A novel Pd/PdHx electrode was prepared by reducing PdCl42- adsorbed on cross-linked poly(4-vinylpyridine) which was introduced in the pores of an aerogel carbon substrate. Nanocrystals of Pd ranging from 2.4 to 29 nm were obtained depending on the cross-linking molecule length and on whether the reduction of the palladium ions was achieved chemically or electrochemically. The maximum hydrogen capacity of the Pd particles was determined to be 165 mAh/g. The uniform particles distribution in the porous substrate structure enables to consider possible application of such electrodes loaded with a variety of catalytic metals in batteries and fuel cells. (C) 2004 The Electrochemical Society.