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.