Dual Band Electrochromic Devices Based on Nb-Doped TiO2 Nanocrystalline Electrodes

Structurally and surficially activated TiO2 nanomaterials for photochemical reactions

Renewable fuels and environmental remediation are of paramount importance in today's world due to escalating concerns about climate change, pollution, and the finite nature of fossil fuels. Transitioning to sustainable energy sources and addressing environmental pollution has become an urgent necessity. Photocatalysis, particularly harnessing solar energy to drive chemical reactions for environmental remediation and clean fuel production, holds significant promise among emerging technologies. As a benchmark semiconductor in photocatalysis, TiO2 photocatalyst offers an excellent solution for environmental remediation and serves as a key tool in energy conversion and chemical synthesis. Despite its status as the default photocatalyst, TiO2 suffers from drawbacks such as a high recombination rate of charge carriers, low electrical conductivity, and limited absorption in the visible light spectrum. This review provides an in-depth exploration of the fundamental principles of photocatalytic reactions and presents recent advancements in the development of TiO2 photocatalysts. It specifically focuses on strategic approaches aimed at enhancing the performance of TiO2 photocatalysts, including improving visible light absorption for efficient solar energy harvesting, enhancing charge separation and transportation efficiency, and ensuring stability for robust photocatalysis. Additionally, the review delves into the application of photodegradation and photocatalysis, particularly in critical processes such as water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide generation, and alcohol oxidation. It also highlights the novel use of TiO2 in plastic polymerization and degradation, showcasing its potential for converting plastic waste into valuable chemicals and fuels, thereby offering sustainable waste management solutions. By addressing these essential areas, the review offers valuable insights into the potential of TiO2 photocatalysis for addressing pressing environmental and energy challenges. Furthermore, the review encompasses the application of TiO2 photochromic systems, expanding its scope to include other innovative research and applications. Finally, it addresses the underlying challenges and provides perspectives on the future development of TiO2 photocatalysts. Through addressing these issues and implementing innovative strategies, TiO2 photocatalysis can continue to evolve and play a pivotal role in sustainable energy and environmental applications.

Visible-Near Infrared Independent Modulation of Hexagonal WO3 Induced by Ionic Insertion Sequence and Cavity Characteristics

Dual-band electrochromic materials have attracted significant attention due to their ability to independently control sunlight and solar heat. However, these materials generally exhibit notable limitations, and the mechanisms for their dual-band independent regulation remain poorly understood. Here, the visible-NIR-independent regulation capabilities of hexagonal WO3 (h-WO3) are introduced for the first time. A structure-activity relationship that perfectly links the microscopic ion insertion sequence and cavity characteristics to the macroscopic dual-band electrochromic properties is established. The progressive ion intercalation process and the distinctive optical activity of the cavities are keys for enabling h-WO3 to independently modulate "bright," "cool," and "dark" modes. Notably, h-WO3 demonstrates superior dual-band electrochromic performance with a broadband full shielding effect from 550 to 2000 nm, achieving the widest full shielding band in dual-band electrochromic studies. Additionally, h-WO3 shows a high discharge capacity of 270.9 mAh m- 2 at 0.25 A m- 2, and requires only 49.1 and 209.7 mAh m- 2 to complete a full round-trip switch between "bright-cool" and "bright-dark" modes, respectively. The constructed device offers a dynamic temperature control range of up to 10.5 °C and supports a maximum voltage of 2.86 V, underscoring its considerable potential for practical applications and energy efficiency.

Self-Powered Dual-Band Electrochromic Supercapacitor Devices for Smart Window Based on Ternary Dielectric Triboelectric Nanogenerator

A dual-band electrochromic supercapacitor device (DESCD) can be driven by an external power supply to modulate solar radiation, which is a promising energy-saving strategy and has broad application prospects in smart windows. However, traditional power supplies, such as batteries, supercapacitors, etc., usually face limited lifetimes and potential environmental issues. Hence, we propose a self-powered DESCD based on TiO2/WO3 dual-band electrochromic material and a ternary dielectric rotating triboelectric nanogenerator (TDR-TENG). The TDR-TENG can convert mechanical energy from the environment into electrical energy to obtain a high output of 840 V, 23.9 µA, and 327 nC. The as-prepared TDR-TENG can drive the TiO2/WO3 film to store energy with a high dual-band modulation amplitude of 41.6% in the visible (VIS) region and 84% in the near-infrared (NIR) region, decreasing the indoor-outdoor light-heat interaction and thereby reducing the building energy consumption. The self-powered DESCD demonstrated in this study has multiple functions of energy harvesting, energy storage, and energy saving, providing a promising strategy for the development of self-powered smart windows.

