A high flux solar simulator allows the lab-scale assessment of solar reactor concepts by irradiating a target with high flux thermal energy, similarly to reactors installed in concentrated solar radiation facilities such as central towers with a heliostat field. In the current study, the design and construction of a high flux solar simulator facility for near realistic solar experiments is presented. A simple, cavity-tubular thermochemical reactor is employed for the evaluation of the redox activity of structured monolithic bodies (foams and honeycombs) consisting entirely of NiFe 2 O 4 w.r.tÁH 2 O splitting, CO 2 splitting and combined H 2 O-CO 2 splitting reactions. Experiments under realistic conditions, i.e. a solar reactor under irradiation, were conducted to assess the solar fuels production capability, which was examined at the structure level and the reactor level. The best performing structure was the NiFe 2 O 4 foam. Further multilevel research (structure, reactor as well as redox material), will improve product yield and reactor efficiency.

The thermal reduction step of substituted ferrites (MFe2O4 where M = Fe, Ni, Co, Gd) and doped ceria (MxCe1-xO2, where M = Ce, Zr, Hf and x = 0.25) in two-step thermochemical cycles for H2O and CO2 splitting is investigated within the DFT+U framework. This thermal reduction step is described as the oxygen vacancy formation energy (reduction enthalpy), i.e. the energy required to create an oxygen vacancy in the crystal lattice. Oxides with a lower oxygen vacancy creation energy are easier to reduce. A Bader charge analysis of the reduction mechanism is carried out providing the charge distribution of the bulk and reduced ions, enabling interrelations of the substitute ions and the resulting reduction energies. Based on the approach presented here, interesting solar fuels producing materials are CoFe2O4, NiFe2O4 and Hf0.25Ce0.75O2.