Understanding the role of magnetic species in nonprecious metal oxygen reduction electrocatalysts

Esposito, Anne Marie

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https://hdl.handle.net/2142/114077 Copy

Description

Title

Understanding the role of magnetic species in nonprecious metal oxygen reduction electrocatalysts

Author(s)

Esposito, Anne Marie

Issue Date

2021-12-01

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

Gewirth, Andrew A

Doctoral Committee Chair(s)

Gewirth, Andrew A

Committee Member(s)

• Murphy, Catherine J
• Rodríguez-López, Joaquín
• Yang, Hong

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Oxygen reduction catalyst
• nonprecious metal
• SQUID magnetometry
• Mössbauer spectroscopy

Abstract

Development and implementation of renewable energy storage and production to replace traditional fossil fuels is a requirement to combat climate change. While many different technologies are promising, many need further understanding of the components to lead to wide implementation. Electrocatalysts are of particular interest to enable the conversion of chemicals into energy. The first chapter of this dissertation describes the challenges faced in the implementation of fuel cells and efforts taken to address those challenges. The next 4 chapters describe the efforts taken to understand the speciation of Fe- and Co-based oxygen reduction reaction (ORR) catalysts. An approach towards energy production uses fuel cells in place of existing combustion-based power production. In a fuel cell, H2 is oxidized at the anode while O2 is reduced at the cathode. Conversion of H2 and O2 to H2O require appropriate catalysts to facilitate the oxidation/reduction reactions. In both cases, precious metals (including Pt and its alloys) can serve as a catalyst, however the low availability and subsequently high cost of Pt poses problems for widespread implementation. The search for an economically viable, highly active, ORR catalyst has led to intense research on nonprecious metal (NPM) ORR catalysts. Chapter 2 of this dissertation describes the experimental methods used to produce the data in the following chapters. Chapter 3 describes the investigation of an Fe-based ORR catalyst utilizing traditional characterization methods such as x-ray photoelectron spectroscopy and Mössbauer spectroscopy as well as an underutilized technique, SQUID magnetometry. The SQUID magnetometry can inform the amount of superparamagnetic/ferromagnetic Fe species in the catalyst. The results from this analysis disagree with the Mössbauer spectroscopy analysis which does not indicate the presence of any superparamagnetic/ferromagnetic Fe species. Additionally, a small molecule probe is used to better understand the role of C in the Fe-based NPM catalyst. This probe indicates that C is playing a significant role in the catalyst ORR activity. Chapter 4 investigates Co-based catalysts using similar techniques as used in chapter 4. Based on the results from the SQUID magnetometry data we are able to synthesize a catalyst that contains 100% superparamagnetic Co species in order to compare the activity toward the ORR to another catalyst containing nearly 100% paramagnetic Co species. Chapter 5 investigates the role of high temperature reductive gas treatments on the activity and characterization of Fe-based NPM ORR catalysts. NH3 and H¬2 high temperature gas treatments improve catalyst activity as compared to the untreated catalyst. 120 min of NH3 treatment yields the most active ORR catalyst, which contains nearly 100% superparamagnetic Fe species. This indicates that both paramagnetic and superparamagnetic Fe species are active for the ORR.

Graduation Semester

2021-12

Type of Resource

Thesis

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Copyright and License Information

Copyright 2021 Anne Marie Esposito

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