Aqueous electrochemical insertion of Na+ into the tungsten oxide hybrid WO3(4,4′-bipyridyl)0.5

Aqueous electrochemical insertion of M+ (Na+ and H+) species into WO3(4,4′-bipyridyl)0.5 has been carried out. The chemical states and structure of the resulting product were analysed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS showed the presence of W6+ as well as the usual reduced W species (W5+) which is responsible for a change in colour. Moreover, the presence of these intercalates correlates with the evolution of the reduced W species. The bulk structure of the layered hybrid, as determined by powder X-ray diffraction, showed no alteration after electrochemistry, in contrast to the same measurements on tungsten trioxide (WO3). This however concurs with single-crystal X-ray studies, which show little change in lattice parameters with Na+ insertion. Four-probe resistance measurements of the layered hybrid coated film display a drop in resistance after electrochemistry, which can be attributed to the injection of charge-carriers into the conduction band.