benxue liu

A high-performance multiscale cellulose-based structural material is constructed through a multiscale interface engineering strategy. The positive and negative charges treatment of microfibers and nanofibers effectively solves the interface bonding problem in multiscale design, and allows them to be easily shaped into complex three-dimensional special-shaped structures. This sustainable material offers superior mechanical and thermal properties compared to petrochemical-based plastics.

Abstract

All-natural materials derived from cellulose nanofibers (CNFs) are expected to be used to replace engineering plastics and have attracted much attention. However, the lack of crack extension resistance and 3D formability of nanofiber-based structural materials hinders their practical applications. Here, a multiscale interface engineering strategy is reported to construct high-performance cellulose-based materials. The sisal microfibers are surface treated to expose abundant active CNFs with positive charges, thereby enhancing their interfacial combination with the negatively charged CNFs. The robust multiscale dual network enables easy molding of multiscale cellulose-based structural materials into complex 3D special-shaped structures, resulting in nearly twofold and fivefold improvements in toughness and impact resistance compared with those of CNFs-based materials. Moreover, this multiscale interface engineering strategy endows cellulose-based structural materials with better comprehensive performance than petrochemical-based plastics and broadens cellulose's potential for lightweight applications as structural materials with lower environmental effects.

Utilizing sugar-derived carbon as a dense matrix to replace petrochemicals preparing C/C composites, and this matrix exhibit a nanocrystalline graphite structure with excellent thermal stability. Sugar-derived carbon matrix C/C composite show excellent ablative resistance at 3000 °C and 10 MW m⁻² heat flux. In addition, the S–C/C is suitabile for the preparation of a large and complex shaped thermal protection component.

Abstract

Sugars are renewable resources essential to human life, but they are rarely used as raw materials for the industrial production of carbon-based materials, especially for the preparation of carbon fiber-reinforced carbon-matrix (C/C) composites, which are extremely useful for the semiconductor and aerospace sectors. Herein, a method utilizing sugar-derived carbon to replace petrochemicals as dense matrix to preparing C/C composites is reported. The matrix from sugar-derived C/C (S–C/C) composites has a nanocrystalline graphite structure that is highly thermally stable and effectively bonded to the carbon fibers. The mechanical properties of the S–C/C composite are comparable to those prepared from petrochemical sources; significantly, it exhibits a linear ablation rate of 0.03 mm s⁻¹ after 200 s of ablation at 3000 °C in 10 MW m⁻² heat flux. This new class of S–C/C is promising for use in a broad range of fields, ranging from semiconductor to aerospace.

High and controllable degrees of macroscopic orientational ordering are demonstrated for mesostructured silica, titania, and carbon films. Judicious selection of synthesis conditions enables the control of the directions and relative rates of solvent removal, surfactant self-assembly, inorganic-oxide cross-linking, and the surfaces at which mesophases grow. The materials exhibit anisotropic properties for applications in separations, catalysis, and energy conversion.

Abstract

Inorganic–organic mesophase materials provide a wide range of tunable properties, which are often highly dependent on their nano-, micro-, or meso-scale compositions and structures. Among these are macroscopic orientational order and corresponding anisotropic material properties, the adjustability of which are difficult to achieve. This is due to the complicated transient and coupled transport, chemical reaction, and surface processes that occur during material syntheses. By understanding such processes, general criteria are established and used to prepare diverse mesostructured materials with highly aligned channels with uniform nanometer dimensions and controllable directionalities over macroscopic dimensions and thicknesses. This is achieved by using a micropatterned semipermeable poly(dimethylsiloxane) stamp to manage the rates, directions, and surfaces at which self-assembling phases nucleate and the directions that they grow. This enables mesostructured surfactant-directed silica and titania composites, including with functional guest species, and mesoporous carbons to be prepared with high degrees of hexagonal order, as well as controllable orthogonal macroscopic orientational order. The resulting materials exhibit novel anisotropic properties, as demonstrated by the example of direction-dependent photocurrent generation, and are promising for enhancing the functionality of inorganic–organic nanocomposite materials in separations, catalysis, and energy conversion applications.

