Thermal decomposition kinetics of light-weight composite NaNH ₂-NaBH ₄ hydrogen storage materials for fuel cells

Pristine and Co-B doped NaNH ₂-NaBH ₄ (2/1 molar rate) hydrogen storage materials were synthesized via a ball milling method. The kinetic parameters, especially the activation energies were calculated by the Achar differential and the Coats-Redfern integral methods, based on the thermogravimetry curves of the decomposition processes of the hydrogen storage materials. The as-obtained activation energy for the pristine NaNH ₂-NaBH ₄ (2/1) is 159.6 kJ/mol, while that for the Co-B doped NaNH ₂-NaBH ₄ (2/1) is 70 kJ/mol, only 43.9% of the former, which indicates the Co-B catalyst can dramatically promote the hydrogen generation reaction. The structural evolution and the hydrogen releasing performance of the Co-B doped NaNH ₂-NaBH ₄ (2/1) were investigated by X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). Then, the catalytic mechanism of NaNH ₂-NaBH ₄ (2/1) decomposition promoted by Co-B was discussed and illustrated. It implies that the existence of Co-B catalyst can promote the loss of electron from H ^-, thus improve the kinetics and accelerate the formation of H ₂ upon heating.