Ion-exchanged Y zeolites with several alkali metal cations and proton have been used to analyze the effect of electrostatic field or basicity. on the hydrogen adsorption at low temperature and low pressure. The adsorption capacity per surface area, isosteric heat of adsorption (-Delta H(ads)), surface coverage and micropore occupancy increase with the decreasing electronegativity of the metals that are introduced in the zeolite. Ion-exchanged zeolites also favorably adsorb hydrogen at relatively low pressures when the electronegativity of the metal is low. This work demonstrates that zeolites with strong electrostatic fields or high basicity are beneficial for high hydrogen uptake especially at low pressure and low temperature. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.