Engineering Solid Oxide CO2 Electrolysis: From Nanoparticle-Decorated Perovskite Cathode to System-Level Modeling

Abstract

Solid oxide electrolysis cell (SOEC) is a promising technology for CO2 electrolysis and subsequent conversion to useful chemicals. This thesis combines the experimental development of new cathode materials with system-level simulation to enhance the performance of SOECs for CO2 electrolysis and assess their applicability for fuel production. There are two components to the work: (1) proposing nanoparticle decorated perovskite cathode material and (2) integration of DAC, SOEC and synfuel production and asses its performance with techno-economic and environmental analysis. In the experimental section, the focus was on the cathode material of the SOEC since it is the limiting factor for CO2 electrolysis. Sr2Fe1.5Mo0.5O6-δ (SFM) has attracted much attention due to its decent performance of CO2 electrolysis. To enhance the SFM performance, it was modified by doping bismuth and nickel to make a new composition of Bi0.1Sr1.9Fe1.4Ni0.1Mo0.5O6-δ (BiSFNiM). The Ni-doping made it possible for Fe–Ni nanoparticles to exsolve in situ when the material was reduced by 5% H2/Ar. Structural characterizations like XRD and Rietveld refinement showed that, during exsolution, the material changed from a pure double perovskite structure to a mixed-phase material with both Ruddlesden–Popper (RP) and residual double perovskite phases and metallic nanoparticles. Using electron microscopy (SEM/TEM/EDS), it showed that Ni migrated to the surface of the perovskite bulk where it forms Fe–Ni nanoparticles. This material, then, was used as the cathode of SOEC and the results showed that these exsolved Fe–Ni nanoparticles significantly improved the electrocatalytic activity for the CO2 reduction reaction (CO2RR). Electrochemical performance tests demonstrated substantial improvements in current density and polarization resistance. The fabricated cell achieved a peak current density of 1.3 A/cm² at 800 °C under an applied voltage of 1.6 V, while it was 1.0 A/cm² for the non-exsolved nanoparticles sample. The second half of this thesis was a process simulation and system-level evaluation of an integrated DAC-SOEC facility. The technology was based on capturing 250,000 tonnes of CO2 from the air each year and turning it into either methanol or synthesis fuel through downstream processes. Methanol production was 36.4 tonnes per hour, while synfuel output was 15.1 tonnes per hour. The techno-economic analysis found that the levelized production cost for methanol was $1.32 per kilogram (nearly double the current market price) and for synfuel, it was $2.78 per kilogram (approximately 45% more than normal expenses). Using Ontario’s electricity grid mix, the simulated plant achieved greenhouse gas emissions of 31.1 gCO2-eq/MJ for methanol and 5.2 gCO2-eq/MJ for synfuel, the latter representing a reduction compared to conventional fossil-based pathways (40 g-CO2-eq/MJ-MeOH and 29 g-CO2-eq/MJ-synfuel). Further sensitivity analysis demonstrated that switching to fully renewable electricity sources, such as hydropower or wind, could push the synfuel production case into a net-negative emissions region. In conclusion, this thesis contributes to both fundamental and applied aspects of CO2 electrolysis. On the material side, it offers a strong plan for boosting cathode performance by co-doping and nanoparticle exsolution. It also gives information about phase stability, exsolution behavior, and catalytic activity. At the system level, it shows that combining DAC and SOEC for sustainable fuel production is possible from a technological, economic, and environmental point of view. The dual approach shows how innovative materials and systems design can work together to help us toward carbon-neutral chemical manufacture.