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Design and Development of Semipermeable Oxide Overlayers for Photocatalytic Hydrogen Production /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Design and Development of Semipermeable Oxide Overlayers for Photocatalytic Hydrogen Production // William Douglas Hiro Stinson.
Author:	Stinson, William Douglas Hiro,
Description:	1 electronic resource (257 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 86-07, Section: B.
Contained By:	Dissertations Abstracts International86-07B.
Subject:	Chemical engineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31768959
ISBN:	9798302163004

Design and Development of Semipermeable Oxide Overlayers for Photocatalytic Hydrogen Production /
Stinson, William Douglas Hiro,

Design and Development of Semipermeable Oxide Overlayers for Photocatalytic Hydrogen Production /William Douglas Hiro Stinson. - 1 electronic resource (257 pages)

Source: Dissertations Abstracts International, Volume: 86-07, Section: B.

Hydrogen, synthesized through water splitting, is poised to play a pivotal role in the transition to a carbon neutral economy. While traditional photovoltaic-electrolysis remains the most market ready technology, generation costs still significantly exceed the U.S. Department of Energy target of 1 $ kg-1. In contrast, photocatalytic water splitting, which uses nano- or micro- sized particles to simultaneously absorb sunlight and drive electrochemical reactions, offers a simpler and potentially low-cost approach to scalable production of hydrogen using renewable energy. Two major challenges in the commercialization of photocatalytic water splitting have been material stability and low solar to hydrogen (STH) conversion efficiencies. Recent studies have demonstrated some progress in achieving long-term stability or improved efficiency, with the latter breakthrough made possible by operating under conditions of concentrated sunlight, elevated temperature and reduced pressure. However, both demonstrations involved co-evolution of oxygen and hydrogen in the same reactor vessel, which poses significant safety risks and increases operational costs due to the need for downstream gas separation. An alternative approach is nature-inspired Z-scheme photocatalysis, where the oxygen and hydrogen evolution reactions occur on two different particles. This strategy offers an intrinsically safe approach to water splitting when the two particles operate in separate reactor compartments. However, Z-scheme photocatalysis introduces additional challenges particularly related to the use of a redox mediator required to shuttle charge between the two compartments. Notably, the prevalence of undesired back reactions of the mediator species leads to reduced STH efficiencies. Thus, designing both oxidation and reduction reaction sites which are more selective towards the desired forward reactions while minimizing undesired back reactions is crucial. One common strategy to enhance reaction selectivity is to apply permselective nanoscopic oxide overlayers to the surface of reaction sites. Although previous studies have overwhelmingly involved the use of chromium oxide overlayers, these studies have had mixed success. To enhance the efficacy of overlayers for Z-scheme water splitting, it is necessary to establish the fundamental design rules governing the transport and kinetic effects of overlayers on photocatalyst performance. Towards that end, this dissertation explores the development of oxide overlayers using model electrocatalytic systems and correlative microscopy, with a particular emphasis on the use and development of scanning electrochemical microscopy (SECM) methods. Chapter 2 focuses on quantifying defects in silicon oxide (SiOx)-overlayers deposited on Pt thin film electrocatalysts, examining their electrochemical selectivity for hydrogen evolution over ferric ion reduction. By correlating SECM activity maps with other characterization techniques, the influence of defects was determined to have a significant impact on the quantified transport properties of the oxide material. A transport model was developed to account for defect contributions, revealing the ferric ion permeability within SiOx overlayers was over an order of magnitude lower than permeabilities determined from analyses that neglected defect contributions. Chapter 3 explores how ionic conductivity, electronic conductivity, and overlayer thickness influence the location of catalytic active sites on oxide-coated electrocatalysts. Titanium oxide (TiOx) or SiOx overlayers were evaluated using a combination of electroanalytical methods and molecular dynamics simulations. This study decoupled the influences of ionic and electronic conductivity on reaction rates towards the oxygen and ferrous oxidation reactions at varying overlayer thicknesses. While both overlayers were permeable to water and oxygen at all thicknesses, TiOx and SiOx overlayers exhibited differing behaviors for ferrous oxidation at increased thicknesses, attributed to the difference in electronic conductivity. These differences dictated the ferrous oxidation occurred on outer surface of the TiOx overlayer but at the catalyst-overlayer interface for SiOx overlayers. Chapter 4 explores the need for a selective overlayer deposition scheme in photocatalytic systems, as coating both oxidation and reduction reaction sites would reduce the overall activity. An area selective atomic layer deposition (AS-ALD) technique was developed on planar model electrocatalysts, achieving both the desired reactivity and area selectivity within a specific thickness range. This technique was subsequentially applied to a model dual-site electrocatalyst system designed to simulate the undesired diffusional coupling of redox reactions occurring between neighboring particles. Selective overlayers deposited by AS-ALD were shown to reduce the undesired diffusional back reactions by over an order of magnitude while maintaining the desired reactivity at both reaction sites. Finally, concluding remarks and future extensions of research described in Chapters 2-4 are presented in Chapter 5, which includes additional use cases for SECM within the development of photocatalysts such as single particle measurements and exploring the role of oxide overlayers on the separation of photo-generated charge carriers.