Selective Electrochromic Regulation for Near-Infrared and Visible Light via Porous Tungsten Oxide Films with Core/Shell Architecture

Dual-band electrochromic smart windows have become a research hotspot owing to their unique ability to selectively control near-infrared (NIR) and visible (VIS) light. However, the design and exploitation of dual-band electrochromic films are still an extreme challenge due to the scarcity of relevant high-performance materials. To solve this issue, we here proposed a type of porous WO₃ film with nanowires/nanoparticles core/shell architecture as a promising candidate, endowing smart windows with a dual-band electrochromic feature. Moreover, the mechanism of the dual-band electrochromism is illustrated by the response of the transmittance spectra in Li⁺-based or TBA⁺-based electrolytes to distinguish the electrochemical behavior and the cyclic voltammetry to determine the degree of diffusion-limited kinetics. Our results indicate that the dual-band electrochromic performance is credited to the progressive electrochemical reduction procedure, in which the capacitive charging process gives rise to NIR regulation and the following ion intercalation contributes to VIS light modulation. Furthermore, we develop a dual-band electrochromic energy storage prototype device utilizing the porous WO₃ film. This work describes a judicious strategy for designing dual-band electrochromic films, promoting the evolution of dual-band electrochromic technology.

High Optical Contrast of Quartet Dual-Band Electrochromic Device for Energy-Efficient Smart Window

A quartet dual-band electrochromic device (ECD) was developed to selectively control the transmittance from the visible to near-infrared wavelengths for the application of an energy-efficient smart window. The new AgNO₃+TBABr+LiClO₄ (ATL)-based electrolyte was developed to independently control the redox reaction of lithium and silver ions to demonstrate the quartet mode of an ECD. A dual-band ECD with a sandwich structure was assembled using an ATL-based electrolyte, WO₃ electrochromic layer, and antimony-doped tin oxide (ATO) ion storage layer. The employed WO₃ and ATO films were fabricated using a nanoparticle deposition system (NPDS), a novel ecofriendly dry deposition method. Four modes, namely, transparent, warm, cool, and all-block modes, were demonstrated via an independent redox reaction of both lithium and silver ions through the simple control of the applied voltage. In the warm mode, the localized surface plasmon resonance effect was exploited by producing silver nanoparticles upon two-step voltage application. Furthermore, since the high surface roughness of the WO₃ thin film fabricated by NPDS maximized the light scattering effect, 0% transmittance at all wavelengths was observed in the all-block mode. Dual-band ECD showed high optical contrasts of 73% and long-term durability over 1000 cycles with no degradation. Therefore, the possibility of controlling transmittance at the target wavelength was confirmed using a simple device with a simple process, suggesting a new strategy for the design of dual-band smart windows to reduce the energy consumption of buildings.

Robust and stable dual-band electrochromic smart window with multicolor tunability

Dual-band electrochromic smart windows (DESWs) can selectively control the transmittance of near-infrared (NIR) and visible (VIS) light, which can significantly reduce building energy consumption. However, almost all the reported DESW colors switch between clear colorless and dark blue. The single color combined with the dazzling visual experience of blue will undoubtedly limit the application scene of DESWs. Herein, for the first time, we report a robust and stable DESW with multicolor conversion capabilities based on the single-component organic polymer polyaniline (PANI). The results show that the progressive electrochemical reaction enabled PANI film to deliver not only efficient and independent control of NIR and VIS light transmittance but also impressive electrochromic performance-rich color conversion (yellow-green-black), good optical modulation (65% at 633 nm and 59% at 1600 nm), high coloration efficiency (367.1 cm² C^-1 at 633 nm and 299.6 cm² C^-1 at 1600 nm), and excellent cycling stability (optical modulation losses of 6% at 633 nm, and 4% at 1600 nm after 10 000 cycles). Thereby, we demonstrated a prototype PANI-based DESW device (10 × 5 cm²), which delivered a multicolor electrochromism together with independent control and modulation of the VIS (sunlight) and NIR (solar heat) transmittance.

