Improving the redox performance of Mn2O3/Mn3O4 pair by Si doping to be used as thermochemical energy storage for concentrated solar power plants

Abstract

Thermal energy storage plays a significant role in concentrated solar power plants. Particularly, thermochemical energy storage has been proposed as a promising future candidate due to its high energy density. One of the most studied thermochemical reactions for this application are redox reactions using metallic oxides. The simplicity of using air as heat transfer fluid and reactant comprises important advantages. Among the studied materials, Mn2O3 has been deeply investigated due to its low cost and toxicity, although its reversibility has been shown to be highly deteriorated when exposed to high temperatures. The main negative effects found in the material are grain growth and densification, known as sintering, causing cyclability loss. Doping of ceramic materials has been proven to be an effective technique to control the sintering effects caused by high temperatures, especially in the production of metallurgical products. In this work, the effect of doping Mn2O3 with Si4+ as a sintering inhibitor for thermochemical energy storage has been studied deeply for the first time. The capacity to withstand 40 redox cycles with different quantities of dopant using two different synthesis routes was tested by TGA analysis. As a main result, dopant segregation on the grain boundaries caused a noticeable reduction of the grain growth and particle shrinkage. Additionally, all the doped samples presented a re-oxidation rate improvement. These two effects worked in a synergetic way providing a noticeable improvement on the cycling behavior of the material, which was particularly improved for low Si content (x = 0.02) using sol-gel synthesis method.