Carbon Nanofiber Aerogels Research Articles

Amine-impregnated elastic carbon nanofiber aerogel templated by bacterial cellulose for CO2 adsorption and separation

Carbon aerogel has become a promising electrode material for CO2 capture and capacitor due to its large specific surface area, well-developed pore structure, adjustable porosity and ultra-high specific power. However, most of the carbon-based materials suffer from poor mechanical properties, low recycling efficiency, and low adsorption capacity, making it difficult to be put into industrial applications on a large scale. Bacterial cellulose (BC) has an ultra-fine reticular structure, a modulus of elasticity that is several to more than ten times that of typical plant fibers, and high tensile strength. In this paper, BC was treated by unidirectional freeze-drying method, and the aerogels with ordered honeycomb pore structure were constructed by unidirectional growth of ice crystals, and the pyrolytic chemical properties of BC were adjusted by using (NH4)2SO4, which effectively prevented the shrinkage and deformation of materials during carbonization, and successfully prepared elastic nanocarbon fiber aerogels. At the same time, the introduction of (NH4)2SO4 made the material realize N doping in the carbonization process, providing more adsorption sites, which was conducive to the adsorption of CO2. Finally, the carbon fiber nanoaerogel was modified by TEPA to further improve its adsorption selectivity for CO2. The prepared elastic carbon nanofiber aerogel (CBCNT) has high CO2 adsorption performance and high selectivity, and its CO2 capture capacity is up to 4.88 mmol/g. At the same time, its capacitance also reached 246F/g.

Miniaturized Hard Carbon Nanofiber Aerogels: From Multiscale Electromagnetic Response Manipulation to Integrated Multifunctional Absorbers

AbstractThe multiscale structural engineering strategy presents a powerful method for tailoring the structural attributes of materials at various levels, enabling the flexible control and manipulation of their electromagnetic properties. Nonetheless, orchestrating the multiscale architecture of polymer‐derived carbon aerogels specifically for microwave absorption poses significant challenges. Herein, aramid‐derived hard carbon nanofiber aerogel microspheres (CNFAMs) featuring a hierarchical skin‐core structure are fabricated through a wet‐spinning technique, combined with reprotonation‐mediated self‐assembly and carbonization processes. The presence of large‐scale voids between neighboring microspheres and the microscale porosity within the microspheres themselves improves impedance matching and promotes microwave reflection and scattering. The distinct graphitic domains and defects serve as pivotal elements for conduction and polarization losses, significantly impacting microwave attenuation. By meticulously tailoring the macroscale dimensions, microscale porous architecture, and nanoscale domains, the optimized CNFAMs demonstrate a remarkable absorption bandwidth of 9.62 GHz at an ultralow filling of 0.97 wt%. Additionally, the implementation of application‐oriented microwave absorption through the innovative integration of polysilsesquioxane‐CNFAMs in a host–guest aerogel is explored. This composite system brings together broadband absorption, superhydrophobicity, thermal insulation, resistance to freezing, and robust tolerance to harsh environments. Such a multifaceted approach is designed to tackle the growing challenges associated with complex electromagnetic environments effectively.

Carbon nanofiber aerogel microspheres with heterogeneous skin-core structure for broadband electromagnetic wave absorption

The advancement in the miniaturization of carbon aerogels into micro-sized spheres represents a significant development in the creation of ultralight, broadband microwave absorbers. Notwithstanding this innovation, there is still a considerable challenge in optimizing microwave absorption (MA) performance through heterointerface engineering within aerogel microspheres. Herein, we have developed skin-core heterogeneous aerogel microspheres by the in situ generation of ZIF-67 nanocrystals on the wet-spun aramid nanofiber (ANF) aerogel microspheres, followed by a high-temperature carbonization process. The resulting Co@C nanoparticle-enshrouded ANF-derived carbon nanofiber aerogel microspheres (Co@C/CNFAMs) demonstrate an exceptional equilibrium between impedance matching and multi-faceted attenuation. Remarkably, the Co@C/CNFAM2 sample attains a maximum effective absorption bandwidth of 8.72 GHz, while maintaining an ultralow filler proportion of 1.5 wt%. Moreover, the Co@C/CNFAM3 sample achieves a minimum reflection loss of −72.34 dB with a filling ratio of 1.2 wt%. Our findings offer a refined approach to the intricate engineering of heterostructures, along with the strategic macrostructural design, paving the way for the development of aerogel-based microwave absorbers that represent the next step in material science innovation.

