Thermochemical heat storage for CSP using Mn2O3/Mn3O4: Effects of Si doping in cyclability improvement

Abstract

Mn2O3/Mn3O4 redox couple is of great interest for thermal energy storage (TES) in concentrated solar power (CSP) plants. The next generation of CSP technologies considers working at temperatures beyond the maximum working temperature affordable by the current TES systems. In the temperature range above 600°C, Mn2O3 thermochemical material presents low cost and toxicity and has been proposed as a suitable material for this application. Nevertheless, the material behavior presents a cyclability deterioration in a long-term use that must be solved before reaching a commercial stage. At present, Fe addition has been presented as a promising approach to improve the cyclability of the material. In this work, the effects of doping Mn2O3 with 1% Si have been studied and the results have been compared with the pure material and an 15% Fe doped sample. The tested materials were synthetized by Pechini process and a dry method and were subjected to 10 redox cycles in a thermobalance. The results have been characterized by XRD and SEM. It has been found that both doping approaches improve considerably the cycling behavior of the Mn2O3 material. Nevertheless, Fe addition does not prevent the sintering effects whereas the Si doped sample presents a stable particle size after 10 redox cycles. This fact may explain the better re-oxidation kinetics rate found in the Si doped sample, which in addition to the low cost of Si, turns this material into a promising approach for future considerations.