Polarization characteristics of Cr-or Ti-doped Raney nickel hydrogen electrodes have been measured as a function of the dopant content. When the doping condition is optimized, the limiting current density becomes approximately twice and the polarization resistance one-sixth of these respective values of non-doped electrodes. Based on the model of the micropore having 1.8 x lo-' cm depth and 3 x lo-" diameter, theoretical polarization curves have been calculated for assumed several cases, and compared with the experimental ones. It is found from the comparison that the increase in the limiting current density is mainly due to a geometrical effect (expansion of the catalytic surface) whereas the lo wering of the polarization resistance is basically of catalytic effect (increase in the exchange current density). The surface analysis by means of XPS reveals that the large part of catalytic surface is covered with an oxide layer of doped metals. This is the reason why such a small amount of additives are so effective on the polarization characteristics. NOMENCLATURE concentration of atomic hydrogen adsorbed on the catalytic surface cH at equilibrium condition H,'concentration in the pore electrolyte CH2 at equilibrium condition, or solubility of HZ in the electrolyte HZ concentration at the surface of catalytic particle diffusion constant of H2 molecules in the pore electrolyte depth of micropore Faraday constant current produced per micropore pore current at distance z density of the local current produced at the pore wall exchange current density for i, current density (referred to apparent working area of electrode) rate constant of dissociative adsorption of Hz rate constant of recombination reaction of H, number of the micropores gas constant radius of micropore temperature transfer coefficient thickness of electrolyte lilm polarization