The CeO ₂  (100) surface , despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. This effect is induced by the first water layer that is in immediate contact with the hydroxylated CeO₂ (100) surface. This ordered water layer creates a key-lock H-bond pattern with the underlying surface hydroxyl groups, hindering the interactions with liquid water. The hydrophobicity is manifested by a measurable water contact angle and a considerable diffusion enhancement of the confined liquid water as compared with bulk water, as reported by Lorenzo Agosta, Kersti Hermansson et al. in their Communication (e202303910). We acknowledge Virginia Carnevali for her help with the cover image.

An innovative nanofibrous hydrogel (nf-gel) constructed with constituent polymer nanofibers is proposed and fabricated using a two-step solvent-exchange method including an essential nonsolvent-quenching step. These nf-gels show remarkably enhanced mechanical properties and swelling resistance compared to their molecular counterparts. Particularly, they are isotropic, distinctly different from conventional fiber reinforced hydrogels.. .

Abstract

Nanofibrous hydrogels are pervasive in load-bearing soft tissues, which are believed to be key to their extraordinary mechanical properties. Enlighted by this phenomenon, a novel reinforcing strategy for polymeric hydrogels is proposed, where polymer segments in the hydrogels are induced to form nanofibers in situ by bolstering their controllable aggregation at the nanoscale level. Poly(vinyl alcohol) hydrogels are chosen to demonstrate the virtue of this strategy. A nonsolvent-quenching step is introduced into the conventional solvent-exchange hydrogel preparation approach, which readily promotes the formation of nanofibrous hydrogels in the following solvent-tempering process. The resultant nanofibrous hydrogels demonstrate significantly improved mechanical properties and swelling resistance, compared to the conventional solvent-exchange hydrogels with identical compositions. This work validates the hypothesis that bundling polymer chains to form nanofibers can lead to nanofibrous hydrogels with remarkably enhanced mechanical performances, which may open a new horizon for single-component hydrogel reinforcement.

Polarization Order

Polarization-switching processes of fluorite-oxide thin films remain elusive due to the challenges of visualizing oxygen ions. In article number 2207736, Chen Ge, Qinghua Zhang, Lin Gu, and co-workers directly capture the transition between ferroelectric and antiferroelectric orders using integrated differential phase-contrast scanning transmission electron microscopy.

A deep-learning-enabled intelligent design method of thermal metamaterials is proposed by using a deep generative model. To realize automatic, real-time, and customizable design of thermal metamaterials, this framework is constructed via a pre-trained deep learning model to achieve an end-to-end mapping relationship between thermal response and microstructure, which provides great flexibility in the on-demand inverse design of thermal metamaterials.

Abstract

Thermal metamaterials are mixture-based materials that are engineered to manipulate, control, and process the flow of heat, enabling numerous advanced thermal metadevices. Conventional thermal metamaterials are predominantly designed with tractable regular geometries owing to the delicate analytical solution and easy-to-implement effective structures. Nevertheless, it is challenging to achieve the design of thermal metamaterials with arbitrary geometry, letting alone intelligent (automatic, real-time, and customizable) design of thermal metamaterials. Here, an intelligent design framework of thermal metamaterials is presented via a pre-trained deep learning model, which gracefully achieves the desired functional structures of thermal metamaterials with exceptional speed and efficiency, regardless of arbitrary geometry. It possesses incomparable versatility and is of great flexibility to achieve the corresponding design of thermal metamaterials with different background materials, anisotropic geometries, and thermal functionalities. The transformation thermotics-induced, freeform, background-independent, and omnidirectional thermal cloaks, whose structural configurations are automatically designed in real-time according to shape and background, are numerically and experimentally demonstrated. This study sets up a novel paradigm for an automatic and real-time design of thermal metamaterials in a new design scenario. More generally, it may open a door to the realization of an intelligent design of metamaterials in also other physical domains.

