Hydrogen is stored by adsorbing the hydrogen to a carbon nanomaterial that includes carbon nanospheres. The carbon nanospheres are multi-walled, hollow carbon nanostructures with a maximum diameter in a range from about 10 nm to about 200 nm. The nanospheres have an irregular outer surface and an aspect ratio of less than 3:1. The carbon nanospheres can store hydrogen in quantities of at least 1.0% by weight.