XPS spectra for a Ni 4 V 3 O 10 sample and the V 2 O 5 powder used for synthesis are shown in Fig. . Even after binding energy referencing to the C 1s peak, the V 2 O 5 O 1s peak is +0.53 eV from its expected position at 530.0 eV, and the V 2p 3/2 peak is +0.51 eV from its expected 517.2 eV. This consistent shift, though, does not prevent the analysis of vanadium oxidation states since it has been shown that despite shifts in O 1s position, the energy difference between the O 1s and V 2p 3/2 peaks is a reliable measure of oxidation state. Expected shifts of binary vanadium oxides are ∼12.80 eV for V 2 O 5 , ∼13.45 eV for VO 2 , and ∼14.50 eV for V 2 O 3 . For the V 2 O 5 reference, this difference is 12.82 eV; for Ni 4 V 3 O 10 it is 13.42 eV. Along with the expected increase in V 2p 3/2 peak width from V 5+ to V 4+ , this peak position difference for Ni 4 V 3 O 10 indicates the presence of V 4+ .