Investigation of the combined Mn-Si oxide system for thermochemical energy storage applications

Combined manganese-silicon oxides are promising candidates for thermochemical energy storage (TCES) since they show a great potential for spontaneous O-2 release as utilized in chemical-looping with oxygen uncoupling (CLOU). For both concepts, as well as mechanical strength, cyclic stability of oxidation and reduction are very important. The high reaction enthalpy of the material at high temperature conditions is one of the most important issues for TCES. Agglomeration and destabilization of the material can occur during redox cycles which results in decreased cyclic stability. In this study, thermal analyses were carried out to investigate the phase transitions and changes of manganese-silicon oxide by comparably slow heating and cooling rate during the thermal cycling. This was conducted in a packed bed reactor to identify the oxygen releasing and consuming stability versus temperature and number of cycles. Phase analyses were carried out to reveal the phase changes during cycling or new formed phase due to side reactions. Results showed that both thermal cyclic stability and oxygen coupling-uncoupling ability increased with increased silica content, from 2 to 10% wt., and the poorest stability was obtained from the sample which has the highest silica content.