Redox Intercalation Reactions of VOPO4.2H2O with Mono-and Divalent Cations

Abstract

The layered oxide hydrate VOPO4-2H2O readily undergoes redox intercalation reactions with alkali-, alkaline-earth-, and transition-metal cations in the presence of a reducing agent to form compounds of general composition MxVOPO4nH2O, where M is the cation and x ≤ 1. The phase relations as x is varied are complex and have been investigated in detail for sodium and cesium cations by powder X-ray diffraction and chemical analysis. A survey of reactions for the cations Li+, K+, Rb+, Mg2+, Mn2+, Co2+, Ni2+, and Zn2+ is described. The interlayer separation of VOPO4-2H2O contracts upon intercalation of cations with the spacing dependent on specific cation and degree of reduction, while the in-plane tetragonal a axis increases with degree of vanadium reduction, independent of the specific interlayer cation. The intercalation reactions of VOPO4-2H2O probably proceed via intercalation of the reducing agent and reduction of electronically isolated vanadium(V) sites, in contrast to the redox chemistry of the transition-metal oxides and sulfides, which involves electron transport through the host lattice. © 1985, American Chemical Society. All rights reserved.