XPS results indicate the presence of Fe 2 O 3 and Cr 2 O 3 oxides (Figure ), while no other elements, such as Mo or Ni (reported in some studies ), were detected. Spectra for these elements are provided in the SI-8. XPS analysis of the Fe 2p region reveals several features that elucidate the chemical states of iron in the sample. The peak at 706.9 eV is typically assigned to metallic iron (Fe 0 ) or a reduced iron species that may coexist with the oxide, suggesting regions of incomplete oxidation. In contrast, the main Fe 2p 3/2 peak at 710.4 eV is attributed to Fe(III) in iron(III) oxide (Fe 2 O 3 ) and is usually the strongest signal in a well-oxidized sample. Additionally, the shake-up satellite observed at 719.7 eV is interpreted as arising from multiplet splitting and charge-transfer effects characteristic of high-spin Fe(III) in Fe 2 O 3 , while the peak at 723.5 eV, corresponding to the Fe 2p 1/2 main emission, typically appears about 13 eV above the Fe 2p 3/2 peak, further confirming the presence of Fe(III) in the oxide. .