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

Ammonia decomposition to H-2 (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 degrees 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 H-2 in NH3 at room temperature; 2) Decomposition step - NaNH2 or KNH2 decomposes to N-2 and H-2 with the regeneration of Na or K which can be performed above 275 degrees 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 H-2 from NH3, but also unravels the potential of chemical looping process for thermal energy storage.