A group from the URJC has developed materials that allow working at temperatures compatible with solar thermal power plants, which, in addition to ensuring compatibility with the installations in terms of thermal shock resistance requirements, reduces the costs associated with the process.
Thermochemical cycles driven by solar thermal energy can be used to generate green hydrogen: a solid material is able to be reduced at high temperature -releasing oxygen- and reoxidized when in contact with water vapor, recovering its initial structure and producing hydrogen. This process has the great advantage of obtaining hydrogen and oxygen separately, using only water as a sustainable raw material. However, its main problem is that it requires very demanding operating conditions in terms of temperature (usually above 1000-1200 ◦C).
Currently, new materials capable of being reduced in the first stage of the process at temperatures below 1000 ◦C, maintaining a considerable hydrogen production, in a stable and sustained manner during a large number of consecutive thermochemical cycles of reduction and oxidation, are being explored and developed. In this line, the Chemical and Environmental Engineering Group (GIQA) of the Spanish University Rey Juan Carlos (URJC) has managed to prepare some active materials for the production of green hydrogen by thermochemical cycles at a significantly lower temperature than that usually used, getting to lower up to 800 ◦C the thermal requirements of the process.
According to the group, “this means not only an increase in the efficiency of the process, but also enormous advantages when considering the implementation of these processes on an industrial scale, given that these operating temperatures are compatible with those that can be reached in currently operating CSP facilities, such as tower solar power plants or parabolic dish plants”.
As the researchers explain, this system implies “lower radiation losses and better absorption of solar radiation”. In addition, “the technical requirements of the reactor construction materials are reduced,” which translates into lower costs. These results, recently reported in the article “Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH” published in Catalysis Today, have been obtained from the preparation of perovskite-type materials, which are characterized by their good ease of reduction and oxidation (redox properties), achieving a significant reduction in the high operating temperatures for obtaining thermochemical green hydrogen.
Specifically, the materials studied are based on metal oxides with ABO3 type perovskite structure. On the initial formulation -with lanthanum (La) in position A and other metals such as cobalt (Co), nickel (Co), iron (Fe) or copper (Cu) in position B- aluminum (Al) has been introduced into the perovskite structure to modify its initial properties. Perovskites with high reduction and oxidation capabilities at low temperature (from the point of view of concentrating solar power), with stable hydrogen yields and no apparent damage or loss of activity during consecutive cycles have been achieved. “This confirms that perovskites are very interesting materials for large-scale hydrogen production from water dissociation by solar-driven thermochemical cycles at low temperatures,” the researchers note.
