Sustainable, low-cost, high-contrast electrochromic displays via host-guest interactions.

Electrochromic (EC) displays with electronically regulating the transmittance of solar radiation offer the opportunity to increase the energy efficiency of the building and electronic products and improve the comfort and lifestyle of people. Despite the unique merit and vast application potential of EC technologies, long-awaited EC windows and related visual content displays have not been fully commercialized due to unsatisfactory production cost, durability, color, and complex fabrication processes. Here we develop a unique EC strategy and system based on the natural host and guest interactions to address the above issues. A completely reusable and sustainable EC device has been fabricated with potential advantages of extremely low cost, ideal user-/environment friendly property, and excellent optical modulation, which is benefited from the extracted biomass EC materials and reusable transparent electrodes involved in the system. The as-prepared EC window and nonemissive transparent display also show comprehensively excellent properties: high transmittance change (>85%), broad spectra modulation covering Ultraviolet (UV), Visible (Vis) to Infrared (IR) ranges, high durability (no attenuation under UV radiation for more than 1.5 mo), low open voltage (0.9 V), excellent reusability (>1,200 cycles) of the device's key components and reversibility (>4,000 cycles) with a large transmittance change, and pleasant multicolor. It is anticipated that unconventional exploration and design principles of dynamic host-guest interactions can provide unique insight into different energy-saving and sustainable optoelectronic applications.

Bistable Electrochromic Ionogels via Supramolecular Interactions for Energy-Efficient Displays.

Bistable electrochromic (EC) materials and systems offer significant potential for building decarbonization through their optical modulation and energy efficiency. However, challenges such as limited design strategies and bottlenecks in cost, fabrication, and color have hindered the full commercialization of energy-saving EC windows and displays, with few materials achieving true bistability. Herein, a novel strategy for designing bistable electrochromic materials is proposed by leveraging supramolecular interactions. These interactions facilitate reversible color transitions, stabilize the colored structure, and enable spatial confinement to inhibit diffusion, thereby achieving bistable electrochromism. The mechanisms and materials underlying these unconventional electrochromic systems are substantiated through detailed characterization. This strategy enables the preparation of low-cost and sustainable transparent electrochromic displays with high performance. Notably, the display information remains clearly visible for more than 2 hours without consuming energy. Involving biomass materials and removable device structures also enhances the sustainability and scalability of EC technology applications and development. Our results demonstrate the crucial role of supramolecular chemistry in the development of cutting-edge materials for applications such as energy-saving smart windows. This article is protected by copyright. All rights reserved.

Molecularly confined hydration in thermoresponsive hydrogels for efficient atmospheric water harvesting.

Water scarcity is a pressing global issue, requiring innovative solutions such as atmospheric water harvesting (AWH), which captures moisture from the air to provide potable water to many water-stressed areas. Thermoresponsive hydrogels, a class of temperature-sensitive polymers, demonstrate potential for AWH as matrices for hygroscopic components like salts predominantly due to their relatively energy-efficient desorption properties compared to other sorbents. However, challenges such as limited swelling capacity due to the salting-out effect and difficulty in more complete water release hinder the effectiveness of conventional hydrogel sorbents. To overcome these limitations, we introduce molecularly confined hydration in thermoresponsive hydrogels by employing a bifunctional polymeric network composed of hygroscopic zwitterionic moieties and thermoresponsive moieties. Here, we show that this approach ensures stable water uptake, enables water release at relatively low temperatures, and exhibits rapid sorption-desorption kinetics. Furthermore, by incorporating photothermal absorbers, the sorbent can achieve solar-driven AWH with comparable water release performance. This work advances the design of AWH sorbents by introducing molecularly confined hydration in thermoresponsive hydrogels, leading to a more efficient and sustainable approach to water harvesting. Our findings offer a potential solution for advanced sorbent design with comprehensive performance to mitigate the freshwater crisis.

Hygroscopic-Microgels-Enabled Rapid Water Extraction from Arid Air.

