Controllable synthesis of borophene aerogels by utilizing h-BN layers for high-performance next-generation batteries.

Borophene is emerging as a promising electrode material for Li, Na, Mg, and Ca ion batteries due to its anisotropic Dirac properties, high charge capacity, and low energy barrier for ion diffusion. However, practical synthesis of active and stable borophene remains challenging in producing electrochemical devices. Here, we introduce a method for borophene aerogels (BoAs), utilizing hexagonal boron nitride aerogels. Borophene grows between h-BN layers utilizing boron-boron bridges, as a nucleation site, where borophene forms monolayers mixed with sp2-sp3 hybridization. This versatile method produces stable BoAs and is compatible with various battery chemistries. With these BoAs, we accomplish an important milestone to successfully fabricate high-performance next-generation batteries, including Na-ion (478 mAh g-1, at 0.5C, >300 cycles), Mg-ion (297 mAh g-1, at 0.5C, >300 cycles), and Ca-ion (332 mAh g-1, at 0.5C, >400 cycles), and Li-S batteries, with one of the highest capacities to date (1,559 mAh g-1, at 0.3C, >1,000 cycles).

Aerogels based on Bacterial Nanocellulose and their Applications.

Microbial cellulose stands out for its exceptional characteristics in the form of biofilms formed by highly interlocked fibrils, namely, bacterial nanocellulose (BNC). Concurrently, bio-based aerogels are finding uses in innovative materials owing to their lightweight, high surface area, physical, mechanical, and thermal properties. In particular, bio-based aerogels based on BNC offer significant opportunities as alternatives to synthetic or mineral counterparts. BNC aerogels are proposed for diverse applications, ranging from sensors to medical devices, as well as thermal and electroactive systems. Due to the fibrous nanostructure of BNC and the micro-porosity of BNC aerogels, these materials enable the creation of tailored and specialized designs. Herein, a comprehensive review of BNC-based aerogels, their attributes, hierarchical, and multiscale features are provided. Their potential across various disciplines is highlighted, emphasizing their biocompatibility and suitability for physical and chemical modification. BNC aerogels are shown as feasible options to advance material science and foster sustainable solutions through biotechnology.

Phase-Tailoring Wx V1-x O2 Meta-Nanofiber Enables Temperature-Editing Energy Control.

Room-temperature phase change materials (RTPCMs) exhibit promise to address challenges in thermal energy storage and release, greatly aiding in numerous domains of human existence and productivity. The conventional RTPCMs undergo inevitable volume expansion, structural collapse, and diffusion of active ingredients while maintaining desirable phase change enthalpy and ideal phase change temperature. Here, a sol-gel 1D-induced growth approach is presented to fabricate meta nanofibers (Meta-NFs) comprised of vanadium dioxide with monoclinic crystal structure, and further achieve the editable phase change temperature from 68 to 37 °C through W-doping, which allowed for tailored length variation of the zigzag V-V bond. Subsequently, Meta-NFs are assembled into 3D aerogels with self-standing architecture, thereby enabling the independent use of the RTPCMs. The obtained metamaterials demonstrate not only the temperature-editing solid-solid phase transition, but also the stiffness of the ceramic matrix, exhibiting the thermal energy control capability at room temperature (37 °C), thermal insulation properties, temperature resistance, and flame retardancy. The effective creation of these fascinating metamaterials might offer new insights for next-generation and self-standing solid-solid RTPCMs.

Scalable Preparation of Polyimide Sandwiched Separator for Durable High-Rate Lithium-Metal Battery.

