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The motion of ions in supercapacitor electrodes produces internal stresses that cause viscoelastic strains. In addition, stresses may be due to external forces applied to structural supercapacitors, which are multifunctional materials that simultaneously store energy and carry structural loads. There are currently no thermodynamics-based models for the coupled electro-chemo-viscoelastic response of electrodes. Here, the same thermodynamics model is used for both the viscoelastic response and the electrochemical response. This mathematical equivalence is a reference from which to study coupling between the viscoelastic and electrochemical responses. The model has two inputs (stress or strain and electric potential or specific charge) and two outputs (strain or stress and specific charge or electric potential). The coupling is studied by adding three constants in the free energy. The convexity of the free energy and the stability of the free response limit the magnitude of the coupling. The unit response matrix is derived, and results are given for the time and frequency domains. The effect of an applied potential on stress is shown to be much more significant than the converse effect. The model compares well to an experiment consisting of a cyclic electric current applied during stress relaxation. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) reduced graphene oxide (rGO)/Ti2CTx MXene hybrid aerogels were effectively prepared by a two-step method involving hydrothermal reaction and freeze-drying. The intimately coupled rGO/Ti2CTx hybrid aerogel combined high electrical conductivity, large interlayer spacing, and excellent mechanical stability of Ti2CTx, which not only effectively prevents the self-restacking of Ti2CTx nanosheets, exposes more active sites exposed, and improves the volume change during the charge/discharge process but also increases the accessibility of ions and promotes the rapid transfer of ions/electrons. As a result, rGO/Ti2CTx 17.5–2.5 as the working electrode of electric double layer capacitors delivers a large specific capacity (107.05 F g−1 at 0.5 A g−1 in a 1M Na2SO4 electrolyte), a high rate capability (maintains 30% of its initial capacitance at 10 A g−1, which is much better than rGO and Ti2CTx), and excellent long-term large-current cycle stability (the initial capacitance remains above 71.1% after 10 000 cycles at 1 A g−1). In addition to providing a high-performance electrode for supercapacitors, this study proposes an efficient and time-saving strategy for constructing 3D structures from 2D materials. [ABSTRACT FROM AUTHOR]

The electric double layer (EDL) has a pivotal role in screening charges on surfaces as in supercapacitor electrodes or colloidal and polymer solutions. Its structure is determined by correlations between the finite-sized ionic charge carriers of the underlying electrolyte, and, this way, these correlations affect the properties of the EDL and of applications utilizing EDLs. We study the structure of EDLs within classical density functional theory (DFT) in order to uncover whether a structural transition in the first layer of the EDL that is driven by changes in the surface potential depends on specific particle interactions or has a general footing. This transition has been found in full-atom simulations. Thus far, investigating the in-plane structure of the EDL for the primitive model (PM) using DFT has proved a challenge. We show here that the use of an appropriate functional predicts the in-plane structure of EDLs in excellent agreement with molecular dynamics simulations. This provides the playground to investigate how the structure factor within a layer parallel to a charged surface changes as a function of both the applied surface potential and its separation from the surface. We discuss pitfalls in properly defining an in-plane structure factor and fully map out the structure of the EDL within the PM for a wide range of electrostatic electrode potentials. However, we do not find any signature of a structural crossover and conclude that the previously reported effect is not fundamental but rather occurs due to the specific force field of ions used in the simulations. [ABSTRACT FROM AUTHOR]

In this paper, we present a continuation of our research on modeling electrolyte solutions within charged pores. We make use of the model developed by Blossey et al. [Phys. Rev. E 95, 060602 (2017)], which takes into account the structural interactions between ions through a bilinear form over the gradients of local ionic concentrations in the grand thermodynamic potential, as well as their steric interactions through the lattice gas model. The structural interactions may describe the effects of the molecular structure of ions at a phenomenological level. For example, these effects include steric effects due to non-spherical shapes of ions, their conformational lability, and solvent effects. In addition, we explore their specific interactions with the pore walls by incorporating external attractive potentials. Our primary focus is on observing the behavior of ionic concentration profiles and the disjoining pressure as the pore width changes. By starting with the local mechanical equilibrium condition, we derive a general expression for the disjoining pressure. Our findings indicate that considering the structural interactions of ions leads to a pronounced minimum on the disjoining pressure profiles at small pore widths. We attribute this minimum to the formation of electric double layers on the electrified surfaces of the pore. In addition, our results demonstrate that the inclusion of the attractive interactions of ions with the pore walls enhances this minimum and shifts it to smaller pore thicknesses. Our theoretical discoveries may be useful for those involved in supercapacitor electrochemical engineering, particularly when working with porous electrodes that have been infused with concentrated electrolyte solutions. [ABSTRACT FROM AUTHOR]

