Mechanism and kinetics of cathodic corrosion of fluorine-doped tin oxide revealed by in situ oblique incident reflectivity difference

[Display omitted] •Cathodic corrosion behavior of FTO was investigated by in situ OIRD.•Cathodic corrosion of FTO proceeds via the reduction of SnO2 to metallic Sn.•Formation rate of Sn is potential-dependent and remains constant at a given potential.•Sn(0) is oxidized and dissolved in the presence of O2 after the polarization. The corrosion behavior of fluorine-doped tin oxide (FTO) under electrochemical cathodic polarization was investigated by in situ oblique incident reflectivity difference (OIRD) combined with other in situ/ex situ techniques. It is revealed that the cathodic corrosion of FTO, which coincides with the hydrogen evolution reaction (HER), proceeds via the reduction of SnO2 to metallic Sn(0). The formation rate of Sn(0) is potential dependent and remains nearly constant at a given potential until it reaches a plateau, representing the maximum thickness/coverage of Sn(0). When the cathodic polarization ceases, the newly formed Sn(0) is slowly oxidized and dissolved in the presence of O2.