the electrolyte to CsOH slowed degradation, likely due to higher solubility of cesium carbonates in solution leading to slower growth of surface deposits. Subsequently, we turned to the literature, where high performance in multivalent cations-based electrolytes due to stabilization of the CO2-radical had been predicted by computational models. In our experimental work, we found that this prediction did not hold due to rapid passivation of the electrode surface by oxides, hydroxides, and hydrides when operated in multivalent cations-based electrolytes. Through these works, we determined the detrimental effect of surface deposit formation on GDEs when operated in mono-and-multivalent electrolytes. We then turned to fuel cell and water electrolysis literature, where often accelerated stress tests have been used to apply multiple potential cycles to electrodes to simulated the effect of startup and shutdown. Simulating the operation of a CO2 electrolyzer operated in variable potential conditions, we found that potential cycling can result in significant restructuring of the catalyst layer and loss of catalyst. This effect occurs specifically in higher (more positive) potential ranges where silver oxide formation takes place. Conversely, cycling at lower (more negative) potentials can have a moderate inhibition effect on carbonate deposit formation, as potential cycling interrupts the precipitation of deposits due to high local concentration of OH- at the catalyst layer. Finally, I have investigated electrolyte-based methods for carbonate deposit inhibition, and have found that mixed KOH and CsOH electrolytes show significant inhibition of carbonate deposits. Additionally, using alternative GDE substrates may impact deposit formation due to the relationship between increased surface roughness and carbonate nucleation. This dissertation demonstrates the power of studying changes in surface morphology and composition as a tool for determining the causes of GDE degradation and performance loss. By studying and quantifying GDE degradation, we can determine which conditions lead to loss of catalyst available for the CO2 reduction reaction and better understand how to engineer long-lasting electrodes for durable CO2RR systems.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Emiliana Cofell

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