reduced-temperature thermochemical redox …...lower thermochemical redox reaction temperature •...
TRANSCRIPT
PI: Arun Majumdar, William ChuehPresenter: Shang Zhai
Stanford Linear Accelerator Center/Stanford UniversityJune 13, 2018
Reduced-Temperature Thermochemical Redox Reactions
Project ID: SLAC
This presentation does not contain any proprietary, confidential, or otherwise restricted information
HydroGEN: Advanced Water Splitting Materials 2
Project Overview
Project PartnerMichael Toney, SLACTo reduce temperature
requirement of thermochemical redox reactions by using poly-cation oxides that can lower phase transition temperature.
Project Vision
Start/End Date 09/01/2016–06/30/2018
Total Funding $150,000
To develop oxides for two-step thermochemical water splitting (TWS) cycle ≤ 1000 °C, which is relevant for large scale hydrogen production.
Project Impact
HydroGEN: Advanced Water Splitting Materials 3
Relevance
• Project goal: Developing novel metal oxides to produce large scale hydrogen at <$2/kg, specifically by reducing thermochemical reaction temperature.
• This reporting period:
• Studied entropy stabilization effect on two-step TWS performance at reduced temperature
• Identified redox active element in the poly-cation oxide (MgFeCoNi)Ox
• Specified phase swing during the TWS cycle
• Stable ten-cycle performance
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Approach- Summary
Project MotivationEntropy-stabilization was found to lower phase transition temperature.
BarriersNarrow thermodynamic window to do two-step TWS within 1000 °C.
Rost, Nat. Commun., 2015
(MgCoNiCuZn)Ox
X-ray diffractionTtran
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Approach- Innovation
• Poly-cation oxide (FeMgCoNi)Ox undergoes phase swing in two-step TWS cycle.
X-ray Diffraction
As synthesized
After 10 cycles at 1300-800 °C
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Accomplishments
• Poly-cation oxide (FeMgCoNi)Ox outperforms state-of-the-art two-step TWS materials.
Normalized yield: measured H2 yield normalized by the yield if Fe goes through complete Fe2+/Fe3+ transition during the TWS cycle.
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Accomplishments
• Fe is the redox active element relevant for two-step TWS of (FeMgCoNi)Ox
X-ray absorption near-edge structure
1s
4p
Continuum
X-ray
M2+
M3+
Edge shift
Edge shift
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Accomplishments
• Kinetics study of poly-cation oxide (FeMgCoNi)Ox at TH = 1300 °Cand TL = 800 °C.
Time [min]
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Accomplishments
• Poly-cation oxide (FeMgCoNi)Ox has good H2O to H2 conversion.
• Outlook and projected outcomes for the remainder of the project’s budget period 1 scope of work:
• Optimizing compositions of poly-cation oxides to further improve its TWS performance.
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Collaboration
Collaborator Project RoleMajumdar Group Material synthesis;
Thermochemical performance characterization;X-ray diffraction
Chueh Group
Toney Group Synchrotron x-ray absorption spectroscopy
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Proposed Future Work
• To develop new materials that can be used for two-step TWS below 1000 °C.
• Mechanism study: what are the role of redox inactive Mg, Co and Ni in the thermochemical redox reactions?
• Thermodynamic hydrogen production limit of specific poly-cation oxide(s).
• To identify reaction rate-determining step(s).
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Project Summary
• Approach• Tuning entropy-stabilization in poly-cation oxide to
lower thermochemical redox reaction temperature• Performance of (FeMgCoNi)Ox
• Two-step TWS within 1100 °C• High hydrogen yield and good H2O to H2 conversion• Phase swing identified: coexistence of rocksalt/spinel
phases• Fe is the redox active element for two-step TWS• Large portion of Fe is active in redox reactions
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Technical Back-Up Slides
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2
2
0 02 2 0
2 2 2
0 002 22 2 0
02 2 0
( ) ( )( )
( ) ( )[ ( ) Rln
( ) Rln ] 0
f x f x xf
Hx x xL
H O
H MO H MOG H H O
xpS MO S MOT S H
x pp
S H Op
δ
δ
δ
δ
−
−
∆ − ∆∆ = −∆ −
−+ −
− + <
0 0 0 01 1 1 1
1
0 21 2 0
( ) ( ) ( ) ( )[
( ) Rln] 0
2
f x x f x x x xH
O
H MO H MO S MO S MOG Tx x
pS Op
δ δ
δ δ− −
∆ − ∆ −∆ = − +
−<
0 0
0
( ) ( )( ) lim f x x f x
f x
H MO H MOH x
xδ
δ δ−
→
∆ −∆∆ =
Thermal Reduction (@TH)
Water Splitting (@TL)
Spontaneous reaction conditions𝟏𝟏𝜹𝜹𝜹𝜹
𝑴𝑴𝑶𝑶𝜹𝜹 →𝟏𝟏𝜹𝜹𝜹𝜹
𝑴𝑴𝑶𝑶𝜹𝜹−𝜹𝜹𝜹𝜹 +𝟏𝟏𝟐𝟐𝑶𝑶𝟐𝟐
𝟏𝟏𝜹𝜹𝜹𝜹𝑴𝑴𝑶𝑶𝜹𝜹−𝜹𝜹𝜹𝜹 + 𝑯𝑯𝟐𝟐𝑶𝑶 →
𝟏𝟏𝜹𝜹𝜹𝜹𝑴𝑴𝑶𝑶𝜹𝜹 + 𝑯𝑯𝟐𝟐
• Functions of x• Temperature dependence neglected
0 0
0
( ) ( )( ) lim x x x
x
S MO S MOS xx
δ
δ δ−
→
−∆ =
H2
MOx-𝛿𝛿𝛿𝛿MOx
O2
TH
TL
H2O
pO2 = 10-5 bar
pH2 = 10-4 barpH2O = 10-1 bar
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TGA system
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Stagnation flow reactor system