All-in-One Gel-Based Electrochromic Devices: Strengths and Recent Developments

Electrochromic devices (ECDs) have aroused great interest because of their potential applicability in displays and smart systems, including windows, rearview mirrors, and helmet visors. In the last decades, different device structures and materials have been proposed to meet the requirements of commercial applications to boost market entry. To this end, employing simple device architectures and achieving a competitive electrolyte are crucial to accomplish easily implementable, high-performance ECDs. The present review outlines devices comprising gel electrolytes as a single electroactive layer (“all-in-one”) ECD architecture, highlighting some advantages and opportunities they offer over other electrochromic systems. In this context, gel electrolytes not only overcome the drawbacks of liquid and solid electrolytes, such as liquid’s low chemical stability and risk of leaking and soil’s slow switching and lack of transparency, but also exhibit further strengths. These include easier processability, suitability for flexible substrates, and improved stabilization of the chemical species involved in redox processes, leading to better cyclability and opening wide possibilities to extend the electrochromic color palette, as discussed herein. Finally, conclusions and outlook are provided.This work has been partially supported by the European Union’s Horizon 2020 research and innovation program under the INNPAPER project (grant agreement No. 760876)

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)

TiO2/AZO bilayer thin films by magnetron sputtering as transparent electrodes for electrochromic devices

Transparent electrodes are dominated by a single material indium tin oxide (ITO). Indium has been classified as a critical raw material by the EU, thus some alternative transparent conductor materials are urgently required. Aluminum zinc oxide (AZO) has emerged as promising substitute due to its high transmittance and low resistivity as well as its low cost and resource availability. However, manufacturing processes for some optoelectronic devices such as electrochromic devices or organic light emitting diodes, chemically attack the AZO layers due to their instability against acidic and basic solutions. Chemical and environmental stability of AZO coatings must be improved to guarantee long-term stability of the devices. In this paper, electrochromic devices based on viologen modified nanostructured TiO2 layers have been manufactured on bilayer electrodes formed by sputtering TiO2 protective films on AZO layers. A thin sputtering TiO2 layer does not electrically insulate the AZO but improves its stability and protects it from being attacked during the deposition of the nanostructured sol-gel TiO2, enabling the fabrication of EC devices that switch properly between a transparent, colorless and a green coloured state. Optical contrast (ΔT %) values up to 40% have been reached with an operating voltage of −1.5 V

Multifunctional touch sensing and antibacterial polymer-based core-shell metallic nanowire composites for high traffic surfaces

The transmission of bacterial infections through contaminated surfaces is nowadays an increasing source of concern, also related to the current pandemic situation. Functional materials that prevent the adhesion of microorganisms and/or induce their eradication thus avoiding fomite transmission are highly needed. In this work, a highly antimicrobial hybrid with sensorial capability is developed to be further applied as interactive high traffic surface coatings. The nanocomposite is composed of polyvinylidene fluoride (PVDF), a highly stable fluorinated polymer, incorporating copper core-shell nanowires (NWs). The NWs comprised of copper and shelled with silver is highly antimicrobial, inducing a full kill effect against Escherichia coli and Staphylococcus epidermidis strains but biocompatible towards mammalian cells at concentrations below 0.5 mg mL1. Further NWs incorporation on PVDF matrix retains its antimicrobial activity reducing in 6.5 logs the E. coli and 4.5 logs the S. epidermidis. NW/PVDF composites demonstrate suitable mechanical and electrical characteristics for the development of capacitive sensing surfaces, allowing for the fabrication of an antimicrobial capacitive touch sensing matrix for interactive surfaces.This work was supported by the Basque Government Industry Department under the ELKARTEK program (KK-2019/00039, KK-2020/00108, and KK-2021/00040) and by the Ministerio de Ciencia e Innovación of the Spanish Government (project SURF-ERA, EXP – 00137314 / CER-20191003). Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/EJ, EGEF, and ESF) was gratefully acknowledged.info:eu-repo/semantics/publishedVersio

Quantitative assessment of the cycling stability of different electrochromic materials and devices

Despite the long history of the development of electrochromism, there are still no generally accepted methods for a quantitative comparison of the cycling stability between different electrochromic materials or devices. By proposing a straightforward three-step procedure, we report a simple set of parameters that describe the cycling stability performance of some of the most frequently used electrochromic materials, namely conducting polymers, transition metal oxides, metallo-supramolecular polymers and viologens. The main features of this procedure are an adequate definition of the testing conditions and the analytical description of the materials performance evolution through continuous cycling. The resulting parameters not only allow us to perform comparative studies among different materials and devices, but to identify tendencies, and therefore establish the corresponding balance, between the testing conditions and the cycling stability/optical performance obtained. This method constitutes a powerful decision-making tool for the academic and the industry-related electrochromic community

A new standard method to calculate electrochromic switching time

The switching time is one of the key parameters used to assess the performance of an electrochromic material or device. In spite of its importance, there is currently no standard for how this parameter is defined, and as a result, it is difficult to compare switching time data between different research groups, and to quantify and assess reported improvements. We propose a standard method for reporting electrochromic switching times, based on straightforward experimental fittings resulting in an analytical expression that can directly correlate obtainable optical contrast values with their corresponding switching times. This analytical expression makes it possible to unambiguously define the performance of an electrochromic material or device using two parameters: a full-switch contrast and a time constant