Abstract
Developing an efficient redox material is crucial for thermochemical cycles that produce solar fuels (e.g. H2 and CO), enabling a sustainable energy supply. In this study, zirconia-doped cerium oxide (Ce1-xZrxO2) was tested in CO2-splitting cycles for the production of CO. The impact of the Zr-content on the splitting performance was investigated within the range 0 ≤ x mogravimetric experiments. The results indicate that there is an optimal zirconium content, x = 0.15, improving the specific CO2-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 theoretical studies attributing the improvements to lattice modification. Introducing Zr4+ into the fluorite structure of ceria compensates for the expansion of the crystal lattice caused by the reduction of Ce4+ to Ce3+. Regarding the reaction conditions, the most efficient composition Ce0.85Zr0.15O2 enhances the required conditions by a temperature of 60 K or one order of magnitude of the partial pressure of oxygen p(O2) compared to pure ceria. The optimal composition was tested in long-term experiments of one hundred cycles, which revealed declining splitting kinetics.
Highlights
Synthesis gas—primarily a mixture of H2 and CO—is one of the most promising sustainable energy carriers when produced from renewable resources
The results indicate that there is an optimal zirconium content, x = 0.15, improving the specific CO2-splitting performance by 50% compared to pure ceria
In order to evaluate their applicability for solar fuel production, they were subjected to thermogravimetric experiments, simulating CO2-splitting cycles
Summary
Synthesis gas (or syngas)—primarily a mixture of H2 and CO—is one of the most promising sustainable energy carriers when produced from renewable resources. Oped that produce syngas from renewable sources (CO2, water) employing solar energy to cover the reaction heat [8,9]. The direct method to produce syngas from solar thermal energy is the thermolysis of water and CO2 molecules in a single step. Injecting water steam instead of (or with) carbon dioxide enables the production of hydrogen (or syngas) While experimental campaigns such as HYDROSOL 2 proved the operability of this process on a solar tower [19,20], identifying that an efficient metal oxide is crucial for the commercialization of this technology. The Zr-content featuring the highest specific yield has been identified and analyzed in terms of reaction conditions and long-term stability
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