Ultra-light, ultra-resilient and ultra-flexible, multifunctional composite carbon nanofiber aerogel for physiological signal monitoring and hazard warning in extreme environments

The emergence of multimodal wearable flexible self-powered electronic devices undoubtedly plays a positive role in areas such as healthcare and energy. However, the preparation of three-dimensional elastic bodies suitable for humidity, temperature, and pressure sensing often involves complex fabrication processes, internal network discontinuities, and difficulties in achieving applications in extreme environments. In this paper, a one-step preparation of three-dimensional fluffy and interlayer porous nanofiber precursors is achieved using direct electrostatic spinning technology. Subsequently, high-temperature calcination and in situ polymerization processes were used to obtain multifunctional composite carbon nanofiber aerogels (MCCNA), which are characterized by ultra-lightness, super elasticity, three-dimensional fluffiness, and interlayer porousness, and are suitable for extreme environments. The ultra-light (53.67 mg cm−3) MCCNA can accurately detect humidity signals over an extremely wide range (10 %RH to 95 %RH), with a minimum temperature response time of 0.5 K. Its pressure response time is only 20 ms, and even after 5000 cycles of pressure loading, it still maintains a stable electrical signal response. Most notably, through demonstration, MCCNA can monitor the actions of firefighters in high-temperature and complex situations such as fires. Furthermore, it can monitor and provide high-temperature warnings for the temperature thresholds in the microenvironment of firefighting suits. The developed self-powered flexible wearable electronic device holds outstanding prospects for applications in healthcare, energy, and extreme conditions.

In-situ synthesis of Co/Co3O4 nanoparticles decorated carbon nanofiber aerogels for lightweight electromagnetic wave absorption rubber composites with multiple loss effects

Carbon-based magnetic absorbents are widely used for electromagnetic wave absorption (EMWA) rubber composites due to the dual electromagnetic wave loss effects of dielectric loss and magnetic loss. Co/Co3O4 nanoparticles decorated carbon nanofiber aerogels (C/Co/Co3O4 aerogels) are prepared by carbonization of nanofiber network structure agarose/cobalt acetate. The in-situ synthetic C/Co/Co3O4 aerogels with carbon nanofiber network structure and controllable particle size of Co/Co3O4 nanoparticles that have the good conductivity and tunable magnetic property increasing both of the dielectric loss and magnetic loss capabilities, which can improve the EMWA performance. Lightweight EMWA rubber composites with 3.75 wt% C/Co/Co3O4 aerogels have the same density as that of silicone rubber (PDMS), the effective absorption band (EAB, frequency for reflection loss<−10 dB) of PDMS/Co-1.25 is aways above 3 GHz when the thickness is bigger than 2.5 mm, the max EAB is 4.24 GHz at the thickness of 2.74 mm. The radar cross section (RCS) reduction can achieve 14 dBm2 when the perfectly electrically conductive (PEC) is covered by a 4.5 mm thick PDMS/Co-1.25. The intensity distributions of electric field, magnetic field and power loss density of EMWA rubber composites are exhibited based on the electromagnetic parameters. The rubber composites based on C/Co/Co3O4 aerogels can be used as lightweight flexible EMWA materials.