Amorphous Mixed-Vanadium-Tungsten Oxide Films as Optically Passive Ion Storage Materials for Solid-State Near-Infrared Electrochromic Devices

Near infrared (NIR) electrochromic (EC) devices that selectively modulate the NIR light without affecting the daylight represent a promising window technology for saving energy consumption of buildings. Current research efforts have been focused on developing NIR-EC materials, while little attention has been directed to the optically passive ion storage materials that are crucial for balancing charges in a full NIR-EC device. Herein, we report that amorphous phase mixed-vanadium-tungsten oxide films exhibit minimum optical change with high ion storage capacity, which enables the usage of the mixed-metal oxides as optically passive counter electrode materials for NIR-EC devices. The mixed-vanadium-tungsten oxide films are synthesized by a room-temperature solution-based photodeposition method that allows us to precisely engineer the metal compositions and thicknesses of the mixed-metal oxide films, thus optimizing their optical inertness and ion storage capability. A solid-state NIR-EC device assembled with the mixed-vanadium-tungsten oxide film as an ion storage layer and the amorphous tungsten oxide hydrate as the NIR-EC layer shows fast response speed with cycling stability up to 10,000 cycles, proving the outstanding charge balancing capability of mixed-metal oxide. Our work provides an efficient strategy for developing optically passive ion storage films with high ion storage capability for high-performance EC devices.

In-Operando Optical Spectroscopy of Field-Effect-Gated Al-Doped ZnO

Transparent conductive oxides (TCO) have the unique characteristics of combining optical transparency with high electrical conductivity; such a property makes them uniquely alluring for applications in visible and infrared photonics. One of their most interesting features is the large sensitivity of their optical response to the doping level. We performed the active electrical manipulation of the dielectric properties of aluminum-doped ZnO (AZO), a TCO-based on Earth-abundant elements. We actively tuned the optical and electric performances of AZO films by means of an applied voltage in a parallel-plate capacitor configuration, with SrTiO₃ as the dielectric, and monitored the effect of charge injection/depletion by means of in-operando spectroscopic ellipsometry. Calculations of the optical response of the gated system allowed us to extract the spatially resolved variations in the dielectric function of the TCO and infer the injected/depleted charge profile at the interface.

Dual-Band Electrochromic Optical Modulation Improved by a Precise Control of Lithium Content in Li4+xTi5O12

Dual-band electrochromic smart windows that can dynamically and independently control incident solar irradiation and visible light are envisioned as intelligent technology to reduce power consumption of buildings. However, there is still a great challenge to put the dual-band electrochromic technology into practice due to some limits in material systems and preparation techniques. Herein, a new electrochromic material of Li₄Ti₅O₁₂ is developed to implement the dual-band optical modulation behavior, which could be further improved by a precise control of the lithium content in the active material. It could separately modulate the light and heat based on regulation of the transmittance of visible and near-infrared light. This enables Li₄Ti₅O₁₂ to operate in three distinct modes of bright, cool, and dark, so as to meet various indoor needs. The optical transmittance contrast reaches over 60% at both visible- and near-infrared-light regions between different modes, and a large range of apparent temperature adjustments (7 °C) could be achieved. The prototype device based on dual-band electrochromic Li₄Ti₅O₁₂ is further developed into a smart window of a house model, which exhibits good optical and thermal modulation behaviors in response to a high-temperature environment. This work provides a new material system for achieving dual-band electrochromic optical modulation toward smart energy-saving window applications.

Plasmonic metal oxides and their biological applications

Metal oxides modified with dopants and defects are an emerging class of novel materials supporting the localized surface plasmon resonance across a wide range of optical wavelengths, which have attracted tremendous research interest particularly in biological applications in the past decade. Compared to conventional noble metal-based plasmonic materials, plasmonic metal oxides are particularly favored for their cost efficiency, flexible plasmonic properties, and improved biocompatibility, which can be important to accelerate their practical implementation. In this review, we first explicate the origin of plasmonics in dopant/defect-enabled metal oxides and their associated tunable localized surface plasmon resonance through the conventional Mie-Gans model. The research progress of dopant incorporation and defect generation in metal oxide hosts, including both in situ and ex situ approaches, is critically discussed. The implementation of plasmonic metal oxides in biological applications in terms of therapy, imaging, and sensing is summarized, in which the uniqueness of dopant/defect-driven plasmonics for inducing novel functionalities is particularly emphasized. This review may provide insightful guidance for developing next-generation plasmonic devices for human health monitoring, diagnosis and therapy.

