Electrochemical Strategy for Flexible and Highly Conductive Carbon Films: The Role of 3-Dimensional Graphene/Graphite Aggregates

In situ growth of binder-free CoNi0.5-MOF/CC electrode for high-performance flexible solid-state supercapacitor application

Metal organic frameworks (MOFs) with binder-free electrodes have shown promise for portable electrochemical energy storage applications. However, their low specific capacitance and challenges associated with the attachment of active materials to the substrate constrain their practical utility. In this research, we prepared a CoNi0.5-MOF/CC electrode by in situ growth of CoNi0.5-MOF on an H2O2-pretreated carbon cloth (CC) without using any binder. It exhibits a higher specific capacitance of 1337.5 F g-1 than that of CoNi0.5-MOF (∼578 F g-1) at a current density of 1 A g-1 and an excellent rate ability of 88% specific capacitance retention at a current density of 10 A g-1 after 6000 cycles. The as-assembled flexible asymmetric solid-state supercapacitor based on the CoNi0.5-MOF/CC positive electrode and a nitrogen-doped graphene (N-Gr) negative electrode exhibits an energy density of 61.46 W h kg-1 at a power density of 1244.56 W kg-1 and holds a stable capacitance of ∼125 F g-1 at 1 A g-1 when the flexible supercapacitor is bent, showing great potential for flexible electronics application. The H2O2 is indicated to play an important role, enhancing the adhesion of CoNi0.5-MOF on CC and reducing its charge transfer resistance by functionalizing the carbon fiber during the pretreatment of the CC matrix. The results provide a great way to prepare a flexible asymmetric solid-state supercapacitor with both high power density and high energy density for practical application.

Efficient, Robust, and Flame-Retardant Electrothermal Coatings Based on a Polyhedral Oligomeric Silsesquioxane-Functionalized Graphene/Multiwalled Carbon Nanotube Hybrid with a Dually Cross-Linking Structure

Graphene electrothermal coatings have attracted considerable attention in recent years due to their important application prospects in a broad range of areas. So far, lots of strategies have been explored for producing them. However, these strategies usually involve a complicated process with sophisticated conditions, limiting their scalable applications. Herein, we demonstrate a facile strategy for preparing efficient, robust, and flame-retardant electrothermal coatings from liquid-phase exfoliated graphene, by combining with multiwalled carbon nanotubes (MWCNTs) and polyhedral oligomeric silsesquioxane (POSS) nanoparticles. This relies on the use of a hyperbranched polyethylene copolymer that simultaneously bears UV-reactive moieties and POSS terminal groups. As a stabilizer, the copolymer can effectively promote the exfoliation of both graphite and MWCNTs in common organic solvents under sonication, rendering the POSS-functionalized graphene and MWCNTs well dispersible in the solvent. From their dispersions, POSS-functionalized graphene/MWCNT hybrid electrothermal coatings have been successfully prepared simply by vacuum filtration and UV irradiation under mild conditions. It has been confirmed that a dually cross-linking structure can be formed in the hybrid system. This significantly improves the thermal resistance of resultant coatings, which remain exhibiting a stable work state even at a temperature high as 280 °C without the occurrence of flammation. Meanwhile, this also endows them with excellent electrothermal performance and service stability. At a relatively low voltage, 15 V, the steady temperature can reach 188.4 °C, with a response time < 30 s; after being alternately folded for 2700 cycles or scraped 200 times, the coating still maintains a stable state. In particular, the process involved is relatively simple with mild conditions. With these features, the coatings obtained herein may find their important applications in the area of wearable devices and household heating systems.

Combining cobalt ferrite and graphite with cellulose nanocrystals for magnetically active and electrically conducting mesoporous nanohybrids

Free-standing mesoporous membranes based on cellulose nanocrystals (CNCs) are fabricated upon the incorporation of cobalt ferrite (CoFe₂O₄) and graphite nanoparticles at concentrations up to 20 wt % through a soft-templating process. Scanning electron microscopy (SEM) and N₂ adsorption-desorption isotherms reveal the development of highly-porous interconnected random 3D structure with surface areas up to 193.9 m² g^-1. Thermogravimetric analysis (TGA) shows an enhanced thermal stability thanks to the formation of a tortuous network limiting the hindrance of degradation by-products. Vibrating sample magnetometer (VSM) reveals a maximum magnetization saturation of 8.77 emu·g^-1 with materials having either ferromagnetic or diamagnetic behaviour upon the incorporation of CoFe₂O₄ and graphite, respectively. Four-point-probe measurements display a maximum electrical conductivity of 9.26 ± 0.04 S·m^-1 when graphite is incorporated into CNCs. A proof of concept for the applicability of synthesized nanohybrids for environmental remediation is provided, presenting the advantage of their easy recovery using external magnetic fields.

Highly Thermoconductive, Thermostable, and Super-Flexible Film by Engineering 1D Rigid Rod-Like Aramid Nanofiber/2D Boron Nitride Nanosheets

Polymer-based thermal management materials have many irreplaceable advantages not found in metals or ceramics, such as easy processing, low density, and excellent flexibility. However, their limited thermal conductivity and unsatisfactory resistance to elevated temperatures (<200 °C) still prevent effective heat dissipation during applications with high-temperature conditions or powerful operation. Therefore, herein highly thermoconductive and thermostable polymer nanocomposite films prepared by engineering 1D aramid nanofiber (ANF) with worm-like microscopic morphologies into rigid rod-like structures with 2D boron nitride nanosheets (BNNS) are reported. With no coils or entanglements, the rigid polymer chain enables a well-packed crystalline structure resulting in a 20-fold (or greater) increase in axial thermal conductivity. Additionally, strong interfacial interactions between the weaved ANF rod and the stacked BNNS facilitate efficient heat flux through the 1D/2D configuration. Hence, unprecedented in-plane thermal conductivities as high as 46.7 W m^-1 K^-1 can be achieved at only 30 wt% BNNS loading, a value of 137% greater than that of a worm-like ANF/BNNS counterpart. Moreover, the thermally stable nanocomposite films with light weight (28.9 W m^-1 K^-1 /10³ (kg m^-3 )) and high strength (>100 MPa, 450 °C) enable effective thermal management for microelectrodes operating at temperatures beyond 200 °C.