Electromagnetic wave absorption performance and rheological behavior of rubber composites with low mass filling rate carbon nanofiber aerogel

With the development of electronic information science and technology, electromagnetic information security and electromagnetic pollution become more and more serious. Electromagnetic wave absorption (EMWA) rubber based on the absorbent of carbon with low density and good corrosion resistance is a kind of good EMWA materials for solving electromagnetic information security and electromagnetic pollution. In this article, three-dimensional network structure carbon nanofiber aerogels (3DNSCAs) are prepared by vacuum annealing of three-dimensional network structure agarose/zinc acetate obtained by freeze-drying of agarose/zinc acetate gel. The EMWA rubber composites with 2.2% (in mass) 3DNSCAs have almost the same density as silicone rubber (PDMS), and the dispersity of 3DNSCAs in PDMS is studied by rheological analysis. The effective absorption bandwidth (EAB, frequency for reflection loss <–10 dB) of the 2 mm thick PDMS/C-800 is 4 GHz, and the minimum value of reflection loss (RLmin) is −52 dB with the thickness of 3.5 mm. The PDMS/C-1000 with the thickness of 3.5 mm has an EAB up to 4.8 GHz. Radar cross section (RCS) reduction of PDMS/C-800 can achieve 20 dB⋅m2 at the frequency of 6 GHz.

Integrating FeOOH with bacterial cellulose-derived 3D carbon nanofiber aerogels for fast and stable capacitive deionization based on accelerating chloride insertion

Faradic capacitive deionization (FDI), as an emerging research branch of capacitive deionization (CDI), has shown its great potential to relieve global water stress owing to its high desalination capacity/efficiency, flexible scale, and zero secondary pollution characteristics. However, the slow desalination kinetics and poor cyclic stability of the anion-capturing electrode of current FDI systems greatly limit its practical application. Herein, we proposed a strategy of interweaving FeOOH nanospindle inside the 3D network structure of carbon nanofiber aerogel to construct a 3D network structure (CNFAs@FeOOH) and further used it as a chloride capture electrode for FDI. As a result, the FDI system equipped with CNFAs@FeOOH enjoys excellent desalination performance with an ultrahigh desalination rate of up to 0.33 mg g−1 s−1. More importantly, the CNFAs@FeOOH-based FDI system enjoys excellent cycling stability with no significant decrease in 100 cycles and only 17.85 % decrease in 200 cycles.

Highly dispersed amorphous nano-selenium functionalized carbon nanofiber aerogels for high-efficient uptake and immobilization of Hg(II) ions

Owing to the strong Hg−Se interaction, Se-containing materials are promising for the uptake and immobilization of Hg(II) ions; compared with metal selenides or selenized compounds, elemental Se contains the highest ratio of Se. However, it remains a challenge to fully expose all the potential Se binding sites and achieve high utilization efficiency of elemental Se. Through rational design on the structure, dispersity, and size of materials, Se/CNF aerogels composed of abundant well-dispersed and amorphous nano-Se have been prepared and applied for the high-efficient uptake and immobilization of Hg(II) ions. The well-dispersion of nano-Se increases the exposure of Se sites, the amorphous structure benefits the easy cleavage of Se−Se bonds, the 3D porous networks of aerogels permit fast ions transport and easy operation. Benefiting from the combination effect of strong Hg−Se interaction and sufficient exposure of Se-enriched sites, the Se/CNF aerogels demonstrate strong binding ability (Kd = 3.8 ×105 mL·g-1), high capacity (943.4 mg·g-1), and preeminent selectivity (αMHg > 100) towards highly toxic Hg(II) ions. Notably, the utilization efficiency of Se in Se/CNF aerogels is as high as 99.5%. Moreover, the strong Hg−Se interaction and extraordinary stability of HgSe could minimize the environmental impact of the spent Se/CNF adsorbents after its disposal.

Multistage pore structure legume-like UiO-66-NH2@carbon nanofiber aerogel modified electrode as an electrochemical sensor for high sensitivity detection of HMIs

Electrode material is the core component of electrochemical sensor, which has a decisive influence on the detection performance of heavy metal ions. A novel electrochemical sensor based on amino modified metal-organic frameworks loaded three-dimensional carbon nanofiber aerogel composite material was proposed. The UiO-66-NH2 was embedded into nanofibers through one-step electrospinning technology to forming a legume-like structure, ensuring the number of active sites N coordination with HMIs, which improved enrichment capacity of the sensor. 3D carbon nanofiber aerogel with multistage pore structure was developed by one-dimensional nanofibers as unit modules, which increases conductive path and HMIs transport channel. Accordingly, the UiO-66-NH2 @carbon nanofiber aerogel modified electrode (N-U@CFA/GCE) as an electrochemical sensor exhibited an ultra-high sensitivity and the low limit of detection for the simultaneous detection of Cd2+ (0.52 nM) and Pb2+ (0.46 nM) using the differential pulse anode stripping voltammetry and was feasible and accurate for the detection of actual environmental water. The novel sensor platform has high sensitivity, stability and anti-interference, which showing great potential on HMIs monitoring.