The ever-growing demands for efficient energy storage accelerate the development of high-rate lithium-metal battery (LMB) with desirable energy density, power density, and cycling stability. Nevertheless, the practical application of LMB is critically impeded by internal temperature rise and lithium dendrite growth, especially at high charge/discharge rates. It is highly desired but remains challenging to develop high-performance thermotolerant separators that can provide favorable channels to enable fast Li+ transport for high-rate operation and simultaneously homogenize the lithium deposition for dendrite inhibition. Polyimide-based separators with superior thermal properties are promising candidate alternatives to the commercial polyolefin-based separators, but previous strategies of designing either nanoporous or microporous channels in polyimide-based separators often meet a dilemma. Here, a facile and scalable approach is reported to develop a polyimide fiber/aerogel (denoted as PIFA) separator with the microporous polyimide fiber membrane sandwiched between two nanoporous polyimide aerogel layers, which can enable LMBs with remarkable capacity retention of 97.2% after 1500 cycles at 10 C. The experimental and theoretical studies unravel that the sandwiched structure of PIFA can appreciably enhance the electrolyte adsorption and ionic conductivity; while, the aerogel coating can effectively inhibit dendrite growth to realize durable high-rate LMBs.

Recent Progress in MOF-Aerogel Fabrication and Applications.

Recent advancements in metal-organic frameworks (MOFs) underscore their significant potential in chemical and materials research, owing to their remarkable properties and diverse structures. Despite challenges like intrinsic brittleness, powdered crystalline nature, and limited stability impeding direct applications, MOF-based aerogels have shown superior performance in various areas, particularly in water treatment and contaminant removal. This review highlights the latest progress in MOF-based aerogels, with a focus on hybrid systems incorporating materials like graphene, carbon nanotube, silica, and cellulose in MOF aerogels, which enhance their functional properties. The manifold advantages of MOF-based aerogels in energy storage, adsorption, and catalysis are discussed, with an emphasizing on their improved stability, processability, and ease of handling. This review aims to unlock the potential of MOF-based aerogels and their real-world applications. Aerogels are expected to reshape the technological landscape of MOFs through enhanced stability, adaptability, and efficiency.

Ultralight Three-Layer Gradient-Structured MXene/ Reduced Graphene Oxide Composite Aerogels with Broadband Microwave Absorption and Dynamic Infrared Camouflage.

Infrared and radar detectors posed substantial challenges to weapon equipment and personnel due to their continuous surveillance and reconnaissance capabilities. Traditional single-band stealth devices are insufficient for dual-band detection in both infrared and microwave bands. To overcome this limitation, a gradient-structured MXene/reduced graphene oxide (rGO) composite aerogel (GMXrGA) is fabricated through a two-step bidirectional freeze casting process, followed by freeze-drying and thermal annealing. GMXrGA exhibits a distinct three-layered structure, with each layer playing a crucial role in microwave absorption. This deliberate design amplifies both the efficiency of microwave absorption and the material's effectiveness in dynamic infrared camouflage. GMXrGA displays an ultralow density of 5.2 mg∙cm-3 and demonstrates exceptional resistance to compression, enduring 200 cycles at a maximum strain of 80%. Moreover, it shows superior microwave absorption performance, with a minimum reflection loss (RLmin) of -60.1 dB at a broad effective absorption bandwidth (EAB) of 14.1 GHz (3.9-18.0 GHz). Additionally, the aerogel exhibits low thermal conductivity (≈26 mW∙m-1∙K-1) and displays dynamic infrared camouflage capabilities within the temperature range of 50-120 °C, achieving rapid concealment within 30 s. Consequently, they hold great potential for diverse applications, including intelligent buildings, wearable electronics, and weapon equipment.

High-Performance Organic Aerogels Tailored for Versatile Recycling Approaches: Recycling-Reforming-Upcycling.

Organic aerogels are emerging as promising materials due to their versatile properties, rendering them excellent candidates for a variety of applications in the fields of thermal insulation, energy storage, pharmaceuticals, chemical adsorption, and catalysis. However, current aerogel designs rely on cross-linked polymer networks, which lack efficient end-of-use solutions, thereby hindering their overall sustainability. In this study, a facile synthesis of organic aerogels with a unique combination of imine and cyanurate moieties is presented, resulting in high-performance, lightweight insulating materials. The aerogels' structure, ensures mechanical robustness, thermal resistance, and hydrophobicity without additional treatments, crucial for long-term performance. Additionally, in response to the currently unsustainable use of cross-linked polymer materials, the molecular design offers diverse avenues of chemical recycling. These include full depolymerization back into the original monomers, partial network fragmentation producing soluble oligomers that can be promptly employed to fabricate new aerogels, and upcycling of aerogel waste into useful building blocks. This work pioneers a novel approach to material design, emphasizing recyclability as a core feature while maintaining high-performance excellence.

