1. Catalyst coated membrane for zero-gap alkaline water electrolyzer
Jaromír Hnát, Michaela Plevová, Jan Žitka, Karel Bouzek
Department of Inorganic Technology
University of Chemistry and Technology Prague

2. Hydrogen and hydrogen economy
Hydrogen as energy vector
produced from renewable sources
energy storage – alternative to batteries
water as side product
Renewable sources
Water electrolysis
Electricity production

3. Alkaline vs. Proton Exchange Membrane water electrolysis

4. Alkaline membrane water electrolysis
Membrane electrode assembly (MEA)
decrease the KOH concentration
differential pressure is possible
lower operational temperature
membrane
membrane
diaphragm
standard setup
anion selective membrane
zero gap arrangement
catalyst coated membrane
anion selective membrane,
ionomer binder and catalyst

5. Experimental part – polymer synthesis
Synthesis in three steps
synthesis of the back bone polymer
block copolymer of
styrene-ethylene-buthylene-styrene
(PSEBS)
chloromethylation
5 wt.% liquid solution in chloroform
was prepared -> polymer binder
introduction of the functional groups
1,4-Diazabicyclo[2.2.2] octane
(DABCO)

6. Experimental part – temperature characterization
TGA/DSC measurement
Linseis STA PT 700 LT device
temperature stability determination
glass transition temperature identification
Ion exchange capacity measurement
measured by UV/VIS spectroscopy
membranes treated:
under air atmosphere
in Cl- cycle
at 20 – 200 °C
for 24 hours
mechanical changes and stability

7. Experimental part – CCM preparation
Catalyst synthesis
NiCo2O4 as anode catalyst
NiFe2O4 as cathode catalyst
prepared by coprecipitation of the nitrates by NaOH
calcined at 325 °C (NiCo2O4) and 475 °C (NiFe2O4)
nickel
cobalt
iron
oxygen
Ion exchange capacity measurement
air-brush spraying technique
polymer substrates
PSEBS-CM
PSEBS-CM-DABCO
ink composition
mixture of catalyst and binder in CHCl3
ratio catalyst:binder equal to 9:1
catalyst load 2.5 or 10 mg cm-2

8. Experimental part – CCM characterization
Scanning electron microscopy
Hitachi S4700 scanning electron microscope
morphology and interface contact of the layers
Alkaline water electrolysis
load curves measurement:
cell voltage – 1.5 – 2.0 V
liquid electrolyte – 1 – 15 wt.% KOH
temperature – 45 °C
electrode area – 4 cm2
galvanostatic test
conditions of the load curves measurement
250 mA cm-2; 20 hours
electrochemical impedance spectroscopy
frequency range – 65 kHz – 1Hz; cell voltage 1.8 V

9. Results – temperature characterization
TGA/DSC
Chemical stability measurement
stability of the backbone polymer
up to 420 °C
stability of the functional groups
up to 200 °C
no glass transition temperature
no changes in IEC up to 120 °C
degradation of the functional
groups at 200 °C

10. Results – first steps PSEBS-CM-DABCO PSEBS-CM
Temperature: 45 °C; liquid electrolyte flow rate: 5 ml min-1; anode – 10 mg NiCo2O4 cm-2, cathode – 10 mg NiFe2O4 cm-2, concentration of the liquid electrolyte indicated in the inset of the figure, Ni foam as substrate, geometrical area 2 x 2 cm2

11. Results – first modification
Alkaline water electrolysis
Dependence of the cell voltage on the time of alkaline water electrolysis using different MEAs (shows in figures inset) at current density 250 mA cm-2. Geometrical area of the electrode 4 cm2, temperature 45 °C, concentration of the liquid electrolyte 10 wt.%, electrolyte flow rate 5 ml min-1.

12. Results – first modification
Morphology
Fig. A – 2.5 mg catalyst cm-2
fresh CCM
Fig. B – 2.5 mg catalyst cm-2
used CCM
Fig. C – 10 mg catalyst cm-2
Fig. D – 10 mg catalyst cm-2
Fig. E – bare Ni foam
Fig. F – 10 mg catalyst cm-2
fresh CCE
CCM used for load curve measurement in 10 wt.% KOH at 45 °C in the cell voltage range 1.5 – 2.0 V with additional 20 hours at current density 250 mA cm-2.

13. Results – PSEBS usage Alkaline water electrolysis load curves
Temperature: 45 °C; liquid electrolyte flow rate: 5 ml min-1; anode – 10 mg NiCo2O4 cm-2, cathode – 10 mg NiFe2O4 cm-2, concentration of the liquid electrolyte indicated in the inset of the figure, Ni foam as substrate, geometrical area 2 x 2 cm2

14. Results – PSEBS usage
Alkaline water electrolysis electrochemical impedance spectroscopy
Values of the system resistance and polarization resistance on KOH concentration evaluated from EIS spectra measured under the conditions of the alkaline water electrolysis at 1.8 V cell voltage.

15. Results – PSEBS usage Alkaline water electrolysis load curves
Dependence of the cell voltage on the time of alkaline water electrolysis using different MEAs (shows in figures inset) at current density 250 mA cm-2. Geometrical area of the electrode 4 cm2, temperature 45 °C, concentration of the liquid electrolyte 10 wt.%, electrolyte flow rate 5 ml min-1.

16. Results
Stable catalyst coated membrane was prepared for the first time
for alkaline water electrolysis.
CCM MEA with catalyst loading 2.5 mg cm-2 showed the comparable
performance to CCE MEA with catalyst loading 10 mg cm-2.
Vital influence of the catalytic layer thickness on the performance
alkaline water electrolysis observed.
Further optimization of the catalytic layer composition and preparation is needed.

17. Thank you for your attention
Financial support of this research by Ministry of the Industry and Trade of the Czech Republic
under project No. FV10529 is gratefully acknowledged.