Sr(NH3)8Cl2-Expanded Natural Graphite composite for thermochemical heat storage applications studied by in-situ neutron imaging

Abstract This work presents an in-situ neutron imaging study of the ammonia sorption reaction in a SrCl2-Expanded Natural Graphite (ENG) composite loaded into a honeycomb-shaped stainless-steel scaffold and enclosed in a thermochemical heat storage (THS) reactor prototype. The performance of SrCl2/Sr(NH3)8Cl2-ENG under different pressures and temperatures was investigated and the spatio-temporal content of ammonia was calculated from neutron radiograms. Quantitative image analysis revealed the formation of Sr(NH3)8Cl2 upon ammonia uptake, while the desorption studies revealed a partial ammonia desorption resulting in the formation of the monoamine phase Sr(NH3)Cl2 via a stepwise release of ammonia. Neutron imaging also allowed the indirect evaluation of the stainless-steel honeycomb heat conductivity and showed that heat is transferred prevalently via the ENG matrix. Finally, neutron tomography of the reactor prototype was performed to ensure the stability of the THS system and composite material throughout the ammonia cycling experiments.