A Facile Strategy To Construct Au@VxO2x+1 Nanoflowers as a Multicolor Electrochromic Material for Adaptive Camouflage

Transition metal oxides (TMOs) are promising inorganic electrochromic materials (ECMs) that can be widely used in electronic displays and adaptive camouflage. However, there are still huge challenges for TMOs to simultaneously achieve multicolor transformation capability and good cycling stability. Herein, we assemble Au-modified (0.01 wt %) V_xO_2x+1 (x > 2) nanoflowers (Au@V_xO_2x+1 NFs) composed of two-dimensional porous nanosheets containing two valences states of vanadium (V⁴⁺ and V⁵⁺). The Au@V_xO_2x+1 NFs exhibits outstanding electrochromic performance with five reversible color transformations (orange, yellow, green, gray, and blue) at a voltage less than 1.5 V and excellent cycling stability (2000 cycles without significant decay). To the best of our knowledge, this is the first time that a single vanadium oxide ECM, rather than a device, realizes five color changes. This work provides a feasible way for the efficient preparation of multicolor electrochromic TMOs. The newly developed Au@V_xO_2x+1 NFs demonstrate the potential application in adaptive camouflage.

Evaluation of Transparent ITO/Nano-Ag/ITO Electrode Grown on Flexible Electrochromic Devices by Roll-to-Roll Sputtering Technology

This paper explores the flexible ITO/nano-Ag/ITO multilayer electrodes grown on polyethylene terephthalate (PET) substrates and processed by a continuous roll-to-roll (R2R) sputtering system at room temperature used for flexible electrochromic device (ECD) applications. The effect of the nano-Ag interlayer thickness on the electrical and optical properties of the flexible ITO/nano-Ag/ITO multilayer was thoroughly investigated. By using R2R-sputtered at an Ag DC power of 0.2 kW, we were able to achieve optimal ITO/nano-Ag/ITO multilayer that exhibits a high optical transmittance of 87.19% and the best figure of merit value (30.93 × 10−3 Ω−1). The EC performance and stability of the flexible devices were tested by a cathodic WO3 coloration. Coloring and bleaching tests show that ITO/nano-Ag/ITO multilayers are highly effective conductors, indicating that the R2R sputtering technique is a promising continuous sputtering process in preparing for the fabrication of optical devices and flexible electronics industries.

Controlling the Shape Anisotropy of Monoclinic Nb12O29 Nanocrystals Enables Tunable Electrochromic Spectral Range

Electrochromic smart windows that modulate the solar transmittance in a wide and selective spectral range can optimize building energy efficiency. However, for conventional materials such as bulk transition metal oxides, the electrochromic spectral range is constrained by their crystal structure with limited tunability. Herein, we report a method to control the shape anisotropy of monoclinic Nb₁₂O₂₉ nanocrystals and obtain a tunable electrochromic spectral range. We demonstrate the synthesis of monoclinic Nb₁₂O₂₉ nanorods (NRs), extending one-dimensionally along the b direction, and monoclinic Nb₁₂O₂₉ nanoplatelets (NPLs), extending two-dimensionally along the b and c directions. Upon electrochemical reduction accompanied by Li insertion, the NR films show increasing absorbance mostly in the near infrared region. In contrast, the NPL films show increasing absorbance in the near infrared region first followed by increasing absorbance in both visible and near infrared regions. To elucidate the influence of shape anisotropy, we used density functional theory to construct the lithiated structures of monoclinic Nb₁₂O₂₉ and in these structures we identified the presence of square planar sites and crystallographic shear sites for Li insertion. By calculating the theoretical spectra of the lithiated structures, we demonstrate that the Li insertion into the square planar sites results in absorption in the near infrared region in both NRs and NPLs due to their extension in the b direction, while the subsequent insertion of Li into the crystallographic shear sites leads to absorption in both visible and near infrared regions, which only occurs in NPLs due to their extension in the c direction.

