Electrolyte/electrode co-optimization for high performance electrochromic devices

Electrochromic smart windows can dynamically regulate solar radiation to save energy and reduce emissions, which are importance in achieving carbon neutrality. The ammonium metatungstate (AMT) electrolyte exhibits reversible change in transmittance under bias voltage, making it a promising low-cost electrochromic material. However, its overall performance is not satisfactory, and there is a lack of effective means to improve the electrochemical behavior of the devices. Herein, we proposed an approach to design high performance electrochromic device via electrolyte/electrode co-optimization. On the one hand, the LiBr additive was screened out to match the half reaction. On the other hand, the ITO electrode was modified by Pt nanoparticles to catalyze the oxidation reactions of Br⁻ at the counter electrode. The resulted device exhibits satisfactory performance such as a large transmittance modulation of 80 %, the fast coloring/bleaching speed (5 s/33 s), and a low driving voltage (1.5–1.8 V). The electrochromic device with Pt/ITO counter electrode has good long-term stability, almost no performance degradation was observed after 1000 cycles. A large-area electrochromic device was fabricated to demonstrate the temperature control capability. This work provides an effective interface engineering approach to improve electrochromic performance, which can be extended to other electrochemical applications.