Pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy in H2S-containing acid solutions

•Effect of H2S on the corrosion behaviour of HEA was investigated.•Pseudo-passivation of HEA in the H2S-containing environment was first found.•Formation of Cr substances resulted in the transition from active to pseudo-passive corrosion.•Pseudo-passivation mechanism of HEA in H2S environments was discussed. The pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy (HEA) in H2S-containing acid solutions was investigated. The results showed that HEA displayed pseudo-passive behaviour in the H2S environment. The reduction reactions of H2S and HS− occurred, leading to a diffusion-controlled region in the cathodic polarization curve. The massive formation of Cr substances on HEA resulted in the transition from active to pseudo-passive corrosion. The film broke down at high potential due to the instability of sulphides. The pseudo-passivation mechanism of HEA in H2S environments was discussed.