Final Report Summary - ARMOS (Advanced multifunctional Reactors for green Mobility and Solar fuels)
The main objective of ARMOS is to advance, the concept of multi-channeled honeycomb monolithic solar reactors for H2 generation from H2O splitting via redox-pair-based thermochemical cycles technology towards the production of “solar syngas” and therefore it focuses on CO2 and combined CO2/H2O splitting. Materials from different families (ferrites, rare earth based oxides etc.) were investigated with respect to their redox activity. The selection of active splitters (ferrites and cerium based oxides) was based on a map (locus) of potential material candidates that was developed with the aid of computational chemistry (Density Functional Theory (DFT) calculations with respect to the theoretical background that can support increased reducibility. A mapping of transition (d-block) as well as rare earth metals of interest, led to the creation of a database that can be accessed online from the URL http://apt.cperi.certh.gr/index.php?option=com_content&view=article&id=189%3Acomputational-materials&catid=9&Itemid=5&lang=en. In addition to the ferrites and Zr-doped cerium oxides, other formulations such as perovskites and mixed Co-ferrite-Al2O3 were also synthesized. In general, the results from the assessment of the redox activity of the ferrites and the cerium-based oxides is in accordance to the results of the DFT calculations. From the ferrite family, the NiFe2O4 had the highest redox activity. The CoFe2O4-Al2O3 mixed oxide had higher redox activity compared to the plain CoFe2O4, indicating that the addition of Al2O3 in the structure enhances the thermal stability of the ferrite. The best performing material in terms of product yield was the Ce0.80Zr0.20O2 both in the case of the H2O and the CO2 splitting. The manufacturing of monolithic bodies consisting entirely of the active material (NiFe2O4) was investigated via shaping of structured monolithic bodies (extrusion, casting using 3D-print molds). Furthermore, a kinetic model was developed for the thermal reduction, H2O and CO2 splitting and co-feeding for the powder and monoliths. A cavity-tube solar reactor was integrated to a high flux solar simulator facility that was developed for the bridging of conventional lab-scale experiments with actual solar field experiments. A control strategy was developed to achieve the temperature profiles for the consecutive splitting and regeneration cycles on the structured reactor. Three different monolithic structures were evaluated (NiFe2O4 foam, extruded and 3D-cast monolith). Although all structures were chemically the same they had different behavior during redox cycles. The NiFe2O4 foam was the best performing structure. Low product yields are not only a result of the inherent chemistry of the material but also of structural limitations that inhibit access of reactants to the redox sites. There is a lot of potential in the optimization of the morphological and geometric characteristics of the monolithic structures by increasing the accessibility of the redox structured bodies from the gaseous reactants. The integration of solar fuels to energy infrastructures was studied based on the utilization of CO2 as a raw material for the solar thermochemical splitting of H2O and CO2 towards the production of solar syngas (H2 and CO). A generic model for calculating point-to-point pipelines transport of CO2 mixtures was established. A study on a CO2 infrastructure network development and optimization was conducted with the aim to provide a viable alternative to syngas production and utilization using renewable energy sources and converting CO2 from a waste into a valuable chemical through the final production of fine chemicals from solar syngas. The studies focused in the geographic area of Greece as well as in a broader geographic assessment of CO2 transportation networks in Europe. No economies of scale emerge if joint pipelines are used, indicating that it is economically advantageous to transfer CO2 directly to the final sinks from the original sources.