1. Development of Oxygen Electrodes for High Temperature and Pressure Alkaline Electrolysis Cells (HTP-AEC)
Jens Q Adolphsen Bhaskar R. Sudireddy,
Vanesa Gil, Christodoulos Chatzichristodoulou

2. ECerS conference 2017, Budapest
Outline
Motivation for the work
Selection of materials
Electrochemical activity towards the OER
Chemical stability of materials at high temperature
Processing porous LaNi0.6Fe0.4O3 electrodes
Motivation and past results (high current density compared to conventional alkaline electrolysis cells
Low overvoltage (high efficiecy)
ECerS conference 2017, Budapest

3. High Temperature and Pressure Alkaline Electrolysis Cells (HTP-AEC)
Mesoporous Electrolyte matrix
Motivation and past results (high current density compared to conventional alkaline electrolysis cells
Low overvoltage (high efficiecy)
Record data from earlier work
3.75 A/cm2 at 1.75 V with
ηel = 85 % (200ºC, 20 bar)
C. Chatzichristodoulou et al. J. Electrochem. Soc, 163, 2016
ECerS conference 2017, Budapest

4. Selection of materials for the OER
O2(g)+
2H2O(l)
Electrochemical activity
Electrochemical stability
Electronic conductivity
Electrode materials for the
Oxygen Evolution Reaction (OER)
4e-
4 OH-aq ?
Metal oxides
Pervoskites active: Most active become amorphous over time
Ni-Fe combination has proven to be a particularly good combination in NiFeOx
Activity
Stability

5. Electrochemical Characterization
Materials Conditions RTP, N2 atmosphere, 1 M KOH, Measurements Chronopotentiometry at 0.5, 1.0, 2.0, 5.0, 10, 25 and 50 mA·cm-2 Amperostatic EIS
LaNiO3
La0.97NiO3
LaNi0.6Fe0.4O3
La0.97Ni0.6Fe0.4O3
La2Ni0.9Fe0.1O4
Well-defined surface area
Electronic conductivity:
LN & LNF: S/cm
L2NF: S/cm
Reference electrode (RHE from Gaskatel)
Working electrode
(Au current collector)
Counter electrode (Pt mesh)
Separator

6. Electrochemical Characterization

7. Electrochemical Characterization
Material
b (V/dec) η
10 mA/cm2
LaNiO3
0.083
0.38
La0.97NiO3
0.092
0.44
LaNi0.6Fe0.4O3
0.13
0.11
0.45
La2Ni0.9Fe0.1O4
0.079
0.40
IrOx [1] -
0.32
Ni0.9Fe0.1Ox [2]
0.030
0.34
PrBaCo2O5+x [3]
~0.07
~0.38
[1] C. C. L. McCrory, S. Jung, J. C. Peters, T. F. Jaramilllo, J. Am. Chem. Soc. 135 ( ), 2013
[2] L. Trotochaud, J. K. Ranney, K. N. Williams, S. W. Boettcher, J. Am. Chem Soc. 134 ( ), 2012
[3] A. Grimaud, K. J. May, C. E. Carlton, Y-L. Lee, M. Risch, W. T. Hong, J. Zhou, Y. Shao-Horn, Nat. Commun. 4 ( ), 2013

8. Electrochemical Characterization
Test with same pellet

9. Sample roughness factors
RRMS (pre) [µm]
RRMS (post)
[µm]
LaNiO3
0.41
0.79
La0.97NiO3
0.44
0.92
LaNi0.6Fe0.4O3
0.37
0.68
La0.97 Ni0.6Fe0.4O3
0.38
0.49
La2Ni0.9Fe0.1O4
0.20
0.81
Initial polished surface
1 µm
Polished surface after electrochemical testing
1 µm

10. Chemical Stability
Porously sintered pellets and as-received powders exposed to concentrated KOH for a week at 100°C/220°C
Pellets crumble after 1-2 weeks when exposed to 45 wt% KOH at 220 deg C
Powder dilluted to remove KOH, heated to remove water and performed XRD

11. Chemical Stability – XRD
Neither LN, LNF nor L2NF are stable at 220 deg C. They all fall apart and it is likely that secondary phases La, Ni and Fe are observed.
It is not an attempt to tell you exactly what phases are formed
○LaNiO3 ● LaNi0.6Fe0.4O3 Δ La2Ni0.9Fe0.1O4
+ La2O3 ♦ LaO(OH) ♠ La(OH)3
* NiO □ NiO(OH) ♥ Ni(OH)2
× Fe2O3 ◊ FeO(OH) ♣ Fe(OH)2

12. Chemical Stability – XRD
L2NF is stable at 100 deg C.
LN is starting to fall apart (mainly La(OH)3 phase being formed)
LNF is not stable at all
○LaNiO3 ● LaNi0.6Fe0.4O3 Δ La2Ni0.9Fe0.1O4
+ La2O3 ♦ LaO(OH) ♠ La(OH)3
* NiO □ NiO(OH) ♥ Ni(OH)2
× Fe2O3 ◊ FeO(OH) ♣ Fe(OH)2

13. Processing of LNF electrode layers
Processing of porous structures for the oxygen evolution reaction
% total porosity
- Hierachical porosity  macropores & mesopores
Optimization of the microstructure of the porous electrode:
- Allow transport of oxygen leaving the pores
- Allow transport of OH- species to reactive sites
Optimal pore size distribution
Percolating phases (gas, solid)
Mesoporosity
Macroporosity

14. Processing of LNF electrode layers
10 µm
200nm
Motivation for using rice starch
200 µm

15. Processing of LNF electrode layers
Top surface
10 µm
Still some challenges – flat substrates
Starch is less visible, adhesion is fine
Cross section
10 µm

16. Thank you for your attention
Acknowledgements
Bent F. Hansen
Jeanette Krambech
Jens Østergaard
Karen Brodersen
Kjeld B. Andersen
Lene Knudsen
Søren Christensen
Søren P. V. Foghmoes