Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than ...batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.
Heteroatom doping and oxygen functionalizations are a promising solution to improve the energy storage performance of nanocarbon materials. The fundamental effects of doping and oxygen functionalization on the physicochemical properties of nanocarbons leading to enhanced supercapacitor performance are reviewed. This article may serve as a reference for fundamental properties and practical applications of heteroatom doped and oxygen functionalized nanocarbons.
Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are ...hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1–3 nm) 2D Ti3C2Tx
with large lateral size of about 8 µm possessing ideal viscoelastic properties are formulated for extrusion‐based 3D printing of freestanding, high specific surface area architectures to determine the viability of manufacturing energy storage devices. The 3D‐printed device achieves a high areal capacitance of 2.1 F cm−2 at 1.7 mA cm−2 and a gravimetric capacitance of 242.5 F g−1 at 0.2 A g−1 with a retention of above 90% capacitance for 10 000 cycles. It also exhibits a high energy density of 0.0244 mWh cm−2 and a power density of 0.64 mW cm−2 at 4.3 mA cm−2. It is anticipated that the sustainable printing and design approach developed in this work can be applied to fabricate high‐performance bespoke multiscale and multidimensional architectures of functional and structural materials for integrated devices in various applications.
A current‐collector‐free, interdigitated‐supercapacitor device is manufactured by 3D printing with water‐based MXene ink. Simple modifications to the ink synthesis and formulation provide unique rheological properties, which enable the printability of 3D structures of up to 25 layers high. The final structures demonstrate high specific area, resulting in high areal capacitance of the micro‐supercapacitor device.
Among 2D materials, MXenes (especially their most studied member, titanium carbide) present a unique opportunity for application via colloidal processing, as they are electrically conductive and ...chemically active, whilst still being easily dispersed in water. And since the first systematic study of colloidal MXene rheology was published in 2018 (
Rheological Characteristics of 2D Titanium Carbide (MXene) Dispersions: A Guide for Processing MXenes
by Akuzum, et al.), numerous works have presented small amounts of rheological data which together contribute to a deeper understanding of the topic. This work reviews the published rheological data on all MXene-containing formulations, including liquid crystals, mixtures and non-aqueous colloids, which have been used in processes such as stamping, patterning, 2D and 3D printing. An empirical model of aqueous titanium carbide viscosity has been developed, and recommendations are made to help researchers more effectively present their data for future rheological analysis.
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The Joule heating properties of an ultralight nanocarbon aerogel are investigated with a view to potential applications as energy‐efficient, local gas heater, and other systems. Thermally reduced ...graphene oxide (rGO) aerogels (10 mg cm−3) with defined shape are produced via emulsion‐templating. Relevant material properties, including thermal conductivity, electrical conductivity and porosity, are assessed. Repeatable Joule heating up to 200 °C at comparatively low voltages (≈1 V) and electrical power inputs (≈2.5 W cm−3) is demonstrated. The steady‐state core and surface temperatures are measured, analyzed and compared to analogous two‐dimensional nanocarbon film heaters. The assessment of temperature uniformity suggests that heat losses are dominated by conductive and convective heat dissipation at the temperature range studied. The radial temperature gradient of an uninsulated, Joule‐heated sample is analyzed to estimate the aerogel's thermal conductivity (around 0.4 W m−1 K−1). Fast initial Joule heating kinetics and cooling rates (up to 10 K s−1) are exploited for rapid and repeatable temperature cycling, important for potential applications as local gas heaters, in catalysis, and for regenerable of solid adsorbents. These principles may be relevant to wide range of nanocarbon networks and applications.
A fundamental study of the direct resistive heating of graphene aerogels demonstrates efficient, uniform, fast, and repeatable Joule heating. The outlined principles pave a route towards new applications of three‐dimensional nanocarbon networks as viable light‐weight, high‐surface‐area local gas heaters and temperature‐controlled catalyst and adsorber supports.
A new direct foaming method to produce macroporous cellular ceramics using surfactants as foam stabilizers is presented. The technology relies on the transition of a stabilized aqueous ceramic powder ...suspension containing a homogeneously dispersed alkane or air–alkane phase into cellular ceramics. The stabilization of the powder suspension and the emulsion is realized with particular emphasis on the interaction of both mechanisms providing enduring stability of the system up to high foaming degrees. Anionic, cationic, and nonionic surfactants were studied with their stabilization and foaming effects. The presence and influence of air bubbles was proved to be of negligible importance. Foaming is then provided by the evaporation of the emulsified alkane droplets, leading to the expansion of the emerging foam and giving rise to solids foams with cell sizes from 0.5 to 3 mm and porosities up to 97.5% after sintering. The microstructures of these filigree ceramics are stable and rigid with dense struts and uniform distributions of the solid phase and the porosity.