Sorbent-based atmospheric water harvesting (AWH) has emerged as a promising decentralized water-production technology to mitigate the freshwater crisis in arid areas. Hydrogels have been regarded as attractive sorbents due to their high water retention and tailorable polymer-water interactions. Yet, the kinetics of water sorption and desorption at low relative humidity (RH) shall be improved for their practical implementation. Here, hygroscopic microgels (HMGs) composed of hydroxypropyl cellulose (HPC) and hygroscopic salt are reported, which achieve a water uptake of ca. 0.5-0.8 g g-1 at 15-30% RH. HMGs enable rapid sorption-desorption kinetics owing to the short-distance diffusion in the microgels and hydrophilicity-hydrophobicity switching of the thermoresponsive HPC. To validate the feasibility of HMGs for moisture extraction, a potential daily water collection of up to equivalent 7.9-19.1 L kg-1 at low RH is demonstrated, enabled by 24-36 operation cycles per day based on the material-level experiments. With renewable raw materials and superior performance, HMGs provide a sustainable approach for rapid moisture extraction in arid climates.

Sorbents for Atmospheric Water Harvesting: From Design Principles to Applications.

Water scarcity caused by climate change and population growth poses a grave threat to human society. Of the different water purification technologies put forward, one presents a promising strategy that is spatially or temporally non-restricted-atmospheric water harvesting (AWH). Here we review recent progress in the design and study of AWH sorbents, ranging from the innovative chemistries to the integration of sophisticated architectures and functional components, and clarify the structure-property-performance relationship that governs the water capture and release processes. Features and limitations of each type of sorbents are summarized to elucidate the optimal working environments and modes. Progress in applications extending from water generation to thermal management and agriculture are discussed. Future developments regarding material modifications, performance measurements, and system optimizations are provided to overcome lingering barriers to sorbent design and implementation.

Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates.

The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from the ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake by salt-based sorbents makes them attractive for AWH, especially in arid environments. However, they often have relatively high desorption heat, rendering water release an energy-intensive process. A  LiCl-incorporating polyacrylamide hydrogel (PAM-LiCl) capable of effective moisture harvesting from arid environments is proposed. The interactions between the hydrophilic hydrogel network and the captured water generate more free and weakly bonded water, significantly lowering the desorption heat compared with conventional neat salt sorbents. Benefiting from the affinity for swelling of the polymer backbones, the developed PAM-LiCl achieves a high water uptake of ≈1.1 g g-1 at 20% RH with fast sorption kinetics of ≈0.008 g g-1  min-1  and further demonstrates a daily water yield up to ≈7 g g-1 at this condition. These findings provide a new pathway for the synthesis of materials with efficient water absorption/desorption properties, to reach energy-efficient water release for AWH in arid climates.

Polyzwitterionic Hydrogels for Highly Efficient High Salinity Solar Desalination.

Interfacial solar vapor generation (SVG) is regarded as a promising and sustainable strategy for clean water production. While many materials have demonstrated excellent evaporation rates under one sun, it remains challenging to design solar evaporators without compromising SVG performance in high-salinity brines (≥10 wt %). Herein, polyzwitterionic hydrogels (PZHs) are proposed as a novel platform for high-salinity solar desalination. Taking advantage of the unique anti-polyelectrolyte effects, PZHs can trap salt ions from the brine water to form a more hydrated polymer network, leading to enhanced SVG performance. PZHs exhibit an exceptional solar evaporation rate of 4.14 kg m-2 h-1 in 10 wt % brine, which is ≈20 % higher than that in pure water. It is anticipated that salt-responsive PZHs may provide insights for the design of next-generation solar desalination systems.

Scalable super hygroscopic polymer films for sustainable moisture harvesting in arid environments.

Extracting ubiquitous atmospheric water is a sustainable strategy to enable decentralized access to safely managed water but remains challenging due to its limited daily water output at low relative humidity (≤30% RH). Here, we report super hygroscopic polymer films (SHPFs) composed of renewable biomasses and hygroscopic salt, exhibiting high water uptake of 0.64-0.96 g g-1 at 15-30% RH. Konjac glucomannan facilitates the highly porous structures with enlarged air-polymer interfaces for active moisture capture and water vapor transport. Thermoresponsive hydroxypropyl cellulose enables phase transition at a low temperature to assist the release of collected water via hydrophobic interactions. With rapid sorption-desorption kinetics, SHPFs operate 14-24 cycles per day in arid environments, equivalent to a water yield of 5.8-13.3 L kg-1. Synthesized via a simple casting method using sustainable raw materials, SHPFs highlight the potential for low-cost and scalable atmospheric water harvesting technology to mitigate the global water crisis.

