Strategies of thermodynamic alternation on organic hydrogen carriers for hydrogen storage application: A review

Abstract

An explosion of interest has arisen using organic-based materials, specifically cyclic organic hydrogen carriers for hydrogen storage due to their high hydrogen storage capacity, high volumetric energy density, reversibility, and non-toxicity. However, the unfavourable thermodynamic properties and high kinetic barriers of hydrogen desorption from these cyclic organic hydrogen carriers make them to be difficult in large-scale applications. In the past decades, tremendous efforts have been devoted to tailor both thermodynamic and kinetic properties of hydrogen absorption and desorption from such materials. Therefore, in this review, methods of fabrication of new materials in order to modify the dehydrogenation thermodynamic properties are discussed, which include the fusion of multiple organic rings, attachment of electron-donating substituents, incorporation of N/O/S atom into the aromatic rings, and introduction of alkali or alkaline earth metals to replace the protic H atom of O–H or N–H groups. Additionally, demonstrations for potential applications via using organic hydrogen carriers such as toluene, N-ethylcarbazole, and dibenzyl toluene are also described. The challenges and perspectives for the cyclic organic hydrogen storage materials are discussed at the end. It is expected that this review could provide new inspiration to expedite the development of cyclic organic hydrogen carriers with high hydrogen capacity and optimum thermodynamics for hydrogen storage.