The shortage of natural resources due to the progression of the human population and environmental pollution has become crucial concern topics to resolve. One of the best ways to resolve this is to develop renewable energy-based storage systems. Supercapacitors are emerging as promising storage systems via providing rapid charging/discharging and high power delivery, but there is a need to explore low-cost, environment-friendly, non-toxic, abundant, and biodegradable electrode materials for supercapacitors. In this regard, biopolymers are observed to be popular for storage applications as they are of high porosity, cost-effective, easily available, low-weight, and environment friendly and have biodegradability properties. The biopolymer-based electrode has a desirable morphology and high surface area and exhibits admirable electrochemical properties. The focus of this report is to highlight (i) the inclusive details of supercapacitors and their types along with strategies to improve their electrochemical performance, (ii) biopolymers and their types used for supercapacitor applications, (iii) various synthesis routes that could be adopted for designing electrode materials based on biopolymers for supercapacitors, and (iv) challenges and future scope of biopolymers as the electrode material in supercapacitor applications. The detailed study here in this report is found to be a topic of interest for the scientific community to fabricate and prepare low-cost, eco-friendly, high electrochemical performance exhibiting electrode materials for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Tellurium (Te) has great potential as high-performance cathode materials for aqueous zinc-ion batteries (AZIBs) owing to high electronic conductivity and volumetric capacity. Nevertheless, its poor utilization and large volume expansion result in insufficient rate and cycle performances, thereby, impeding practical application. Herein, a kind of Te/carbon composite was prepared via a ball-milling method, in which Te nanocrystals were tightly confined in few-layer expanded graphite (EG) with Te–C bonds (denoted as Te@EG). In addition to maintaining structural stability, such unique nanocomposite shows abundant electrochemically active sites and efficient charge transfer channels, which is beneficial to the utilization of Te. More importantly, the Te–C bonds between Te nanocrystals and EG can enhance the adsorption of Zn2+ and reduce the Zn2+ migration barrier, which contributes to promoting electrochemical kinetics. Consequently, the Te@EG cathode for the AZIBs exhibits sufficient specific capacity (412 mAh g–1 at 0.1 A g–1), high-rate performance (284 mAh g–1 at 3 A g–1), and reliable cycling stability (94% capacity retention at 1 A g–1 after 500 cycles). Furthermore, the soft-packaged Zn//Te@EG battery delivers excellent flexibility and cycling stability. This study offers a perspective on rational design of Te-based cathodes for practical AZIBs. [ABSTRACT FROM AUTHOR]

