Remarkable irreversible and reversible dehydrogenation of LiBH4 by doping with nanosized cobalt metalloid compounds

Nanosized cobalt sulfide and cobalt boride were synthesized and doped into LiBH4 to improve the dehydrogenation properties of this important candidate for hydrogen storage. With respect to CoSx doping, the dehydrogenation temperature (peak temperature observed by mass spectrometry) of pristine LiBH4 can be reduced from 440 °C to 175 °C with a maximum capacity of 6.7 wt% at 50% doping. Unfortunately, B2H6 is liberated and the process is not reversible because the CoSx dopant reacts with LiBH4 to form more stable compounds. By changing CoSx to CoBx, a reversible dehydrogenation was realized with greatly improved reversibility. The dehydrogenation temperature was reduced to 350 °C with a maximum capacity of 8.4 wt% at 50% doping amount. It is very significant that CoBx is stable and the release of B2H6 is eliminated. A reversible hydrogen desorption of about 5.3 wt% can be achieved with a LiBH4 + 50% CoBx mixture under a mild rehydrogenation condition of 400 °C at 10 MPa H2. It is obvious that CoSx acts as a reactant even though the dehydrogenation is greatly enhanced, while CoBx behaves as a catalyst significantly promoting the dehydrogenation and reversibility of LiBH4.