English

ISBN: 9798302163004Subjects--Topical Terms:

560457
Chemical engineering.
Subjects--Index Terms:

Electrochemistry

Design and Development of Semipermeable Oxide Overlayers for Photocatalytic Hydrogen Production /
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520 $a Hydrogen, synthesized through water splitting, is poised to play a pivotal role in the transition to a carbon neutral economy. While traditional photovoltaic-electrolysis remains the most market ready technology, generation costs still significantly exceed the U.S. Department of Energy target of 1 $ kg-1. In contrast, photocatalytic water splitting, which uses nano- or micro- sized particles to simultaneously absorb sunlight and drive electrochemical reactions, offers a simpler and potentially low-cost approach to scalable production of hydrogen using renewable energy. Two major challenges in the commercialization of photocatalytic water splitting have been material stability and low solar to hydrogen (STH) conversion efficiencies. Recent studies have demonstrated some progress in achieving long-term stability or improved efficiency, with the latter breakthrough made possible by operating under conditions of concentrated sunlight, elevated temperature and reduced pressure. However, both demonstrations involved co-evolution of oxygen and hydrogen in the same reactor vessel, which poses significant safety risks and increases operational costs due to the need for downstream gas separation. An alternative approach is nature-inspired Z-scheme photocatalysis, where the oxygen and hydrogen evolution reactions occur on two different particles. This strategy offers an intrinsically safe approach to water splitting when the two particles operate in separate reactor compartments. However, Z-scheme photocatalysis introduces additional challenges particularly related to the use of a redox mediator required to shuttle charge between the two compartments. Notably, the prevalence of undesired back reactions of the mediator species leads to reduced STH efficiencies. Thus, designing both oxidation and reduction reaction sites which are more selective towards the desired forward reactions while minimizing undesired back reactions is crucial. One common strategy to enhance reaction selectivity is to apply permselective nanoscopic oxide overlayers to the surface of reaction sites. Although previous studies have overwhelmingly involved the use of chromium oxide overlayers, these studies have had mixed success. To enhance the efficacy of overlayers for Z-scheme water splitting, it is necessary to establish the fundamental design rules governing the transport and kinetic effects of overlayers on photocatalyst performance. Towards that end, this dissertation explores the development of oxide overlayers using model electrocatalytic systems and correlative microscopy, with a particular emphasis on the use and development of scanning electrochemical microscopy (SECM) methods. Chapter 2 focuses on quantifying defects in silicon oxide (SiOx)-overlayers deposited on Pt thin film electrocatalysts, examining their electrochemical selectivity for hydrogen evolution over ferric ion reduction. By correlating SECM activity maps with other characterization techniques, the influence of defects was determined to have a significant impact on the quantified transport properties of the oxide material. A transport model was developed to account for defect contributions, revealing the ferric ion permeability within SiOx overlayers was over an order of magnitude lower than permeabilities determined from analyses that neglected defect contributions. Chapter 3 explores how ionic conductivity, electronic conductivity, and overlayer thickness influence the location of catalytic active sites on oxide-coated electrocatalysts. Titanium oxide (TiOx) or SiOx overlayers were evaluated using a combination of electroanalytical methods and molecular dynamics simulations. This study decoupled the influences of ionic and electronic conductivity on reaction rates towards the oxygen and ferrous oxidation reactions at varying overlayer thicknesses. While both overlayers were permeable to water and oxygen at all thicknesses, TiOx and SiOx overlayers exhibited differing behaviors for ferrous oxidation at increased thicknesses, attributed to the difference in electronic conductivity. These differences dictated the ferrous oxidation occurred on outer surface of the TiOx overlayer but at the catalyst-overlayer interface for SiOx overlayers. Chapter 4 explores the need for a selective overlayer deposition scheme in photocatalytic systems, as coating both oxidation and reduction reaction sites would reduce the overall activity. An area selective atomic layer deposition (AS-ALD) technique was developed on planar model electrocatalysts, achieving both the desired reactivity and area selectivity within a specific thickness range. This technique was subsequentially applied to a model dual-site electrocatalyst system designed to simulate the undesired diffusional coupling of redox reactions occurring between neighboring particles. Selective overlayers deposited by AS-ALD were shown to reduce the undesired diffusional back reactions by over an order of magnitude while maintaining the desired reactivity at both reaction sites. Finally, concluding remarks and future extensions of research described in Chapters 2-4 are presented in Chapter 5, which includes additional use cases for SECM within the development of photocatalysts such as single particle measurements and exploring the role of oxide overlayers on the separation of photo-generated charge carriers.
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653 $a Photocatalysis
653 $a Scanning electrochemical microscopy
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