Developing advanced electrode materials for supercapacitors (SCs) has received incredible attention. The suitable electrode for high capacitance and energy density are significant challenges for SCs. This work reports an efficient hydrothermal synthesis of MoS2 nanosheets on carbon cloth (MoS2@CC). The large surface area of the binder-free MoS2@CC electrode provides rich active sites and an improved electrolyte ion diffusion rate. The MoS2@CC electrode exhibits good electrochemical performance by delivering a high specific capacitance of 947 F g−1 at the current density of 1.0 A g−1 and retains an excellent capacitance of 96.5% over 10 000 cycles. The high performance of the MoS2@CC electrode can be clarified through density functional theory (DFT) calculations. The DFT outcomes reveal that the electrode possesses favorable Li-ion intercalation and adsorption properties. The calculated adsorption energy of −0.352 eV at the hollow site shows the high stability of the system. The low energy barrier of path 1 (0.83 eV) easily facilitates Li-ions in the electrode material, which is beneficial for its fast electrochemical performance. The obtained results of the MoS2@CC electrode present improved pseudocapacitive performance, showing a significant possibility for high-performance SCs' application. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) are attractive as promising energy storage devices because of their distinctive attributes, such as high power density, good current charge/discharge ability, excellent cyclic stability, reasonable safety, and low cost. Electrode materials play key roles in achieving excellent performance of these SCs. Among them, binary transition metal sulfides (BTMSs) have received significant attention, attributed to their high conductivity, abundant active sites, and excellent electrochemical properties. This topic review aims to summarize recent advances in principles, design, and evaluation of the electrochemical performance for nanostructured BTMSs (including nickel–cobalt sulfides, zinc–cobalt sulfides, and copper–cobalt sulfides.) and their nanocomposites (including those carbon nanomaterials, transition metal oxides, binary transition metal oxides, transition metal sulfides, and polymers). Nanostructuring of these BTMSs and nanocomposites as well as their effects on the performance were discussed, including nanoparticles, nanospheres, nanosheets, nanowires, nanorods, nanotubes, nanoarrays, and hierarchitectured nanostructures. Their electrochemical performance has further been reviewed including specific capacitance, conductivity, rate capability, and cycling stability. In addition, the performance of hybrid supercapacitors (HSCs) assembled using the nanostructured BTMSs as the cathodes also have been summarized and compared. Finally, challenges and further prospects in the HSCs-based BTMS electrodes are presented. [ABSTRACT FROM AUTHOR]

Use of internal and external stimuli can be an alternative tool to address the limitations of a supercapacitor for its enhanced electrochemical properties. Influence of internal stimuli, such as redox active dopants and vacancies, can alter the electronic structure or phase of the electrode material, leading to an improved redox behavior of the pseudo-capacitors by virtue of electron polarizations, leading to a better electrochemical charge transfer kinetics. On the other hand, external stimuli, such as applied magnetic field, can alter the diffusion characteristics of the active ions in the electrolyte, thereby changing the ion/charge rearrangement and ion diffusion characteristics within supercapacitor electrodes. This Perspective emphasizes the importance of these two aspects, supported by an in-depth literature review to give a comprehensive overview of internal and external stimuli effects in designing the model systems for future electrochemical applications. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations of complex electrochemical systems, such as ionic liquid supercapacitors, are increasingly including the constant potential method (CPM) to model conductive electrodes at a specified potential difference, but the inclusion of CPM can be computationally expensive. We demonstrate the computational savings available in CPM MD simulations of ionic liquid supercapacitors when the usual non-periodic slab geometry is replaced with fully periodic boundary conditions. We show how a doubled cell approach, previously used in non-CPM MD simulations of charged interfaces, can be used to enable fully periodic CPM MD simulations. Using either a doubled cell approach or a finite field approach previously reported by others, fully periodic CPM MD simulations produce comparable results to the traditional slab geometry simulations with a nearly double speedup in computational time. Indeed, these savings can offset the additional cost of the CPM algorithm, resulting in periodic CPM MD simulations that are computationally competitive with the non-periodic, fixed charge equivalent simulations for the ionic liquid supercapacitors studied here. [ABSTRACT FROM AUTHOR]

One of the main problems faced by 2D materials used in supercapacitor applications when scaling up is restacking, such that their gravimetric capacitances become dramatically inferior to that of their monolayer forms. This study analyzes the Raman spectra of transferred layers of CVD-graphene revealing decoupling and rotational stacking of layers, with the potential of retention of intrinsic monolayer properties. Rotationally stacked layers have the potential to mitigate restacking and, thus, are capable of easing ion intercalation and boosting their performance in supercapacitor applications. In this pursuit, binder-free supercapacitors are fabricated out of chemical vapor deposited bilayer graphene, successively transferred to form rotationally stacked multilayers. Supercapacitors constructed with rotationally stacked four-layer graphene have an incredible specific gravimetric capacitance of 316.1 F g−1 at 1 mV s−1, with a corresponding energy density of 28.1 Wh kg−1 and ∼100% capacitance retention at 10 000 cycles. [ABSTRACT FROM AUTHOR]