A novel lightweight Al battery is constructed using a dendrite-free carbon aerogel film (CAF) anode and a high-loading integrated graphite composite carbon aerogel film (GCAF) cathode. O-containing functional groups on the CAF induce Al deposition. The zero-volume expansion of the GCAF results in better stability. A CAF‖GCAF full battery exhibits excellent charge–discharge performance toward fast storage of fluctuating electricity.

Abstract

Al batteries have great potential for renewable energy storage owing to their low cost, high capacity, and safety. High energy density and adaptability to fluctuating electricity are major challenges. Here, a lightweight Al battery for fast storage of fluctuating energy is constructed based on a novel hierarchical porous dendrite-free carbon aerogel film (CAF) anode and an integrated graphite composite carbon aerogel film (GCAF) cathode. A new induced mechanism by the O-containing functional groups on the CAF anode is con-firmed for uniform Al deposition. The GCAF cathode possesses a higher mass utilization ratio due to the extremely high loading mass (9.5–10.0 mg cm⁻²) of graphite materials compared to conventional coated cathodes. Meanwhile, the volume expansion of the GCAF cathode is almost negligible, resulting in better cycling stability. The lightweight CAF‖GCAF full battery can adapt well to large and fluctuating current densities owing to its hierarchical porous structure. A large discharge capacity (115.6 mAh g⁻¹) after 2000 cycles and a short charge time (7.0 min) at a high current density are obtained. The construction strategy of lightweight Al batteries based on carbon aerogel electrodes can promote the breakthrough of high-energy-density Al batteries adapted to the fast storage of fluctuating renewable energy.

Nature Materials, Published online: 28 June 2023; doi:10.1038/s41563-023-01602-4

A bicontinuous conducting polymer hydrogel with high electrical conductivity, stretchability and fracture toughness in physiological environments achieves high-fidelity monitoring and effective stimulation of tissues and organs.

A rapid synthesis method is developed to introduce Zr-MOF nanozyme coating into cellulose nanofibers, resulting in the formation of processable macro-micro porous aerogel composites with high metal–organic framework (MOF) loadings. The hierarchically structured MOF nanozymes monolithic aerogel enables excellent accessibility to catalytic active sites for fast and efficient hydrolytic detoxification of organophosphorus-based nerve agent simulants and pesticides from contaminated water.

Abstract

Metal–organic frameworks (MOFs) with Lewis acid catalytic sites, such as zirconium-based MOFs (Zr-MOFs), comprise a growing class of phosphatase-like nanozymes that can degrade toxic organophosphate pesticides and nerve agents. Rationally engineering and shaping MOFs from as-synthesized powders into hierarchically porous monoliths is essential for their use in emerging applications, such as filters for air and water purification and personal protection gear. However, several challenges still limit the production of practical MOF composites, including the need for sophisticated reaction conditions, low MOF catalyst loadings in the resulting composites, and poor accessibility to MOF-based active sites. To overcome these limitations, a rapid synthesis method is developed to introduce Zr-MOF nanozyme coating into cellulose nanofibers, resulting in the formation of processable monolithic aerogel composites with high MOF loadings. These composites contain Zr-MOF nanozymes embedded in the structure, and hierarchical macro-micro porosity enables excellent accessibility to catalytic active sites. This multifaceted rational design strategy, including the selection of a MOF with many catalytic sites, fine-tuning the coating morphology, and the fabrication of a hierarchically structured monolithic aerogel, renders synergistic effects toward the efficient continuous hydrolytic detoxification of organophosphorus-based nerve agent simulants and pesticides from contaminated water.

Thermal conductivity imaging via frequency-domain thermoreflectance enables the detection of localized microscale suppression in thermal conductivity at the grain boundaries of thermoelectric SnTe. By employing a Gibbs excess approach, a thermal boundary resistance is extracted from the images, establishing a correlation between misorientation angle and thermal resistance. These findings demonstrate the capability of thermal imaging in extracting structure–property relationships.

Abstract

Grain-boundary engineering is an effective strategy to tune the thermal conductivity of materials, leading to improved performance in thermoelectric, thermal-barrier coatings, and thermal management applications. Despite the central importance to thermal transport, a clear understanding of how grain boundaries modulate the microscale heat flow is missing, owing to the scarcity of local investigations. Here, thermal imaging of individual grain boundaries is demonstrated in thermoelectric SnTe via spatially resolved frequency-domain thermoreflectance. Measurements with microscale resolution reveal local suppressions in thermal conductivity at grain boundaries. Also, the grain-boundary thermal resistance – extracted by employing a Gibbs excess approach – is found to be correlated with the grain-boundary misorientation angle. Extracting thermal properties, including thermal boundary resistances, from microscale imaging can provide comprehensive understanding of how microstructure affects heat transport, crucially impacting the materials design of high-performance thermal-management and energy-conversion devices.

Au atoms tend to form a thin, crystalline layer on graphene surfaces via van der Waals epitaxy, resulting in translucent, conductive films. Translucent yet reflective Au/graphene hybrids are invisible to the naked eye but can be clearly identified at IR wavelength. Au/graphene hybrids can be applied to a wide range of thermal management applications ranging from energy harvesting and storage to military applications.

Abstract

Translucent Au/graphene hybrid films are shown to be effective in reducing thermal emission from the underlying surfaces when the deposition thickness of Au is close to the percolation threshold. The critical Au deposition thickness for an abrupt change in emissivity is reduced from 15 nm (Si substrate) to a percolation-threshold-limited thickness of 8.5 nm (graphene/Si substrate) because of the chemical inertness of graphene leading to the deposited Au atoms forming a thin, crystalline layer. The effect of the graphene layer on the optical properties of the hybrid film is highlighted by a drastic increase in infrared absorptivity, whereas the visible absorptivity is marginally affected by the presence of a graphene layer. The level of thermal emission from the Au/graphene hybrid films with the percolation-threshold-limited Au thickness is stable even with high background temperatures of up to 300 °C and mechanical strains of ≈4%. As an example of a thermal management application, an anti-counterfeiting device is demonstrated; thermal-camouflage-masked text fabricated with an Au/graphene hybrid film is discernible only using a thermographic camera. Ultrathin metal film assisted by a graphene layer will provide a facile platform for thermal management with semi-transparency, flexibility, and transferability to arbitrary surfaces.

High-temperature thermochromic fluorescence up to 473 K and robust structural and optical reversibility of 80 cycles are demonstrated in Rb₂MnBr₄(H₂O)₂ and related crystals. Such unique features showcase a multicolor anti-counterfeiting label based on a broad temperature gradient and multidimensional information encryption application.

Abstract

Thermochromic fluorescent materials (TFMs) characterized by noticeable emission color variation with temperature have attracted pervasive attention for their frontier application in stimulus-response and optical encryption technologies. However, existing TFMs typically suffer from weak PL reversibility as well as limited mild operating temperature and severe temperature PL quenching. PL switching under extreme conditions such as high temperature will undoubtedly improve encryption security, while it is still challenging for present TFMs. In this work, high-temperature thermochromic fluorescence up to 473 K and robust structural and optical reversibility of 80 cycles are observed in Rb₂MnBr₄(H₂O)₂ and related crystals, which is seldom reported for PL changes at such a high temperature. Temperature-driven nonluminous, red and green light emission states can be achieved at specific temperatures and the modulation mechanism is verified by in situ optical and structural measurements and single particle transition. By virtue of this unique feature, a multicolor anti-counterfeiting label based on a broad temperature gradient and multidimensional information encryption applications are demonstrated. This work opens a window for the design of inorganic materials with multi-PL change and the development of advanced encryption strategies with extreme stimuli source.

A “dynamic covalent network” reconstruction strategy is proposed for the fabrication of sustainable cellulosic bioplastics. By introducing dynamic linkages between cellulose chains, this cellulosic bioplastic is imparted with good thermo-processability, competitive mechanical properties, excellent water and solvent resistance, as well as chemical and biological degradability. This approach provides a new route for developing sustainable and degradable bioplastics from resource-abundant biomass.

Abstract

The growing environmental concern over petrochemical-based plastics continuously promotes the exploration of green and sustainable substitute materials. Compared with petrochemical products, cellulose has overwhelming superiority in terms of availability, cost, and biodegradability; however, cellulose's dense hydrogen-bonding network and highly ordered crystalline structure make it hard to be thermoformed. A strategy to realize the partial disassociation of hydrogen bonds in cellulose and the reassembly of cellulose chains via constructing a dynamic covalent network, thereby endowing cellulose with thermal processability as indicated by the observation of a moderate glass transition temperature (T _g = 240 °C), is proposed. Moreover, the cellulosic bioplastic delivers a high tensile strength of 67 MPa, as well as excellent moisture and solvent resistance, good recyclability, and biodegradability in nature. With these advantageous features, the developed cellulosic bioplastic represents a promising alternative to traditional plastics.

This work builds a modeling method from the atomic scale to the macroscale for porous electrodes. Simulations reveal that supercapacitors based on porous graphdiynes of AB stacking structure can achieve both higher capacitance and ionic conductivity than AA stacking. This is ascribed to more intense image forces in AB stacking.

Abstract

Porous graphdiynes are a new class of porous 2D materials with tunable electronic structures and various pore structures. They have potential applications as well-defined nanostructured electrodes and can provide platforms for understanding energy storage mechanisms underlying supercapacitors. Herein, the effect of stacking structure and metallicity on energy storage with such electrodes is investigated. Simulations reveal that supercapacitors based on porous graphdiynes of AB stacking structure can achieve both higher double-layer capacitance and ionic conductivity than AA stacking. This phenomenon is ascribed to more intense image forces in AB stacking, leading to a breakdown of ionic ordering and the formation of effective “free ions”. Macroscale analysis shows that doped porous graphdiynes can deliver outstanding gravimetric and volumetric energy and power densities due to their enhanced quantum capacitance. These findings pave the way for designing high-performance supercapacitors by regulating pore topology and metallicity of electrode materials.

Ultrastrong and superstretchable ionogels tougher than that of metals are produced through the synergy of force-induced crystallization and halometallate ionic liquid created supramolecular ionic networks. The prepared ionogels with environmental applicability and sustainability are expected to replace lightweight high-strength materials, such as plastics and rubbers in the applications of aerospace, robotics, and other fields.

Abstract

Common natural and synthetic high-strength materials (such as rubber, plastics, ceramics, and metals) undergo the occurrence of poor deformability. Achieving high strength and large deformation simultaneously is a huge challenge. Herein, high-strength ionogels are developed through the synergy of force-induced crystallization and halometallate ionic liquid created supramolecular ionic networks. The prepared poly(vinyl alcohol)/halometallate ionic liquid ionogels show excellent mechanical properties, including ultimate fracture stress (63.1 ± 2.1 MPa), strain (5248 ± 113%), and unprecedented toughness (1947 ± 52 MJ m⁻³), which is much higher than that of most metals and alloys. Furthermore, the ionogels can achieve reversibility by water to realize green recovery and restoration of damaged mechanical properties.

An ultralight and hyperelastic nanofiber-woven hybrid carbon assembly (NWHCA) is fabricated by nanofiber weaving of isotropic porous and mechanical brittle quasi-aerogels. The 3D-ordered lamella–bridge-structured NWHCA exhibits outstanding electrochemical activity and mechanical elasticity ascribing to the combination of metallogel-derived quasi-aerogel hybridization and nitrogen/phosphorus co-doping. Integrated wearable sensing devices based on NWHCA are demonstrated for detecting sophisticated human motions.

Abstract

The development of a 3D carbon assembly with a combination of extraordinary electrochemical and mechanical properties is desirable yet challenging. Herein, an ultralight and hyperelastic nanofiber-woven hybrid carbon assembly (NWHCA) is fabricated by nanofiber weaving of isotropic porous and mechanical brittle quasi-aerogels. Upon subsequent pyrolysis, metallogel-derived quasi-aerogel hybridization and nitrogen/phosphorus co-doping are integrated into the NWHCA. Finite element simulation indicates that the 3D lamella–bridge architecture of NWHCA with the quasi-aerogel hybridization contributes to resisting plastic deformation and structural damage under high compression, experimentally demonstrated by complete deformation recovery at 80% compression and unprecedented fatigue resistance (>94% retention after 5000 cycles). Due to the superelasticity and quasi-aerogel integration, the zinc–air battery assembled based on NWHCA shows excellent electrochemical performance and flexibility. A proof-of-concept integrated device is presented, in which the flexible battery powers a piezoresistive sensor, using the NWHCA as the air cathode and the elastic conductor respectively, which can detect full-range and sophisticated motions while attached to human skin. The nanofiber weaving strategy allows the construction of lightweight, superelastic, and multifunctional hybrid carbon assemblies with great potential in wearable and integrated electronics.

Nacre-mimetic nanocomposite aerogels featuring a “porous brick and fiber” architecture are fabricated via in situ nanoscale hetero-assembly and ambient pressure drying, in which mesoporous minerals are generated in a lamellar cellulose nanofibrous network. The aerogels integrate challenging requirements of thermal superinsulation, excellent compressive stiffness, superelasticity, high bending flexibility, good impact resistance, and easy scalability for robust thermal management under extreme conditions.

Abstract

Thermal protection under extreme conditions requires materials with excellent thermal insulation properties and exceptional mechanical properties to withstand a variety of complex external stresses. Mesoporous silica aerogels are the most widely used insulation materials due to their ultralow thermal conductivity. However, they still suffer from mechanical fragility and structural instability in practical applications. Herein, a nacre-mimetic nanocomposite aerogel, synthesized via in situ growth of inorganic minerals in a lamellar cellulose nanofibrous network, is reported. The multiscale structural adaptation of the inorganic–organic components endows nanocomposite aerogels with rapid configuration recovery during ambient pressure drying. The resulting aerogels show ultralow thermal conductivities (17.4 mW m⁻¹ K⁻¹ at 1.0 atm). These aerogels also integrate challenging mechanical properties, including high compressive stiffness to resist deformation under the pressure of an adult, superelasticity to prevent static and dynamic stress cracking even under the crushing of a vehicle (1.6 t), and high bending flexibility to adapt to any surface. Moreover, they exhibit excellent structural stability under fatigue stress/strain cycles over a wide temperature range (−196 to 200 °C). The combination of high thermal insulation performance and excellent mechanical properties offers a potential material system for robust thermal superinsulation under extreme conditions, especially for aerospace applications.

In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved in perovskite frameworks is visualized by investigating the precursor species. The feasibility of modulating the quantum wells structure for the fabrication of low-dimensional perovskite photovoltaics is further verified.

Abstract

The multiple quantum wells (QWs) distribution in low-dimensional perovskite films hinders charge transport due to the fundamental difficulty of controlling crystal growth from precursor solutions, yielding poorly homogeneous low-dimensional perovskite solar cells (PSCs), especially in upscaling fabrication. Here, efficient low-dimensional PSCs are realized by modulating the colloidal assembly behavior in the precursor solution to induce intermediate structures. In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved lead iodide-dominated colloidal soft framework is visualized by investigating the precursor species differences under hydrogen bonding interactions. Subsequently, solid-state reactions emerge and the formamidine (FA)-based perovskite films exhibit significantly suppressed multiple QWs distribution. Encouragingly, the FA device (n=9, by meniscus-assisted coating) achieves a power conversion efficiency (PCE) of 20.28 % for a size of 0.04 cm² and a PCE of 15.35 % for a mini-module of 16.94 cm² with superior stability.

A long-focus thermal lens with equivalent negative thermal conductivity is designed and experimentally realized to achieve a remote heating/cooling effect. The thermal lens consists of active thermal metasurfaces, which are constructed by p/n-type semiconductor pairs driven by a DC power supply. The proposed method can also achieve other novel thermal effects, such as thermal superlens and thermal tunneling effects.

Abstract

Remote temperature control can be obtained by a long-focus thermal lens that can focus heat fluxes into a spot far from the back surface of the lens and create a virtual thermal source/sink in the background material, around which the temperature field distribution can be remotely controlled by varying the parameters of the thermal lens. However, because of the lack of negative thermal conductivity, existing thermal lenses have extremely short focal lengths and cannot be used to remotely control the temperature field around the virtual thermal source/sink. In this study, a general approach is proposed to equivalently realize materials with negative thermal conductivity using elaborately distributed active thermal metasurfaces (ATMSs). Subsequently, the proposed ATMS is used to implement a novel thermal lens with a long focal length designed using transformation thermodynamics, and finally realize the ATMS with realistic materials and experimentally verify the performance of the designed long-focus thermal lens (measured focal length of 19.8 mm) for remote heating/cooling. The proposed method expands the scope of the thermal conductivity and provides new pathways to realize unprecedented thermal effects with effective negative thermal conductivity, such as “thermal surface plasmon polaritons,” a thermal superlens, the thermal tunneling effect, and the thermal invisible gateway.

A new chemical mechanism for the generation of gaseous N₂O₅ in atmosphere via the photocatalytic oxidation of NO₂ on TiO₂ is shown, and this new source of N₂O₅ may have important implications to the near-ground air quality in urban areas and day time due to the presence of both abundant TiO₂-containing building materials and high NO_x concentrations.

Abstract

N₂O₅ is an important intermediate in the atmospheric nitrogen cycle. Using a flow tube reactor, N₂O₅ was found to be released from the TiO₂ surface during the photocatalytic oxidation of NO₂, revealing a previously unreported source of N₂O₅. The rate of N₂O₅ release from TiO₂ was dependent on the initial NO₂ concentration, relative humidity, O₂/N₂ ratio, and irradiation intensity. Experimental evidence and quantum chemical calculations showed that NO₂ can react with the surface hydroxyl groups and the generated electron holes on the TiO₂, followed by combining with another NO₂ molecule to form N₂O₅. The latter was physisorbed on TiO₂ and had a low adsorption energy of −0.13 eV. Box model simulations indicated that the new source of N₂O₅ released from TiO₂ can increase the daytime N₂O₅ concentration by up to 20 % in urban areas if abundant TiO₂-containing materials and high NOx concentrations were present. This joint experimental/theoretical study not only demonstrates a new chemical mechanism for N₂O₅ formation but also has important implications for air quality in urban areas.

Nature Materials, Published online: 13 April 2023; doi:10.1038/s41563-023-01508-1

Alternative solid electrolytes with enhanced thermal and chemical stability are key for advancing lithium batteries. A soft solid electrolyte with improved stability and ionic conductivity, overcoming several limitations of conventional materials, is now reported.

Low-dose integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM) enables visualization of oxygen shifting during polarization switching and correlated polar–nonpolar phase transitions among multiple metastable phases in ZrO₂ nanocrystals. Bidirectional transitions between antiferroelectric and ferroelectric orders and interfacial polarization relaxation are clarified at unit-cell scale. Meanwhile, polarization switching is strongly correlated with polar–nonpolar phase transitions among O/M/T phases.

Abstract

Unconventional ferroelectricity in fluorite-structure oxides enables tremendous opportunities in nanoelectronics owing to their superior scalability and silicon compatibility. However, their polarization order and switching process remain elusive due to the challenges of visualizing oxygen ions in nanocrystalline films. In this work, the oxygen shifting during polarization switching and correlated polar–nonpolar phase transitions are directly captured among multiple metastable phases in freestanding ZrO₂ thin films by low-dose integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM). Bidirectional transitions between antiferroelectric and ferroelectric orders and interfacial polarization relaxation are clarified at unit-cell scale. Meanwhile, polarization switching is strongly correlated with Zr–O displacement in reversible martensitic transformation between monoclinic and orthorhombic phases and two-step tetrahedral-to-orthorhombic phase transition. These findings provide atomic insights into the transition pathways between metastable polymorphs and unravel the evolution of polarization orders in (anti)ferroelectric fluorite oxides.