Advances in electrochromic materials

The development of a Microsoft® Excel® spreadsheet is described, for the accurate calculation of CIE (Commission Internationale de l’Eclairage) 1931 xy chromaticity coordinates and luminance data from visible region absorption spectra recorded in transmission mode. Using firmly established CIE principles, absorbance-wavelength data from visible spectra are taken as input, with chromaticity coordinates being generated as output. Colour stimulus measurement example calculation results are firstly presented for aqueous solutions of the dyes, Erythrosin B (red, x, y = 0.608, 0.365), Acid Green 25 (x, y = 0.086, 0.298) and Remaxol Brilliant Blue R (x, y = 0.153, 0.045), and then for tracking electrochromic in situ colour stimulus changes in the methyl viologen and di-n-heptyl viologen systems. The quantification of colour during each viologen dication to cationradical reduction process, and each reverse (oxidation) process, showed that subtle changes in both hue and luminance could be detected, with evidence of colour contributions from both the cation radical and the cation radical dimer. Ruthenium purple (RP) films on transmissive tin-doped indium oxide (ITO)/glass substrates have been synthesised by a novel electrochemical coagulation technique. Using the CIE system of colorimetry, the colour stimulus of the electrochromic RP films and the changes that take place on reversibly switching to the colourless form have been calculated from in situ visible spectra recorded under electrochemical control. (Continues...)

Room-Temperature Self-Standing Cellulose-Based Hydrogel Electrolytes for Electrochemical Devices

The trend of research towards more sustainable materials is pushing the application of biopolymers in a variety of unexplored fields. In this regard, hydrogels are attracting significant attention as electrolytes for flexible electrochemical devices thanks to their combination of ionic conductivity and mechanical properties. In this context, we present the use of cellulose-based hydrogels as aqueous electrolytes for electrochemical devices. These materials were obtained by crosslinking of hydroxyethyl cellulose (HEC) with divinyl sulfone (DVS) in the presence of carboxymethyl cellulose (CMC), creating a semi-IPN structure. The reaction was confirmed by NMR and FTIR. The small-amplitude oscillatory shear (SAOS) technique revealed that the rheological properties could be conveniently varied by simply changing the gel composition. Additionally, the hydrogels presented high ionic conductivity in the range of mS cm−1. The ease of synthesis and processing of the hydrogels allowed the assembly of an all-in-one electrochromic device (ECD) with high transmittance variation, improved switching time and good color efficiency. On the other hand, the swelling ability of the hydrogels permits the tuning of the electrolyte to improve the performance of a printed Zinc/MnO2 primary battery. The results prove the potential of cellulose-based hydrogels as electrolytes for more sustainable electrochemical devices.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 760876 (INNPAPER)

Reading the rainbow: tailoring the properties of electrochromic polymers

The completion of the color palette has yielded a family of electrochromic polymers (ECPs) each able to absorb in unique regions across the visible spectrum. Synthetically, by varying the electronic content of phenylene type moieties coupled with the donor 3,4-propylenedioxythiophene (ProDOT), high band gaps can be achieved absorbing short wavelength light, yielding a family of yellow-to-transmissive electrochromic polymers. Using the synthetic approach to tune specific absorptions in a discrete region of the visible spectrum, a family of electrochromic polymers that possess sharpened or broadened absorption spectra relative to electrochromic materials previously produced has been developed. By varying the steric hindrance of dioxythiophenes along a conjugated backbone, new hues of magenta and blue have been achieved. Through progressively adding more steric hindrance and twisting the polymer backbone, the absorbance of a polymer can be pushed towards shorter wavelengths, allowing more red light and less blue light to pass through a film. This unequal passing of long and short wavelengths reduces the overall purple color that is normally exhibited by a previous magenta ECP, thereby giving brighter, truer magenta colored materials. By reducing steric hindrance and relaxing the polymer backbone, the opposite can be achieved: pushing the absorbance of a polymer to longer wavelengths allows more blue and less red light to transmit. These polymers also exhibit highly transmissive oxidized states that are attainable at low potentials. In the quest to achieve black (or dark as defined by low L*) to transmissive ECPs with suitable contrast for window or eyewear applications, a relaxed donor-acceptor architecture has been explored. These materials give broad neutral state absorptions with a %Tint (380-780 nm) > 50 %, bringing these materials closer to realization.Ph.D

New electrochromic systems: multicolored, semi-solid and easy-to-make

266 p.La presente tesis doctoral aborda la temática de los sistemas electrocromicos centrándose en la obtención de nuevas coloraciones, especialmente coloraciones neutras (gris y negro) así como dispositivos multielectrocrómicos de fácil fabricación y manteniendo configuraciones de dispositivos sencillas.Para alcanzar estos objetivos, el desarrollo técnico de la tesis se ha centrado en dos puntos principales: 1) la síntesis de nuevos materiales electrocrómicos, concretamente viológenos, con sustituyentes de diferente naturaleza para ampliar la gama de coloraciones y 2) el desarrollo de un nuevo concepto de electrolito basado en un fluido de naturaleza no-Newtoniana viscoelástico. En relación al primer punto, se han sintetizado viológenos tanto exentos de grupo de anclaje para ser incorporados en dispositivos de mezcla única (¿All-in-one¿), como provistos de un grupo de anclaje que les permita unirse covalentemente a una capa nanoestructurada de TiO2, (¿layered¿) presentando velocidades de adsorción muy rápidas. En relación al segundo punto, el desarrollo de un electrolito de base acuosa con propiedades viscoelásticas ha permitido mantener las buenas prestaciones de los electrolitos líquidos y sólidos actuales, pero mejorando algunas de sus limitaciones y permitiendo una fácil fabricación y manejo.IK4 CIDETE