An unexpectedly shrunken bandgap in V₂O₅ nanoparticles

Synchrotron x-ray spectroscopy was employed to determine the effects of nanostructuring on electronic band structure in V₂O₅, a promising cathode material and widely used catalyst. V₂O₅nanoparticle and bulk powders were characterized via P-XRD, electron microscopy, and diffuse reflectance ultraviolet/visible/near-infrared spectroscopy to confirm the optical bandgap. X-ray emission spectroscopy revealed the nanoparticle valence band O 2<i>p</i>states to be upshifted relative to the bulk, while x-ray absorption spectroscopy and resonant inelastic x-ray scattering showed the lowest V 3<i>d</i>conduction band states to be static. Together, these changes (in conjunction with an increased density of unoccupied lower conduction band states) produce a shrunken bandgap in the V₂O₅nanoparticles that defies the Burstein-Moss effect. Changes in nanoparticle band structure are generally attributed to oxygen vacancy defects. While nanostructure bandgap reduction is in line with much previous computational work, it is unexpected from most previous experimental results. To our knowledge, this is the first synchrotron x-ray spectroscopy study of a shrunken bandgap achieved in pure V₂O₅nanoparticles.