All-in-One Fast response Electrochromic Devices Based on PAAm/P2W18 hydrogel without additional electrolytes

All-in-one electrochromic devices (ECDs) have potential applications in wearable stretchable electronics. However, ECDs today are inflexible, slow to respond and at risk of electrolyte leakage. We have prepared a novel electrochromic hydrogel by introducing polyoxometalates [P2W18O62] 6− (P2W18) into polyacrylamide (PAAm) via ionic and covalent cross-linking. Negatively charged P2W18 have ionic conductive properties, thus the hydrogel is able to undergo electrochromic behavior without the addition of electrolytes. PAAm/P2W18 hydrogel has good flexibility and tensile properties, high transparency and a simple preparation process. The PAAm/P2W18 hydrogel is reversibly switchable between colorless and dark blue over a voltage range from 0 V to -2.8 V. The ECDs had a large transmittance contrast (53.7%), fast response time (coloring/bleaching times of 6.9 s and 5.6 s) and satisfactory coloring efficiency (125.5 cm2/C). PAAm/P2W18 hydrogel has good open-circuit memory properties which maintains coloring state after 7 days of power off. The sandwich-structured (ITO/hydrogel/ITO) electrochromic device based on this hydrogel is simple to manufacture, low in cost and fast in response, which have potential applications in the fields of smart windows, energy-saving displays, and anti-glare mirrors.