A new processing route for high‐performance graded ceramic filters is presented. The direct foaming process is based on the transition of a surfactant‐stabilized alkane dispersion in a stabilized ...aqueous ceramic powder suspension into mechanically stable ceramic foams with porosities up to 90%. The cell size distribution and, consequently, the permeability of the filters could be efficiently adjusted by the control of the high alkane phase‐emulsified suspension (HAPES) microstructure during emulsification. Furthermore, open porous graded structures are produced by combining HAPES layers with different droplet sizes. The tailored microstructural features, providing controlled permeabilities as well as high compressive strength of the cellular ceramics are of special interest for applications where fluid transport through ceramic microstructures is required. These include filters, in particular for aerosol filtration, temperature control membranes in autothermal reforming, catalytic supports including supports for batteries as well as matrices for immobilized microorganisms.
Open porous mechanically stable ceramic foams are developed by a simple direct foaming process. The new processing route is based on the transition of a surfactant stabilized highly concentrated ...alkane phase homogeneously distributed in a stabilized aqueous ceramic powder suspension into high performance ceramic foams with porosities up to 90% and cell sizes ranging from 3 to 200
μm. The droplet size distribution of the high alkane phase emulsified suspensions (HAPES) is efficiently controlled by the stirring velocity during emulsification experimentally investigated for varying powder particle contents. Stable foams with tailored structural features can be prepared by adjusting the rheological characteristics of HAPES being dependent on the system and process parameters. The influence of the emulsification stirring velocity on the resulting HAPES droplet size is analysed on the basis of the Taylor model of mechanical shearing describing the stresses responsible for the fragmentation of the droplets.
•ZnO/α-Fe2O3 composite deposited on plasma chamber wall (ZF-W) are investigated.•ZF-W is compared with plasma treated mixture deposited on target substrate (ZF-S).•Structural studies are conducted by ...XRD, TEM, PL, Raman and Mossbauer spectroscopy.•Cationic arrangement and oxygen vacancy defects play a role in structural variations.•ZF-W shows excellent methyl blue adsorption without any external light sources.
While conventional cleaning to remove the coating from plasma chamber walls becomes essential to reproduce the desired materials on the target substrate for widespread applications, an attention towards wall-deposited materials is scarce. Recycling those waste materials to value-added product is of great importance for sustainable progress of our modern society. Herein, we investigated the materials deposited on the wall of plasma chamber, explored their promising features and compared them with conventionally grown materials. A mixture of ZnO and α-Fe2O3 (ZF) exposed to high energy plasma was collected from the wall (ZF-W) and also from the substrate (ZF-S) to check the feasibility of providing same quality products. With same lattice constant of hematite, magnetite and zinc ferrites, ZF-W differs from ZF-S in coercivity, saturation magnetization, ferromagnetic stoichiometry and defects. In addition, degradation of Methyl Blue (MB) dye in ZF-W without use of any external light sources are comparable, more stable and durable in comparison to ZF-S. The slight differences obtained in the property-performances between ZF-W and ZF-S are attributed to the cationic arrangement and the oxygen vacancy defects present in the structure. The study reflects the potentiality of ZF-W as a promising active material for wastewater treatment just as one can use ZF-S. These findings clearly depict that the unused products with altered intrinsic properties obtained after plasma treatment has similar or even better potential to its actual targeted product and thus can be utilized properly thereby saving cost and time and, hence generates an unexplored direction for the materials science community.
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While conventional cleaning to remove the coating from plasma chamber walls becomes essential to reproduce the desired materials on the target substrate for widespread applications, an attention ...towards wall-deposited materials is scarce. Recycling those waste materials to value-added product is of great importance for sustainable progress of our modern society. Herein, we investigated the materials deposited on the wall of plasma chamber, explored their promising features and compared them with conventionally grown materials. A mixture of ZnO and α-Fe2O3 (ZF) exposed to high energy plasma was collected from the wall (ZF-W) and also from the substrate (ZF-S) to check the feasibility of providing same quality products. With same lattice constant of hematite, magnetite and zinc ferrites, ZF-W differs from ZF-S in coercivity, saturation magnetization, ferromagnetic stoichiometry and defects. In addition, degradation of Methyl Blue (MB) dye in ZF-W without use of any external light sources are comparable, more stable and durable in comparison to ZF-S. The slight differences obtained in the property-performances between ZF-W and ZF-S are attributed to the cationic arrangement and the oxygen vacancy defects present in the structure. The study reflects the potentiality of ZF-W as a promising active material for wastewater treatment just as one can use ZF-S. These findings clearly depict that the unused products with altered intrinsic properties obtained after plasma treatment has similar or even better potential to its actual targeted product and thus can be utilized properly thereby saving cost and time and, hence generates an unexplored direction for the materials science community.
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