Prediction of thermodynamically reversible hydrogen storage reactions utilizing Ca-M(M= Li, Na, K)-B-H systems: a first-principles study

摘要

Calcium borohydride is a potential candidate for onboard hydrogen storage because it has a high gravimetric capacity (11.5 wt.%) and a high volumetric hydrogen content (~130 kg m~(?3)). Unfortunately, calcium borohydride suffers from the drawback of having very strongly bound hydrogen. In this study, Ca(BH_4)_2 was predicted to form a destabilized system when it wasmixed with LiBH_4, NaBH_4, orKBH_4. The release of hydrogen from Ca(BH_4)_2 was predicted to proceed via two competing reaction pathways (leading to CaB6 and CaH_2 or CaB_(12)H_(12) and CaH_2) that were found to have almost equal free energies. Using a set of recently developed theoretical methods derived from first principles, we predicted five new hydrogen storage reactions that are among the most attractive of those presently known. These combine high gravimetric densities (>6.0 wt.%H_2) with have low enthalpies [approximately 35 kJ/(mol~(?1) H_2)] and are thermodynamically reversible at low pressure within the target window for onboard storage that is actively being considered for hydrogen storage applications. Thus, the first-principles theoretical design of new materials for energy storage in future research appears to be possible.