Elastic SiC Aerogel for Thermal Insulation: A Systematic Review.

SiC aerogels with their lightweight nature and exceptional thermal insulation properties have emerged as the most ideal materials for thermal protection in hypersonic vehicles; However, conventional SiC aerogels are prone to brittleness and mechanical degradation when exposed to complex loads such as shock and mechanical vibration. Hence, preserving the structural integrity of aerogels under the combined influence of thermal and mechanical external forces is crucial not only for stabling their thermal insulation performance but also for determining their practicality in harsh environments. This review focuses on the optimization of design based on the structure-performance of SiC aerogels, providing a comprehensive review of the inherent correlations among structural stability, mechanical properties, and insulation performance. First, the thermal transfer mechanism of aerogels from a microstructural perspective is studied, followed by the relationship between the building blocks of SiC aerogels (0D particles, 1D nanowires/nanofibers) and their compression performance (including compressive resilience, compressive strength, and fatigue resistance). Moreover, the strategy to improve the high-temperature oxidation resistance and insulation performance of SiC aerogels is explored. Lastly, the challenges and future breakthrough directions for SiC aerogels are presented.

A Screening Approach to the Safe-and-Sustainable-by-Design Development of Advanced Insulation Materials.

Herein, a Safe-and-Sustainable-by-Design (SSbD) screening strategy on four different inorganic aerogel mats and two conventional mineral wools for ranking purposes is demonstrated. Given that they do not consist of particles, the release is first simulated, addressing three occupational exposure scenarios, realistic for their intended use as building insulators. No exposure to consumers nor to the environment is foreseen in the use phase, however, aerosols may be released during mat installation, posing an inhalation risk for workers. All four aerogel mats release more respirable dust than the benchmark materials and 60% thereof deposits in the alveolar region according to modelling tools. The collected aerogel dust allows for subsequent screening of hazard implications via two abiotic assays: 1) surface reactivity in human blood serum; 2) biodissolution kinetics in lung simulant fluids. Both aerogels and conventional insulators show similar surface reactivity. Differences in biodissolution are influenced by the specifically designed organic and inorganic structural modifications. Aerogel mats are better-performing insulators (2-fold lower thermal conductivity than the benchmark) However, this work demonstrates how investment decisions can be balanced with safety and sustainability aspects. Concepts of analogy and similarity thus support easily accessible methods to companies for safe and economically viable innovation with advanced materials.

Highly Flexible and Superelastic Graphene Nanofibrous Aerogels for Intelligent Sign Language.

Highly flexible and superelastic aerogels at large deformation have become urgent mechanical demands in practical uses, but both properties are usually exclusive. Here a trans-scale porosity design is proposed in graphene nanofibrous aerogels (GNFAs) to break the trade-off between high flexibility and superelasticity. The resulting GNFAs can completely recover after 1000 fatigue cycles at 60% folding strain, and notably maintain excellent structural integrity after 10000 cycles at 90% compressive strain, outperforming most of the reported aerogels. The mechanical robustness is demonstrated to be derived from the trans-scale porous structure, which is composed of hyperbolic micropores and porous nanofibers to enable the large elastic deformation capability. It is further revealed that flexible and superelastic GNFAs exhibit high sensitivity and ultrastability as an electrical sensors to detect tension and flexion deformation. As proof, The GNFA sensor is implemented onto a human finger and achieves the intelligent recognition of sign language with high accuracy by multi-layer artificial neural network. This study proposes a highly flexible and elastic graphene aerogel for wearable human-machine interfaces in sensor technology.

A Universal Biomacromolecule-Enabled Assembly Strategy for Constructing Multifunctional Aerogels with 90% Inorganic Mass Loading from Inert Nano-Building Blocks.

