The composition of passive film formed on nickel coating with high density nano-scale twins (NT) in borate buffer solution without and with NaCl 0.02M were investigated by X-ray photoelectron spectroscopy (XPS),and compared with that of passive film formed on industrial electrolytic (IE) nickel.The results indicated that oxide films formed on NT coating were integrated and compact,while the passive films formed on IE nickel were porous and not integrated.This was demonstrated by existence of metal Ni in passive film on IE nickel after etching more than 20s.Both the passive films formed on NT coating and IE nickel had a mixed oxide structure,which were composed of NiO,Ni(OH)2 and Ni2O3.Comparing with that of IE nickel,the passive film formed on NT coating in borate buffer solution was homogeneous and had a bilayer oxide structure,consisting of a Ni(OH)2 and Ni2O3 rich outer layer and a NiO rich inner layer.XPS spectra showed that no chloride ions existed in passive films and the relative proportion of OH- was more than that of O2- in passive films on NT and IE nickels,which indicated that chloride ions did not participate in the formation of passive films and that both the passive film had a strong buffer action against chloride penetration.Adsorption of ions on passive films was further investigated by potential of zero free charge (pzfc) measurement.It was found that pzfc of NT coating was more negative than that of IE nickel,which indicated that NT structure made the adsorption of Cl- on the surface of Ni more difficult,and consequently decreased its susceptibility of pitting corrosion.