A Universal Mechanochemistry Allows On-Demand Synthesis of Stable and Processable Liquid Metal Composites.

Gallium-based liquid metal (LM) is regarded as one of the most promising candidates for the new-generation jigsaw of stretchable electronics. Nonetheless, the obstacle for the LM application lies in its high surface tension and easy fluidity which leads to great difficulty in handling and processing. Herein, a cross-mechanochemistry between liquid metal and inorganic solid, mediated via the coordination binding between the empty electronic orbits of the former and the lone electron pair of the latter is reported. The mechanism is validated via density functional theory calculation and electron energy loss spectroscopy, and experimentally proven to be universally applicable for various liquid metals and inorganic solids. With the unique mechanochemistry, simple ball milling allows on-demand transformation of the liquid metal into a low-surface-tension liquid, semi-solid paste, or even solid powder. The overcoming of the intrinsic high surface tension of the liquid metal with this approach unleashes the freedom to easily process the liquid metal composites into polymer composites or as direct molding processable paste and printable electronic ink.

Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives.

Atmospheric water harvesting (AWH) is emerging as a promising strategy to produce fresh water from abundant airborne moisture to overcome the global clean water shortage. The ubiquitous moisture resources allow AWH to be free from geographical restrictions and potentially realize decentralized applications, making it a vital parallel or supplementary freshwater production approach to liquid water resource-based technologies. Recent advances in regulating chemical properties and micro/nanostructures of moisture-harvesting materials have demonstrated new possibilities to promote enhanced device performance and new understandings. This perspective aims to provide a timely overview on the state-of-the-art materials design and how they serve as the active components in AWH. First, the key processes of AWH, including vapor condensation, droplet nucleation, growth, and departure are outlined, and the desired material properties based on the fundamental mechanisms are discussed. Then, how tailoring materials-water interactions at the molecular level play a vital role in realizing high water uptake and low energy consumption is shown. Last, the challenges and outlook on further improving AWH from material designs and system engineering aspects are highlighted.

Polyzwitterionic Hydrogels for Efficient Atmospheric Water Harvesting.

Atmospheric water harvesting (AWH) is regarded as one of the promising strategies for freshwater production desirable to provide sustainable water for landlocked and arid regions. Hygroscopic materials have attracted widespread attention because of their water harvesting performance. However, the introduction of many inorganic salts often leads to aggregation and leakage issues in practical use. Here, polyzwitterionic hydrogels are developed as an effective AWH material platform. Via anti-polyelectrolyte effects, the hygroscopic salt coordinated with polymer chains could capture moisture and enhance the swelling property, leading to a strong moisture sorption capacity. The hydrogel shows superior AWH performance (0.62 g g-1 , 120 minutes for equilibrium at 30 % relative humidity) and produces 5.87 L kg-1 freshwater per day. It is anticipated that the polyzwitterionic hydrogels with unique salt-responsive properties could provide new insights into the design and synthesis of next-generation AWH materials.

Controlled Vertically Aligned Structures in Polymer Composites: Natural Inspiration, Structural Processing, and Functional Application.

Vertically aligned structures, which are a series of characteristic conformations with thickness-direction alignment, interconnection, or assembly of filler in polymeric composite materials that can provide remarkable structural performance and advanced anisotropic functions, have attracted considerable attention in recent years. The past two decades have witnessed extensive development with regard to universal fabrication methods, subtle control of morphological features, improvement of functional properties, and superior applications of vertically aligned structures in various fields. However, a systematic review remains to be attempted. The various configurations of vertical structures inspired from biological samples in nature, such as vertically aligned structures with honeycomb, reed, annual ring, radial, and lamellar configurations are summarized here. Additionally, relevant processing methods, which include the transformation of oriented direction, external-field inducement, template method, and 3D printing method, are discussed in detail. The diverse applications in mechanical, thermal, electric, dielectric, electromagnetic, water treatment, and energy fields are also highlighted by providing representative examples. Finally, future opportunities and prospects are listed to identify current issues and potential research directions. It is expected that perspectives on the vertically aligned structures presented here will contribute to the research on advanced multifunctional composites.