Inert inorganic nano-building blocks, such as carbon nanotubes (CNTs) and boron nitride (BN) nanosheets, possess excellent physicochemical properties. However, it remains challenging to build aerogels with these inert nanomaterials unless they are chemically modified or compounded with petrochemical polymers, which affects their intrinsic properties and is usually not environmentally friendly. Here, a universal biomacromolecule-enabled assembly strategy is proposed to construct aerogels with 90 wt% ultrahigh inorganic loading. The super-high inorganic content is beneficial for exploiting the inherent properties of inert nanomaterials in multifunctional applications. Taking chitosan-CNTs aerogel as a proof-of-concept demonstration, it delivers sensitive pressure response as a pressure sensor, an ultrahigh sunlight absorption (94.5%) raising temperature under light (from 25 to 71 °C within 1 min) for clean-up of crude oil spills, and superior electromagnetic interference shielding performance of up to 68.9 dB. This strategy paves the way for the multifunctional application of inert nanomaterials by constructing aerogels with ultrahigh inorganic loading.

Confining N-Doped Carbon Dots into PtNi Aerogels Skeleton for Robust Electrocatalytic Methanol Oxidation and Oxygen Reduction.

Noble metallic aerogels with the self-supported hierarchical structure and remarkable activity are promising for methanol fuel cells, but are limited by the severe poisoning and degradation of active sites during electrocatalysis. Herein, the highly stable electrocatalyst of N-doped carbon dots-PtNi (NCDs-PtNi) aerogels is proposed by confining NCDs with alloyed PtNi for methanol oxidation and oxygen reduction reactions. Comprehensive electrocatalytic measurements and theoretical investigations suggest the improvement in structure stability and regulation in electronic structure for better electrocatalytic durability when confining NCDs with PtNi aerogels. Notably, the NCDs-PtNi aerogels perform 12-fold higher activity than that of Pt/C and maintain 52% of their initial activity after 5000 cycles toward acidic methanol oxidation. The enhanced stability and activity of NCDs-PtNi aerogels are also evident for oxygen reduction reactions in different electrolytes. These results highlight the effectiveness of stabilizing metallic aerogels with NCDs, offering a feasible pathway to develop robust electrocatalysts for fuel cells.

Strain Effects in Ru-Au Bimetallic Aerogels Boost Electrocatalytic Hydrogen Evolution.

To improve the sluggish kinetics of the hydrogen evolution reaction (HER), a key component in water-splitting applications, there is an urgent desire to develop efficient, cost-effective, and stable electrocatalysts. Strain engineering is proving an efficient strategy for increasing the catalytic activity of electrocatalysts. This work presents the development of Ru-Au bimetallic aerogels by a simple one-step in situ reduction-gelation approach, which exhibits strain effects and electron transfer to create a remarkable HER activity and stability in an alkaline environment. The surface strain induced by the bimetallic segregated structure shifts the d-band center downward, enhancing catalysis by balancing the processes of water dissociation, OH* adsorption, and H* adsorption. Specifically, the optimized catalyst shows low overpotentials of only 24.1 mV at a current density of 10 mA cm-2 in alkaline electrolytes, surpassing commercial Pt/C. This study can contribute to the understanding of strain engineering in bimetallic electrocatalysts for HER at the atomic scale.

Electric Field-Induced Ordered-Structural Aerogels Enable Superinsulation and Multifunctionality.

1D flexible fibers assembled 3D porous networked ceramic fiber aerogels (CFAs) are developed to overcome the brittleness of traditional ceramic particle aerogels. However, existing CFAs with disordered and quasi-ordered structures fail to balance the relationship between flexibility, robustness, and thermal insulation. Creating novel architectural CFAs with an excellent combination of performances has proven extremely challenging. In this paper, a novel strategy is adopted to fabricate porous mullite fibrous aerogels (MFAs) with ordered structures by combining fiber sedimentation and electric field-induced fiber alignment techniques. For the first time, electric field-induced alignment of ceramic fibers is utilized to prepare bulk aerogels on a large scale. The resulting MFAs exhibit ultra-low high-temperature thermal conductivity of 0.0830 W m-1 K-1 at 1000 °C, anisotropic mechanical and sound absorption performances, and multifunctionality in terms of the combination of thermal insulation, sound absorption, and hydrophobicity. The successful synthesis of such fascinating materials may provide new insights into the design and development of multifunctional CFAs for various applications.

