The reduction of iron and chromium oxides with diffusible hydrogen was analyzed by XPS and AR-XPS in ex situ experiments. The reduction was monitored by iteratively measuring the high-resolution Fe2p and Cr2p peaks. Fe-Cr monocrystalline samples were electrochemically charged on one side then transferred to the XPS chamber where the reduction of the oxides attributed to diffused hydrogen was monitored on the opposite side. The reduction leads to a continuous alteration in the high-resolution Fe2p peak which is iteratively measured during hydrogen permeation. Further analysis showed slight effect of hydrogen on the chromium oxides but a reduction of iron Fe³⁺ to Fe²⁺ oxides. Although the nature of the oxide was altered, the thickness remained unchanged.

Figure 1: Evolution of the Cr2p spectrum acquired on a Fe/Cr sample as a function of time after cathodic hydrogen loading for 1h30: a) 2D image of the Cr2p spectra, b) Spectra corresponding to the arrows indicated in a) and showing that the chromium oxide present in the oxide film seem to be affected minimally by the presence of hydrogen. The thickness of the oxide film does not change as shown by the intensity of the substrate which remains constant.

Figure 2: Evolution of the Fe2p spectrum acquired on a Fe/Cr sample as a function of time after cathodic loading with hydrogen for 1h30: a) 2D image of the Fe2p spectra showing an evolution of the shape of this peak up to a steady state indicated by the white dotted line, b) Spectra corresponding to the arrows indicated on a) and showing that the hydrogen tends to reduce the oxide film without altering its thickness as shown by the intensity of the substrate which remains constant.