A dual-scale transport model of the porous ceria based on solar thermochemical cycle water splitting hydrogen production

Solar thermochemical cycle converts the full-spectrum range of solar irradiation into chemical energy, which can then be stored or transported, paving the route to achieving carbon neutrality. This cycle involves complex heat and mass transfer processes in porous media, and a relatively complete mathematical model has not been established yet. In particular, there is a lack of a heat and mass transfer model that couples particle scale and macro scale, which is of great theoretical value for the design of solar thermochemical cycle reactors. A comprehensive model combining transport of species in the porous bed (macroscopic) and the lattice oxygen within the particles (mesoscopic) is developed. Dilute mass transfer model and P-1 radiation model are adopted in this model. Based on the model validation by comparing it with existing experimental data, the unsteady heat and mass reaction process, and transportation in the solar thermochemical cycle are investigated under dual-scales. For the oxidation and reduction process respectively, the peak deviation between the model and the experiment is less than 2 s, which thoroughly validated our model. The additional results show that the local thermal and mass non-equilibrium effect and the parameters at the macro and micro scales have a significant influence on the temperature distribution and reaction kinetics. The oxidation process is faster than the reduction process, but the transport time scales in macroscopic (axial) and mesoscopic (radial) direction is of the same order. The increase of reactant concentration can effectively raise the peak value of the hydrogen production, but the product in the oxidation stage is not only limited by the oxidant concentration but also affected by the final state in the reduction stage.