B-site Ni-doping and MgO/TiO2 modified CaMnO3-δ for thermal energy storage

Abstract

Thermochemical energy storage (TCES) is recognized as one of the most promising energy storage technologies to date, capable of mitigating the spatiotemporal mismatch in the utilization of solar energy. Calcium-based perovskite (CaMnO3₋δ) has emerged as a prospective candidate for thermochemical energy storage applications; however, CaMnO3₋δ suffers from poor cyclic stability and insufficient reaction depth when employed in high-temperature TCES systems. This study optimizes the Ni doping at the B-site on the CaMnO3₋δ via the modified Pechini method. Their phase composition, redox kinetics, thermal energy storage density, and cyclic durability were systematically characterized. The results demonstrate that moderate Ni doping (x ≤ 0.10) effectively enhances the specific surface area of the materials from 7.906 to 14.177 m²/g, facilitates the formation of oxygen vacancies, and notably elevates the highest reaction depth δ of 0.374 ( x = 0.10), while enabling complete reoxidation. Correspondingly, the total thermal storage density is improved from 900.68 kJ/kgABO3 for the pristine sample to 1085.01 kJ/kgABO3 (x = 0.05) and 1208.79 kJ/kgABO3 (x = 0.10), exhibits a higher thermochemical energy storage density than most B-site doped CaMnO3₋δ materials. X-ray photoelectron spectroscopy (XPS) analysis reveals that the structural stability and reaction enthalpy of the perovskite materials are enhanced by Ni doping due to the increased binding energy of lattice oxygen. Subsequently, composite modification with 5% MgO and 5% TiO2 were conducted to improve the cyclic stability of the CMN10 sample. The results show that the MgO composite-modified CMN10 sample(CMNM) exhibits a mere reduction capacity decay of 0.62% after 200 cycles, while the TiO2 composite sample(CMNT) also obtains enhanced cyclic stability compared with the CMN10. This work provides experimental evidence for the theoretical design and performance optimization of high-performance perovskite-based thermochemical energy storage materials.