The Prospect of Hydrogen Storage Using Liquid Organic Hydrogen Carriers

Abstract

Reducing CO2 emissions is an urgent global priority. The enforcement of a CO2 tax, stringent regulations, and investment in renewables are some of the mitigation strategies currently in place. For a smooth transition to renewable energy, the energy storage issue must be addressed decisively. Hydrogen is regarded as a clean energy carrier; however, its low density at ambient conditions makes its storage challenging. The storage of hydrogen in liquid organic hydrogen carriers (LOHC) systems has numerous advantages over conventional storage systems. Most importantly, hydrogen storage and transport in the form of LOHC systems enables the use of the existing infrastructure for fuel. From a thermodynamic point of view, hydrogen storage in LOHC systems requires an exothermic hydrogenation step and an endothermic dehydrogenation step. Interestingly, hydrogenation and dehydrogenation can be carried out at the same temperature level. Under high hydrogen pressures (typically above 20 bar as provided from electrolysis or methane reforming), LOHC charging occurs and catalytic hydrogenation takes place. Under low hydrogen pressures (typically below 5 bar), hydrogen release from the LOHC system takes place. Hydrogen release from charged LOHC systems is always in conflict between highly power-dense hydrogen production and LOHC stability over many charging/discharging cycles. We therefore discuss the role of different catalyst materials on hydrogen productivity and LOHC stability. The use of density functional theory techniques to determine adsorption energies and to identify rate-determining steps in the LOHC conversion processes is also described. Furthermore, the performance of a LOHC dehydrogenation unit is strongly dependent on the applied reactor configuration. Industrial implementation of the LOHC technology has started but is still in an early stage. Related to this, we have identified promising application scenarios for the South African energy market.

Reliability of liquid organic hydrogen carrier‐based energy storage in a mobility application

“…A promising approach to overcome this problem is represented by the LOHC technology . LOHCs (liquid organic hydrogen carrier) store hydrogen in a chemical bonded form through reversible, catalytic hydrogenation.…”

Hydrogen Production from Formic Acid Attained by Bimetallic Heterogeneous PdAg Catalytic Systems

“…In such molecules, H 2 is stored and delivered through reversible hydrogenation and dehydrogenation chemical reactions upon utilisation of suitable catalysts [11]. Among the virtues of LOHC is the fact that they may use the existing infrastructure for fuel [12]. Although the first studies on LOHCs took place in the early 1980s, a renewed interest has emerged in the last years [11,13].…”

Effect of a Substituent in Cyclopentadienyl Ligand on Iridium-Catalyzed Acceptorless Dehydrogenation of Alcohols and 2-Methyl-1,2,3,4-tetrahydroquinoline

“…The reactions were performed under more diluted conditions than those for secondary alcohols to suppress undesired side reactions, such as self-condensation, leading to ester product. Dehydrogenation reaction of benzyl alcohol (8) in refluxing toluene was carried out in the presence of 0.5 mol% of iridium catalyst to produce benzaldehyde (9). Catalyst 3a exhibited a slightly lower performance compared with catalyst 3b and 3e ( The catalytic abilities of iridium complexes (3) were also examined in the dehydrogenation reaction of 2-octanol (6) as an aliphatic alcohol in refluxing THF ( Table 2).…”

“…Moreover, the resulting hydrogen gas can be used as a promising energy carrier owing to its high weight energy density and carbon neutrality. These characteristics make the significance of acceptorless dehydrogenation much greater in the field of organic synthesis as well as energy science [4][5][6][7][8][9]. Owing to the catalytic activity of ruthenium complexes in dehydrogenation reactions of alcohols [10,11], considerable efforts have been made to improve catalytic systems with the development of complexes such as pincer-type ruthenium or iridium complexes with non-innocent behavior of the pincer ligands (Scheme 1a) [12][13][14][15][16][17][18][19][20][21][22].…”