The electrochemical behavior and the characteristic of 2205 duplex stainless steel under various hydrogen charging conditions in borate buffer solution containing chloride ion were evaluated by potentiodynamic measurements, electrochemical impedance spectroscopy, capacitance measurements (Mott-Schottky approach) and anodic polarization experiments. The results indicate that the hydrogen generated by cathodic charging process decreased the corrosion resistance of 2205 duplex stainless steel (DSS), especially the pitting resistance of passive film. Due to the hydrogen charging, the semiconductor characteristic of the passive film changed from n-type and p-type coexisting to just n-type existing, and the pitting susceptibility increased. Along with the charging process, the critical concentration of chloride for breakdown of passive film decreased and the repassvation process was prevented by hydrogen.are widely applied in nuclear, petroleum and marine industry because of their good mechanical properties, excellent corrosion resistance and economic advantages [1,2].The corrosion and stress corrosion cracking resistance of duplex stainless steelsDSSs depend on the composition, structure and the passivity of the surface [3][4][5]. The passive film on the surface of stainless steel plays a critical role on protecting duplex stainless steelsDSSs from general and localized corrosion.The hydrogen atoms, generating from electrochemical processes such as pickling, electroplating, cathodic reaction of corrosion and cathodic protection, etc., could be adsorbed on the metal surface and diffuse into metals [6][7][8][9]. Some studies had shown that this process resulted in increasing corrosion rates of alloys [10,11]. Some [12][13][14][15][16] also stated that hydrogen reduced the corrosion resistance and decreased the stability of passive films.It is known that the passive film presents semiconductor properties, which influences the pitting susceptibility of the passive film [17]. Based on measuring capacitance of the interface layer formed in the passive film and the Helmholtz layer, Mott-Schottky analysis is widely used as a method to study the electronic characteristics of passive film. Using this method, Yu [18] and Zeng [19] showed that hydrogen increased the capacitance and donor density of the passive films formed on steels and the increased amount decreased with increasing film formation potentials.High donor densities in passive films corresponded to high pitting susceptibility in general. By the same method, Yang et al. [20,21] found that for the passive films formed on austenitic stainless steels, hydrogen caused a conductivity inversion from p-type to n-type of the passive films. The n-type passive film had a higher pitting susceptibility than p-type passive film.As is known to all, chloride ions play a vital role in the breakdown of a passive film. The chloride ions narrowed the passivation region and improved pitting susceptibility [22,23]. Experimental evidence indicated that there was a synergic effect between h...