Typically considered to be one of the most stable elements due to its high melting and boiling points, rhenium is often found in nickel based superalloys, but also finds use in olefin metahtesis and reforming catalysis. Rhenium can exhibit multiple oxidation states, with +7, +6, +4 and +2 the most common in materials analysed by XPS.
Figure 1, shows the spectra of a partially oxidised rheinium foil exhibiting metallic Re (green), ReO2 (blue) and Re2O7 (yellow) states.
High valence rhenium oxides can undergo disproportionation during XPS analysis , so a suitable methodology, such as rapid acquisition and recording the Re(4f) region first and again at the end should be considered.
|Material||Re(4f 7/2) Binding Energy / eV||Reference|
|Re Metal||40.4 (Calibrated to Fermi Level)|||
|Re2O7||46.8 (Calibrated to C(1s) at 284.8 eV)||[1, 2]|
|NH4ReO4||46.3 (Calibrated to C(1s) at 284.8 eV)|||
|ReO2||43.0 (Std. Dev. of 0.6 eV)|| , ()|
|ReO3||44.2 (Std. Dev of 1.3 ev)|| , ()|
 S. Iqbal, M. L. Shozi and D. J. Morgan, X‐ray induced reduction of rhenium salts and supported oxide catalysts, Surf. Inter. Anal. 49 (2017) 223-226. Read it here: https://doi.org/10.1002/sia.6076
 Measured at HarwellXPS on a Thermo K-Alpha+ spectrometer, which has been calibrated using the internal ISO calibration method.
 Average of measurements from NIST. NIST Standard Reference Database 20, Version 4.1, http://dx.doi.org/10.18434/T4T88K