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Tungsten trioxide nanodots show promise in electrochromic and photochromic devices

Nanodots have a high surface-to-volume ratio, which enables the introduction (intercalation)/removal of guest cations in electrochromic applications. That’s why scientists from Shandong University in China and the University of Alberta in Canada use tungsten trioxide (WO3) nanodots enable rapid color switching in electrochromic devices, and the large surface-to-volume ratio of nanodots accelerates proton intercalation under sunlight to increase the coloration rate of photochromic effects.

Taking advantage of these properties, the WO assembly is tailored to the ligands3 nanodots show promising electrochromic activity. Their work is a truly interdisciplinary endeavor that integrates chemistry, materials science and optics.

“WO3 Nanodot colloids can reduce production costs and hold promise for low-cost electrochromic devices,” says Haizeng Li, a professor of optics at Shandong University. “That’s why we’re working on nanodots.”

Electrochromic/photochromic

Their electrochromic work focuses on polaronic reactions caused by the intercalation of guest cations. “Fundamentally, our electrochromic devices use electrochemical photonics, which enables the use of adjustable optical devices such as variable optical attenuators, optical switches, addressable displays, touchscreen devices, and especially energy-efficient smart windows for buildings,” explains Li. “When it comes to our photochromic work, it involves photogating reactions that lead to the coloring effect.”

The most surprising aspect of this research? “Easy increase in entropy of crystalline WO3 thanks to a simple solution,” says Li. “To our knowledge, this is the first reported approach to increasing the entropy of crystallized materials. This is a moment that fills me with pride, knowing that we made the seemingly impossible possible.”

The team demonstrated “the use of WO3 nanodots in zinc anode-based electrochromic devices, which we are pioneering in,” says Li. “Our devices enable dynamic transparency control and electrical energy storage. Imagine that future dynamic windows could not only control transparency, but also store energy like a battery.

Besides, WO3 nanodots can be used in photochromic hydrogels and textiles. “Photochromic hydrogels can adhere to regular glass, providing photochromic functionality,” Li says. “When it comes to photochromic textiles, in addition to their photochromatic properties, they also offer radiative cooling properties, which makes them ideal for smart clothing.”

After the synthesis of amorphous WO3 nanodots, the team’s next main challenges include constructing high-performance electrochromic devices based on a zinc anode. “Since we are not chemists, we will have to delve into colloidal chemistry to tailor the ligands on the WO surface3 nanodots,” says Li.

Scaling the production of tungsten oxide nanodots

During Li’s more than 10 years of electrochromic research, his goal was to create low-cost electrochromic windows. “Although our current work successfully synthesizes high-quality WO3 nanodots, scalability remains key,” he says.

The team’s future work will focus on scaling up the production of these WOs3 nanodots. “In our future research on photochromic hydrogel, we intend to implement appropriate sealing techniques to ensure long-term stability,” says Li. “Similarly, for photochromic textiles, our goal is to design washable variants to facilitate their applications in real-world conditions.”

FURTHER READING

P. Liu et al., Adv. Function. Mother. (March 30, 2024); https://doi.org/10.1002/adfm.202400760.