Fast and Stable Zinc Anode‑Based Electrochromic Displays Enabled by Bimetallically Doped Vanadate and Aqueous Zn^(2+)/Na^(+)Hybrid Electrolytes

Vanadates are a class of the most promising electrochromic materials for displays as their multicolor characteristics.However,the slow switching times and vanadate dissolution issues of recently reported vanadates significantly hinder their diverse practical applications.Herein,novel strategies are developed to design electrochemically stable vanadates having rapid switching times.We show that the interlayer spacing is greatly broadened by introducing sodium and lanthanum ions into V_(3)O_(8)interlayers,which facilitates the transportation of cations and enhances the electrochemical kinetics.In addition,a hybrid Zn^(2+)/Na^(+)electrolyte is designed to inhibit vanadate dissolution while significantly accelerating electrochemical kinetics.As a result,our electrochromic displays yield the most rapid switching times in comparison with any reported Zn-vanadate electrochromic displays.It is envisioned that stable vanadate-based electrochromic displays having video speed switching are appearing on the near horizon.

Viologen-based flexible electrochromic devices

Electrochromic technology has gained significant attention in various fields such as displays,smart windows,biomedical monitoring,military camouflage,human-machine interaction,and electronic skin due to its ability to provide reversible and fast color changes under applied voltage.With the rapid development and increasing demand for flexible electronics,flexible electrochromic devices(FECDs)that offer smarter and more controllable light modulation hold great promise for practical applications.The electrochromic material(ECM)undergoing color changes during the electrochemical reactions is one of the key components in electrochromic devices.Among the ECMs,viologens,a family of organic small molecules with 1,1'-disubstituted-4,4'-dipyridinium salts,have garnered extensive research interest,due to their well-reversible redox reactions,excellent electron acceptance ability,and the ability to produce multiple colors.Notably,viologen-based FECDs demonstrate color changes in the liquid or semisolid electrolyte layer,eliminating the need for two solid electrodes and thus simplifying the device structure.Consequently,viologens offer significant potential for the development of FECDs with high optical contrast,fast response speed,and excellent stability.This review aims to provide a comprehensive overview of the progress and perspectives of viologen-based FECDs.It begins by summarizing the typical structure and recent exciting developments in viologen-based FECDs,along with their advantages and disadvantages.Furthermore,the review discusses recent advancements in FECDs with additional functionalities such as sensing,photochromism,and energy storage.Finally,the remaining challenges and potential research directions for the future of viologen-based FECDs are addressed.

An overview of recent progress in the development of flexible electrochromic devices

Electrochromic materials are capable of reversibly switching their colors or optical properties through redox reactions under applied voltages,which have shown great potential applications including smart windows,nonemissive displays,optical filters,among others.Although the current rigid electrochromic devices have shown emerging interest and developed rapidly,many applications(e.g.,wearable/deformable optoelectronics)are blocked due to their inflexible features.Herein,the adaption of rigid electrochromic devices to flexible ones is of particular interest for the new era of smart optoelectronics.In this review,the current state-of-the-art achievements of flexible electrochromic devices(FECDs)are highlighted,along with their design strategies and the choice of electrochromic materials.The recent research progress of FECDs is reviewed in detail,and the challenges and corresponding solutions for real-world applications of FECDs are discussed.Furthermore,we summarize the basic fabrication strategies of FECDs and their potential applications.In addition,the development trend,the perspectives,and the outlook of FECDs are discussed at the end of this Review,which may provide recommendations and potential directions to advance the practical applications of FECDs.

MXene-based all-solid flexible electrochromic microsupercapacitor

With the increasing demand for multifunctional optoelectronic devices,flexible electrochromic energy storage devices are being widely recognized as promising platforms for diverse applications.However,simultaneously achieving high capacitance,fast color switching and large optical modulation range is very challenging.In this study,the MXenebased flexible in-plane microsupercapacitor was fabricated via a mask-assisted spray coating approach.By adding electrochromic ethyl viologen dibromide(EVB)into the electrolyte,the device showed a reversible color change during the charge/discharge process.Due to the high electronic conductivity of the MXene flakes and the fast response kinetics of EVB,the device exhibited a fast coloration/bleaching time of 2.6 s/2.5 s,a large optical contrast of 60%,and exceptional coloration efficiency.In addition,EVB acted as a redox additive to reinforce the energy storage performance;as a result,the working voltage window of the Ti_(3)C_(2)-based symmetric aqueous microsupercapacitor was extended to 1 V.Moreover,the device had a high areal capacitance of 12.5 mF cm^(−2)with superior flexibility and mechanical stability and showed almost 100%capacitance retention after 100 bending cycles.The as-prepared device has significant potential for a wide range of applications in flexible and wearable electronics,particularly in the fields of camouflage,anticounterfeiting,and displays.

Reversible Zn^(2+) Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows

Zinc-anode-based electrochromic devices(ZECDs) are emerging as the next-generation energy-e cient transparent electronics. We report anatase W-doped TiO_(2) nanocrystals(NCs) as a Zn^(2+) active electrochromic material. It demonstrates that the W doping in TiO_(2) highly reduces the Zn^(2+) intercalation energy,thus triggering the electrochromism. The prototype ZECDs based on W-doped TiO_(2) NCs deliver a high optical modulation(66% at 550 nm),fast spectral response times(9/2.7 s at 550 nm for coloration/bleaching),and good electrochemical stability(8.2% optical modulation loss after 1000 cycles).

Transparent inorganic multicolour displays enabled by zinc-based electrochromic devices

Electrochromic displays have been the subject of extensive research as a promising colour display technology.The current state-of-the-art inorganic multicolour electrochromic displays utilize nanocavity structures that sacrifice transparency and thus limit their diverse applications.Herein,we demonstrate a transparent inorganic multicolour display platform based on Zn-based electrochromic devices.These devices enable independent operation of top and bottom electrochromic electrodes,thus providing additional configuration flexibility of the devices through the utilization of dual electrochromic layers under the same or different colour states.Zn-sodium vanadium oxide(Zn-SVO)electrochromic displays were assembled by sandwiching Zn between two SVO electrodes,and they could be reversibly switched between multiple colours(orange,amber,yellow,brown,chartreuse and green)while preserving a high optical transparency.These Zn-SVO electrochromic displays represent the most colourful transparent inorganic-based electrochromic displays to date.In addition,the Zn-SVO electrochromic displays possess an open-circuit potential(OCP)of 1.56 V,which enables a self-colouration behaviour and compelling energy retrieval functionality.This study presents a new concept integrating high transparency and high energy efficiency for inorganic multicolour displays.