Abstract
Reduction of CO2 to CO and O2 in the solid oxide electrolysis cell (SOEC) has the potential to play a crucial role in closing the CO2 loop. Carbon deposition in nickel-based cells is however fatal and must be considered during CO2
electrolysis. Here, the effect of operating parameters is investigated
systematically using simple current-potential experiments. Due to
variations of local conditions, it is shown that higher current density
and lower fuel electrode porosity will cause local carbon formation at
the electrochemical reaction sites despite operating with a CO outlet
concentration outside the thermodynamic carbon formation region.
Attempts at mitigating the issue by coating the composite
nickel/yttria-stabilized zirconia electrode with carbon-inhibiting
nanoparticles and by sulfur passivation proved unsuccessful. Increasing
the fuel electrode porosity is shown to mitigate the problem, but only
to a certain extent. This work shows that a typical SOEC stack
converting CO2 to CO and O2 is limited to as little as 15–45% conversion due to risk of carbon formation. Furthermore, cells operated in CO2-electrolysis
mode are poisoned by reactant gases containing ppb-levels of sulfur, in
contrast to ppm-levels for operation in fuel cell mode.
Original language | English |
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Journal | Journal of Power Sources |
Volume | 373 |
Pages (from-to) | 54-60 |
ISSN | 0378-7753 |
DOIs | |
Publication status | Published - 2017 |
Keywords
- High temperature electrolysis
- CO2 reduction
- Carbon formation
- Sulfur poisoning
- Electrode gradients
- Mitigation