Catalytic effect of titanium nitride nanopowder on hydrogen desorption properties of NaAlH4 and its stability in NaAlH4

Single crystalline titanium nitride (TiN) nanopowder is synthesized by a mechano-chemical reaction between titanium chloride (TiCl3) and lithium nitride (Li3N) by means of high-energy ball milling. The TiN nanopowder has an average particle size of 6 nm and is introduced into sodium alanate (NaAlH4) as a catalyst. During hydrogen sorption cycles, TiN-catalyzed NaAlH4 exhibits a greater hydrogen desorption rate and higher hydrogen capacity than TiCl3-catalyzed NaAlH4. Contradicting thermodynamic predictions, in situ X-ray diffraction results reveal that TiN nanopowder remains stable and produces no by-products (e.g., Ti–Al compounds) in the reaction with NaAlH4 during hydrogen desorption. In situ Raman spectroscopy also confirms the stability of TiN nanopowder in NaAlH4. This implies that the sustained hydrogen sorption kinetics and hydrogen capacity of TiN-catalyzed NaAlH4 originate from the structural and chemical stability of TiN nanopowder in NaAlH4 for the given conditions of the hydrogen cycle test.