(281f) La and Yb Incorporated Zr-Doped Ceria for Solar Thermochemical CO2 Splitting: Thermodynamics and Oxidation Kinetics Study

Two-step solar thermochemical redox cycles potentially represent one of the most practical routes towards producing solar derived fuels from H₂O and CO₂. For example, experimental efficiencies of thermochemical CO₂ splitting have been demonstrated on the order of 5 % using ceria shaped in reticulated porous ceramic (RPC) structures [1], but are limited in reduction capability of pure ceria even at high reduction temperatures. Doping ceria with tetravalent dopants (e.g. Zr⁴⁺) has been successful in terms of better reducibility due to low reaction enthalpy, but the synthesis gas (syngas, i.e. H₂/CO for H₂O/CO₂ splitting) productivity of Zr-doped ceria was significantly limited by the slow oxidation kinetics [2]. Numbers of additional dopants have been incorporated to Zr-doped ceria to enhance the syngas productivity [3, 4], but details in reaction mechanism via fundamental studies of thermodynamics and oxidation kinetics still need to be clarified.

In this work, we address the effect of additional trivalent dopants on Zr-doped ceria and the corresponding reaction mechanism, specifically focusing on structural analysis, thermodynamics, and oxidation kinetics in the context of dopant ionic radius and valence. Thermogravimetric analysis (TGA) and mass spectrometry were performed at two different temperature regimes (i.e. T ≥ 700 °C and T < 700 °C) to clarify the reaction mechanism at each temperature regime during thermochemical CO₂ splitting. Detailed structural analysis via Raman spectroscopy, calculated thermodynamic and kinetic properties are also presented, and the associated doping strategy is proposed for the potential redox materials development based on the doped ceria system.

References

[1] D. Marxer, P. Furler, M. Takacs, A. Steinfeld, Solar thermochemical splitting of CO2 into separate streams of CO and O-2 with high selectivity, stability, conversion, and efficiency, Energy & Environmental Science 10(5) (2017) 1142-1149.

[2] F. Call, M. Roeb, M. Schmücker, H. Bru, D. Curulla-Ferre, C. Sattler, R. Pitz-Paal, Thermogravimetric Analysis of Zirconia-Doped Ceria for Thermochemical Production of Solar Fuel, American Journal of Analytical Chemistry 04(10) (2013) 37-45.

[3] A. Le Gal, S. Abanades, N. Bion, T. Le Mercier, V. Harle, Reactivity of Doped Ceria-Based Mixed Oxides for Solar Thermochemical Hydrogen Generation via Two-Step Water-Splitting Cycles, Energy & Fuels 27(10) (2013) 6068-6078.

[4] D. Arifin, A. Ambrosini, S.A. Wilson, B. Mandal, C.L. Muhich, A.W. Weimer, Investigation of Zr, Gd/Zr, and Pr/Zr - doped ceria for the redox splitting of water, International Journal of Hydrogen Energy 45(1) (2020) 160-174.