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Development of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Development of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction./
Author:	Kreider, Melissa Ellen.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	323 p.
Notes:	Source: Dissertations Abstracts International, Volume: 83-02, Section: B.
Contained By:	Dissertations Abstracts International83-02B.
Subject:	Emissions. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28550779
ISBN:	9798522939816

Development of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction.
Kreider, Melissa Ellen.

Development of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 323 p.

Source: Dissertations Abstracts International, Volume: 83-02, Section: B.

Thesis (Ph.D.)--Stanford University, 2021.

This item must not be sold to any third party vendors.

Eliminating greenhouse gas emissions to mitigate the effects of climate change is a global imperative. To achieve this goal, the world's dependence on fossil fuels must be ended and renewable energy technologies must be developed and deployed on a massive scale. The electrocatalytic oxygen reduction reaction (ORR) is an important limiting step in several promising technologies, including fuel cells, metal-air batteries, and the sustainable synthesis of hydrogen peroxide. Polymer electrolyte membrane fuel cells (PEMFCs) are a clean and efficient technology for converting chemical energy, e.g. in the form of hydrogen fuel, into electrical energy for transportation and backup power generation. The majority of the efficiency losses in a PEMFC are due to the sluggish kinetics of the ORR, requiring significant loadings of platinum-based catalysts at the cathode. The scarcity and high cost of platinum is therefore a limiting factor for the widespread development of PEMFC technologies. In this dissertation, we develop several low-cost, non-precious metal ORR catalysts for acidic and alkaline media, as well as techniques for understanding the relationship between performance and material properties.In acidic media, transition metal-nitrogen-carbon type catalysts have shown the highest performance, while in alkaline media a wider variety of materials including transition metal (TM) oxides and metal-free carbon catalysts also show promising activity. The main group of materials studied in this dissertation are the TM nitrides, which show promising electrical conductivity and acid stability. In alkaline media, we will further explore the performance of modified TM oxide materials, utilizing corrosion-resistance frameworks. For all catalysts, we seek to improve fundamental understanding of the active surface of the catalyst using extensive in situ and ex situ materials characterization, careful electrochemical testing, and complementary theoretical studies.First, we investigate the performance of a thin film, carbon-free nickel nitride catalyst, finding substantial ORR activity in acidic and alkaline media. We identify significant surface oxidation with testing and air exposure. Utilizing electrochemical cycling and stability testing informed by Pourbaix diagrams, the role of surface oxidation in determining catalyst activity and stability is explored. This work demonstrates the importance of understanding material surface properties and stability.Following on this work, we use a molybdenum (oxy)nitride thin film system to probe the role of structure and composition in ORR performance in acidic conditions. Using extensive materials characterization, the depth-dependent structure and composition of the films are determined, discovering the high O content in the bulk of films with a highlydefected structure. This bulk O content is found to be the strongest predictor of ORR activity. Furthermore, the surface of the catalyst is found to undergo substantial oxidation with air exposure and reduction with electrochemical testing. We use in situ characterization techniques to understand the material changes that occur during reaction, particularly those associated with potential-dependent catalytic behavior, finding that the catalyst surface undergoes distortion, amorphization, and O incorporation. We identify a potential window in which the intrinsic catalytic activity can be enhanced without the roughening or dissolution that lead to instability. This work demonstrates how ex situ and in situ techniques can be used to develop a rigorous understanding of a catalyst material, which can then be leveraged to optimize catalyst performance.

ISBN: 9798522939816Subjects--Topical Terms:

3559499
Emissions.

Development of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction.
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520 $a Eliminating greenhouse gas emissions to mitigate the effects of climate change is a global imperative. To achieve this goal, the world's dependence on fossil fuels must be ended and renewable energy technologies must be developed and deployed on a massive scale. The electrocatalytic oxygen reduction reaction (ORR) is an important limiting step in several promising technologies, including fuel cells, metal-air batteries, and the sustainable synthesis of hydrogen peroxide. Polymer electrolyte membrane fuel cells (PEMFCs) are a clean and efficient technology for converting chemical energy, e.g. in the form of hydrogen fuel, into electrical energy for transportation and backup power generation. The majority of the efficiency losses in a PEMFC are due to the sluggish kinetics of the ORR, requiring significant loadings of platinum-based catalysts at the cathode. The scarcity and high cost of platinum is therefore a limiting factor for the widespread development of PEMFC technologies. In this dissertation, we develop several low-cost, non-precious metal ORR catalysts for acidic and alkaline media, as well as techniques for understanding the relationship between performance and material properties.In acidic media, transition metal-nitrogen-carbon type catalysts have shown the highest performance, while in alkaline media a wider variety of materials including transition metal (TM) oxides and metal-free carbon catalysts also show promising activity. The main group of materials studied in this dissertation are the TM nitrides, which show promising electrical conductivity and acid stability. In alkaline media, we will further explore the performance of modified TM oxide materials, utilizing corrosion-resistance frameworks. For all catalysts, we seek to improve fundamental understanding of the active surface of the catalyst using extensive in situ and ex situ materials characterization, careful electrochemical testing, and complementary theoretical studies.First, we investigate the performance of a thin film, carbon-free nickel nitride catalyst, finding substantial ORR activity in acidic and alkaline media. We identify significant surface oxidation with testing and air exposure. Utilizing electrochemical cycling and stability testing informed by Pourbaix diagrams, the role of surface oxidation in determining catalyst activity and stability is explored. This work demonstrates the importance of understanding material surface properties and stability.Following on this work, we use a molybdenum (oxy)nitride thin film system to probe the role of structure and composition in ORR performance in acidic conditions. Using extensive materials characterization, the depth-dependent structure and composition of the films are determined, discovering the high O content in the bulk of films with a highlydefected structure. This bulk O content is found to be the strongest predictor of ORR activity. Furthermore, the surface of the catalyst is found to undergo substantial oxidation with air exposure and reduction with electrochemical testing. We use in situ characterization techniques to understand the material changes that occur during reaction, particularly those associated with potential-dependent catalytic behavior, finding that the catalyst surface undergoes distortion, amorphization, and O incorporation. We identify a potential window in which the intrinsic catalytic activity can be enhanced without the roughening or dissolution that lead to instability. This work demonstrates how ex situ and in situ techniques can be used to develop a rigorous understanding of a catalyst material, which can then be leveraged to optimize catalyst performance.
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