Outperformed electrochromic behavior of poly(ethylene glycol)-template nanostructured tungsten oxide films with enhanced charge transfer/transport characteristics

Porous tungsten oxide films of nanocrystalline tungsten oxide embedded in an amorphous tungsten oxide matrix have been synthesized via poly(ethylene glycol) (PEG)-template sol-gel technique with peroxopolytungstic acid precursor. The effects of PEG addition on the microstructure and electrochromic performance of the tungsten oxide films are investigated. Charge transfer/transport properties in the tungsten oxide films are studied by electrochemical impedance spectroscopy (EIS) as well. Triclinic tungsten oxide film is formed in the absence of PEG. The PEG-template tungsten oxide film demonstrates an electrochromic performance superior to that of the crystalline tungsten oxide film, including larger transmittance modulation and coloration/bleaching efficiency as well as faster response times. EIS measurements indicate that faster charge-transfer rates at the tungsten oxide/electrolyte interface and larger Li+ diffusion coefficients in tungsten oxide are achieved in the PEG-template film. We suggest that the PEG-template tungsten oxide film with a porous crystalline/amorphous nanostructure provides an effective means for charge transfer/transport to encourage its superior electrochromic performance.