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

Concerns of petroleum dependence and environmental pollution prompt an urgent need for new sustainable approaches in developing polymeric products. Biobased polymers provide a potential solution, and biobased nanocomposites further enhance the performance and functionality of biobased polymers. Here we summarize the unique challenges and review recent progress in this field with an emphasis on self-assembly of inorganic nanoparticles. The conventional wisdom is to fully disperse nanoparticles in the polymer matrix to optimize the performance. However, self-assembly of the nanoparticles into clusters, networks, and layered structures provides an opportunity to address performance challenges and create new functionality in biobased polymers. We introduce basic assembly principles through both blending and in situ synthesis, and identify key technologies that benefit from the nanoparticle assembly in the polymer matrix. The fundamental forces and biobased polymer conformations are discussed in detail to correlate the nanoscale interactions and morphology with the macroscale properties. Different types of nanoparticles, their assembly structures and corresponding applications are surveyed. Through this review we hope to inspire the community to consider utilizing self-assembly to elevate functionality and performance of biobased materials. Development in this area sets the foundation for a new era of designing sustainable polymers in many applications including packaging, construction chemicals, adhesives, foams, coatings, personal care products, and advanced manufacturing.

Energy storage electrochromic devices in the era of intelligent automation

The current intelligent automation society faces increasingly severe challenges in achieving efficient storage and utilization of energy. In the field of energy applications, various energy technologies need to be more intelligent and efficient to produce, store, transform and save energy. In addition, many smart electronic devices facing the future also require newer, lighter, thinner and even transparent multi-functional power supplies. The unique properties of electrochromic energy storage devices (ECESDs) have attracted widespread attention. In the field of energy applications, they have high potential value and competitiveness. This review focuses on the electrochromic basic principles, and the latest technological examples of ECESDs, which are related to materials and device structures. Simultaneously, this review makes a detailed comparison and summary of example performances. Moreover, the review compares the current mainstream energy storage devices: lithium batteries and supercapacitors, and the main challenges of ECESDs are discussed. Finally, the future development directions in the field of electrochromic energy storage are predicted.

Manipulating atomic defects in plasmonic vanadium dioxide for superior solar and thermal management

Vanadium dioxide (VO₂) is a unique active plasmonic material due to its intrinsic metal-insulator transition, remaining less explored. Herein, we pioneer a method to tailor the VO₂ surface plasmon by manipulating its atomic defects and establish a universal quantitative understanding based on seven representative defective VO₂ systems. Record high tunability is achieved for the localized surface plasmon resonance (LSPR) energy (0.66-1.16 eV) and transition temperature range (40-100 °C). The Drude model and density functional theory reveal that the charge of cations plays a dominant role in the numbers of valence electrons to determine the free electron concentration. We further demonstrate their superior performances in extensive unconventional plasmonic applications including energy-saving smart windows, wearable camouflage devices, and encryption inks.

Jelly-Inspired Injectable Guided Tissue Regeneration Strategy with Shape Auto-Matched and Dual-Light-Defined Antibacterial/Osteogenic Pattern Switch Properties

Periodontitis is a bacterial infectious disease leading to the loss of periodontal supporting tissues and teeth. The current guided tissue regeneration (GTR) membranes for periodontitis treatments cannot effectively promote tissue regeneration for the limited antibacterial properties and the excessively fast degradation rate. Besides, they need extra tailoring according to variform defects before implantation, leading to imprecise match. This study proposed an injectable sodium alginate hydrogel composite (CTP-SA) doped with cubic cuprous oxide (Cu₂O) and polydopamine-coated titanium dioxide (TiO₂@PDA) nanoparticles for GTR. Inspired by the gelation process of the jelly, the phase change (liquid to solid) of CTP-SA after injection could automatch variform bone defects. Meanwhile, CTP-SA exhibited broad-spectrum antibacterial capabilities under blue light (BL) irradiation, including Streptococcus mutans (one of the most abundant bacteria in oral biofilms). Moreover, the reactive oxygen species released under BL excitation could accelerate the oxidation of Cu⁺ to Cu²⁺. Afterward, osteogenesis could be enhanced through two factors simultaneously: the stimulation of newly formed Cu²⁺ and the photothermal effect of CTP-SA under near-infrared (NIR) irradiation. Collectively, through this dual-light (blue and NIR) noninvasive regulation, CTP-SA could switch antibacterial and osteogenic modes to address requirements of patients at different healing stages, thereby realizing the customized GTR procedures.

