Thermogravimetric Analysis of Zirconia-Doped Ceria for Thermochemical Production of Solar Fuel

Abstract

Developing an efficient redox material is crucial for thermochemical cycles that produce solar fuels (e.g. H 2 and CO), enabling a sustainable energy supply. In this study, zirconia-doped cerium oxide (Ce 1−x Zr x O 2) was tested in CO 2 -split-ting cycles for the production of CO. The impact of the Zr-content on the splitting performance was investigated within the range 0 ≤ x < 0.4. The materials were synthesized via a citrate nitrate auto combustion route and subjected to ther-mogravimetric experiments. The results indicate that there is an optimal zirconium content, x = 0.15, improving the specific CO 2 -splitting performance by 50% compared to pure ceria. Significantly enhanced performance is observed for 0.15 ≤ x ≤ 0.225. Outside this range, the performance decreases to values of pure ceria. These results agree with theo-retical studies attributing the improvements to lattice modification. Introducing Zr 4+ into the fluorite structure of ceria compensates for the expansion of the crystal lattice caused by the reduction of Ce 4+ to Ce 3+ . Regarding the reaction conditions, the most efficient composition Ce 0.85 Zr 0.15 O 2 enhances the required conditions by a temperature of 60 K or one order of magnitude of the partial pressure of oxygen p(O 2) compared to pure ceria. The optimal composition was tested in long-term experiments of one hundred cycles, which revealed declining splitting kinetics.