N-phenyl-carbazole as a potential liquid organic hydrogen carrier: Thermochemical and computational study

Abstract

The liquid organic hydrogen carriers (LOHCs) are promising materials for hydrogen storage. The standard molar enthalpy of formation, ΔfHmo(cr, 298.15 K) = (196.0 ± 4.9) kJ·mol−1, of N-phenyl-carbazole was obtained from high-precision combustion calorimetry. The standard molar enthalpy of sublimation ΔcrgHmo(298.15 K) = (116.1 ± 1.7) kJ·mol−1 and vaporisation ΔlgHmo(298.15 K) = (100.5 ± 1.6) kJ·mol−1 of N-phenyl-carbazole were derived from the vapour pressure temperature dependences measured by the transpiration method. The standard molar enthalpy of fusion ΔcrlHmo = (19.4 ± 0.3) kJ·mol−1 at Tfus = 367.9 K was measured by DSC. Gas phase molar enthalpy of formation of N-phenyl-carbazole calculated by the high-level quantum-chemical method G4 ΔfHmo(g, 298.15 K) = (312.9 ± 3.5) kJ·mol−1, was in an excellent agreement with the experimental result (312.1 ± 5.2) kJ·mol−1. The hydrogenation/dehydrogenation reaction enthalpy result (−519.3 ± 6.6) kJ·mol−1 of N-phenyl-carbazole was calculated and compared with the data for other potential liquid organic hydrogen carriers. Phase transition enthalpies were validated with the help of empirical methods. A set of thermodynamic properties of N-phenyl-carbazole were recommended as reliable benchmark properties for thermochemical calculations. Due to the high hydrogen storage capacity, as well as the ability to form overcooled liquid even by room temperature, this compound could be considered as seminal candidate for LOHC.