Plasmonic Oxygen-Deficient TiO2-x Nanocrystals for Dual-Band Electrochromic Smart Windows with Efficient Energy Recycling

Dual-band electrochromic smart windows capable of the spectrally selective modulation of visible (VIS) light and near-infrared (NIR) can regulate solar light and solar heat transmittance to reduce the building energy consumption. The development of these windows is however limited by the number of available dual-band electrochromic materials. Here, plasmonic oxygen-deficient TiO_2-x nanocrystals (NCs) are discovered to be an effective single-component dual-band electrochromic material, and that oxygen-vacancy creation is more effective than aliovalent substitutional doping to introduce dual-band properties to TiO₂ NCs. Oxygen vacancies not only confer good near-infrared (NIR)-selective modulation, but also improve the Li⁺ diffusion in the TiO_2-x host, circumventing the disadvantage of aliovalent substitutional doping with ion diffusion. Consequently optimized TiO_2-x NC films are able to modulate the NIR and visible light transmittance independently and effectively in three distinct modes with high optical modulation (95.5% at 633 nm and 90.5% at 1200 nm), fast switching speed, high bistability, and long cycle life. An impressive dual-band electrochromic performance is also demonstrated in prototype devices. The use of TiO_2-x NCs enables the assembled windows to recycle a large fraction of energy consumed in the coloration process ("energy recycling") to reduce the energy consumption in a round-trip electrochromic operation.

Synthesis and Dual-Mode Electrochromism of Anisotropic Monoclinic Nb12O29 Colloidal Nanoplatelets

Transition metal oxide nanocrystals with dual-mode electrochromism hold promise for smart windows enabling spectrally selective solar modulation. We have developed the colloidal synthesis of anisotropic monoclinic Nb₁₂O₂₉ nanoplatelets (NPLs) to investigate the dual-mode electrochromism of niobium oxide nanocrystals. The precursor for synthesizing NPLs was prepared by mixing NbCl₅ and oleic acid to form a complex that was subsequently heated to form an oxide-like structure capped by oleic acid, denoted as niobium oxo cluster. By initiating the synthesis using niobium oxo clusters, preferred growth of NPLs over other polymorphs was observed. The structure of the synthesized NPLs was examined by X-ray diffraction in conjunction with simulations, revealing that the NPLs are monolayer monoclinic Nb₁₂O₂₉, thin in the [100] direction and extended along the b and c directions. Besides having monolayer thickness, NPLs show decreased intensity of Raman signal from Nb-O bonds with higher bond order when compared to bulk monoclinic Nb₁₂O₂₉, as interpreted by calculations. Progressive electrochemical reduction of NPL films led to absorbance in the near-infrared region (stage 1) followed by absorbance in both the visible and near-infrared regions (stage 2), thus exhibiting dual-mode electrochromism. The mechanisms underlying these two processes were distinguished electrochemically by cyclic voltammetry to determine the extent to which ion intercalation limits the kinetics, and by verifying the presence of localized electrons following ion intercalation using X-ray photoelectron spectroscopy. Both results support that the near-infrared absorption results from capacitive charging, and the onset of visible absorption in the second stage is caused by ion intercalation.

Electrically Activated UV-A Filters Based on Electrochromic MoO3-x

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO₃ and WO₃ are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO_3-x-based electrically activated ultraviolet (UV) filters. The MoO_3-x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H⁺ injection/extraction in MoO_3-x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325-800 nm), with a peak of ∼60% in the UV-A range (350-392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm² C^-1 are achieved.

Enhanced Coloration Efficiency of Electrochromic Tungsten Oxide Nanorods by Site Selective Occupation of Sodium Ions

Coloration efficiency is an important figure of merit in electrochromic windows. Though it is thought to be an intrinsic material property, we tune optical modulation by effective utilization of ion intercalation sites. Specifically, we enhance the coloration efficiency of m-WO_2.72 nanocrystal films by selectively intercalating sodium ions into optically active hexagonal sites. To accurately measure coloration efficiencies, significant degradation during cycling is mitigated by introducing atomic-layer-deposited Al₂O₃ layers. Galvanostatic spectroscopic measurement shows that the site-selective intercalation of sodium ions in hexagonal tunnels enhances the coloration efficiency compared to a nonselective lithium ion-based electrolyte. Electrochemical rate analysis shows insertion of sodium ions to be capacitive-like, another indication of occupying hexagonal sites. Our results emphasize the importance of different site occupation on spectroelectrochemical properties, which can be used for designing materials and selecting electrolytes for enhanced electrochromic performance. In this context, we suggest sodium ion-based electrolytes hold unrealized potential for tungsten oxide electrochromic applications.

