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

Abstract

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 (ΔrHm(d)⊖ = 51.68 kJ/molH2) 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.