In this work, composite adsorbent materials are prepared using metal halide salts and expanded natural graphite (ENG). Ammonia adsorption and desorption pressure concentration isotherms of composite adsorbents are experimentally measured. The van't Hoff plots are constructed to calculate the enthalpy of a reaction during adsorption and desorption. The average value of adsorption enthalpies (∆Had) for MnCl2 + ENG and CaCl2 + ENG are 55.821 and 33.434 kJ mol−1, respectively, and average values of desorption enthalpies (∆Hdes) are 73.817 and 73.016 kJ mol−1, respectively. Comparison of ammonia sorption properties of composites and their corresponding plain salts is done. Thermodynamic analysis of adsorption thermal energy storage (ATES) system) showed that maximum gravimetric energy storage density for MnCl2 + ENG based system is 1394.83 kJ kg−1 (158.85 kWh m−3) at energy storage and ambient temperatures of 172°C and 35°C, respectively. The same for CaCl2 + ENG based system is 1350.86 kJ kg−1 (165.85 kWh m−3) at storage and ambient temperatures of 92°C and 35°C, respectively. Volumetric energy storage density is higher for CaCl2 + ENG based ATES system since it has higher density. Thermodynamic performance of composite‐based systems is compared with plain salts (MnCl2‐CaCl2) based thermal energy storage system.

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In the present work, composite material, Mg‐50 wt% LaNi5, is thermodynamically characterized for thermochemical energy storage application, and its mechanism of hydrogen absorption is studied by using Johnson‐Mehl‐Avrami (JMA) equation. Pressure concentration isotherms (PCI) of the composite during hydrogen absorption and desorption are measured at 250°C, 300°C, 350°C, and 375°C. The enthalpy of absorption and enthalpy of desorption are calculated as 62.082 and 66.009 kJ/mol H2. Absorption kinetics is measured at 250°C, 300°C, and 350°C with hydrogen supply pressures of 10, 20, and 30 bar. The activation energies are calculated at different supply pressures using Arrhenius equation. Based on activation energy, the rate‐limiting steps are identified. A thermochemical energy storage method is proposed based on equilibrium pressure‐temperature relation obtained during absorption and desorption. The amount of thermochemical energy stored and recovered per kg of the composite is calculated based on reaction enthalpies and hydrogen concentration. The maximum theoretical thermochemical energy stored and recovered at a temperature of 350°C is calculated as 1452.198 and 1365.804 kJ/kg respectively. The maximum theoretical energy storage efficiency is estimated as 0.94. Hence, the composite, Mg‐50 wt% LaNi5, can be used as thermochemical energy storage material in the temperature range of 250°C‐350°C with a thermochemical energy storage capacity of 0.403 kWh/kg composite.