*Review* **Solid–Gas Thermochemical Energy Storage Materials and Reactors for Low to High-Temperature Applications: A Concise Review**

**Anti Kur \*, Jo Darkwa, John Calautit, Rabah Boukhanouf and Mark Worall**

Buildings, Energy and Environment Research Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK

**\*** Correspondence: anti.kur@nottingham.ac.uk

**Abstract:** Thermochemical energy storage materials and reactors have been reviewed for a range of temperature applications. For low-temperature applications, magnesium chloride is found to be a suitable candidate at temperatures up to 100 ◦C, whereas calcium hydroxide is identified to be appropriate for medium-temperature storage applications, ranging from 400 ◦C up to 650 ◦C. For the high-temperature range (750–1050 ◦C), oxides of cobalt, manganese, and copper are found to have the redox behaviour required for thermochemical heat storage. However, some of these materials suffer from low thermal conductivities, agglomeration, and low cyclability and, therefore, require further improvements. The concept of enhancing thermal conductivities through additives such as nanomaterials has been encouraging. From an operational point of view, fluidized-bed reactors perform better than fixed- and moving-bed reactors due to better particle interactions. There is, however, a need for the reaction bed to be further developed toward achieving optimum heat and mass transfers. Agitated fluidized-bed reactors have shown encouraging results and are suggested for further exploration. A combination of appropriate computational tools can facilitate an in-depth understanding of bed dynamics.

**Keywords:** thermal energy storage; thermochemical energy storage; thermochemical reactors; solid– gas reactions; modelling; simulation