Carbon-based supercapacitors have been extensively explored by the virtue of their exceptional performance in terms of charge-storage capacity, electrical conductivity, and good stability. However, the rush to find potential approaches for increasing their specific capacitance and specific energy without adversely affecting the specific power is still exciting. Herein, we synthesized hierarchically structured carbon-based composites based on 2D MXene sheets with an interconnected conductive porous network of 1D graphene nanoribbons (GNRs). Synergistic effects arising due to the defect engineering of 2D MXene sheets with 1D GNRs led to high surface-area, effective ion-transport, and improved structural robustness of the composite electrodes, thereby enhancing the specific capacitance along with specific energy of device while preserving its specific power. The electrochemical studies revealed that the composites with 1 wt.% GNRs (GMX-B) outperformed when the composition of GNRs was varied from 0.5 to 1.5 wt. % in MXene (GMX-A, GMX-B, and GMX-C). In comparison to pristine MXene and pristine GNRs, GMX-B exhibited ∼2.54 and ∼2.74 folded higher capacitance of 238.96 F/g at 0.6 A/g current density, respectively, a higher capacitance retention of 72.16% for a scan rate from 10–140 mV/s as well as a good cyclic stability of 85.11% over 10 000 charge/discharge cycles. Furthermore, GMX-B electrode achieved a high specific energy of 4.066 Wh/Kg while maintaining a specific power of 210.640 W/Kg as compared to pristine MXene (1.597 Wh/Kg at 211.989 W/Kg) and pristine GNRs (1.482 Wh/Kg at 211.089 W/Kg). Thus, we anticipated that the use of hierarchically engineered 1D/2D carbon-based composites with considerable improvement in its interfacial properties holds great potential to achieve high-performing energy-storage devices. [ABSTRACT FROM AUTHOR]

Porous carbons have attracted substantial interest within the realm of energy storage applications. However, their traditional production methods often involve the use of elevated temperatures. In this study, we introduce a simple technique to transform titanium silicon carbide (Ti3SiC2) MAX phases into porous carbons, known as carbide-derived carbons (CDCs), at room temperature by selective etching of the metal atoms (Ti and Si). We investigate how temperature affects the activation of CDCs so formed with potassium hydroxide to enhance their electrochemical properties. Our results unveil the remarkable potential of CDCs activated at 700 °C, demonstrating superior electrochemical performance with a specific capacitance of 198 F g−1 at a scan rate of 20 mV s−1 in a three-electrode configuration. The symmetric supercapacitor based on CDC-700 maintains a respectable specific capacitance of 98 F g−1 at 1 A g−1 and an energy density of 13.7 Wh kg−1 at a power density of 1 kW kg−1. This cost-effective approach offers a pathway for large-scale CDC production, with excellent specific supercapacitor characteristics, promising advancements in energy storage technology. [ABSTRACT FROM AUTHOR]

The highly porous and binder-free flexible paper electrodes can enhance the specific capacitance of symmetric supercapacitors (SCs) due to their large surface and effective ion diffusion pathways. We synthesized the exfoliated graphite (ExG) by the thermal exfoliation method of chemically treated graphite flakes and compressed it into a paper-like thin sheet (binder-free) of ∼0.15 mm thickness. The coin cell SCs with copper (Cu) and stainless steel (SS) as current collectors have been fabricated for the electrochemical measurement. The cyclic voltammetry and galvanostatic charge/discharge measurements are investigated at various scan rates and current densities. The SCs with Cu foil as a current collector perform better than SS-based SCs. The Cu current collector-based SCs showed a specific capacitance of 37.08 mF cm−2, whereas it was ∼29.98 mF cm−2 for SS-based SCs at a 0.01 V s−1 scan rate across a 0–0.6 V potential window. Approximately no degradation in charge storage capacity for more than 15 000 cycles at 0.1 V s−1 shows the ultra-stability of the flexible ExG-based binder-free electrodes. A digital watch is powered using the fabricated pouch cell supercapacitor with copper-based current collectors to show the potential of SCs. [ABSTRACT FROM AUTHOR]

