Storage of Hydrogen in Reversible Aromatic Organic Liquids

The first part of this chapter includes a brief description of key traditional hydrogen storage technologies (e.g. compressed gas, cryo-compressed, liquid hydrogen, etc.). Furthermore, a background information on the hydrogen storage using liquid organic hydrogen carriers (LOHCs) is provided. Various types of aromatic LOHC molecules are then introduced, with emphasis on their respective properties (e.g. hydrogen storage capacity, boiling point, and melting point) and the characteristics of promising LOHCs. This is followed by a discussion of the catalytic processes pertaining to the storage and release of hydrogen. Among the various LOHCs that are considered here, it is the commercially available dibenzyltoluene that has emerged as an excellent hydrogen storage medium. Challenges associated with current LOHC technology has led to the concepts of direct LOHC fuel cells (FCs) and electrochemical hydrogenation as emerging hydrogen storage methods, considered also worthy of exploration. We include an interesting discussion on ammonia, liquid hydrogen, LOHC-based hydrogen applications such as the coupling of renewable energy storage (power to gas) in the industries (chemical, petrochemical, food, and glass manufacturing), power (electricity generators, hydrogen fuel cells [HFCs]), and sustainable emission-free mobility (cars, trains, heavy-duty trucks). A brief description of commercially available systems is also included, illustrating the current maturity level of this technology. Finally, this chapter concludes with a short summary and outlook.