Internal Free Volume Directs Hydration-Induced Amorphization of Hollow α-V2O5

Hollow particles are designed to keep their cavities open, but a cavity can also be consumed as a structural resource. Thin-walled hollow α-V2O5 converts in aqueous ZnSO4 at 80 °C into a filled, hydrated, amorphous phase, Zn0.23(OH)0.46V2O5·1.0H2Oa charge-balanced composition from ICP-OES and TGA that assumes V5+ and hydroxide compensation of the zinc. Electron tomography shows the cavity disappearing as the particle grows from 246 to about 420 nm, with 6% of the vanadium lost to solution. The hollow shell takes up three times the water of commercial V2O5. Diffraction and vibrational spectroscopy show loss of long-range order and a 13 Å hydrated gallery; V K-edge XANES shows the vanadyl V5+ site of α-V2O5 surviving. Zn K-edge EXAFS gives Zn−O = 2.03 Å with a six-coordinate model in every state. The transformed phase has a smaller slow-process impedance and a larger initial utilization than crystalline controls, and DFT + U models of a reduced amorphous network with the same Zn content stabilize ionized Zn in O-rich disordered sites. Cycling changes the vanadium site, which does not recover on charge, and buries the surface under zinc hydroxy-sulfate. Internal free volume directs hydration-induced amorphization; stabilizing the product is a separate problem.