Emulsion-Based Multiscale Structural Design Realizes Lightweight and Superelastic Graphene Aerogels for Electromagnetic Interference Shielding.

Ultralight graphene aerogels with high electrical conductivity and superelasticity are demanded yet difficult to produce. A versatile emulsion-based approach is demonstrate to optimize multiscale structure of lightweight, elastic, and conductive graphene aerogels. By constructing Pickering emulsion using graphene oxide (GO), poly (amic acid) (PAA), and octadeyl amine (ODA), micron-level close-pore structure is realized while thermal shrinkage mismatch between GO and PAA creates numerous nanowrinkles during thermal annealing. GO nanosheets are bridged by PAA-derived carbon, enhancing the structural integrity at molecular level. These multiscale structural features facilitate rapid electron transport and efficient load transfer, conferring graphene aerogels with intriguing mechanical and electromagnetic interference (EMI) shielding properties. The emulsion-based graphene aerogel with an ultralow density of ≈3.0 mg cm-3 integrates outstanding electrical conductivity, air-caliber thermal insulation, high EMI shielding effectiveness of 75.0 dB, and 90% strain compressibility with superb fatigue resistance. Intriguingly, thanks to the gel-like rheological behavior of the emulsion, ultralight graphene scaffolds with programmable geometries are obtained by 3D printing. This work provides a general approach for the preparation of ultralight and superelastic graphene aerogels with excellent EMI shielding properties, showing broad application prospects in various fields.

Electrothermally-Driven Ultrafast Chemical Modulation of Multifunctional Nanocarbon Aerogels.

Ultrahigh-temperature Joule-heating of carbon nanostructures opens up unique opportunities for property enhancements and expanded applications. This study employs rapid electrical Joule-heating at ultrahigh temperatures (up to 3000 K within 60 s) to induce a transformation in nanocarbon aerogels, resulting in highly graphitic structures. These aerogels function as versatile platforms for synthesizing customizable metal oxide nanoparticles while significantly reducing carbon emissions compared to conventional furnace heating methods. The thermal conductivity of the aerogel, characterized by Umklapp scattering, can be precisely adjusted by tuning the heating temperature. Utilizing the aerogel's superhydrophobic properties enables its practical application in filtration systems for efficiently separating toxic halogenated solvents from water. The hierarchically porous aerogel, featuring a high surface area of 607 m2 g-1, ensures the uniform distribution and spacing of embedded metal oxide nanoparticles, offering considerable advantages for catalytic applications. These findings demonstrate exceptional catalytic performance in oxidative desulfurization, achieving a 98.9% conversion of dibenzothiophene in the model fuel. These results are corroborated by theoretical calculations, surpassing many high-performance catalysts. This work highlights the pragmatic and highly efficient use of nanocarbon structures in nanoparticle synthesis under ultrahigh temperatures, with short heating durations. Its broad implications extend to the fields of electrochemistry, energy storage, and high-temperature sensing.

Ultralight and Robust Covalent Organic Framework Fiber Aerogels.

