Guest-free hydroquinone (HQ) clathrate was synthesized by the gas-phase reaction between host HQ and guest CO2 molecules, followed by removal of the CO2 guests by controlled heating process. The H-2 storage capacity of the guest-free HQ clathrate is highly sensitive to the loading pressure; at 298 K, it was found to be 0.19 wt.% at 10 MPa and 0.38 wt.% at 35 MPa. In particular, the guest-free HQ clathrate also exhibits an extremely fast uptake and release of H-2 in a time scale of a few seconds. (C) 2012 Elsevier B.V. All rights reserved.