Post on 05-Jul-2015
Guidelines for materials selection and optimization
in electrochemical conversion of fuels
J.R.Frade
University of Aveiro, PortugalUniversity of Aveiro, Portugal
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Fuel cells
Clean; High η
Hydrocarbons
Partial oxidationor Reforming
e.g. CH4+1/2O2 → CO+2H2
Electricity Chemicals
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Purification
H2
Effects of fuel/air atmospheres on cell materials
-Redox behaviour-Stability limits under reducing conditions
-Structural changes-Effects on transport properties, etc.
-Effects on carbon deposition-Effects of contaminants (S-tolerance) etc.?
-Thermochemical or thermomechanical failure
-…
Interactions between cell materials-Processing-Operation
-Maintenance, thermal cycling, etc.
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
α
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Reducing cnditions imposed by H2
2H2 + O2 ↔ 2H2O;Po2 = (pH2O/pH2)2 exp(-∆G/RT)
-27
-23
-19
-15
-11
0.7 0.8 0.9 1
103/T; K-1
log
(Po
2/a
tm)
CH4; 99%
Conversion
CH4;
1%
H2;
99%
H2; 1%
1000ºC 900ºC 800ºC 700ºC
α
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Reducing cnditions imposed by CH4, ...
0.0
0.2
0.4
0.6
0.8
1.0
-30 -20 -10
log(Po2/atm)
Mo
le f
rac
tio
ns
0
0.2
0.4
0.6
0.8
1
1.2
Th
eore
tica
l op
en c
ell v
olt
age
T=1100 K; H2O/CH4=0.02
H2
CO
CO2
H2O
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Guidelines for redox tolerance of metallic electrocatalysts in H2 atmospheres
Nb
MnCr
Co
FeMo
Cu
W
Ni
10
1000 600 500
Ir
H2/H2O
10-1
8001200
-30
-25
-20
-15
-10
-5
0
0.5 0.7 0.9 1.1 1.3
103/T; (K-1)
log
(Po
2/a
tm)
T (ºC)
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Stability limits of SOFC cathode materials and catalysts under reducing conditions
-25
-20
-15
-10
-5
0
1000 1100 1200 1300
T (K)
log
(pO
2/a
tm)
LaMnO3
LaFeO3
highest CO Yield
LaCoO3
La2NiO4
(Sr,La)CoO3 −δ
2LaMnO3 ↔ La2O3 + 2MnO + 1/2O2
2LaCoO3 ↔ La2CoO4 + CoO + 1/2O2
...
2 0 3 0 4 0 5 0 6 0 7 0
2 θ ,
Inte
nsity
, a.u
.
L S M C T 2
L S M C T 5
L S M C T 4
L S M C T 4
L S M C T 2s i n t e r e d a t 1 7 7 3 K i n a i r
s i n t e r e d a t 1 7 7 3 K i n a i r
s i n t e r e d a t 1 7 7 3 K i n a i r
a n n e a l e d a t 1 2 2 3 Kp ( O 2 ) = 1 1 0 - 1 8 a t m
a n n e a l e d a t 1 2 2 3 Kp ( O 2 ) = 1 1 0 - 1 8 a t m
M n O
Structural changes and property degradation under reducing conditions
LSMCT2 = (La0.55Sr0.45)0.95Mn0.5Cr0.3Ti0.2O3-δ;
LSMCT4 = (La0.35Sr0.65)0.95Mn0.5Cr0.1Ti0.4O3-δ...
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
- 1 5 - 1 0 - 5 0
l o g p ( O 2 ) ( a t m )
- 4 0
- 2 0
0
2 0
4 0
6 0
α, µ
V/K
0 . 0
0 . 5
1 . 0
1 . 5
log
σ (S
Scm
-1)
A
B
1
2
3
T = 1 2 2 3 K
- 1 5 - 1 0 - 5 0
( L a 0 . 7 5 S r 0 . 2 5 ) 0 . 9 5 M n 0 . 5 C r 0 . 5 O 3 - δ
( L a 0 . 5 5 S r 0 . 4 5 ) 0 . 9 5 M n 0 . 5 C r 0 . 3 T i 0 . 2 O 3 - δ
( L a 0 . 3 5 S r 0 . 6 5 ) 0 . 9 5 M n 0 . 5 C r 0 . 1 T i 0 . 4 O 3 - δ
( L a 0 . 2 5 S r 0 . 7 5 ) 0 . 9 5 M n 0 . 5 T i 0 . 5 O 3 - δ
- 4 0
- 2 0
0
2 0
4 0
1 . 2
1 . 3
1 . 4
T = 1 0 7 3 K
C
D
8 . 2 8 . 6 9 . 0 9 . 4
1 0 4 / T , K - 1
- 2 8
- 2 2
- 1 6
- 1 0
log
p(O
2) (a
tm)
R e g i m e 1( L a 0 . 7 5 S r 0 . 2 5 ) 0 . 9 5 M n 0 . 5 C r 0 . 5 O 3 - δ
( L a 0 . 3 5 S r 0 . 6 5 ) 0 . 9 5 M n 0 . 5 C r 0 . 1 T i 0 . 4 O 3 - δ
( L a 0 . 2 5 S r 0 . 7 5 ) 0 . 9 5 M n 0 . 5 T i 0 . 5 O 3 - δ
- 3 1
- 2 3
- 1 5
- 7
1
( L a 0 . 2 5 S r 0 . 7 5 ) 0 . 9 5 M n 0 . 5 T i 0 . 5 O 3 - δr e g i m e 1r e g i m e 2r e g i m e 3
8 . 0 8 . 5 9 . 0 9 . 5 1 0 . 0 1 0 . 5
B
A
L a 0 . 8 5 S r 0 . 1 5 C r O 3 / L a C r O 3 + S r O + C r 2 O 3
L a M n O 3 / L a O + M n O
M n 3 O 4 / M n O
L a M n O 3 / L a O + M n O
M n 3 O 4 / M n O
T i O 1 . 9 9 5Stability range estimated from
sudden changes in conductivity and Seebeck coefficient.
