Improvement of dehydrogenation kinetics of 2LiBH4-MgH2 composite by doping with activated carbon nanofibers

2LiBH4-MgH2 composite is doped with 1, 5, 10, 20, and 30 wt. % activated carbon nanofibers (ACNFs), prepared by heat and KOH treatment of polyacrylonitrile (PAN)-based nanofibers for reversible hydrogen storages. Alteration of unit cell parameters and reduction of particle size of hydride materials are obtained after doping with 1-10 wt. % ACNFs, in accordance with good dispersion of ACNFs in hydride matrices, while those of the sample with higher ACNFs contents (20-30 wt. %) are comparable with milled 2LiBH4-MgH2 without ACNFs. Reduction of dehydrogenation temperature and faster kinetics are obtained with increase of ACNFs content. For example, dehydrogenation temperatures of MgH2 and LiBH4 decrease significantly from 375 to 312 °C and from 440 to 384 °C, respectively, after doping with 30 wt. % ACNFs. Besides, under the same temperature and pressure conditions (T = 400 °C under vacuum), the sample without ACNFs liberates 54% of theoretical H2 storage capacity within 9 h, while the samples with ACNFs release up to 74%. Since no chemical interaction between ACNFs and hydride materials is detected, the improvement of dehydrogenation kinetics of 2LiBH4-MgH2 composite doped with ACNFs can be due to (i) increase of hydrogen diffusion pathway from the dispersion of ACNFs in hydride matrices and (ii) good thermal conductivity of ACNFs, beneficial to heat transport during de/rehydrogenation.