TiO2 Nanostructured Films for Electrochromic Paper Based-Devices

Electrochromic titanium dioxide (TiO2) nanostructured films were grown on gold coated papers using a microwave-assisted hydrothermal method at low temperature (80 °C). Uniform nanostructured films fully covered the paper substrate, while maintaining its flexibility. Three acids, i.e., acetic, hydrochloric and nitric acids, were tested during syntheses, which determined the final structure of the produced films, and consequently their electrochromic behavior. The structural characteristics of nanostructured films were correlated with electrochemical response and reflectance modulation when immersed in 1 M LiClO4-PC (lithium perchlorate with propylene carbonate) electrolyte, nevertheless the material synthesized with nitric acid resulted in highly porous anatase films with enhanced electrochromic performance. The TiO2 films revealed a notable contrast behavior, reaching for the nitric-based film optical modulations of 57%, 9% and 22% between colored and bleached states, at 250, 550 and 850 nm, respectively in reflectance mode. High cycling stability was also obtained performing up to 1500 cycles without significant loss of the electrochromic behavior for the nitric acid material. The approach developed in this work proves the high stability and durability of such devices, together with the use of paper as substrate that aggregates the environmentally friendly, lightweight, flexibility and recyclability characters of the substrate to the microwave synthesis features, i.e., simplicity, celerity and enhanced efficiency/cost balance.

Dual-Band Electrochromic Devices with a Transparent Conductive Capacitive Charge-Balancing Anode

Dual-band electrochromic devices (DBEDs), which can selectively modulate near-infrared (NIR) and visible (VIS) light transmittance through electrochromism, have gained increasing interest as a building energy saving technology. The technology is strongly dependent on the progress in electrochromic materials. Most current research has focused on the dual-band properties of the cathode materials, leaving the charge-balancing anode materials under-explored by comparison. This is a report of our study on the suitability of tin-doped indium oxide (ITO) nanocrystals (NCs) as a capacitive anode material for DBEDs. The ITO NCs are electrically conductive and VIS light transparent throughout the device operating range. As a result, they would not affect the NIR-selective modulation of the electrochromic device like most other anode materials do. The high surface area and good conductivity of the ITO NCs facilitate the adsorption/desorption of anions; thereby increasing their effectiveness as an ion storage thin film on the anode to balance the cathode charge. The best DBED prototype assembled from an ITO NC anode and a WO_3-x cathode showed effective and independent control of VIS light and NIR transmittance with high optical modulation (71.1% at 633 nm, 58.1% at 1200 nm), high coloration efficiency (95 cm² C^-1 at 633 nm, 220 cm² C^-1 at 1200 nm), fast switching speed, good bistability, and cycle stability.

Tunable Near-Infrared Localized Surface Plasmon Resonance of F, In-Codoped CdO Nanocrystals

Nanocrystals (NCs) of transparent conducting oxides with a localized surface plasmon resonance (LSPR) in the near-infrared (NIR) spectral region show promising electrochromic properties for the development of a new generation of dynamic "smart windows". In this regard, we exploit thin films of F, In-codoped CdO (FICO) NCs as active coatings for electrochromic devices. The control over the dopants concentration in FICO NCs results in fine tuning of their LSPR across the NIR region of the electromagnetic spectrum. Highly transparent mesoporous electrodes were prepared from colloidal FICO NCs by in situ ligand exchange of the pristine organic capping ligands. This approach preserves the optical and electrical properties of native NCs and delivers highly homogeneous, nonscattering films with a good electronic coupling between the NCs. We achieved a dynamic control over the LSPR frequency by reversible electrochemical doping, hence a spectrally selective modulation of the optical transmittance in the NIR region of the solar spectrum, which carries nearly 50% of the whole solar heat. Spectroelectrochemical characterization, coloration efficiency, and switching kinetics results indicate that thin film based on FICO NCs are potential candidates for plasmonic electrochromic applications. Moreover, the high electron mobility and wide optical bandgap of FICO makes NCs of this material suitable for large-area devices capable of dynamically controlling the heat load coming from the solar infrared radiation, without affecting the visible light transmittance.

