An investigation has been conducted on use of, for example, an alloy as a hydrogen-storing material expected to be applicable to a hydrogen-storing system in a fuel-cell vehicle or the like. However, when a hydrogen-storing alloy is used, its hydrogen storage capacity is insufficient. In addition, depending on kinds of metal to be used, the alloy not only has low durability but also involves problems in terms of price and reserve.
On the other hand, use of a carbon material that raises no concern about exhaustion of resources and is relatively inexpensive has been investigated. For example, Patent Literature 1 describes a carbon material whose hydrogen storage quantity is increased by expanding an average distance between carbon layers to 0.5 nm or more to cause the carbon layers to hold hydrogen therebetween. In addition, Patent Literature 2 describes an activated carbon material with an increased hydrogen storage quantity as a result of possession of a pore diameter of 0.3 nm or more and 1.5 nm or less.