Hydrogen gas production and storage cycle with benzyl alcohol/benzaldehyde

Abstract

Hydrogen gas (H₂) has attracted significant attention as a clean energy source. To realise a sustainable society, the development of methods for green H₂ production from water and safe H₂ storage is essential. Organic hydrides, which can store H₂ via covalent bonding under ambient conditions, are promising H₂ storage materials. Primary alcohols, which can be produced from biomass and release H₂ under mild conditions (80–220 °C) due to their small dehydrogenation enthalpies, have garnered attention as new candidates for application as organic hydrides. In this work, we demonstrated a reversible H₂ storage cycle with primary alcohols/aldehydes. Specifically, we focused on benzyl alcohol and relatively stable benzaldehyde. Benzyl alcohol was completely dehydrogenated by warming (180 or 220 °C) in the presence of a metal complex catalyst to obtain benzaldehyde, which was then completely hydrogenated to benzyl alcohol using the same catalyst under H₂ (1 atm), thereby accomplishing a reversible H₂ storage cycle. Additionally, we used alcoholic fermentation with baker's yeast as a hydrogenation method without requiring precious metal catalysts or H₂, and benzaldehyde was completely hydrogenated to store hydrogen directly from water and nicotinamide adenine dinucleotide (NADH). This work revealed the reversible H₂ storage capability of primary alcohols/aldehydes as organic hydrides, and conceptually demonstrated a green H₂ production and storage cycle by combining hydrogen storage using alcoholic fermentation and H₂ release.