Characterizations of composite NaNH_2-NaBH_4 hydrogen storage materials synthesized via ball milling

摘要

Composite NaNH_2-NaBH_4 (molar ratio of 2/1) hydrogen storage materials are prepared by a ball milling method with various ball milling times. The compositions and hydrogen generation characteristics are investigated by means of X-ray diffraction (XRD) and thermo gravimetric-differential thermal analysis (TG-DTA). The structural characteristics imply that ball milling produces a new phase of Na_3(NH_2)_2BH_4, and mechanical energy accumulated in the ball milling process may be responsible for the phase change of Na_3(NH_2)_2BH_4. TG-DTA demonstrates that the phase change temperature of the composite NaNH_2-NaBH_4 (2/1) ball milled for 16 h is 141.8 ℃, and the melting point is 197.3 ℃; below 400 ℃, composite hydrogen storage material is mainly decomposed to give hydrogen and Na_3BN_2; while above 400 ℃, the previous by-product Na_3BN_2 continues to decompose so as to give metal Na gradually.