To obtain an understanding of the mechanism of chromium particle occlusion in electrodeposited stainless-steel-type coatings, the U.S. Bureau of Mines has studied the effect of chromium particles on nickel electrodeposition. The chromium particles catalyzed nickel electrodeposition on a vitreous carbon surface. Chromium particle additions, when added to watt's-type electrolytes, of 0.33M, 0.67M, and 1.00M niso4, shifted the nickel reduction wave to more positive potentials on a vitreous carbon surface. From rotating cylinder electrode studies, it was concluded that nickel deposition with or without chromium particles is a kinetically limited rather than a mass-transfer-limited process. Electrochemical impedance spectroscopy experiments with and without chromium particles verified the rate-determining step proposed by epelboin, with the ni+(ads) limiting the nickel electrodeposition. The chromium particles appear to enhance the formation of this ni+(ads) intermediate.