A nanocrystalline tungsten oxide electrochromic coating with excellent cycling stability prepared via a complexation-assisted sol–gel method

Abstract

In order to enhance the electrochromic performance of sol–gel derived WO₃ coatings, especially the electrochemical cycling stability, a small amount of dopamine (DA) is introduced into a peroxotungstic acid (PTA) precursor sol to form complexes with tungsten on the surface of PTA colloidal nanoparticles. The DA molecules act as a precursor stabilizer, giving the sol a very long shelf life, which is crucial for practical applications, and also play the role of a structure-directing agent, providing a nanocrystal-embedded amorphous WO₃ coating by annealing at 300 °C. Compared with the corresponding neat WO₃ coating, the modified WO₃ coating prepared from the complex sol gives much higher optical contrast, a faster switching speed and a higher coloration efficiency. It also shows excellent long-term cycling stability (maintaining a stable high contrast up to 35 000 cycles), which is far superior to not only the reference neat WO₃ coating but also WO₃ coatings prepared via other wet chemical routes. The excellent cycling stability may be attributed to the buffering effect of the nanocrystal-embedded amorphous regions, which accommodate the volume change of the nanocrystals induced by ion insertion/extraction. The uniform distribution of the nanometer-sized amorphous and crystal regions may help to reduce stress concentration and hence suppress erosion caused by local stress.