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Film capacitors with high energy storage are becoming particularly important with the development of advanced electronic and electrical power systems. Polymer-based materials have ...stood out from other materials and have become the main dielectrics in film capacitors because of their flexibility, cost-effectiveness, and tailorable functional properties. A core issue for achieving films with high performance is to process a material with high dielectric permittivity and breakdown strength but low dielectric loss. Nanocomposites and all-polymer dielectrics are two promising avenues to address this issue. Thus, in this work, the advances of the past decade are highlighted to reflect the latest developments in polymer-based film dielectrics. The key factors of dielectric properties, including polarization mechanisms, dielectric breakdown strength, filler–matrix interface, and hierarchical structures are discussed in detail. A comprehensive understanding of the fabrication of polymer-based materials with special constituents, molecular segments, and microstructures will provide guidance to engineers on the fabrication of polymer-based materials with high performance.
Hybrid fillers composed of carbon nanotubes (CNTs) grown on graphene nanoplatelets (GNPs) were dispersed into epoxy matrix to serve as promising reinforcements. And the CNT–GNP/epoxy composite shows ...distinctive self-sensing behavior for in situ monitoring the onset of irreversibly permanent deformation. Here it has been established that the embedding of CNT–GNP hybrids into pristine epoxy endows optimum dispersion of CNTs and GNPs as well as better interfacial adhesion between the carbon fillers and matrix, which results in a significant improvement in load transfer effectiveness. Remarkably enhanced mechanical properties in the CNT–GNP/epoxy composite were achieved at ultralow hybrid loading (0.5wt.%). The tensile modulus showed ∼40% increase and the tensile strength was enhanced by ∼36% with respect to the neat epoxy. The reinforcement efficiency of the CNT–GNP hybrids is found to outperform that of the CNT+GNP mixture predicted using the modified Halpin-Tsai modeling. The in situ electrical resistance of the CNT–GNP/epoxy composite initially increases to its maximum value and then begins to decrease with the appearance of residual strain and irreversible deformation, which is remarkably different from the randomly oriented CNTs filled composites only with monotonic increase of the resistance until their catastrophic fracture.
Regulating the coordination environment of atomically dispersed catalysts is vital for catalytic reaction but still remains a challenge. Herein, an ionic exchange strategy is developed to fabricate ...atomically dispersed copper (Cu) catalysts with controllable coordination structure. In this process, the adsorbed Cu ions exchange with Zn nodes in ZIF‐8 under high temperature, resulting in the trapping of Cu atoms within the cavities of the metal−organic framework, and thus forming Cu single‐atom catalysts. More importantly, altering pyrolysis temperature can effectively control the structure of active metal center at atomic level. Specifically, higher treatment temperature (900 °C) leads to unsaturated Cu–nitrogen architecture (CuN3 moieties) in atomically dispersed Cu catalysts. Electrochemical test indicates atomically dispersed Cu catalysts with CuN3 moieties possess superior oxygen reduction reaction performance than that with higher Cu–nitrogen coordination number (CuN4 moieties), with a higher half‐wave potential of 180 mV and the 10 times turnover frequency than that of CuN4. Density functional theory calculation analysis further shows that the low N coordination number of Cu single‐atom catalysts (CuN3) is favorable for the formation of O2* intermediate, and thus boosts the oxygen reduction reaction.
An ionic exchange strategy is developed to fabricate atomically dispersed CuNC material with unsaturated CuN centers (CuN3 moieties), which possesses a higher half‐wave potential of 180 mV and the 10 times turnover frequency than that with CuN4 moieties in the oxygen reduction reaction (ORR) test. Furthermore, the optimum CuN3 catalyst demonstrates a better performance in ORR and zinc–air batteries compared with commercial Pt/C.
Carbon nanotubes (CNTs) based percolative polymer nanocomposites own a high dielectric constant at a small amount of CNTs. However, CNTs are easy to connect with each other directly in the vicinity ...of percolation threshold (fc), which unavoidably leads to an abrupt increase in dielectric loss. Herein, we propose a facile way to fabricate core-shell structured CNTs@amorphous carbon (CNTs@AC) hybrids by chemical vapor deposition (CVD). The CNT@AC hybrids were subsequently integrated into polyvinylidene fluoride (PVDF) matrix to fabricate CNTs@AC/PVDF dielectric nanocomposites by the combination of solution casting and extrusion-injection procedures. The uniform AC shell provides an insulative interlayer for the adjacent CNTs, which not only hinders the direct contact of CNTs but also improves the dispersibility of CNTs in PVDF matrix. Compared with pristine CNTs (P-CNTs)/PVDF nanocomposites, the fc increases from 7.16 vol % to 11.81 vol % and the dielectric loss decreases from 83.66 to 1.35 for the CNTs@AC-60/PVDF nanocomposites, which indicates that the percolation behavior is delayed. The results indicate that the influence of AC interlayer on the dielectric performance of the nanocomposites after percolation is much more evident than that before percolation. All these results demonstrate that this strategy is effective to enhance the dielectric performance of polymer nanocomposites and the design concept could be extended to other carbon hybrids materials.