Stability limits
T(K) 104/T log(pO2) at pH2:pH2O=1:1
η=0 η=0.1V η=0.2V
973 10.28 -20.8 -18.8 -16.7
1073 9.32 -18.3 -16.4 -14.5
1173 8.53 -16.2 -14.5 -12.8
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Typical dependence of ionic and electronic conductivity of CGO20 solid electrolytes
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
-4
-3
-2
-1
-25 -20 -15 -10 -5 0
log(Po2/atm)
log
{ σe/(
S/c
m)}
n-type
p-type
Ionic
700ºC
Predictions of methane conversion of ionic transport number and open cell voltage of a
CGO-based cell
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0
CH4 conversion
t I,av
CH4
700ºC
900ºC
0.0
0.4
0.8
1.2
0.0 0.2 0.4 0.6 0.8 1.0
CH4 conversionO
pe
n c
ell
vo
lta
ge
(V
)
CH4
700ºC
900ºC
α
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Predictions of carbon deposition
0.0
0.2
0.4
-30 -20 -10
log(Po2/atm)
Mo
le f
ract
ion
s
0
1
2
Ch
emic
al a
ctiv
ity
of
carb
on
T=1100 K; H2O/CH4=0.02
2CO → C + O2
CO
CO
2
Strategies to minimize the risks of carbon deposition:-Steam reforming-Substitution of metallic catalysts by alternative catalysts
α
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
PdS
NiS
CoS
FeS
PtS
RuS
Cu2S
-6
-4
-2
0
0.8 0.9 1.0 1.1 1.2
103/T; K-1
log
(pH
2S
/pH
2)
M+H2S↔MS+H2
Better S-tolerance
Poorer S-tolerance
Is thermodynamics useful to predict Sulphur tolerance?
Thermal expansion mismatchin a thin La10Si5AlO26+x electrolyte layer on a thick LSMCT
substrate, with firing at 1250ºC
ε = ∆L/Lo = ∆α.∆Tσ= ε E/(1-ν)
Typical for ceramics: E>100 GPa and ν≈0.3. For ∆α≈2x10-6 K-1, and ∆T≈1000ºC
ε ≈ − 0.002; σ ≈ - 300 MPa (delamination!)
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Thermal expansion mismatch and ionic conductivity at 800ºC, in air
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
Composition α.10 6; Κ−1 σ I ;S/cm T, K Ea(kJ/mol)
La2Ni0.8Cu0.2O4+δ 13.3 0.11* - -
LSFC 12.9 0.01 1073-1223 206
LSM 11.7 1.3×10-5 - -
LSFC - 50 wt% CGO 12.6 0.04 1023-1223 82
LSM - 50 wt% CGO
11.7 0.03
1023-1223
104
La10Si5AlO26.5
9.1 0.08
973-1223
56
Dense tubular membranes of SrFe0.7Al0.3O3-δ with Al2O3 addition.
Chemical expansion under air/5%H2
0
0.2
0.4
0.6
600 700 800 900 1000
103/T; K-1
10
2 x∆
L/L
o
-22
-20
-18
-16
-14
-12
log
(pO
2/at
m)
LSMCT5
LSMCT0
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008
ε = ∆L/Lo; σ = ε E/(1-ν)for ε=0.005; σ>200MPa (risks of fracture!)
EDS spectra showing cation diffusion accross the CGO buffer layer in
apatite/CGO/ LSMCT4 and LSGM/CGO/LSMCT4 arrangements
Interdiffusion between cell materials
4 . 0 4 . 5 5 . 0 5 . 5 6 . 0 6 . 5
E , k e V
Inte
nsit
y, a
.u.
e l e c t r o l y t e b u l kn e a r e l e c t r o l y t e / i n t e r l a y e r i n t e r f a c e
L a
C r
G dC e
e l e c t r o l y t e : L a 1 0 S i 5 A l O 2 6 . 5
i n t e r l a y e r : C e 0 . 8 G d 0 . 2 O 1 . 9
e l e c t r o d e : L S M C T 4
e l e c t r o l y t e : L S G M
i n t e r l a y e r : C e 0 . 8 G d 0 . 2 O 1 . 9
e l e c t r o d e : L S M C T 4
M n
A
B
L a
L a
L a
L a
L a
L a
L a
L a
L a
C eC e
C e
C eC e
C r
C rC r
M n
M nM n
G d
Economia de HEconomia de H2: Un desafio para Portugal, Vimeiro, Nov.17, 2008: Un desafio para Portugal, Vimeiro, Nov.17, 2008