proton ceramic steam electrolysers · proton ceramic steam electrolysers einar vøllestad1, r....
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Proton Ceramic Steam Electrolysers
Einar Vøllestad1, R. Strandbakke1, Dustin Beeaff2 and T. Norby1
1University of Oslo, Department of Chemistry, 2CoorsTek Membrane Sciences AS
Theoretical considerations on proton ceramic electrolysis operation
Development and performance of tubular Proton Ceramic Electrolysers (PCEs)
Literature data for Proton Ceramic
Electrolysers (PCEs)
Electrolyte Anode Temperature i
(mA cm2)
ASR
(Ωcm2)
η (%) Ref
SSY541 SSC 600 100 4 ~80 Matsumoto,
2012
BCZY53-Zn BSCF 800 55 20 50 Li, 2013
BZCY72 LSCF 700 100 6 50 Babiniec,
2015
BCZY53-Zn LSCM-
BCZYZ
700 2000 6-8 22 Gan, 2012
BCZY62 BSCF 600 1050 0.5 99 (?) Yoo, 2013
BCZY53 SSC-BCZY 700 400 1 - He, 2010
Key question: What is the origin of the low faradaic efficiencies observed in many PCEs?
Degradation and decomposition in H2O
Operating Principles of Proton Ceramic
Electrolysers (PCEs)
Anode Cathode Electrolyte
2H2O
O2
4H+
U e-
2H2O O2 + 4H+ +4e-
0 e- + h+ h+
e- + h+ 0
Rion Zel,a Zel,c
Re-
4H+ +4e- 2H2
O2-
Potentials through a solid oxide electrolyser
OCV
SOEC
EF
EF
Electrolyte
O2 H2 x
SOFC
Electronic conductivity distribution during
PCE operation
SOEC
σp ∝ pO21/4 ∝ exp(EF/4)
σp
O2 H2 x
Electrolyte
σe
σp,OCV
The effect of partial electronic conductivity
on faradaic efficiency
0.0 0.5 1.0 1.5 2.01.0
1.5
2.0
Vo
lta
ge
Current
0
10
20
30H
2 pro
du
ctio
n (m
L m
in-1)
te = 0
te = 0
The effect of partial electronic conductivity
on faradaic efficiency
0.0 0.5 1.0 1.5 2.01.0
1.5
2.0
Vo
lta
ge
Current
0
10
20
30
te = 0.25
H2 p
rod
uctio
n (m
L m
in-1)
te = 0
te = 0
te = 0.25
The effect of partial electronic conductivity
on faradaic efficiency
0.0 0.5 1.0 1.5 2.01.0
1.5
2.0
Vo
lta
ge
Current
0
10
20
30
te = 0.5t
e = 0.25
H2 p
rod
uctio
n (m
L m
in-1)
te = 0
te = 0
te = 0.25
te = 0.5
Electrode performance and steam content
significantly influence faradaic efficiency
1.25 1.50 1.75
60
80
Fa
rad
ay e
ffic
ien
cy (
%)
Voltage (V)
1.1 1.2 1.3 1.4 1.5 1.6 1.760
70
80
90
pH2O
= 0.5
pH2O
= 0.75
Fa
rad
ay e
ffic
ien
cy (
%)
Voltage
pH2O
= 0.95
Anode performance
UN Rion Zel,a Zel,c
Re-
Steam content dependence with fixed tH = 0.8 Anode dependence for with fixed tH = 0.8
Tubular half-cell production
Dip-coating
suspensions
NiO based paste
Wet milling of precursors
Solid State Reactive Sintering
Extrusion of BZCY72-NiO support
Spray-coating BZCY72 electrolyte
Dense tubular half-cells achieved
Dense electrolyte @
1550C – 24h
1610C – 6h
40 microns
Steam electrode: Ba1-xGd0.8La0.2+xCo2O6-δ
1: H. Ding et al., International Journal of Hydrogen Energy (2010).
2: R. Strandbakke et al., Solid State Ionics (2015).
3: Y. Lin et al., Journal of Power Sources (2008).
4: J. Dailly et al., Electrochimica Acta (2010).
