Investigations on substituted Si-doped Mn2O3/Mn3O4 redox pair for thermochemical energy storage

Abstract

Next-generation concentrated solar power plants with thermochemical energy storage can meet the demand for peak regulation and power supply, which stimulates the development and application of low-priced metal oxide thermochemical thermal storage materials. Mn-based composite metal oxide is a competitive candidate for large-scale applications given its character of being non-toxic, cheap, and highly efficient. However, the utilization of pure Mn2O3 suffers from sintering, which limits its re-oxidation and hence affects the applicability. In this study, Si is introduced to solve the above problems and improve the reaction characteristics of pure Mn2O3. (Mn1−xSix)2O3 is synthesized by substituent doping, with the best performance at x = 3 % and 5 %, reaching 96.18 % and 94.71 % of reduction conversion rate, respectively. The performance decay of the (Mn0.95Si0.05)2O3 sample was tested and evaluated, with reduction conversions of 90.92 % and 63.64 % after 50 and 300 cycles, respectively. A series of characterization results confirm that Si4+ is successfully doped into the Mn2O3 lattice, introducing defects into the crystal structure, which is favorable for the oxidation reaction. Density functional theory calculations of oxygen adsorption/dissociation and oxygen diffusion indicate that the doped Mn-Si oxides have lower reaction potentials and energies, which explains the promotion of the re-oxidation reaction by Si. By investigating the thermochemical energy storage properties and mechanism of Mn-Si composite metal oxides, we provide guidance for large-scale, cheap, and eco-friendly energy storage applications.