Liquid Organic Hydrogen Carriers (LOHCs): Toward a Hydrogen-free Hydrogen Economy

Abstract

The need to drastically reduce CO emissions will lead to the transformation of our current, carbon-based energy system to a more sustainable, renewable-based one. In this process, hydrogen will gain increasing importance as secondary energy vector. Energy storage requirements on the TWh scale (to bridge extended times of low wind and sun harvest) and global logistics of renewable energy equivalents will create additional driving forces toward a future hydrogen economy. However, the nature of hydrogen requires dedicated infrastructures, and this has prevented so far the introduction of elemental hydrogen into the energy sector to a large extent. Recent scientific and technological progress in handling hydrogen in chemically bound form as liquid organic hydrogen carrier (LOHC) supports the technological vision that a future hydrogen economy may work without handling large amounts of elemental hydrogen. LOHC systems are composed of pairs of hydrogen-lean and hydrogen-rich organic compounds that store hydrogen by repeated catalytic hydrogenation and dehydrogenation cycles. While hydrogen handling in the form of LOHCs allows for using the existing infrastructure for fuels, it also builds on the existing public confidence in dealing with liquid energy carriers. In contrast to hydrogen storage by hydrogenation of gases, such as CO or N, hydrogen release from LOHC systems produces pure hydrogen after condensation of the high-boiling carrier compounds. This Account highlights the current state-of-the-art in hydrogen storage using LOHC systems. It first introduces fundamental aspects of a future hydrogen economy and derives therefrom requirements for suitable LOHC compounds. Molecular structures that have been successfully applied in the literature are presented, and their property profiles are discussed. Fundamental and applied aspects of the involved hydrogenation and dehydrogenation catalysis are discussed, characteristic differences for the catalytic conversion of pure hydrocarbon and nitrogen-containing LOHC compounds are derived from the literature, and attractive future research directions are highlighted. Finally, applications of the LOHC technology are presented. This part covers stationary energy storage (on-grid and off-grid), hydrogen logistics, and on-board hydrogen production for mobile applications. Technology readiness of these fields is very different. For stationary energy storage systems, the feasibility of the LOHC technology has been recently proven in commercial demonstrators, and cost aspects will decide on their further commercial success. For other highly attractive options, such as, hydrogen delivery to hydrogen filling stations or direct-LOHC-fuel cell applications, significant efforts in fundamental and applied research are still needed and, hopefully, encouraged by this Account.

Construction of a Nanoporous Highly Crystalline Hexagonal Boron Nitride from an Amorphous Precursor for Catalytic Dehydrogenation

“…[32][33][34] But the realization of this future economy relies on the development of ah ighly efficient catalytic system for the reversibility and high selectivity of LOHC, [35] especially the N-ethylcarbazole (NEC) and dodecahydro-N-ethylcarbazole (12H-NEC) cycle systems. [32][33][34] But the realization of this future economy relies on the development of ah ighly efficient catalytic system for the reversibility and high selectivity of LOHC, [35] especially the N-ethylcarbazole (NEC) and dodecahydro-N-ethylcarbazole (12H-NEC) cycle systems.…”

Hydrogenation of CO2 at ambient pressure catalyzed by a highly active thermostable biocatalyst

“…Molecular hydrogen (H 2 ) has been considered as promising alternative technologies either for mobile applications or to store excess electricity generated at off-peak times by wind or solar power. However, the practical application is struggling because of the low volumetric energy density and the explosion hazard when stored in large amounts [7, 8]. One way to overcome these limitations is the transient conversion of H 2 into other chemicals, for example so-called liquid organic hydrogen carriers (LOHC), with elevated volumetric energy density.…”

“…One way to overcome these limitations is the transient conversion of H 2 into other chemicals, for example so-called liquid organic hydrogen carriers (LOHC), with elevated volumetric energy density. Among the multiple technologies envisioned for overcoming this problem, CO 2 hydrogenation to formic acid represents a promising solution [7, 9]. Formic acid combines its liquid nature with low toxicity and easy handling, prerequisites for the storage and further utilization.…”

Die selektive Arenhydrierung bietet einen direkten Zugang zu gesättigten Carbo‐ und Heterocyclen

“…Klassische Methoden wie aromatische Substitutionen, Kondensationen und Kreuzkupplungen ermçglichen den Zugang zu unzähligen Aren-und Heteroarensubstraten. [5] Zudem gewinnt die Verwendung der Arenhydrierung fürdie Synthese gesättigter funktioneller Moleküle in der Feinchemie an Bedeutung.S o ermçglichte die enantioselektive Hydrierung von Chinolinen einen effizienten Zugang zu Te trahydrochinolinalkaloiden wie (À)-Galipinin (4). Der strategische Wert der Tr ansformation spiegelt sich in einer Reihe industrieller Anwendungen in einem Maßstab von mehr als tausend Tonnen wider.…”