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. A calcium-based perovskite (CaMnO_3−δ) has emerged as a prospective candidate for thermochemical energy storage applications; however, CaMnO_3−δ suffers from poor cycling stability and insufficient reaction depth when employed in high-temperature TCES systems. This study optimizes the Ni doping at the B-site on the CaMnO_3−δ via a modified Pechini method. Their phase composition, redox kinetics, thermal energy storage density, and cycling durability were systematically characterized. The results demonstrate that moderate Ni doping (x ≤ 0.10) effectively increases the specific surface area of the materials from 7.906 to 14.177 m² g⁻¹, facilitates the formation of oxygen vacancies, and notably increases the highest reaction depth δ to 0.374 (for the sample with x = 0.10), while enabling complete reoxidation. Correspondingly, the total thermal storage density is improved from 900.68 kJ kg_ABO3⁻¹ for the pristine sample to 1085.01 kJ kg_ABO3⁻¹ (for the sample with x = 0.05) and 1208.79 kJ kg_ABO3⁻¹ (for the sample with x = 0.10), which exhibit a higher thermochemical energy storage density than most B-site doped CaMnO_3−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 was conducted to improve the cycling stability of the CMN10 sample. The results show that the MgO composite-modified CMN10 sample (CMNM) exhibits a reduction capacity decay of only 0.62% after 200 cycles, while the TiO₂ composite sample (CMNT) also shows enhanced cycling stability compared with the CMN10 sample. This work provides experimental evidence for the theoretical design and performance optimization of high-performance perovskite-based thermochemical energy storage materials.