Fe-single-atom catalyst nanocages linked by bacterial cellulose-derived carbon nanofiber aerogel for Li-S batteries

Li-S battery (LSB) is promising for achieving high capacity. Still, its development is hindered by the complex redox process with sluggish kinetics and particularly the resulting lithium polysulfides (LiPS) shuttle effects. Single-atom catalysts (SACs), with their maximized atom utilization, could effectively chemisorb soluble LiPSs and expedite the sulfide conversion reaction kinetics. Here we report incorporating Fe single metal atom catalyst (Fe-SAC) in the sulfur cathode design and its electrocatalytic effects. Fe-doped ZIF-8 nanocages were introduced into a cheap biomass bacteria cellulose. A pyrolysis process converted them into an aerogel structure with Fe-SAC-functionalized N-doped carbon nanocages linked by a carbon nanofiber network (FeSA-NC@CBC), which was applied as a scaffold to fabricate freestanding and binder-free sulfur cathodes. We conducted electrochemical measurements to reveal Fe-SAC functions including lowering energy barriers for S8 reduction to liquid-phase LiPSs and further to solid-phase Li2S2/Li2S and accelerating Li2S2/Li2S nucleation and deposition, as corroborated by our theoretical calculation results. Benefiting from the synergistic effects of highly active Fe-SAC and three-dimensional conductive network, the sulfide reaction kinetics is improved, which can diminish LiPS shuttle effects and therefore improve LBS rate performance and cycling stability. Accordingly, the fabricated FeSA-NC@CBC composite cathode delivers an excellent rate capability at 2C with a reversible capacity of 840 mAh/g and a long-term cyclic stability of 800 mAh/g at 1C after 500 cycles.

Bacterial cellulose derived carbon nanofiber aerogel assembled with redox active hydrogel and alpha-MoO3 nanoplate for high-performance supercapacitors

Dual-asymmetric supercapacitors (DASCs) with high capacitive performance were developed in this work through carefully design and configuration of all the capacitor components. Free-standing carbon aerogel was directly utilized as the positive electrode, which was fabricated by pyrolyzing bacterial cellulose (BC) aerogel. Its porous structure afforded it excellent interface with the redox active electrolyte. Redox active hydrogel electrolyte based on mixed-valence iron ions (PVA/H2SO4/Fe3+/2+) was prepared with a freezing-thawing method and combined with the carbon aerogel to form the positive compartment of the capacitors. Meanwhile, α-MoO3 nanoplates were fabricated by hydrothermal method and used for the fabrication of negative electrodes, which were assembled with conventional PVA/H2SO4 hydrogel electrolyte to form the negative compartment. The as-assembled DASCs showed a specific capacitance of 560.8 F g−1 at 1 A g−1 and energy density of 131.6 Wh kg−1, indicating its remarkable capacitive performance. Moreover, the optimized DASC displayed a remarkable long-term cycling stability. This work on the design and assembly of the battery-like supercapacitor with carbon aerogel electrodes combined with their corresponding hydrogel electrolytes afforded a new configuration to fabricate the devices with high performance.

