Hydrogen storage technologies: Methyl-substituted biphenyls as an auspicious alternative to conventional liquid organic hydrogen carriers (LOHC)

Derivatives of biphenyls, namely mono-, di- and tert- methyl substituted biphenyls, can be considered as promising hydrogen carriers. The absolute vapour pressures of nine methyl-substituted biphenyls were measured using the transpiration method. The vapour pressures available in the literature for methylbiphenyls were collected and analyzed. The standard molar enthalpies of vaporization/sublimation of methyl substituted biphenyls were derived from the temperature dependencies of the vapour pressures. The experimental enthalpies of vaporization were validated using Kovats's indices. The enthalpies of fusion of four methylbiphenyls were measured by DSC. The standard molar enthalpy of formation of the liquid 3,3'-dimethylbiphenyl was determined using high precision combustion calorimeter. The enthalpies of formation of methylbiphenyls available in the literature were collected and combined with the evaluated enthalpies of vaporization/sublimation to obtain their gas-phase enthalpies of formation. High-level G3MP2 and G4 quantum-chemical methods were used to establish consistency of the experimental and theoretical results. The enthalpies of the reversible hydrogenation/dehydrogenation reactions of the biphenyls were calculated and compared with conventional liquid organic hydrogen carriers. (C) 2021 Elsevier Ltd.