High pressure H(2) adsorption isotherms at N(2) liquid temperature were recorded for the series of cubic nitroprussides Ni(1-x)Co(x)[Fe(CN)sNO] with x = 0 0 5 0 7 1 The obtained data were interpreted according to the effective polarizing power for the metal found at the surface of the cavity The cavity volume where the hydrogen molecules are accumulated was estimated from the amount of water molecules that are occupying that available space in the as synthesized solids considering a water density of 1 g/cm(3) The calculated cavity volume was then used to obtain the density of H(2) storage in the cavity For the Ni con taming material the highest storage density was obtained in a cavity volume of 448 5 A(3) up to 10 4 hydrogen molecules are accumulated for a local density of 77 6 g/L above the density value corresponding to liquid hydrogen (71 g/L) Such high value of local density was interpreted as related to the electrostatic contribution to the adsorption potential for the hydrogen molecule within the cavity (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved