High conductivity, large mechanical strength, and elongation are important parameters for soft electronic applications. However, it is difficult to find a material with balanced electronic and mechanical performance. Here, a simple method is developed to introduce ion-rich pores into strong hydrogel matrix and fabricate a novel ionic conductive hydrogel with a high level of electronic and mechanical properties. The proposed ionic conductive hydrogel is achieved by physically cross-linking the tough biocompatible polyvinyl alcohol (PVA) gel as the matrix and embedding hydroxypropyl cellulose (HPC) biopolymer fibers inside matrix followed by salt solution soaking. The wrinkle and dense structure induced by salting in PVA matrix provides large stress (1.3 MPa) and strain (975%). The well-distributed porous structure as well as ion migration-facilitated ion-rich environment generated by embedded HPC fibers dramatically enhances ionic conductivity (up to 3.4 S m −1 , at f = 1 MHz). The conductive hybrid hydrogel can work as an artificial nerve in a 3D printed robotic hand, allowing passing of stable and tunable electrical signals and full recovery under robotic hand finger movements. This natural rubber-like ionic conductive hydrogel has a promising application in artificial flexible electronics.

A smart window that dynamically modulates light transmittance is crucial for building energy efficiently, and promising for on‐demand optical devices. The rapid development of technology brings out different categories that have fundamentally different transmittance modulation mechanisms, including the electro‐, thermo‐, mechano‐, and photochromic smart windows. In this review, recent progress in smart windows of each category is overviewed. The strategies for each smart window are outlined with particular focus on functional materials, device design, and performance enhancement. The advantages and disadvantages of each category are summarized, followed by a discussion of emerging technologies such as dual stimuli triggered smart window and integrated devices toward multifunctionality. These multifunctional devices combine smart window technology with, for example, solar cells, triboelectric nanogenerators, actuators, energy storage devices, and electrothermal devices. Lastly, a perspective is provided on the future development of smart windows.

A passive turnoff Passive radiative cooling technology uses the infrared atmospheric window to allow outer space to be a cold sink for heat. However, this effect is one that is only helpful for energy savings in the warmer months. Wang et al . and Tang et al . used the metal-insulator transition in tungsten-doped vanadium dioxide to create window glass and a rooftop coating that circumvents this problem by turning off the radiative cooling at lower temperatures. Because the transition is simply temperature dependent, this effect also happens passively. Model simulations suggest that these materials would lead to energy savings year-round across most of the climate zones in the United States. —BG

Thermally responsive hydrogel with a transition temperature of ~32 °C was for the first time studied as a novel candidate in thermochromic application. Unprecedented solar modulating ability (ΔTsol) of 25.5% and high average luminance transmittance (Tlum) of 70.7% were achieved.

Architectural windows that smartly regulate indoor solar radiation by changing their optical transmittance in response to thermo-stimuli have been developed as a promising solution toward reducing the energy consumption of buildings. Recently, energy-efficient smart window technology has attracted increasing scientific interest, with the exploration of energyefficient novel materials as well as integration with practical techniques to generate various desired multi-functionalities. This review systematically summarizes emerging thermoresponsive materials for smart window applications, including hydrogels, ionic liquids, perovskites, metamaterials, and liquid crystals. These are compared with vanadium dioxide (VO2), a conventional and extensively studied material for thermochromic smart window applications. In addition, recent progress on cutting-edge integrated techniques for smart windows is covered, including electro-thermal techniques, self-cleaning, wettability and also 2 integration with solar cells for bifunctional energy conservation and generation. Finally, opportunities and challenges relating to thermochromic smart windows and prospects for future development are discussed. features (Figure 1b); (2) passivity, with their automatic response to temperature cutting down the need for switch systems, for example electrical control requiring external energy and human manipulation; (3) rational stimulus-response, with regulation by indoor temperature rather than UV-triggered optical modulation in photochromic materials. The table of contents entry:Smart windows are promised significant contribution to the economization of building energy consumption. The rapid development of thermoresonsive materials and integrated techniques provide novel directions beyond conventional pure VO2-based thermochromic smart windows. The review summarizes emerging materials, including hydrogels, ionic liquids, perovskites, and metamaterials and integrated techniques, covering electro-thermal devices, self-cleaning, wettability, and integration with solar cells.

High symmetric porous Co3O4 hollow dodecahedra constructed by nanometer‐sized building blocks are rationally synthesized by templating against Co‐containing zeolitic imidazolate framework‐67. The well‐defined hollow structure and highly porous framework render these hollow dodecahedra exhibit high specific capacity, excellent cycling stability and superior rate capability when evaluated as an anode material for lithium‐ion batteries.

Black phosphorus (BP) is an emerging two-dimensional (2D) material with a natural bandgap, which has unique anisotropy and extraordinary physical properties. Due to its puckered structure, BP exhibits strong in-plane anisotropy unlike other layered materials. The bandgap tunability of BP enables a wide range of ultrafast electronics and high frequency optoelectronic applications ranging from telecommunications to thermal imaging covering the nearly entire electromagnetic spectrum, whereas no other 2D material has this functionality. Here, recent advances in the synthesis, fabrication, anisotropic physical properties, and BP-based devices including field effect transistors (FETs) and photodetectors, are discussed. Recent passivation approaches to address the degradation of BP, which is one of the main challenges to bring this material into real world applications, are also introduced. Finally, a comment is made on the recent developments in other emerging applications, future outlook and challenges ahead in BP research.

Vanadium dioxide (VO ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τ , low luminous transmittance (T ), and undesirable solar modulation ability (ΔT ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO . This Review focuses on hydrothermal synthesis, physical properties of VO polymorphs, and their transformation to thermochromic VO (M), and discusses the advantages, challenges, and prospects of VO (M) in energy-efficient smart windows application.