Zn-incorporated joule-heated carbon nanofiber aerogel-supported Cu catalyst for hydrogen production via methanol steam reforming

Conventional Cu-based catalysts are affected by disadvantages, such as uneven temperature distribution, non-uniformity of mass and heat transfer, slow heating rate, and difficult replacement. To address these, a three-dimensional (3D) Zn-incorporated Joule-heated carbon nanofiber aerogel (CNFA)-supported Cu catalyst, was prepared via a facile one-pot method. The optimized catalyst, Cu10–Zn10/CNFA, exhibited an 83.1% conversion of CH3OH and 0.01% selectivity of CO at 250 °C. This improvement was due to Zn species acting as both an isolating agent, which inhibited thermal transmigration and aggregation of Cu-containing nanoparticles during heat treatment, and a combining agent, which provided numerous Cu–ZnO interfaces that enabled strong interactions between Cu and ZnO, which improved the activity and stability of the methanol steam reforming (MSR) reaction. This study reveals the feasibility of utilizing Joule-heated CNFA-supported catalysts for MSR reactions and opens a new avenue for designing and fabricating 3D-ordered porous catalysts related to this transformation.

A Joule-heated carbon nanofiber aerogel-supported catalyst for hydrogen production via methanol steam reforming

Copper (Cu)-containing catalysts are preferable in the methanol steam reforming (MSR) process because of their abundant sources, low cost, and high low-temperature activities. During operation, Cu-containing catalysts are typically heated by an external heat source and are most commonly used in their macroscopic powdered form, leading to uneven temperature distributions, nonuniform mass/heat transfer, slow heating rates, and difficult replacement. These issues must therefore be addressed in the design of specific catalysts for the MSR reaction. Herein, a three-dimensional Joule-heated carbon nanofiber aerogel (CNFA)-supported catalyst (Cu/CNFA-op10) was prepared by a facile one-pot method and followed by the catalytic evaluation. It was found that the even temperature distribution, effective heat/mass/electron transfer, and uniform distribution of the Cu nanoparticles, were responsible for the excellent catalytic activities. In addition, the deactivation of the CNFA-supported catalyst was also found and caused by the aggregation and sintering of Cu0/+ nanoparticles, the deposition of amorphous carbon on the surface of active sites, and the chemical state transition of the active particles. In this proof-of-concept demonstration, the high catalytic activity of the Joule-heating-driven catalyst provides a novel strategy for further designing and fabricating 3D monolithic catalysts related to the MSR reaction.

Well-aligned MXene@MoS2/Carbon nanofiber aerogels reinforced epoxy composites with splendid thermal and tribological performance

Epoxy resin (EP) composites are attracting intensive interest for aviation aircraft applications due to superior machinability and high corrosion resistance. However, the poor tribological performance of EP matrix greatly limits its wide application because of highly brittle and weak thermal properties. Herein, we constructed a vine-like MXene@MoS2/Carbon nanofiber aerogel (MMoCA) via directed freezing method and cellulose carbonization treatment. The obtained MMoCA exhibited long-range-aligned 3D porous lamellar structure and the MXene@MoS2 attached to carbon nanofiber surface presented good dispersion inside the aerogel. Such a novel aerogel bestowed the EP composites with outstanding thermal properties through constructing continuous oriented thermal diffusion channels inside the EP matrix. Meanwhile MMoCA reinforced EP composites (MMoCA-EP) showed great potential in tribological application, resulting from the rapid friction heat dissipation and high-quality transfer films during the friction process. This study has a significant guidance to develop high performance polymer composites in the frontier field of tribology.

SiC junction enhanced carbon nanofiber aerogels with extremely high specific strength and ultra-low thermal conductivity

C/SiC aerogels with both ultra-low thermal conductivity and extremely high strength were fabricated by freeze casting. SiC junctions originated from pyrolysis of polycarbosilane (PCS) were formed between carbon nanofibers (Cf) to enhance the strength of aerogels. The effects of PCS content and total solid content on the phase composition, pore structure, thermal conductivity and compressive property were studied. The fabricated aerogels possess hierarchical pore structure. In the micro-scale, it contains circular pores with size of about 15 µm, while it is mesoporous and macroporous in the nano-scale. Both thermal conductivity and compressive strength increase with the increase in PCS content. Through tailoring PCS content and total solid content, Cf/SiC aerogels with porosity of 99.5%, thermal conductivity of 33 mW·m−1·K−1 and compressive strength of 7.14 MPa can be obtained. The specific strength of the fabricated Cf/SiC aerogels is up to 467.6 MPa/(g/cm3), which is the highest value for ceramic aerogels.

