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Ti-doped [1,1,1,1] paracyclophane(PCP) and its derivatives have been designed by substituting heteroatoms boron and nitrogen and studied their hydrogen storage properties using density functional theory. Heteroatom substitution is important for stronger Ti-binding whereas Ti-doping for light weight, almost empty d- orbital and its stronger interaction with H 2 molecules. Six configurations are obtained: PB1,PB2(boron substitution), PN1,PN2 (nitrogen substitution) and PBN1,PBN2(boron and nitrogen co-substitution). Stability of all Ti-doped structures has been confirmed using cohesive and formation energy. PCP, PB1, PB2, PN1, PN2, PNB1 and PNB2 show gravimetric hydrogen uptake capacity(adsorption energy) as 5.52(0.67),6.90(0.5),6.90(0.53),5.37(0.6),5.37(0.61), 5.48(0.7) and 5.48(0.74 eV) wt% respectively. Ti-doped boron substituted structures show required H 2 uptake capacity, suitable adsorption energy, thermodynamically favorable H 2 adsorption at ambient conditions, moderate desorption temperature, structural and thermodynamic stability, thus more suitable for hydrogen storage than nitrogen substituted and boron and nitrogen co-substituted structures. Ti-doped boron substituted PCP is a promising reversible hydrogen storage candidate. [Display omitted] • Ti-doped B/N or B and N substituted paracyclophane(PCP) is considered for H 2 uptake. • B-substituted Ti-PCP is more suitable for H 2 storage compared to other structures. • Ti atom strongly bind with B-substituted Ti-PCP compared to other structures. • One extra H 2 gets adsorbed on each Ti on B-substituted Ti-PCP than Ti-PCP [ABSTRACT FROM AUTHOR]

We have innovatively designed and assessed the hydrogen storage properties of a single Ti-doped C 20 nanocage and its B, N or B and N heteroatom substituted derivatives with the help of the density functional theory approach for the first time to the best of our knowledge. Out of fifteen designed structures by substituting heteroatoms, only 8 structures are found to be suitable for Ti doping and H 2 adsorption viz. C 20 , C 12 N 8 , C 12 B 8 , C 12 B 4 N 4 , C 10 B 5 N 5 , C 10 B 10 , B 10 C 10 and B 10 N 10. Their formation energy and cohesive energy values confirm the stability of all the structures. Ti atom binds more strongly with B, N or B and N heteroatom substituted C 20 nanocage than unsubstituted C 20 nanocage which is necessary to avoid clustering for multiple Ti doped nanocages. Among the eight Ti doped nanocages considered, H 2 molecules strongly interact with Ti-doped C 12 B 4 N 4 nanocage. The binding strength of Ti atom with nanocages decreases during the hydrogen adsorption process. The obtained H 2 adsorption energy values for all the structures are within the range of 0.2–0.7 eV, which is conducive to reversible hydrogen storage. Calculated Gibbs free energy-corrected H 2 adsorption energy values at different temperature and pressure indicate favorable H 2 adsorption over the entire pressure range at room temperature. For Ti doped C 20 , C 12 N 8 , C 12 B 8 , C 10 B 5 N 5 , C 10 B 10 , B 10 N 10 , and B 10 C 10 nanocages, H 2 adsorption is thermodynamically favorable below 360, 350, 300, 285, 235, 277, and 251 K, respectively at 1 atm pressure. From PDOS analysis, it is observed that the 1s orbital of H overlaps with 3d orbital of Ti atom. The highest H 2 desorption temperature is observed for the C 12 B 4 N 4 Ti nanocage, and the lowest for C 10 B 10 Ti, aligning well with the calculated adsorption energy values. As H 2 desorption temperature is high, the stability of Ti-doped nanocages at high temperature (634 K) is confirmed using ab initio molecular dynamics simulations. Bader's quantum theory in atoms in molecules is used to prove the weak non-covalent interaction between all the atoms. [Display omitted] • C 20 Ti and its B, N or B and N substituted derivatives are considered for H 2 storage. • Substitution of heteroatoms in C 20 Ti enhances the binding strength of Ti atom. • B 10 C 10 Ti is the most stable among the eight Ti doped nanocages considered. • Favorable H 2 adsorption for wide range of pressure at room temperature. • H 2 molecule shows better affinity with C 12 B 4 N 4 Ti. [ABSTRACT FROM AUTHOR]