Regulation Mechanism And Experimental Study On Thermochemical Energy Storage Characteristics Of Perovskite-type Metal Oxides

Thermal energy storage is one of the most common and potential energy storage technologies.Thermochemical energy storage technology is widely concerned because of high energy storage density,but its energy storage temperature range is relatively fixed,leading to temperature gaps with high utilization value.Therefore,it is urgent to develop flexible thermochemical energy storage media with tunable temperatures.Thermochemical energy storage media based on perovskite-type metal oxides have the advantages of wide temperature range,high tunability and crystal structural stability,which can meet diversified energy storage requirements.In this thesis,the experimental and mechanism research on thermal energy storage performance and regulation method of perovskites are carried out,laying a foundation for the development and application of thermochemical energy storage technology.For the problems of low re-oxidation rate and energy storage density of medium-temprature perovskites,the phase reconstruction is realized by substitution doping method in this thesis.The reaction reversibility can be increased to 87.88%when doping 50mol%Ba element at the A-site of SrCoO_3-δ.The thermal energy storage temperature of the Sr_0.5Ba_0.5CoO_3-δsample is 300℃.Its energy storage density can reach 828.22k J/kg,which is an excellent medium-termperature thermal energy storage material.The improvement mechanism is explored,indicating the improvement of re-oxidation activity can be attributed to the promotion effect of composite crystal on the phase transition kinetics and the increase of oxygen active sites.The simulation results of density functional theory（DFT）show that Ba-doping helps to increase the surface adsorption energy,thus promoting the oxygen adsorption process and re-oxidation reaction.The above research provides theoretical support for the performance optimization of the thermochemical energy storage materials.In order to meet the thermal enegy storage demand of higher temperature,a targeted temperature regulation method based on oxygen vacancy engineering is proposed in this thesis.The oxygen vacancy formation energy can be increased by doping Mn element at the B-site of BaCoO_3-δ,resulting in the temperature regulation in the range of 400-700℃.The reduction enthalpy reaches the maximum at the doping ratio of 15mol%.The thermal energy storage temperature of the BaCo_0.85Mn_0.15O_3-δsample is 601℃.Its energy storage density is 849.11k J/kg,which is an efficient high-termperature thermal energy storage material with high flexibility.In addition,the high-temperature cycling stability test shows that doping Mn element can reduce the grain surface energy to inhibit the grain boundary diffusion and grain growth during the sintering process,thus improving the sintering resistance.The relevant research provides a reference for prolonging the cycling life of the high-temperature energy storage materials.Finally,the application prospect of perovskite-type thermochemical energy storage materials used for thermal proctective coating of solar receivers is explored in this thesis.The coating is mainly composed of perovskite powder,potassium silicate binder,Si C thermal conductive filler and transition coating.Its adhesion can reach the highest level and absorptivity can reach 0.9619.The thermal protective performance test shows that the Sr_0.5Ba_0.5CoO_3-δcoating can reduce the fluctuation difference of the wall temperature by 39.7%under unstable solar radiation.After 600 high-temperature aging cycles,the conversion rate of reduction and oxidation reactions remains above89.09%and 81.43%respectively,and the absorptivity remains above 0.9385.This work is expected to provide a reference for the design optimization,mechanism research and diversified applications of perovskite-type thermochemical energy storage materials.