In this paper, a data-driven-based computational homogenization method based on neural networks is proposed to describe the nonlinear electric conduction in random graphene-polymer nanocomposites. In ...the proposed technique, the nonlinear effective electric constitutive law is provided by a neural network surrogate model constructed through a learning phase on a set of RVE nonlinear computations. In contrast to multilevel (FE
2
) methods where each integration point is associated with a full nonlinear RVE calculation, the nonlinear macroscopic electric field-electric flux relationship is efficiently evaluated by the surrogate neural network model, reducing drastically (by several order of magnitudes) the computational times in multilevel calculations. Several examples are presented, where the RVE contains aligned graphene sheets embedded in a polymer matrix. The nonlinear behavior is due to the modeling of the tunelling effect at the scale of graphene sheets.
Efficient and low-cost electrocatalysts for oxygen reduction reaction (ORR) were the key for scalable application of metal–air batteries and fuel cells. Herein, iron-based nitrogen-doped carbon ...catalysts (Fe–N–C
wood
) were prepared, using hydrothermal-pyrolysis-treated wood-derived nitrogen-doped carbon as the support. This support possessed large specific surface area and macro–meso–micro hierarchical porous networks, ensuring fluent mass transfer of electrolyte and oxygen species. In the ORR electrochemical test, Fe–N–C
wood
catalyst showed an excellent activity, with a half-wave potential of 0.90 V in 0.1 M KOH, and a half-wave potential of 0.70 V in 0.1 M HClO
4
. Moreover, durability tests illustrated that Fe–N–C
wood
possessed high stability and methanol tolerance. The Fe–N–C
wood
-based Zn–air battery delivered a peak power density of 231 mW cm
−2
, suggesting its potential applications in sustainable energy conversion systems.
Graphical abstract
A highly efficient ORR electrocatalyst was obtained by embedding iron nanoparticles with hydrothermal-pyrolysis-treated wood-derived carbon.
Carbon nanotubes have unprecedented electronic properties and large specific areas as nanoscale fillers, but their potential has not been fully realized in polymer composites due to the poor ...dispersion and weak interfacial interaction. Here, we present a robust and simple procedure to prepare polymer-based composites with a remarkable molecular level interaction at interfaces through melt-mixing pristine multiwalled carbon nanotubes (MWNTs) within poly(vinylidene fluoride) (PVDF) matrix. The interfacial interaction is confirmed by Raman spectroscopy as well as the formation of much thin PVDF layer on individual MWNT. The resultant nanocomposite with a huge interfacial area possesses a giant dielectric permittivity (3800) of 3 orders of magnitude higher than the PVDF matrix, while retaining a low conductivity level (6.3 × 10−5 S.m−1) and an excellent thermal stability. These results could be explained by a reinforced Maxwell−Wagner−Sillars (MWS) effect based on the remarkable molecular level interaction.
Function-integration in glass fiber (GF) reinforced polymer composites is highly desired for developing lightweight structures and devices with improved performance and structural health monitoring. ...In this study, homogeneously aligned carbon nanotube (CNT) shell was in situ grafted on GF by chemical vapor deposition (CVD). It was demonstrated that the CNT shell thickness and weight fraction can be modulated by controlling the CVD conditions. The obtained hierarchical CNTs-GF/epoxy composites show highly improved electrical conductivity and thermo-mechanical and flexural properties. The composite through-plane and in-plane electrical conductivities increase from a quasi-isolator value to ∼3.5 and 100 S/m, respectively, when the weight fraction of CNTs grafted on GF fabric varies from 0% to 7%, respectively. Meanwhile, the composite storage modulus and flexural modulus and strength improve as high as 12%, 21%, and 26%, respectively, with 100% retention of the glass transition temperature. The reinforcing mechanisms are investigated by analyzing the composite microstructure and the interfacial adhesion and wetting properties of CNTs-GF hybrids. Moreover, the specific damage-related resistance variation characteristics could be employed to in situ monitor the structural health state of the composites. The outstanding electrical and structural properties of the CNTs-GF composites were due to the specific interfacial and interphase structures created by homogeneously grafting aligned CNTs on each GF of the fabric.
Dielectric elastomer (DE) is one type of promising field-activated electroactive polymer. However, its significant electromechanical actuated properties are always obtained under a giant electric ...voltage, which greatly restricts the potential applications of DE. In the present work, the well-constructed core-shell TiO2@SiO2 nanoparticles were fabricated by using the classical Stöber method. A series of TiO2@SiO2 nano-architectures-filled polydimethylsiloxane (PDMS) composites were prepared via solution blending and compression-molding procedures. Benefiting from the additional SiO2 shell, both the interfacial compatibility between fillers and matrix and core-shell interfacial interaction can be improved. The TiO2@SiO2/PDMS nanocomposites exhibit a significantly enhanced in-plane actuated strain of 6.08% under a low electric field of 30 V·μm−1 at 16 vol.% TiO2@SiO2 addition, which is 180% higher than that of neat PDMS. The experimental results reveal that the well-designed core-shell structure can play an important role in both improving the electromechanical actuated property and maintaining a good flexibility of DE composites. This research provides a promising approach for the design of the novel composites with advanced low-field actuated electromechanical property in next generation DE systems.
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