PEC Materials: Theory and Modeling · 2. Follow the PEC R&D feedback loop 3. Use state-of-the-art,...
Transcript of PEC Materials: Theory and Modeling · 2. Follow the PEC R&D feedback loop 3. Use state-of-the-art,...
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PEC Materials: Theory and Modeling
DOE AMR
Yanfa Yan
May 10, 2011
Project ID #PD052
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PEC Materials: Theory and Modeling
Yanfa Yan, Wan-Jian Yin, Su-Huai Wei, Mowafak Al-Jassim, and John Turner
National Renewable Energy Laboratory, Golden, Colorado
May 10, 2011 Project ID #PD052
This presentation does not contain any proprietary, confidential, or otherwise restricted information
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• Start date: 2007 for this task• Project end date: Oct. 2011*• Percent complete: 75%*
• Barriers addressed– Y. Materials efficiency– Z. Materials durability– AB. Materials synthesis
• Total project funding– Part of NREL PEC Program
• Funding received in FY10~ $ 120K
• Funding for FY11: ~ $ 100K─ *Project continuation and direction
determined annually by DOE
• Note: Task with PD035- Turner
Timeline
Budget
Barriers
• University of Hawaii – Nicolas Gaillard
• University of California – Eric McFarland
• University of Nevada –Clemens Heske
Partners
Overview
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SrBi
CaV
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(eV) ZnV
Znint
MgV
SrV
Caint
MgintMgBi
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CaBi
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Synthesis
Materials
science
Characterization
Analysis
Theory
Standardization
Nanotechnology
PECworking group
PEC Working Group:Evaluating working directionsSharing and building-up knowledgeAccelerating research progress
DOE Goal:1000h @STH > 8% (2013)Projected PV electrolysis cost: $10 ~ 15/kg H2
Theoretical discovery of new PEC materials
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Objectives - Relevance
The main focus of the project is to:
• Understand the performance of current PEC materials
• Provide guidance and solution for performance improvement
• Design and discover new materials
and
• Provide theoretical basis for go/no-go decisions to DOE PEC H2 projects.
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Approach1. Work closely with other DOE H2 projects
2. Follow the PEC R&D feedback loop
3. Use state-of-the-art, first-principles, density-functional theory calculation, which can calculate important properties:
• Band structure • Optical absorption• Defect and doping effects• Surface chemistry• Structural stability
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Breaking symmetry by group-IIIA and group-IIIB alloys to enhance optical absorption of Cu delafossite
Optical Absorption Coefficient
Optical absorption is enhanced by alloying Ga and In with Y
Previous Technical Accomplishments and Progress
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New Technical Accomplishments and Progress 1. Rational band structure engineering of TiO2 for
improved PEC water splitting
1. Charge balanced donor-acceptor alloying
2. Using 4d, 5d TM acceptor
3. Using higher p-orbital donors
4. High concentration of the alloying elements
Overcome solubility limit, reduce charged defects, improve materials quality
Lift up the conduction band
Raise the valence band
Enhance optical absorption, improve hole mobility
Strategies
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New Technical Accomplishments and Progress (Cont.)
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New Technical Accomplishments and Progress (Cont.)
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Br
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VIIAVIAVA
Atom
ic p
orbi
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y (e
V) 2p 3p 4p
IVA
C
Si
Ge
Isovalent impurities: S, SePotential candidates as acceptor: N, C, P, Si, As
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New Technical Accomplishments and Progress (Cont.)
Pure TiO2
Calculated (GGA) band structure
(Ta, N) 3.1%(O) (Ta, N) 12.5%(O)
Sufficient foreign elements must be incorporated to enhance carrier mobilities
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New Technical Accomplishments and Progress (Cont.)
Calculated (GGA) absorption coefficient
Sufficient foreign elements must be incorporated to obtain good optical absorption
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New Technical Accomplishments and Progress (Cont.)
Possible donor-acceptor combinations
(donor, acceptor) (2 donors, acceptor) (donor, 2 acceptors)
TaN
W C Ta
C Ta
MoN N
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New Technical Accomplishments and Progress (Cont.)
GGA + band gap correction at Γ point: low concentration
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New Technical Accomplishments and Progress (Cont.)
GGA + band gap correction at Γ point: high concentration
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New Technical Accomplishments and Progress (Cont.)
Good combinations
(Ta, N), (Nb, N), (2Ta, C), (2Nb, C)
Low concentration:
High concentration:
(Mo, 2N), (W, 2N)
Phys. Rev. B 82, 045106 (2010)
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New Technical Accomplishments and Progress (Cont.)
2. Superior doping properties of BiVO4
Atomic Structure of BiVO4
PEC properties of BiVO4
Excellent optical absorption coefficient
Good Valence band edge position
Good carrier mobility
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New Technical Accomplishments and Progress (Cont.)
Na on Bi can lead to good p-type of BiVO4
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New Technical Accomplishments and Progress (Cont.)
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SrBi
CaV
Srint
Form
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ergy
(eV) ZnV
Znint
MgV
SrV
Caint
MgintMgBi
ZnBi
CaBi
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0.0 0.5 1.0 1.5 2.0 2.5
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Fermi Energy (eV)
CaV
MgV ZnV
Caint
ZnBi
Mgint
MgBi
Znint
CaBi
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SrV
Srint
SrBi
Ca and Sr doping can lead to good p-type of BiVO4
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New Technical Accomplishments and Progress (Cont.)
Mo and W doping can lead to good n-type of BiVO4
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New Technical Accomplishments and Progress (Cont.)
BiVO4 has superior doping properties -
It can be doped both good n-type and p-type
These excellent doping properties are required for PEC H2 production application
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Collaborations
• University of Hawaii: improving the performance of WO3 and CGS PEC materials
• University of California: understanding the performance of Fe2O3
• University of Nevada: determining electronic structures of oxides• MV System: understanding amorphous SiC materials.
Active collaborations continued via frequent conference calls and meetings during DOE quarterly working group meetings.
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• Continue to support the DOE Fuel Cell Technologies Program.
• Continue to provide understanding and direction to DOE PEC H2 projects.
• Explore Cu-containing oxides as PEC material candidates that may lead to promising performance.
• Band structure engineering of BiVO4 for PEC application.
• Develop strategies for engineering existing popular oxides.
• Explore electronic and optical properties of non-oxide PEC materials, such as nitrides and carbides.
Proposed Future Work
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Project SummaryRelevance: Provide advice to other DOE PEC H2 projects and assist with understanding of performance.
Approach: Use first-principle density-functional theory.
Technical Accomplishments and Progress: Proposed strategies for band structure engineering of TiO2 for improved PEC water splitting performance. Demonstrated superior doping properties of BiVO4.
Collaborations: Active partner of University of Hawaii, University of California, University of Nevada, and MVSystems.
Future Work: Continue to support the DOE H2 Program by exploring new materials.
Yanfa Yan303-384-6456