Effect of lattice water on the proton diffusion mechanism in hydrated tungsten trioxide nanostructures

Abstract Hydrated tungsten trioxide has been investigated extensively and was demonstrated to exhibit rapid proton conduction. For the purpose of fabricating electrochemical energy storage devices with higher power density, it is crucial to figure out the proton transport and storage mechanisms exactly. In this work, we have characterized the electrochemical performance and microstructure evolution during electrochemical reaction of hexagonal hydrated tungsten trioxide nanorods with different lattice water contents by ex situ XRD and Raman. With the decrease of lattice water content, the contribution of the capacitive charge storage decreases evidently, and both lattice distortion and lattice disorder increase significantly in the process of ion intercalation. Therefore, we suppose that the existence of lattice water in tungsten oxide offers a much more flexible mechanical deformation during the process of proton insertion and proton diffuse in tungsten trioxide based on the bridging oxygen mechanism. Besides that, proton prefer to be inserted/extracted in/from hydrated tungsten trioxide in the form of hydrated hydrogen ions (H 3 O + ) when the lattice water decreases apparently. These results provides significant insight towards the understanding of proton transport in hydrated tungsten trioxide and can serve as a pattern for the compositional design of cathode materials for proton battery and supercapacitor.