Nanocrystalline face-centered cubic (FCC) Co powder encapsulated within graphite layers was fabricated by an arc discharge method. Its electrochemical hydrogenation properties were investigated and compared with those of the hexagonal close packed (HCP) structure. Both exhibited a similar stabilized discharge capacity of approximately 350 mAh/g that can be attributed to the CoH(x)/Co reaction. During the cyclic charge/discharge, transition between HCP-Co and FCC-Co took place. Graphite encapsulation was beneficial to the cycle stability of the FCC powder. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.