5: M. Shang et al., RSC Advances, (2013)
1.0 1.1 1.2 1.3 1.4 1.5 1.6
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Rp (
cm
2)
GBCF / BZCY [1]
BSCF / BCY [3]
Pr2NiO
4 / BCY [4]
LSCF / BCY [4]
BSCF / BCY [4]
BGLC (x=0) / BZCY [2]
BCZF [5]
log
(R
p (
cm
2))
1000/T (K-1)
750 700 650 600 550 500 450 400 350
0.1
1
10
T (C)
1. Cap and seal segment using glass ceramic from CoorsTek
2. Deposit Ba0.7Gd0.8La0.5Co2O6-δ as steam electrode by paint brush
3. Firing in dual atmosphere:
1000°C
2% O2 outside, 5% H2 inside
Ecell = 1.4 V during firing
4. Gold paste applied as current collector
Steam electrode processing on reduced tubes
Cell 1 Area: 5 cm2
Electrolysis with single phase BGLC electrode
0
1
2
3
4
5
550°C
600°C
650°C
700°C
Current (A)
700°C
650°C
600°C
550°C
H2 p
rod
uctio
n (
Nm
L m
in-1)
Farad
aic H 2
pro
duction
0.00 0.25 0.50 0.75 1.00
0 50 100 150 200
1.0
1.5
2.0
700°C600°C550°C 650°C
Po
ten
tia
l (V
)
Current density (mA cm-2)
Anode:
pO2 = 30 mbarpH
2 = 0.3 bar
ptot
= 3 bar
ptot
= 3 bar
pO2 = 80 mbar
pH2O = 1.5 bar
Cathode:1.0 1.5 2.0
40
60
80
100
550°C
600°C
650°C
700°C
Fa
rad
aic
eff
icie
ncy (
%)
Potential (V)
Faradaic efficiencies vs cell potential
Electrolysis with single phase BGLC electrode
0
1
2
3
4
5
550°C
600°C
650°C
700°C
Current (A)
700°C
650°C
600°C
550°C
H2 p
rod
uctio
n (
Nm
L m
in-1)
Farad
aic H 2
pro
duction
0.00 0.25 0.50 0.75 1.00
0 50 100 150 200
1.0
1.5
2.0
700°C600°C550°C 650°C
Po
ten
tia
l (V
)
Current density (mA cm-2)
Anode:
pO2 = 30 mbarpH
2 = 0.3 bar
ptot
= 3 bar
ptot
= 3 bar
pO2 = 80 mbar
pH2O = 1.5 bar
Cathode:
Impedance at 600°C for increasing galvanostatic bias
4 5 6 7 8
3
2
1
0
-1
OCV
50
100
300Z
// (
cm
2)
Z/ (cm
2)
Poor adhesion and delamination of the electrode layer observed in post characterization - Improved processing route needed
1. BZCY72- Ba0.5Gd0.8La0.7Co2O6-δ applied as steam electrode
Fired in air at 1200°C for 5h
Infiltrated with nanocrystalline
Ba0.5Gd0.8La0.7Co2O6-δ
Thin Pt layer current collection
2. Capped and sealed at 1000°C
Semi-dual atmosphere to keep BGLC layer intact
3. NiO reduction at 800°C in 10% H2 for 24h
Kept in electrolytic bias during reduction to avoid re-oxidation
Steam electrode processing on unreduced tubes
Cell 2 Area: 11 cm2
Electrolysis with composite BZCY-BGLC
electrode
0
5
10
15
20
400°C
500°C
600°C
H2 p
rod
uctio
n (
Nm
L m
in-1)
Farad
aic
H 2 p
rodu
ctio
n
700°C
0 100 200Current Density (mA cm
-2)
0 1 2 3
1.0
1.5
2.0
Anode:
pO2 = 30 mbarpH
2 = 0.5 bar
ptot
= 3 bar
ptot
= 3 bar
pO2 = 30 mbar
400°C
500°C
600°C
Vo
lta
ge
(V
)
Current (A)
700°C
pH2O = 1.5 bar
Cathode:
4 5 6 7 8 9
-2
0
2
4
Zreal
(cm2)
400°C
500°C
600°C
-Zim
700°C
0.3 0.4 0.5 0.6 0.7 0.8 0.9Z
real ()
EIS at 300mA galvanostatic operation
Electrolysis with composite BZCY-BGLC
electrode
0
5
10
15
20
400°C
500°C
600°C
H2 p
rod
uctio
n (
Nm
L m
in-1)
Farad
aic
H 2 p
rodu
ctio
n
700°C
0 100 200Current Density (mA cm
-2)
0 1 2 3
1.0
1.5
2.0
Anode:
pO2 = 30 mbarpH
2 = 0.5 bar
ptot
= 3 bar
ptot
= 3 bar
pO2 = 30 mbar
400°C
500°C
600°C
Vo
lta
ge
(V
)
Current (A)
700°C
pH2O = 1.5 bar
Cathode:
0 1 2 3
2
4
6
8
10
500°C
AS
R (
cm
2)
Current (A)
600°C
700°C
Calculated from dV / dI
Calculated ASR from IV curves
Improved faradaic efficiency primarily due
to enhanced electrode kinetics
4 5 6 7 8 9-2
0
2
4
Cell 1
Z// (
cm
2)
Z/ (cm
2)
Cell 2
600C
30 mA cm-2
0 50 100 150 200
1.0
1.5
2.0
Cell 1
Cell 2
Vo
lta
ge
(V
)
Current density (mA cm-2)
0
20
40
60
80
100
Fa
rad
aic
effic
ien
cy (
%)
Conclusions
Proton Ceramic Electrolysers may suffer from electronic leakage during
operation due to relatively high p-type conductivity in oxidizing conditions
Operation at high overpotentials will induce higher electronic conductivity
within the electrolyte material
Improved electrode performance and higher steam pressures may reduce
electronic leakage
Tubular PCEs were made based on BZCY-NiO tubular supports, spray
coated BZCY72 electrolytes and BGLC steam electrodes
Enhanced faradaic efficiencies observed with improved anode performance
Current densities of 220 mA cm-2 at 600°C observed with > 80% faradaic efficiency
Contact resistance may still contribute significantly to the ohmic resistance of the electrolyser
Acknowledgements
The research leading to these results has
received funding from the European
Union's Seventh Framework Programme
(FP7/2007-2013) for the Fuel Cells and
Hydrogen Joint Technology Initiative
under grant agreement n° 621244.