We have prepared CuS and CuS-rGO nanocomposites via the hydrothermal method. The physical properties of the synthesized materials were studied through x-ray diffraction and scanning electron microscopy. The supercapacitor characteristics were evaluated by cyclic voltammetric and galvanostatic charge–discharge studies. The cyclic voltammetric studies conform the pseudocapacitive nature of CuS and CuS-rGO electrodes. The specific capacitance of CuS was obtained as 207, 150, and 97 F/g at a current density of 0.5, 5, and 20 A/g, respectively. The rGO-CuS nanocomposite showed improved specific capacitance of 350, 251, and 149 F/g at current densities of 0.5, 5, and 20 A/g, respectively. [ABSTRACT FROM AUTHOR]

The rapid advancement of biomedical technology has sparked increasing interest in developing biodegradable implantable energy storage devices for applications in biosensors and bioelectronics. However, the limited energy density, biocompatibility, and degradability of existing materials have posed significant challenges to their widespread adoption in the biomedical field. In response, this study presents an electrode material for a solid-state biodegradable supercapacitor consisting of an array structure of molybdenum oxide (MoOx) nanosheets in situ grown on water-soluble molybdenum foil (Mo-foil). The MoOx@Mo-foil electrode exhibits exceptional electrochemical performance, suppressing previous designs. It demonstrated a high capacitance of 433.3 F/g at 1 A/g, and even at 10 A/g, it has a favorable rate capability of 48.9%. Furthermore, cycling stability test revealed an outstanding endurance, with an impressive retention of 88.0% after 5000 cycles. An symmetrical supercapacitor was assembled by combining two MoOx@Mo-foil electrodes with remarkable energy storage capabilities and cycling stability of 94.3% over 5000 cycles. Additionally, the biodegradable supercapacitor exhibited a high energy density of 40.95 Wh/kg at 600.48 W/kg. Moreover, the device is fully biodegradable, which paves the way for advancing the field of bioelectronics and propelling the development of sustainable energy storage technologies for biomedical applications. [ABSTRACT FROM AUTHOR]

In the present work, novel nanocrystals (NCs) of carbon nanospheres (Cx) (5%, 10%, and 15%) anchored on Gd3+:SeO2 (Cx:Gd3+@SeO2) were synthesized and characterized by XRD (x-ray diffraction), SEM (scanning electron microscopy), SEM-energy dispersive x-ray, UV-visible, x-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, and Raman analytical techniques. XRD analysis showed that the synthesized Cx:Gd3+@SeO2 NCs exhibit mixed tetragonal phase. Gd3+@SeO2 NCs transformed into irregular flake-like morphology with increasing percentage of Cx. Optical property studies showed the presence of Cx in Gd3+@SeO2 NCs matrix leads to tuning of bandgap (Eg). Incorporation of Cx leads to decrease in the bandgap from 3.64 to 3.58 eV. XPS investigation revealed chemical composition and valence state of Cx:Gd3+@SeO2 NCs. Carbon-based materials, especially, carbon nanospheres, have attracted much attention due to their good conductivity, low cost, high surface area, porosity, etc. Upon doping Cx, the conducting network of the Gd3+@SeO2 lattice is improvised, which forms hollow structures and facilitates penetration of the electrolyte. Raman studies confirmed the formation of Gd-O-Gd/Gd2O3, Se-O-Se/SeO2, and C-H (D and G) fringes. Supercapacitor properties of Cx:Gd3+@SeO2 NCs investigated in 3M KOH solution using three electrode system showed specific capacitance of 239.4 F/g at current density of 0.5 A/g with 89% capacitance retention over 3000 cycles. The synthesized nanocrystals can be used as potential candidates for optical devices and battery applications. [ABSTRACT FROM AUTHOR]

