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 -splitting 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 thermogravimetric 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 theoretical 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.

Ceria Doped with Zirconium and Lanthanide Oxides to Enhance Solar Thermochemical Production of Fuels

“…In a previous study 45 , we reported that doping ceria with zirconia enhances the cycle performance, which is in concert with studies from other groups [46][47][48][49] . The optimum Zr-content was identified to be 15%.…”

“…As it was found for the Zr doping test series, the reduction extent approximates its following oxidation extent 45 . Accordingly, complete reoxidation is achieved.…”

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

“…A consensus on the beneficial effect ofanyway well-known from automotive emission control catalysts [137,138] -blending of CeO 2 with ZrO 2 with additions of La 2 O 3 to induce thermal stability seems to having been established [38,128,139]. However, in terms of doping with other cations, as mentioned in [81] "…in most cases the improvement in thermal reduction relative to undoped ceria is modest, and in some cases H 2 production by WS actually decreases…".…”

“…A plethora of dopants, basically lanthanides and alkaline earths, has been tested to improve the redox/thermal stability characteristics [38,125,[133][134][135][136]. A consensus on the beneficial effect ofanyway well-known from automotive emission control catalysts [137,138] -blending of CeO 2 with ZrO 2 with additions of La 2 O 3 to induce thermal stability seems to having been established [38,128,139].…”

“…2. General schematic of the solar-aided, two-step, redox-oxide-pair-based, water and/or carbon dioxide splitting thermochemical cycle for syngas production (adapted from [37,38]). of CO 2 was proposed as early as 1980 [45] but targeted at that time to producing carbon rather than CO as a source for hydrocarbon fuels.…”