Reversible Zn2+/Al3+ intercalation in niobium-substituted polyoxometalates and demonstration of energy storage smart windows

Electrochromic energy storage devices with diversified functions that can realize intelligent visualization of the energy status with the naked eye are highly desirable for intelligent electronic technology. Polyoxometalates (POMs) as a promising electrochromic energy storage material are bottlenecked by limited choices in the electrolyte to achieve high-performance electrochromic smart windows. Herein, we report a novel tri-niobium substituted Dawson-type POM alpha-K-9[P2W15Nb3O62]center dot 18H(2)O (P2W15Nb3) coated TiO2 as an electrochromic electrode for non-aqueous electrochromic energy storage smart windows, utilizing a dual-ion electrolyte with Zn2+ and Al3+. Our findings suggest that the synergistic effects of the dual-ion Zn2+/Al3+-ion electrolyte on P2W15Nb3 films greatly promote the electrochromic and electrochemical properties: high optical contrast (90% at 650 nm) in the 350-1500 nm range, large areal capacity (52 mF cm(-2) at 0.66 mA cm(-2)), fast switching time and good cycling stability. Remarkably, a bi-functional electrochromic energy storage device (EESD) was also successfully assembled using a P2W15Nb3 composite film and a hydrothermally prepared NiO film. This dual-ion Zn2+/Al3+ electrolyte opens a new direction for the development of POM based smart windows with high contrast, long life-time stability and excellent energy storage.

Automated summary

In this study, a novel tri-niobium substituted Dawson-type POM alpha-K-9[P2W15Nb3O62]center dot 18H(2)O (P2W15Nb3) coated TiO2 was utilized as an electrochromic electrode for non-aqueous electrochromic energy storage smart windows, utilizing a dual-ion electrolyte with Zn2+ and Al3+. The dual-ion Zn2+/Al3+ electrolyte greatly promoted the electrochromic and electrochemical properties of P2W15Nb3 films, resulting in high optical contrast, large areal capacity, fast switching time, and good cycling stability. Furthermore, a bi-functional electrochromic energy storage device (EESD) was successfully assembled using a P2W15Nb3 composite film and a hydrothermally prepared NiO film.