Thermal insulation and antioxidation of vertical graphene oxide‐grafted carbon nanofiber aerogels with ceramic coating

AbstractIn this work, composite aerogels with low thermal conductivity and antioxidation were prepared by introducing graphene oxide (GO) on the carbon nanofibers (CNFs) surface, followed by ceramic coating. CNFs surface‐grafted vertical morphology of GO was used as an enhancer to hinder the heat radiation transmission. The introduced shrinkage‐resistant ceramic coating was used as an antioxidant barrier for carbon materials. The anti‐shrinking ceramic coating was obtained by heat treatment of coating with wrinkle morphology to complete the ceramic transformation. The wrinkle morphology of the coating originated from the gradient crosslinking of the coating before its ceramic transformation. Among them, the gradient crosslinking of the coating could be done by irradiation crosslinking and crosslinker impregnation crosslinking. The thermal insulation and antioxidant of the composite aerogel were jointly investigated. Moreover, the mechanism of CNFs surface grafting GO and the anti‐shrinkage mechanism of the coating were systematically discussed. The experimental results showed that the aerogel exhibited excellent thermal insulation and oxidation resistance in a wide range of temperatures. The structural design of the aerogel not only weakened the thermal radiation transmission to the CNFs aerogel but also significantly enhanced the antioxidant.

Recyclable Joule heated low shrinkage carbon nanofiber aerogels for microscale oil/water separation

• A freeze-shaping method for fabricating CNFA was proposed. • A novel CNFA was designed by directly using 1D CNF with a vine-wrapped tree structure. • Hydrophobic-lipophilic CNFA with lightweight, high porosity, great elasticity, and high Joule-heating efficiency was obtained. • The cyclic stability of CNFA was proved to be high efficiency Joule-heated adsorption for microscale levels acetone (87%) and DMF (92%). Aerogels have shown great potential as oil adsorbents but their application to the removal of microscale oil from water and their recycling remains problematic. The present work proposed a freeze-shaping method for fabricating carbon nanofiber aerogels (CNFAs) based on the direct use of one-dimensional (1D) carbon nanofibers (CNF) rather than carbonization of polymer aerogels. This technique greatly reduces volume shrinkage and increases the three-dimensional (3D) structural stability of the material. Carbon nanotubes (CNT) and gelatinized starch were incorporated in these aerogels as a conductive enhancement agent and binder, respectively, forming a “vine (CNT)-wrapped tree (CNF)” structure that improved mechanical and Joule-heating performance. The effects of glutaraldehyde added to aerogels as a cross-linking agent on mechanical properties and microstructure were also systematically investigated. The optimized CNFAs combined with low density, high porosity, good elasticity, and superior Joule-heating efficiency along with suitable adsorption capacity, excellent selectivity, and cycling stability. This material was able to selectively remove 87% and 92% of microscale acetone and dimethylformamide (DMF), respectively, from the water after nine cycles of adsorption and Joule-heating. The present work demonstrates a novel means of designing and fabricating a low shrinkage CNFA with outstanding Joule-heating performance having potential practical applications in the remediation of organic pollution.

Compressible, superelastic and fatigue resistant carbon nanofiber aerogels derived from bacterial cellulose for multifunctional piezoresistive sensors

