Analysis • Outlet gas composition was analyzed by gas-
chromatography and with humidity sensor • Materials were characterized by XRD, SEM/EDX
and Raman spectroscopy
NiSn as coking-resistant cathode catalyst for the high-temperature H2O/CO2 co-electrolysis
B. Choi, N. Bogolowski, J.-F. Drillet| [email protected]| 1st September 2016 – 31st August 2019
Chemical Technology
Motivation & Challenges • By opting for the ambitious '‘Energiewende” strategy, Germany´s
government decided to substitute nuclear plants by renewable energy sources. However, these are subjected to unforeseeable seasonal and climatic fluctuations
• Innovative energy storage strategies are required for grid-balancing • Electricity can be stored in gaseous form such as in H2 or H2+CO (syngas) via
electrolysis (Power-to-Gas) and transformed e.g. into fuels (Power-to-Liquid) • HT co-electrolysis of H2O and CO2 appears to be a promising technology • Activity and stability of Ni-cermets should be improved. Ni percolation and
carbon formation at high pressure can lead to catalyst degradation • NiSn as alternative coking resistant cathode material; reversible phase
formation in the presence of high water content is challenging
1 SOEC working principle & possible products
2
Results Reactor outlet gas composition
• NiSn is active for reverse water-gas shift reaction • Absolute activity of NiSn for CO production is
lower than that of Ni, but Ni mass-normalized activities are similar
• Highest CO yield at H2: CO2 = 1: 1 (mol%)
SEM analysis
• Particle sintering after one week of experiment • Sinter activity increases with temperature
4 XRD and Raman analysis
• Although samples had been cooled down under reducing atmosphere (10% H2 in Ar), slight formation of SnO2 and NiO phase in NiSn XRD
• In Raman spectra (not shown here), no peak related to amorphous or graphitic carbon was visible on Ni and NiSn after 100 h of testing
Conclusions & Outlook • NiSn is active for RWGS but prone to slight phase segregation into NiO and
SnO2
• No carbon formation observed at Ni and NiSn
• Further alternative materials e.g. perovskites will be investigated
• Tests at higher pressure and for longer exposure time are planed
5 Acknowledgements: The German Federal Ministry of Education and Research (BMBF) is gratefully acknowledged for financial support and project partners for fruitful cooperation.
6
Experimental NiSn catalyst preparation • NiSn catalyst material was prepared by
melting Tin and Nickel in a centrifugal casting oven under argon atmosphere
• The crushed ingot was ball-milled to powder
3 Reactor experiments • 5g NiSn and Ni powder were tested regarding
activity for reverse water-gas shift reaction (RWGS) in a quartz tube reactor at 750 and 850 °C under different H2/CO2 atmospheres
CO and water production by RWGS @ NiSn and Ni
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Mol
ar fr
actio
n
x(CO2)/(x(CO2)+x(H2))
y(H2O) y(H2) y(CO) y(CH4) y(CO2)
Pure H2Pure CO2
Ni at 750°C
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Pure CO2Pure H2
Mol
ar fr
actio
n
x(CO2)/(x(CO2)+x(H2))
y(H2O) y(H2) y(CO) y(CH4)
y(CO2)
Ni2Sn3 at 750°C
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Mol
ar fr
actio
n
x(CO2)/(x(CO2)+x(H2))
y(H2O) y(H2) y(CO) y(CH4) y(CO2)
Ni at 850 °C
Pure H2 Pure CO2
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Mol
ar fr
actio
n
x(CO2)/(x(CO2)+x(H2))
y(H2O) y(H2) y(CO) y(CH4) y(CO2)
Ni2Sn3 at 850 °C
Pure H2 Pure CO2
• CO can be produced either via reverse water-gas shift or electrochemically
XRD of NiSn and Ni before and after experiment
SEM images of NiSn and Ni
Int.
/ a.u
.
Pristine Ni-powder
Ni after 850°C
[331
][4
00][2
22]
[311
]
Ni after 750°C
[111
]
[200
]
[220
]
20 40 60 80
Ni 00-004-0850
2θ / deg
Int.
/ a.u
.
Pristine Ni3Sn2-powder
# *
Ni3Sn2 after 850°C
#
*# #
Ni3Sn2 after 750°C
[101
][1
00]
[002
]
[102
]
[110
]
[201
][1
12]
[103
][2
02]
[211
][1
00] [212
][3
00]
20 40 60 80
Ni3Sn2 00-006-0414*NiO 00-044-1159#SnO2 00-041-1445
2θ / deg
Ni3Sn2 Ni
850°C
750°C
850°C
750°C
