Homogeneous and Heterogeneous Catalysis at Work in Lightweight Inorganic Hydride Dehydrogenation (Chemical Hydrogen Storage)

Dear Colleagues,

The quest for new solid-state materials for hydrogen storage is continuously growing. Hydrogen is the lightest element in the Universe, and H₂ has the largest gravimetric energy density of all chemical substances. Unfortunately, H₂ has a very low density both as a gas and as a liquid. Therefore, its volumetric energy density is very low, which is a major drawback for the utilization of H₂ as a gas, in particular for electronics (mobile hydrogen fuel cell technology) and in the automotive world (hydrogen reservoirs to be used on fuel-cell-powered cars). Hydrogen could be chemically stored into stable and non-toxic compounds that easily release it on demand, under mild temperature and pressure conditions. In addition, an easy regeneration of the “spent fuel” would be desirable. The optimal material for this task has not been found yet, but a range of (old and) new lightweight solid hydrides with fascinating properties have been (re)discovered and examined from a different perspective in recent years. Lightweight hydrides containing metals from Groups 1/2 (Li, Na, Mg, Ca) and elements from Groups 13/15 (B, Al, N) of the Periodic Table are of particular interest in this regard, as they offer an appropriate balance of volumetric (r_v) and gravimetric (r_m) hydrogen densities. Among them are ammonia borane (NH₃BH₃ (AB); r_m = 19.6 wt.% H), amine boranes (RNH₂BH₃, R = aliphatic ring or chain), hydrazine (H₂N-NH₂, r_m = 12.5 wt.% H), hydrazine borane (N₂H₄∙BH₃ (HB); r_m = 15.4 wt.% H), hydrazine bis(borane) (N₂H₄∙2BH₃ (HBB); r_m = 16.7 wt.% H), borohydrides (M(BH₄); M = Li, Na) and aluminum hydrides (alanates) (M(AlH₄); M = Li, Na). Up to four equivalents of high-purity (carbon-free) hydrogen can be extracted from these molecules under relatively mild temperature conditions through the employ of a metal-containing homogeneous or heterogeneous catalyst. The former is an organometallic/coordination compound containing assorted metal ions from all over the Periodic Table, while the latter consists of supported monometallic, multimetallic or core-shell M(0) nanoparticles (NPs). The metallic NPs are normally deposited on the support through a sequential impregnation/reduction protocol. In all cases, the catalyst efficiency is measured and compared in terms of the number of H₂ equivalents produced, reaction rate and operative temperature. This Special Issue aims to collect full papers/critical reviews on the topic of catalyzed lightweight inorganic hydride dehydrogenation, possibly covering all the aforementioned contexts. Scientific productions of both experimental and computational nature are welcome.

Dr. Andrea Rossin
Guest Editor

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