Complex hydrides are inorganic materials that are best described as salts, which are built from complex anions containing hydrogen as terminal ligand, such as the BH4– (tetrahydroborate or borohydride) or AlH4– (alanate) anions and counteractions from many different groups in the periodic table.
Most of the attention drawn by complex hydrides in the recent past is owed to their large gravimetric hydrogen capacity, i.e. nominal hydrogen-content per weight unit, which makes them competitive candidates for solid state on-board hydrogen storage. This was first suggested in 2001 for LiBH4. In such materials the hydrogen molecule can be eliminated either by hydrolysis or electrolysis at elevated temperatures. The target implementation are fuel-cell driven vehicles, where the generated hydrogen (the fuel) is reacted with oxygen to generate an electric current capable of powering a car, for instance.
Next to hydrogen storage our group is focusing increasingly on the second relevant energy-related application of complex hydrides, which concerns the electrolyte in all-solid-state batteries. Both the electrochemical stability as well as vivid structural dynamics of, in particular, materials based on the tetrahydroborate anion BH4– are properties favoring the development of novel superionic materials.