Visible and infrared electrochromism of bis(2-(2-(2-hydroxyethoxy)ethoxy)ethyl) viologen with sodium carboxymethyl chitosan-based hydrogel electrolytes

Abstract

Electrochromic devices (ECDs) which able to absorb the solar spectrum of visible (400–780 nm) and infrared (780–2000 nm) have attracted considerable attention due to the light control and energy-saving properties. In this paper, a electrochromic derived derivative of viologens, bis (2-(2-(2-hydroxyethoxy)ethoxy)ethyl) viologen bromide (HEV2+2Br−) was successfully synthesized and added to novel environmentally benign hydrogel electrolytes containg deionized water, sodium carboxymethyl chitosan and vitamin C (as electron mediators for the first time) as an electrochromic chromophore. The electrochromic devices on the basic of electrochromic materials (HEV2+2Br−) and hydrogel electrolytes underwent reversible switching between colorlessness and deep purple hues upon the potential ranges from 0 V to −1.2 V. Spectroelectrochemical studies demonstrated that HEV-based gel devices showed exceptional electrochromic behaviors with low driving voltage of −0.80 V, satisfactory optical contrast (unambiguously exceeded 64.13%) and high coloration efficiency (up to 243 cm2/C at 520 nm and 119 cm2/C at 865 nm) in the visible and infrared radiation. In consideration of their good electrochromic performance and environmentally friendly properties of benign hydrogel electrolytes containing HEV, the HEV-based gel devices have brilliant potentialities as candidates for related electrochromic applications for energy-efficient architecture.