Hydrogen storage is a crucial element in advancing clean transportation systems and grid resiliency. However, A hydrogenation mechanism that directly forms magnesium borohydride avoids issues known to inhibit the speed at which a hydrogen vehicle can be refueled. Hydrogen molecules (gray) dissociate on exposed magnesium (blue) layers of magnesium diboride and migrate to boron (green) edge sites to form borohydride units (BH4, center, light green and light gray). Source: LLNLhigh-pressure storage tanks now used by hydrogen-fueled vehicles limit infrastructure practicality and lead to compression losses.

The potential for development of more compact onboard storage capacities and reduced operating pressures is offered by solid-state hydrogen storage in complex metal hydrides may offer much more compact onboard storage systems and reduced operating pressures. There are limitations here, too: such hydrides are often characterized by poor kinetics and multi-step hydrogenation pathways that are not well understood.

Research conducted by U.S. Department of Energy’s Lawrence Livermore National Laboratory scientists promises to remove some of these impediments. Their studies have revealed the key mechanism by which magnesium diboride (MgB₂) absorbs hydrogen and advanced understanding of the reaction pathway that converts MgB₂ to its highest hydrogen capacity form, magnesium borohydride (Mg(BH₄)₂). This layered superconductor compound is a particularly promising storage material because of its high hydrogen content and attractive thermodynamics.

In the initial stages of hydrogen exposure, MgB₂ can hydrogenate to Mg(BH4)2 without the formation of intermediate compounds that inhibit the speed at which a hydrogen vehicle can be refueled. The ability to eliminate them marks progress toward making MgB₂ practically viable. Hydrogenation was also demonstrated to proceed in two separate reaction stages as hydrogen molecules split and migrate to exposed edges in the material.