Chemical Looping Ammonia Decomposition Mediated by Alkali Metal and Amide Pairs for H2 Production and Thermal Energy Storage

Ammonia decomposition to H₂ (ADH) is one of the key reactions in the ammonia-based energy system. Recent research has been focused on developing more active and affordable catalysts, however, few can operate below 500 °C and typically require the expensive metal ruthenium. Herein, a fundamentally different thermal ADH via a chemical looping process (CLADH) mediated by alkali metal and its amide pairs, which can work under lower temperatures than the catalytic process, is reported. This CLADH consists of two steps: 1) Ammoniation step ̶ NH₃ reacts with Na or K to generate NaNH₂ or KNH₂, respectively, accompanied by releasing one-third of H₂ in NH₃ at room temperature; 2) Decomposition step ̶ NaNH₂ or KNH₂ decomposes to N₂ and H₂ with the regeneration of Na or K which can be performed above 275 °C. Additionally, due to the significant enthalpy change in the two-step reactions of this CLADH, −78.0 kJ mol⁻¹ for the first step and 123.9 kJ mol⁻¹ for the second, using the Na and NaNH₂ pair—suggest potential for thermal energy storage. This work not only reports an alternative route to produce H₂ from NH₃, but also unravels the potential of chemical looping process for thermal energy storage.