Multifunctional Polypyrrole-Coated Mesoporous TiO2 Nanocomposites for Photothermal, Sonodynamic, and Chemotherapeutic Treatments and Dual-Modal Ultrasound/Photoacoustic Imaging of Tumors

TiO₂ nanoparticles have emerged as satisfactory sonosensitizers in sonodynamic therapy over the years, but shortcomings such as poor drug loading capability and inadequate techniques to construct suitable TiO₂ nanoparticles, limit their broader applications. Hence, in this paper, versatile nanocomposites that combine mesoporous TiO₂ nanoparticles (mTiO₂ s) with the promising photothermal material, polypyrrole (PPY) to exert synergistic therapeutic effects on tumors are fabricated. The PPY-coated mesoporous TiO₂ nanocomposites (mTiO₂ @PPYs) act as drug delivery vehicles and ultrasonically activated sonosensitizers as well as photothermal agents. Besides, mTiO₂ @PPY may have potential as an ultrasound/photoacoustic (US/PA) imaging contrast agent. The mTiO₂ @PPY shows a favorable drug loading and good photothermal conversion ability. Moreover, intracellular reactive oxygen species generation is verified. The in vitro cell experiments on HepG2 and 4T1 cells demonstrate that honokiol (HNK)-loaded mTiO₂ @PPY has satisfactory cytotoxicity under laser and US irradiation, and the results are further validated by animal experiments. The ability of mTiO₂ @PPY as a contrast agent for US and PA imaging is investigated both in vitro and in vivo. The results indicate that mTiO₂ @PPY-HNK has multitherapeutic effects and bimodal imaging property, which shows great prospect as a novel nanosystem in antitumor applications.

Niobium doped tungsten oxide mesoporous film with enhanced electrochromic and electrochemical energy storage properties

Exploring high performance cathode materials is of great means for the development of bi-functional electrochromic energy storage devices. Herein, Nb-doped WO₃ mesoporous films as integrated high-quality cathode are successfully constructed via a facile sol-gel method. Chemical state and crystallinity of the WO₃ based films are significantly influenced by doping concentration. Compared with the pure WO₃, the optimal Nb-doped film shows improved optical-electrochemical properties with high specific capacity (74.4 mAh g^-1 at 2 A g^-1), excellent high-rate capability, large optical contrast (61.7% at 633 nm), and ultra-fast switching speed (3.6 s and 2.1 s for coloring and bleaching process, respectively). These positive features suggest the potential application of Nb-doped WO₃ mesoporous cathode. Our research paves the way for the development of multifunctional photoelectrochemical energy devices.

Ultrafine Ceramic Grains Embedded in Metallic Glass Matrix: Achieving Superior Wear Resistance via Increase in Both Hardness and Toughness

As structural materials, crystalline or metallic glass materials have attracted scientific and practical interests. However, some mechanisms involving critical size and shear bands have adverse effects on their mechanical properties. Here, we counter these two effects by introducing a special structure with ultrafine ceramic grains (with a diameter of ∼2.0 nm) embedded into a metallic glass matrix, wherein the grains are mainly composed of a Ta-W-N solid solution structure in nature, surrounded by a W-based amorphous matrix that contains Ta and N atoms. Such a structure is in situ formed during preparation, which combines the merits of both phases to achieve simultaneous increase in hardness and toughness relative to references (pure TaN and W) and thus superior wear resistance. Even more remarkable, a favorable variation of increased hardness but reduced elasticity modulus can be induced by this structure. Intrinsically, ultrafine ceramic grains (free of dislocations), embedded in the metallic glass matrix, could prevent shear band propagation within the glass matrix and further improve the hardness of the matrix material. In return, such glass matrix allows for stiffness neutralization and structural relaxation to reduce the elasticity modulus of ceramic grains. This study will offer a new guidance to fabricate ultrahigh-performance metal-based composites.

Efficient Charge Separation in Plasmonic ZnS@Sn:ZnO Nanoheterostructure: Nanoscale Kirkendall Effect and Enhanced Photophysical Properties

Tetravalent Sn doped ZnO nanocrystals show excellent plasmonic absorbance in the visible region. Plasmonic ZnS@Sn:ZnO core-shell heterostructures have been synthesized by the anion exchange process where the O^2- is exchanged by S^2- anion. An increase of sulfur concentration induces interior hollow structures arising from the different diffusion rates of O^2- and S^2- ions. Gradual transformation of wurtztie ZnO nanocrystals in the anion exchange process stabilizes the wurtzite crystalline phase of ZnS. Carrier concentration and various types of intrinsic defect states in both ZnO and ZnS result in ultraviolet, blue, and green emissions. The coexistence of exciton-plasmon coupling in the same nanoparticle and efficient electron-hole separation in type II heterostructure increases the photocatalytic activity and photo current gain.