Fully Organic Bulk Polymer with Metallic Thermal Conductivity and Tunable Thermal Pathways.

Electrically insulating polymers are indispensable for electronic and energy applications, but their poor thermal conduction has increasingly become a bottleneck for high-performance devices. Highly drawn low-dimensional polymeric fibers and thin films can exhibit metallic conductivity. Extending this to bulk materials required by real world applications is prohibitive due to the additional interfacial thermal conduction barriers. It is demonstrated that highly aligned ultrahigh molecular weight polyethylene microfibers can be incorporated into a silicone matrix to yield a fully organic bulk polymer composite with a continuous vertical phonon pathway. This leads to a perpendicular thermal conductivity of 38.27 W m-1 K-1 , at par with metals and two orders of magnitude higher than other bulk organic polymers. Taking further advantage of the mechanical flexibility of the microfibers, the processing method offers the freedom to tailor heat transfer pathways in a macroscopic 3D space. The material/process opens up opportunities for efficient thermal management in high-performance devices.

A Multidirectionally Thermoconductive Phase Change Material Enables High and Durable Electricity via Real-Environment Solar-Thermal-Electric Conversion.

A solar thermoelectric generator (STEG) that generates electricity from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. The integration of a phase-change material (PCM) with the STEG even more enables engines to durably generate power in spite of solar radiation flux. However, its photothermal conversion and output electricity is still limited (<15 W/m2) by the PCM's deficient thermal management performance, i.e., restricted thermal conductivity and nonuniform heat-transfer behavior under concentrated sunlight radiation. In this study, a biomimetic phase-change composite, with centrosymmetric and a multidirectionally aligned boron nitride network embedded in polyethylene glycol, is tailored for the STEG via a radial ice-template assembly and infiltration strategy, which behaves in a highly and multidirectionally thermoconductive way and enables a rapid transfer of heat flux and uniform temperature distribution with respect to even a spot-like heat source. As a consequence, a powerful STEG is tactfully designed via the integration of this high-thermal-management characteristic and maximum collection of solar beams, for durable and real-environment solar-thermal-electric conversion, with its photothermal energy conversion efficiency of up to 85.1% and a high peak power density of 40.28 W/m2.

Metal-Level Robust, Folding Endurance, and Highly Temperature-Stable MXene-Based Film with Engineered Aramid Nanofiber for Extreme-Condition Electromagnetic Interference Shielding Applications.

Polymer-based electromagnetic interference (EMI) shielding materials possess many irreplaceable advantages than metals, such as superior flexibility, easy processing, and low density. However, impeded by their limited mechanical properties, inferior temperature resistance and unsatisfactory electrical conductivity, it is still challenging to extend their shielding applications under some extreme conditions, i.e., <-50 or >200 °C. Herein, we report an ultrathin, highly robust, superflexible, and temperature-stable film via engineering a worm-like aramid nanofiber (ANF) into the rod-like microscopic configuration, followed with self-assembly with Ti3C2Tx (MXene) into a hierarchical brick-and-mortar architecture. With stiff and symmetric aromatic rings fully straightened and well packed into a crystalline form in the backbone, this rod-like ANF enables an augmented network with effective energy dissipation, resulting in the metal-like mechanical properties, i.e., unprecedented tensile strength (300.5 MPa), high Young's modulus (13.6 GPa), and excellent folding endurance (>10 000 times). More significantly, this MXene/ANF composite film with outstanding specific EMI shielding effectiveness (8814.5 dB cm2 g-1) and flame retardancy performs a broad range of operations in the temperature range from -100 °C (355 MPa) to 300 °C (136 MPa), in which >99% electromagnetic waves could be eliminated; this promises its potential EMI shielding applications even in some extreme conditions.