Spinel-type CuFe2O4 nanoparticles were synthesized by a solvothermal method using ethylene glycol as solvent and polyvinylpyrrolidone (PVP) as dispersant. The characterization results showed that the average diameter of the hollow-spherical CuFe2O4 was approximately 100 nm with homogeneous morphology and negligible agglomeration. CuFe2O4 was used as the active electrode material to explore its supercapacitive properties in different concentrations of KOH electrolytes. It was found that the CuFe2O4 hollow-spherical nanoparticles exhibit potential electronic performance in supercapacitor, with a specific capacitance of 368.2 F/g and capacitance stability retention of 91.0% after 2000 cycles at the current density of 5 A/g in 3 mol/L KOH electrolyte. The present findings demonstrate that the CuFe2O4 electrode materials can have important implications with practical prospects in energy storage systems. [ABSTRACT FROM AUTHOR]

Interactions between polymers and graphene can have synergistic effects such as doping, thereby improving the performance of graphene-based devices. In this study, the effects of doping graphene with the n-type dopant polyethylenimine were investigated. The doping-induced changes in the optical contrast of the graphene films were investigated through simulations and experiment. It was experimentally observed that the doping induced a maximum decrease of 63% in the sheet resistance of reduced graphene oxide (RGO) films. The effects of the doping on RGO-based supercapacitor electrodes were examined; the specific capacitance was improved by approximately 3%–11%, with a maximum value of 205 ± 22 F/g (or 260 ± 50 F/cm2). These results can facilitate future research on combining polymers and graphene-based materials for various applications. [ABSTRACT FROM AUTHOR]

Electrochemical surface plasmon resonance (ESPR) is applied to evaluate the relative static differential capacitance at the interface between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid (IL) and a gold electrode, based on the relationship between the SPR angle and surface charge density on the electrode. Potential-step and potential-scan ESPR measurements are used to probe the dynamics of the electric double layer (EDL) structure that exhibit anomalously slow and asymmetrical characteristics depending on the direction of potential perturbation. EDL dynamics respond at least 30 times more slowly to changes of potential in the positive direction than in the negative direction. ESPR experiments with the positive-going potential scan are significantly affected by the slow dynamics even at a slow scan. The surface charge density that reflects the relative static capacitance is obtained from the negative-going potential scans. The evaluated quasi-static differential capacitance exhibits a camel-shaped potential dependence, thereby agreeing with the prediction of the mean-field lattice gas model of the EDL in ILs. ESPR is shown to be an effective experimental method for determining relative values of the static differential capacitance. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated the supercapacitor performance of pristine and composites of spinel NiCo2O4 with a multi-walled carbon nanotube (MWCNT) assembled in a two-electrode cell configuration. Spinel NiCo2O4 and NiCo2O4@MWCNT composites were synthesized via a facile hydrothermal method. The supercapacitive performance of as-synthesized NiCo2O4 and NiCo2O4@MWCNT fabricated on Ni-foam was studied in a 0.5M K2SO4 electrolyte using electrochemical measurement techniques. The symmetric cell configuration of NiCo2O4@MWCNT delivers high specific capacitance (374 F/g at 2 A/g) with high energy density and power density (95 Wh/kg and 3 964 W/kg, respectively) compared to that of pristine NiCo2O4 electrodes (137 F/g at 0.6 A/g). Furthermore, the energy storage performance of the asymmetric cells of NiCo2O4//MWCNT and NiCo2O4@MWCNT//MWCNT was studied to enhance cycling stability (retention of 74.85% over 3000 cycles). We have also theoretically studied the supercapacitance performance of pristine NiCo2O4 and NiCo2O4@SWCNT hybrid structures through its structural and electronic properties using density functional theory predictions. The higher specific capacitance of the NiCo2O4@SWCNT hybrid system with high power density and energy density is supported by the enhanced density of states near the Fermi level and increased quantum capacitance of the hybrid structure. We have theoretically computed the diffusion energy barrier of K+ ions of the K2SO4 electrolyte in the NiCo2O4 layer and compared it with the diffusion barrier for Na+ ions. The lesser diffusion energy barrier for K+ ions in the NiCo2O4 layer contributes toward higher energy storage capacity. Thus, owing to superior electrochemical performance of NiCo2O4 composites with MWCNTs, it can serve as a high-performance electrode material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

