Stoichiometric vanadium oxides studied by XPS

Abstract

Recovery of vanadium oxide from steelmaking slag is of great interest for Swedish steel producers and the technique for assessing the oxidation state of vanadium is crucial in the optimization of vanadium recovery. There is a large spread in the reported values of published V2p 3/2 binding energy values for various oxidation states of vanadium. Therefore, an extensive analysis of vanadium oxide standards was performed aimed at obtaining reliable data and improved methods for the preparation of representative oxide standards. Powdered oxide standards of V 2 O 5 , VO 2 , V 2 O 3 , and VO, with purity better than 99%, were chosen. In their as-received state, all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of X-ray photoelectron spectroscopy spectra for vanadium oxides at lower oxidation states. Therefore, different methods for obtaining a representative surface for vanadium oxide standards were tested. The experimental results show high sensitivity of vanadium oxide standards to argon ion etching. Hence, a method to obtain a representative surface of standards by special heat treatment is proposed. Such approach was developed using a preparation chamber (furnace) attached to an X-ray photoelectron spectroscopy instrument. The annealing was performed in a vacuum at defined temperatures from 400 to 900 C for 4-24 h; the annealing parameters were selected based on thermodynamic equilibrium data for vanadium oxides. Experimental fitting parameters (peak position E and full width of half maximum of the peak) for vanadium V2p 3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides.

Synthesis of vanadium doped LiMnPO4 by an improved solid-state method

“…Now we first attempt to apply this approach to indentify the valence of V in LiMn 1 À x V x PO 4 . From the measured XPS spectra, the experimental Δ values of our samples are all ranged from 14.1 to 14.3 eV, indicating that the oxidation states of V is þ 3 [24]. Moreover, the bind of V2p 3/2 of LiMn 1 À x V x PO 4 samples was also fitted and the binding energy is around 517.3 eV, matching with that observed in Li 3 V 2 (PO 4 ) 3 (517.2 eV) [25] and again suggesting that the oxidation state of V in our doped sample is þ 3.…”

“…In the previous reports [13,14], the valence of V in LiMn 1 À x V x PO 4 /C was determined to be þ 3 based on the binding energy (BE) of V2p 3/2 . Herein two methods are adopted to analyze the XPS and evaluate the oxidation state of V. According to the work of Hryha et al [24], the difference in binding energies between the O1s (VO x ) core level and the V2p 3/2 level (Δ ¼ BE(O1s) -BE (V2p 3/2 )) was better for use in determining the oxidation state of the vanadium in oxides. Now we first attempt to apply this approach to indentify the valence of V in LiMn 1 À x V x PO 4 .…”

“…Since vanadium can present in different oxidation states, the valence of V in LiMn 1 À x V x PO 4 /C was studied by XPS which has been intensively used to determine the oxidation state of V [17,20,24]. Fig.…”

Fast Supercapacitors Based on Graphene‐Bridged V2O3/VOx Core–Shell Nanostructure Electrodes with a Power Density of 1 MW kg−1

“…These three peaks were also observed in the composite after the hydrogen thermal treatment; nevertheless, a tiny shoulder was detected at the lower binding energy of the V 2p 3/2 peak at around 512.9 eV, which may be assigned to the vanadium metallic state V 2+ due to over-reduction. [ 37 ] In general, V 4+ was found to be the dominating oxidation state on the surface of both composites. This was not a surprise even though XRD analysis of Figure 2 e indicated that the "bulk" of the vanadium oxide particle was V 2 O 3 after hydrogen thermal processing.…”

Natural and induced growth of VO2 (M) on VO2 (B) ultrathin films

“…6(a). The position of these peaks was ascribed to 517.4 eV, 516.1 eV, 514.1 eV and 512.9 eV, respectively 28 and the spectra were fitted using the CasaXPS software and a Shirley function to remove the background. The vanadium valence state content of the VO 2 films shown in Fig.…”