Hydrogen Storage Materials: Room-Temperature Wet-Chemistry Approach toward Mixed-Metal Borohydrides

The poor kinetics of hydrogen evolution and the irreversibility of the hydrogen discharge hamper the use of transition metal borohydrides as hydrogen storage materials, and the drawbacks of current synthetic methods obstruct the exploration of these systems. A wet‐chemistry approach, which is based on solvent‐mediated metathesis reactions of precursors containing bulky organic cations and weakly coordinating anions, leads to mixed‐metal borohydrides that contain only a small amount of “dead mass”. The applicability of this method is exemplified by Li[Zn2(BH4)5] and M[Zn(BH4)3] salts (M=Na, K), and its extension to other systems is discussed. Avoiding “dead mass”: Hydrogen‐rich mixed‐metal borohydrides, which are promising materials for the chemical storage of hydrogen, were prepared by a wet‐chemistry approach. This method is based on a metathesis reaction, does not lead to a high percentage of “dead mass” (metal halides and coordinated solvents), and was exemplified for a series of MZn(BH4) borohydrides (M=Li, Na, K).