Carbon aerogels have been widely exploited for wearable piezoresistive sensing thanks to their fascinating properties such as ultralow density, high electrical conductivity, superelasticity, and fatigue resistance, but to date, maintain high mechanical performances and high sensitivity in a wide pressure range still remains a huge challenge for carbon aerogels based piezoresistive sensors. Herein, we propose a simple but efficient morphology-maintained carbonization strategy by tailoring the pyrolysis chemistry of BC to fabricate superelastic and fatigue-resistant carbon nanofiber aerogels. Bacterial cellulose hydrogels are fabricated as nanofiber aerogels with a 3D-interconnected honeycomb-like structure by unidirectional freeze-drying technology, while the rational introduction of (NH 4 ) 2 SO 4 significantly inhibits the shrinkage and deformation of bacterial cellulose nanofiber aerogels during the carbonization process, enabling the retention of the 3D-interconnected honeycomb-like structure after carbonization. The as-prepared carbon nanofiber aerogels (CNFAs) exhibit exceptional mechanical performances of high compressibility (up to 99% strain), superelasticity (∼97.4%, 500 cycles at 90% compression), and fatigue resistance (up to 10 000 cycles). Moreover, the CNFAs derived sensor possesses a high sensitivity (5.66 kPa −1 ) at a wide pressure range (0–28 kPa), and a fast response time (∼100 ms), enabling the CNFAs-based sensor to monitor signals of the human body, spatial pressure, and voice recognition. These fascinating attributes make the CNFAs highly attractive for flexible wearable devices. • Biomass-based carbon nanofiber aerogels were designed for Multifunctional sensors. • The carbon nanofiber aerogel reveals a 3D-interconnected honeycomb-like structure. • Superior compressibility and fatigue resistance surpasses other carbon aerogels. • The carbon nanofiber aerogel possesses a high sensitivity at a wide pressure range.

Carbon nanofiber aerogel/silicon oxycarbide composites for enhanced electromagnetic interference shielding

Lightweight electromagnetic-interference (EMI)-shielding materials are urgently needed in harsh environments to tackle the increasing electromagnetic pollution and hazards. Herein, carbon-nanofiber-aerogel (CNFA) modified silicon oxycarbide (CNFA/SiOC) composites were prepared following a precursor infiltration pyrolysis procedure by using three-dimensional CNFA as a skeleton. Their structures and mass densities (0.28–1.35 g/cm3) were tunable by adjusting the content of the polysiloxane precursor in the impregnating solution. The lightweight CNFA/SiOC composite featured a continuous conductive network and a highly porous structure in the SiOC matrix, resulting in high specific shielding effectiveness (SE) (up to 68.9 dB cm3/g with SEtotal of 19.3 dB) due to enhanced conductance loss and multi-reflection/scattering. When the density is increased, the CNFA/SiOC composite can deliver EMI SE as high as 27.5 dB due to the generation of defective carbon and carbon dangling bonds as well as abundant interfaces between carbon nanofibers (CNFs) and SiOC, which induce polarization loss. Moreover, the CNFA/SiOC composite exhibits good oxidation resistance with SEtotal retention of above 98% after heat treatment at 600°C for 2 h in air, which arises from the effective protection of CNFs by SiOC.

Highly Dispersive Co@N‐C Catalyst as Freestanding Bifunctional Cathode for Flexible and Rechargeable Zinc–air Batteries

The design of efficient cathode with great cycle performance, high flexibility, and low cost is essential for the commercialization of zinc–air battery (ZAB). Herein, we report the exploration of freestanding bifunctional cathode with rationally designed structures, namely, tiny Co nanoparticles embedded in N‐doped carbon nanofiber aerogels, which have desired features including uniform Co dispersity, balanced distribution of N‐C species, hierarchically porous structure with increased fraction of meso‐ to micropores, and moderate amounts of defects. Accordingly, the as‐fabricated cathodes exhibit positive half‐wave potential of 0.82 V for oxygen reduction and small overpotential of 350 mV at 10 mA cm−2 for oxygen evolution, respectively, which deliver smaller reversible oxygen electrode index (0.76 V) than the commercial Pt/C+RuO2 (0.80 V) and most Co‐based electrocatalysts ever reported. Impressively, the as‐constructed liquid rechargeable ZAB behaves high peak power density (160 mW cm−2), large specific capacity (759.7 mAh g−1 at 10 mA cm−2, tested after 120 h of OCV tests), and robust stability over 277 h. Moreover, the as‐assembled quasi‐solid‐state ZAB using such freestanding cathode represents excellent mechanical flexibility and outstanding cycle performance, regardless of being serviced under extremely bending conditions from 0° to 180°, underscoring their promising applications as durable bifunctional cathode for portable metal–air batteries.