The interaction between atomic hydrogen and microporous carbon is investigated by density functional theory (DFT) calculations. To reveal how the nanographene structures affect the atomic hydrogen uptake, which is caused by hydrogen spillover, chemisorption energies of a hydrogen atom on four graphene-like fragments are compared: a condensed hexagonal plane, two buckybowls, and a heptagon-containing curved structure. It is shown that hydrogen atoms adsorb strongly at the edge sites and on convex surfaces. Two hydrogen diffusion paths on the carbon surface are examined: hydrogen migration along the C-C bond and hydrogen desorption. The results suggest that a probable path depends on the nanographene structure.