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[Display omitted] • Be/Li doped C 24 nanocage and its derivative (C 12 B 12) are considered for H 2 storage. • Boron atom substitution helps in preventing clustering of metal atoms. • Metal doped C 12 B 12 nanocages show higher H 2 uptake capacity than metal doped C 24. • Metal atom bind strongly with C 12 B 12 nanocage than C 24 nanocage. • Binding energy of metal with nanocage decides no. of metal atom that can be doped. The hydrogen storage on Be/Li doped C 24 and its boron substituted derivative(C 12 B 12) is studied using density functional theory(DFT). Doping of four and six Be atoms on tetragonal rings of C 24 and C 12 B 12 nanocage, respectively is possible. This difference is due to lower(higher) binding energy of Be atoms with C 24 (C 12 B 12) than its cohesive energy in bulk. Doping of six Be atoms on C 24 disturbs the cage. Doping of six Li atoms on tetragonal rings of C 24 and C 12 B 12 is possible without disturbing the cage as binding energy of Li atoms with both the cages is higher than its cohesive energy in bulk. Metal doped C 12 B 12 shows higher H 2 uptake capacity than C 24. H 2 molecules interact more strongly with Be doped nanocages than Li doped nanocages. The metal atoms bind more strongly with C 12 B 12 nanocage than C 24. From formation energy, metal doped C 12 B 12 are more stable than metal doped C 24. Though Li doped nanocages show higher H 2 uptake capacity, they are not suitable for hydrogen storage at ambient conditions. Be doped nanocages are more suitable for hydrogen storage at ambient conditions. [ABSTRACT FROM AUTHOR]