Characterizations of composite NaNH 2–NaBH 4 hydrogen storage materials synthesized via ball milling

Abstract

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 °C, and the melting point is 197.3 °C; below 400 °C, composite hydrogen storage material is mainly decomposed to give hydrogen and Na 3BN 2; while above 400 °C, the previous by-product Na 3BN 2 continues to decompose so as to give metal Na gradually.