Highly Thermoconductive, Thermostable, and Super-Flexible Film by Engineering 1D Rigid Rod-Like Aramid Nanofiber/2D Boron Nitride Nanosheets.

Polymer-based thermal management materials have many irreplaceable advantages not found in metals or ceramics, such as easy processing, low density, and excellent flexibility. However, their limited thermal conductivity and unsatisfactory resistance to elevated temperatures (<200 °C) still prevent effective heat dissipation during applications with high-temperature conditions or powerful operation. Therefore, herein highly thermoconductive and thermostable polymer nanocomposite films prepared by engineering 1D aramid nanofiber (ANF) with worm-like microscopic morphologies into rigid rod-like structures with 2D boron nitride nanosheets (BNNS) are reported. With no coils or entanglements, the rigid polymer chain enables a well-packed crystalline structure resulting in a 20-fold (or greater) increase in axial thermal conductivity. Additionally, strong interfacial interactions between the weaved ANF rod and the stacked BNNS facilitate efficient heat flux through the 1D/2D configuration. Hence, unprecedented in-plane thermal conductivities as high as 46.7 W m-1 K-1 can be achieved at only 30 wt% BNNS loading, a value of 137% greater than that of a worm-like ANF/BNNS counterpart. Moreover, the thermally stable nanocomposite films with light weight (28.9 W m-1 K-1 /103 (kg m-3 )) and high strength (>100 MPa, 450 °C) enable effective thermal management for microelectrodes operating at temperatures beyond 200 °C.

Green Production of Regenerated Cellulose/Boron Nitride Nanosheet Textiles for Static and Dynamic Personal Cooling.

Personal cooling technology using functional clothing that could provide localized thermal regulation instead of cooling the entire space is regarded as a highly anticipated strategy to not only facilitate thermal comfort and human health but also be energy-saving and low-cost. The challenge is how to endow textiles with prominent cooling effect whenever the wearer is motionless or sportive. In this study, high content of edge-selective hydroxylated boron nitride nanosheets (BNNSs) up to 60 wt % was added into a biodegradable cellulose/alkaline/urea aqueous solution, and then regenerated cellulose (RCF)/BNNS multifilaments were successfully spun in a simple, low-cost, and environmentally friendly process, which was demonstrated to serve as both static and dynamic personal cooling textile. Typically, excellent axial thermal conductivity of RCF/BNNS filament rendered that body-generated heat could directly escape from skin to the outside surface of the textile by means of thermal conduction, achieving a much better static personal cooling result through continuous thermal radiation. Besides, synergistic effect between excellent heat dissipation capability and good hygroscopicity also resulted in much better dynamic cooling effect once the wearer is doing some sports, whose efficiency was even better than commercial hygroscopic textiles such as cotton and RCF.

Design and Preparation of a Unique Segregated Double Network with Excellent Thermal Conductive Property.

It is still a challenge to fabricate polymer-based composites with excellent thermal conductive property because of the well-known difficulties such as insufficient conductive pathways and inefficient filler-filler contact. To address this issue, a synergistic segregated double network by using two fillers with different dimensions has been designed and prepared by taking graphene nanoplates (GNPs) and multiwalled carbon nanotubes (MWCNT) in polystyrene for example. In this structure, GNPs form the segregated network to largely increase the filler-filler contact areas while MWCNT are embedded within the network to improve the network-density. The segregated network and the randomly dispersed hybrid network by using GNPs and MWCNT together were also prepared for comparison. It was found that the thermal conductivity of segregated double network can achieve almost 1.8-fold as high as that of the randomly dispersed hybrid network, and 2.2-fold as that of the segregated network. Meanwhile, much higher synergistic efficiency (f) of 2 can be obtained, even greater than that of other synergistic systems reported previously. The excellent thermal conductive property and higher f are ascribed to the unique effect of segregated double network: (1) extensive GNPs-GNPs contact areas via overlapped interconnections within segregated GNPs network; (2) efficient synergistic effect between MWCNT network and GNPs network based on bridge effect as well as increasing the network-density.