The role of Solid Oxide Cells (SOCs) in the energy sector goes beyond their conventional operation and utilization for electricity generation. A Solid Oxide Cell is a device that can in principle operate in (a) fuel cell mode, i.e for generating electricity through the electrochemical combination of a fuel (e.g. H₂, CH₄ or CO) with oxygen, and in (b) electrolysis mode, i.e. for the production of fuels (e.g. hydrogen from water, CO from CO₂, or syngas from mixtures of water and CO₂). Given the versatile operability of a single solid-state device, the need for efficient performance and stability, is crucial. Any Reversible SOC (rSOC), as shown in Figure 1, operating on the CO₂ cycle (SOEC mode: electrolysis of CO₂, SOFC mode: electrochemical reaction of CO and oxygen for power generation), faces similar problems regarding degradation and carbon built up, as in the case of SOFCs operating on C-containing fuels. In this context, the performance, tolerance to carbon deposition, reversibility and stability of doped lanthanum chromite ceramic electrodes (LSC-M) ^{[1, 2]}, under cycling operation between CO₂ electrolysis (SOEC mode) and power generation through the electrochemical reaction of CO and oxygen (SOFC mode), is discussed. During this study it is concluded that although the state-of-the-art Ni-YSZ electrode presents high activity for both CO₂ electrolysis and CO/CO₂ vs. O₂ fuel cell operation, it suffers from significant degradation initiated during electrolysis of CO₂ and resulting in >50% performance loss within the first complete cycle of measurements. This severe degradation is a combined result of the instability (coarsening) of Ni-YSZ in CO-CO₂ environment as well as of the evolvement of carbon deposition, in the form of Ni carbonyls. The later species are highly volatile, making it important to choose operating conditions for which carbonyl formation is less favourable. Moreover, Ni-YSZ composites are prone to degradation by re-oxidation caused by exposure to pure CO₂. On the contrary, the synthesized LSC-M perovskites present a significantly stable performance. The steady state IV curves and AC impedance measurements of the prepared cells under CO₂ splitting and CO oxidation revealed the superior performance. Cells with LSCF show high initial performance in CO₂ SOEC and CO/CO₂SOFC operation and exhibit remarkable stability and reversibility under cycling between operation modes.

Acknowledgement

The authors would like to acknowledge financial support from the European Space Agency (ESA Contract: 4000108849/13/NL/ΕΚ) and the European Union’s Fuel Cells and Hydrogen 2 Joint Undertaking (SElySOs project, Grant Agreement No. 671481).

References

1. K.M. Papazisi, S. Balomenou and D. Tsiplakides, Journal of Applied Electrochemistry, 40 (2010) 1875-1881.

2. K.M. Papazisi, D. Tsiplakides, S. Balomenou, I. Waernhus, C.S. Ilea, A. Vik, M. Schautz, Proceedings of the 11^thEuropean Space Power Conference (2016) Paper B032.

Figure caption:

Figure 1: Operational principle of a Reversible Solid Oxide Cell on the CO₂ cycle: CO₂ electrolysis (top) and CO-fueled SOFC for power generation (bottom).