Comprehensive thermodynamic study of alkyl-biphenyls as a promising liquid organic hydrogen carriers

Finding suitable hydrogen carriers is a real challenge for science and engineering. Alkyl-biphenyls have sufficient hydrogen storage density and are not expensive. Experimental and theoretical thermochemical studies (vapour pressure measurements and combustion calorimetry) of mono- and di-alkyl-substituted biphenyls were carried out. The standard molar vaporization enthalpies were derived from the temperature dependence of the vapor pressures measured by the transpiration method. The thermodynamic data on phase transitions (crystal-gas, crystal-liquid, and liquid-gas) available in the literature were collected and evaluated. High-level quantum-chemical methods (G3MP2 and G4) were used both to check the experimental values of the enthalpies of isomerization reactions and to estimate the enthalpies of hydrogenation/dehydrogenation reactions of monoand di-alkyl-substituted biphenyls.