Development of Ta3N5 as an Efficient Visible Light-responsive Photocatalyst for Water Oxidation

Handle URI:
http://hdl.handle.net/10754/582311
Title:
Development of Ta3N5 as an Efficient Visible Light-responsive Photocatalyst for Water Oxidation
Authors:
Nurlaela, Ela ( 0000-0003-2903-7766 )
Abstract:
Along with many other solar energy conversion processes, research on photocatalytic water splitting to generate hydrogen and oxygen has experienced rapid major development over the past years. Developing an efficient visible-light-responsive photocatalyst has been one of the targets of such research efforts. In this regard, nitride materials, particularly Ta3N5, have been the subject of investigation due to their promising properties. This dissertation focuses on the fundamental parameters involved in the photocatalytic processes targeting overall water splitting using Ta3N5 as a model photocatalyst. The discussion primarily focuses on relevant parameters that are involved in photon absorption, exciton separation, carrier diffusion, carrier transport, and catalytic efficiency. A collection of theoretical and experimental studies of properties associated with Ta3N5 have been utilized to obtain a comprehensive understanding of this material. The fundamental structural and optoelectronic properties of Ta3N5 have been addressed. From the electronic properties, the dielectric constant and effective masses have been calculated. Because of its high dielectric constant and relatively low effective masses, Ta3N5 is promising for photocatalytic reaction applications. Studies of lattice dynamics, optical properties, and band positions have been able to clearly show that the synthesized Ta3N5 is essentially non-stoichiometric and that a truly pure phase of Ta3N5 has never been achieved, even though XRD has shown a pure phase sample. The photophysical properties of Ta3N5, such as the absorption coefficient, carrier mobility, and carrier lifetime, have been experimentally measured by synthesizing Ta3N5 thin films. Very low kinetic properties with very low transport properties and fast carrier recombination explained why overall water splitting has never been achieved with Ta3N5 as a photocatalyst to date. The extent to which the surface states of Ta3N5 photocatalysts affect photocatalytic performance has been investigated. The surface topmost layer is demonstrated to play a critical role in the photocatalytic activity of Ta3N5; further research on the surface properties of Ta3N5 should be conducted to understand and improve charge separation and the resulting photocatalytic activity. Finally, a remarkable improvement in the photocatalytic OER has been achieved with the addition of cobalt as a cocatalyst. There is a trade-off between the optimum contact of hole transfer from bulk Ta3N5 to the surface of the cobalt cocatalyst and providing active sites for the electrochemical reaction. Knowing the characteristics of cobalt on the Ta3N5 surface, further improvement was attempted by adding a noble metal to the CoOx/Ta3N5 photocatalyst system, where a synergetic effect of CoOx and noble metals was observed.
Advisors:
Takanabe, Kazuhiro ( 0000-0001-5374-9451 )
Committee Member:
Han, Yu ( 0000-0003-1462-1118 ) ; Domen, Kazunari; Lai, Zhiping ( 0000-0001-9555-6009 )
KAUST Department:
Physical Sciences and Engineering (PSE) Division; Chemical and Biological Engineering Program
Program:
Chemical and Biological Engineering
Issue Date:
Sep-2015
Type:
Dissertation
Appears in Collections:
Dissertations; Physical Sciences and Engineering (PSE) Division; Chemical and Biological Engineering Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorTakanabe, Kazuhiroen
dc.contributor.authorNurlaela, Elaen
dc.date.accessioned2015-11-18T11:28:21Zen
dc.date.available2015-11-18T11:28:21Zen
dc.date.issued2015-09en
dc.identifier.urihttp://hdl.handle.net/10754/582311en
dc.description.abstractAlong with many other solar energy conversion processes, research on photocatalytic water splitting to generate hydrogen and oxygen has experienced rapid major development over the past years. Developing an efficient visible-light-responsive photocatalyst has been one of the targets of such research efforts. In this regard, nitride materials, particularly Ta3N5, have been the subject of investigation due to their promising properties. This dissertation focuses on the fundamental parameters involved in the photocatalytic processes targeting overall water splitting using Ta3N5 as a model photocatalyst. The discussion primarily focuses on relevant parameters that are involved in photon absorption, exciton separation, carrier diffusion, carrier transport, and catalytic efficiency. A collection of theoretical and experimental studies of properties associated with Ta3N5 have been utilized to obtain a comprehensive understanding of this material. The fundamental structural and optoelectronic properties of Ta3N5 have been addressed. From the electronic properties, the dielectric constant and effective masses have been calculated. Because of its high dielectric constant and relatively low effective masses, Ta3N5 is promising for photocatalytic reaction applications. Studies of lattice dynamics, optical properties, and band positions have been able to clearly show that the synthesized Ta3N5 is essentially non-stoichiometric and that a truly pure phase of Ta3N5 has never been achieved, even though XRD has shown a pure phase sample. The photophysical properties of Ta3N5, such as the absorption coefficient, carrier mobility, and carrier lifetime, have been experimentally measured by synthesizing Ta3N5 thin films. Very low kinetic properties with very low transport properties and fast carrier recombination explained why overall water splitting has never been achieved with Ta3N5 as a photocatalyst to date. The extent to which the surface states of Ta3N5 photocatalysts affect photocatalytic performance has been investigated. The surface topmost layer is demonstrated to play a critical role in the photocatalytic activity of Ta3N5; further research on the surface properties of Ta3N5 should be conducted to understand and improve charge separation and the resulting photocatalytic activity. Finally, a remarkable improvement in the photocatalytic OER has been achieved with the addition of cobalt as a cocatalyst. There is a trade-off between the optimum contact of hole transfer from bulk Ta3N5 to the surface of the cobalt cocatalyst and providing active sites for the electrochemical reaction. Knowing the characteristics of cobalt on the Ta3N5 surface, further improvement was attempted by adding a noble metal to the CoOx/Ta3N5 photocatalyst system, where a synergetic effect of CoOx and noble metals was observed.en
dc.language.isoenen
dc.subjectTa3N5en
dc.subjectPhotocatalysten
dc.subjectWater splittingen
dc.subjectSolar energyen
dc.titleDevelopment of Ta3N5 as an Efficient Visible Light-responsive Photocatalyst for Water Oxidationen
dc.typeDissertationen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical and Biological Engineering Programen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberHan, Yuen
dc.contributor.committeememberDomen, Kazunarien
dc.contributor.committeememberLai, Zhipingen
thesis.degree.disciplineChemical and Biological Engineeringen
thesis.degree.nameDoctor of Philosophyen
dc.person.id118582en
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