This work presents an ultraviolet-assisted photochemical doping strategy for realizing the modification of Ti3C2Tx MXene. In this strategy, nitrogen atoms are easily doped into Ti3C2Tx MXene, and harmful fluorine-containing terminal groups are effectively removed from the Ti3C2Tx MXene under UV light irradiation. The results further show that the nitrogen doping level is ∼2.99 at. %, and the interlayer spacing of Ti3C2Tx MXene increases from 1.271 to 1.363 nm after the nitrogen doping. The nitrogen-doped Ti3C2Tx MXene exhibits a higher specific capacitance of 491 F g−1 (1176 F cm−3) at 2 mV s−1 than raw Ti3C2Tx MXene (292 F g−1) when used as a supercapacitor electrode material. Moreover, a nitrogen-doped Ti3C2Tx quasi-solid-state supercapacitor device can yield an energy density of 14.9 Wh kg−1 at 750 W kg−1. Therefore, this work affords a simple and highly versatile route for fabricating high-performance MXene materials for supercapacitors. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have become known as an attractive group of materials for energy storage applications because of their spectacular characteristics, like porous properties, tunable chemical compositions, and adaptable geometry morphologies. Herein, we produce hierarchical nanostructures based on MOF-71 by using a straightforward one-pot cold plasma method to prepare a high-performance dual Ni/Co-MOF-reduced graphene oxide (Ni/Co-MOF@rGO) material as a supercapacitor electrode. Interestingly, the as-synthesized nanostructure displays a special morphology with superior energy storage capability (3093.72 F g − 1 at 1 A g − 1 ). Furthermore, we fabricated an asymmetric device using Ni/Co-MOF@rGO as a high-rate positive electrode and activated carbon (AC) as a negative electrode (Ni/Co-MOF@rGOǁAC). This hybrid device presents an impressive specific energy of 81.82 W h k g − 1 , a specific power of 2750 W k g − 1 , and superior cycling stability (94.7% initial capacity retention after 3700 cycles) at a current density of 1 A g − 1 . The synergistic effect of metal cores and reduced graphene oxide features in a cold plasma atmosphere produced a hierarchical three-dimensional nanostructure with more electroactive sites, which was advantageous for high-efficiency redox processes. This work clearly states the cold-plasma synthesis of MOF nanocomposite with desired morphological characteristics for energy storage applications. [ABSTRACT FROM AUTHOR]

In this work, electron temperature was measured with both the asymmetric double Langmuir probe (ADLP) and the single Langmuir probe to investigate the reliability of the ADLP on the electron temperature measurement in multi-temperature Maxwellian plasmas. A series of I–V traces of the ADLP were obtained at various plasma conditions with different area ratios and analyzed with different methods including conventional ADLP analysis and two-temperature Maxwellian fitting with results measured by a single planar Langmuir probe analyzed with three-temperature Maxwellian fitting as reference. The measured Te of the ADLP is found to reflect that of the temperature of the degraded primary electrons when the area ratio of the probe tips is close to ∼16 and approaches the real effective electron temperature as the area ratio increases to a value of ∼30% higher than that measured by a single Langmuir probe, which occurs even when the area ratio is higher than the flux ratio of electrons and ions entering their respective sheaths. This effect is consistent with the distortion effect of Langmuir probe I–V traces caused by the presence of hotter electron species, which was computationally reconstructed and agreed well with the experimental observations. This result implies that an area ratio, possibly ∼20 times much larger than what was conventionally assumed, is needed for an ADLP to be reliably treated as a single Langmuir probe in practical settings, where electron energy distribution functions of plasmas are generally expected to be multi-temperature Maxwellian. This effect is also analogous to the current balance between a single Langmuir probe and the device wall, implying that this effect would also affect the application of the single Langmuir probe in plasmas, where the ion loss to the device wall can be reduced, such as plasmas in miniaturized devices, strong magnetic fields, or a highly ion-neutral collisional environment. [ABSTRACT FROM AUTHOR]