Shaping covalent organic frameworks (COFs) into macroscopic objects with robust mechanical properties and hierarchically porous structure is of great significance for practical applications but remains formidable and challenging. Herein, a general and scalable protocol is reported to prepare ultralight and robust pure COF fiber aerogels (FAGs), based on the epitaxial growth synergistic assembly (EGSA) strategy. Specifically, intertwined COF nanofibers (100-200 nm) are grown in situ on electrospinning polyacrylonitrile (PAN) microfibers (≈1.7 µm) containing urea-based linkers, followed by PAN removal via solvent extraction to obtain the hollow COF microfibers. The resultant COF FAGs possess ultralow density (14.1-15.5 mg cm-3) and hierarchical porosity that features both micro-, meso-, and macropores. Significantly, the unique interconnected structure composed of nanofibers and hollow microfibers endows the COF FAGs with unprecedented mechanical properties, which can fully recover at 50% strain and be compressed for 20 cycles with less than 5% stress degradation. Moreover, the aerogels exhibit excellent capacity for organic solvent absorption (e.g., chloroform uptake of >90 g g-1). This study opens new avenues for the design and fabrication of macroscopic COFs with excellent properties.

One-Pot Hydrothermal-Derived rGO/MXene/Sulfur Composite Aerogels as Free-Standing Cathodes in Lithium-Sulfur Batteries.

The confinement and high utilization of sulfur in the cathodes is critical for improved cycling performance of lithium-sulfur batteries. In this case one-pot hydrothermal strategy is developed to produce rGO/MXene/sulfur composite aerogels where sulfur is in situ trapped in the 3D rGO/MXene conductive skeleton. The optimized composite aerogels as free-standing cathodes delivery a specific capacity of 951 mAhg-1 after 100 cycles at 0.2 C with a low fading rate of 0.062 % per cycle. The excellent cycling performance is correlated with highly oxidized MXene and in situ formed sulfate/thiosulfate complex layer in the long-term cycles.

Reduced graphene oxide/SiC nanowire composite aerogel prepared by a hydrothermal method with excellent thermal insulation performance and electromagnetic wave absorption performance.

In aerospace and downhole exploration, materials must function reliably in challenging environments characterized by high temperatures and complex electromagnetic (EM) interference. Graphene oxide (GO) aerogels are promising materials for thermal insulation, and the incorporation of silicon carbide nanowires can enhance their mechanical properties, thermal stability and EM absorption efficiency. In this context, citric acid acts as both a cross-linking and reducing agent, facilitating the formation of a composite aerogel comprising GO and SiC nanowires (rGO/m-SiC NWs). Compared with GO aerogels, the representative composite aerogel sample rGS4 demonstrated significantly improved mechanical properties (yield strength increased by 0.031 MPa), outstanding thermal stability (ability to withstand temperatures up to 800 °C) and remarkably low thermal conductivity (measuring just 0.061 W m-1K-1). Importantly, the composite aerogels displayed impressive EM absorption characteristics, including a slim profile (2.5 mm), high absorption capacity (-42.23 dB) and an exceptionally broad effective absorption bandwidth (7.47 GHz). Notably, the specific effective absorption bandwidth of composite aerogels exceeded that of similar composite materials. In conclusion, rGO/m-SiC NWs exhibited exceptional mechanical properties, remarkable thermal stability, efficient thermal insulation and outstanding microwave absorption capabilities. These findings highlight their potential for use in high-temperature and electromagnetically challenging environments.

Structural Features of the Porous Network of Poly(Urethane) Aerogels via Gas Permeability Measurements.

The permeability for gases through polyurethane (PUR) aerogels prepared from unsorted PUR scraps by means of a recycling technique is measured with a dynamic pressure method. The permeabilities are in the range of 10-15 to 10-13 m2 and thus reflect the pore morphology observed with scanning electron microscopy. The permeability depends on the envelope density and microstructural features of the aerogels and decreases with increasing inner surface area. The comparison of the permeability with the Porod constant, which is obtained independently via small-angle X-ray scattering (SAXS), yields a high consistency with the expected theoretical relationship. However, a calculation of inner surface area based on permeability yields lower results than expected from data based on the established SAXS technique, revealing that the famous Carman-Kozeny law correlates only by trend, which is attributed to additional gas transport through the micro- and mesopores. A possible approach for the correlation of this behavior to the tortuosity is given. Several models accounting for the combined action of viscous flow, Knudsen diffusion, and molecular slip along pore walls are fitted to the experimental data, effectively qualifying the permeability measurement as time-efficient and inexpensive technique for the characterization of structural features of aerogels.