Novel Liquid Organic Hydrogen Carriers with High Hydrogen Performance: NPhCZ/18H-NPhCZ

Exploring the potential liquid organic hydrogen carriers (LOHCs) with high efficiency can promote the advancement of hydrogen storage technology. In this work, a new LOHC member of the carbazole family, perhydro-N-phenylcarbazole (18H-NPhCZ), was first proposed for its high theoretical hydrogen storage capacity (6.9 wt %) and available dehydrogenation reaction enthalpy (Δ_rH_m(d)^⊖ = 51.68 kJ/mol_H2) based on theoretical calculations. The hydrogenation and dehydrogenation performances were evaluated and exhibited high efficiency in the optimized reaction conditions. The results indicated that 4.74 wt % of H₂ was released from 18H-NPhCZ dehydrogenation within 15 min. The combination of experiments and density functional theory (DFT) calculations was employed to investigate the possible intermediates and H₂ uptake and release mechanisms. It was found that the elementary reaction from 6H-NPhCZ to NPhCZ was regarded as the rate-limiting step. Furthermore, to balance the storage hydrogen capacity and liquid state at room temperature, a brand-new MIX-LOHC hydrogen storage system (18H-M-B2P1, 6.44 wt %) containing both 18H-NPhCZ and perhydro-dibenzyltoluene (18H-DBT) was successfully proposed as well. It achieved an almost 100% of H₂ uptake for 4-6 h and a practical H₂ release amount of 6.08 wt % for 10 h. The efficient cycle cohydrogenation and codehydrogenation measurements after 160 h also suggested the stability and reliability of the applications in the hydrogen storage field.