Capacitance Enhancement Research Articles

Enhanced quantum capacitance of MX4 (M = Fe, Co, Ni, Cu, and Zn; X = N, P) moieties embedded graphene: a DFT study

In this work, density functional theory calculations are performed to study the impact of embedding transition metal-(N/P)4 moieties in graphene on its geometric structure, electronic properties, and quantum capacitance. Enhancement of quantum capacitance of transition metal doped nitrogen/phosphorus pyridinic graphenes is observed, which is directly related to the availability of states near the Fermi level. The findings show that electronic properties and hence quantum capacitance of graphene can be tuned by varying transition metal dopants and/or their coordination environment. Modified graphenes can suitably be chosen as positive or negative electrodes of asymmetric supercapacitors depending upon the values of quantum capacitance and stored charges. Furthermore, quantum capacitance can be enhanced by widening the working voltage window. The results can serve as guidelines for the design of graphene-based electrodes in supercapacitor applications.

General Design Concepts for CAPodes as Ionologic Devices

AbstractCapacitive analogues of semiconductor diodes (CAPodes) present a new avenue for energy‐efficient and nature‐inspired next‐generation computing devices. Here, we disclose the generalized concept for bias‐direction‐adjustable n‐ and p‐CAPodes based on selective ion sieving. Controllable‐unidirectional ion flux is realized by blocking electrolyte ions from entering sub‐nanometer pores. The resulting CAPodes exhibit charge‐storage characteristics with a high rectification ratio (96.29 %). The enhancement of capacitance is attributed to the high surface area and porosity of an omnisorbing carbon as counter electrode. Furthermore, we demonstrate the use of an integrated device in a logic gate circuit architecture to implement logic operations (‘OR’, ‘AND’). This work demonstrates CAPodes as a generalized concept to achieve p‐n and n‐p analogue junctions based on selective ion electrosorption, provides a comprehensive understanding and highlights applications of ion‐based diodes in ionologic architectures.

General Design Concepts for CAPodes as Ionologic Devices.

Capacitive analogues of semiconductor diodes (CAPodes) present a new avenue for energy-efficient and nature-inspired next-generation computing devices. Here, we disclose the generalized concept for bias-direction-adjustable n- and p-CAPodes based on selective ion sieving. Controllable-unidirectional ion flux is realized by blocking electrolyte ions from entering sub-nanometer pores. The resulting CAPodes exhibit charge-storage characteristics with a high rectification ratio (96.29 %). The enhancement of capacitance is attributed to the high surface area and porosity of an omnisorbing carbon as counter electrode. Furthermore, we demonstrate the use of an integrated device in a logic gate circuit architecture to implement logic operations ('OR', 'AND'). This work demonstrates CAPodes as a generalized concept to achieve p-n and n-p analogue junctions based on selective ion electrosorption, provides a comprehensive understanding and highlights applications of ion-based diodes in ionologic architectures.

Oxygen-Enriched Hierarchical Nanoporous Carbon Electrodes for Supercapacitors

Enhancing the energy storage capacity of carbon electrodes is a key challenge to developing high-performance supercapacitors. In this study, we design an oxygen-enriched hierarchical nanoporous carbon electrode using laser fabrication and subsequent electrochemical activation, which demonstrates superior energy storage capacity. The carbon electrode is first obtained through the carbonization of phenolic resin under instantaneous high temperature induced by laser, resulting in multiple ion transport channels and a specific capacitance of 64.17 mF cm–2 at the current density of 0.2 mA cm–2. To further improve the performance, electrochemical activation is successfully conducted, leading to a 12.1-fold increase of the specific capacitance of the carbon electrodes. It is found that O–C═O-containing functional groups formed during the activation process significantly contribute to the high capacitance enhancement. In a 1 M H2SO4 electrolyte, the activated hierarchical nanoporous carbon electrode delivers a high specific capacitance of 778.3 mF cm–2 under the same test conditions. Additionally, the abundant porous structure and excellent reversibility of redox reaction of the oxygen-containing functional groups enable the assembled supercapacitor to obtain a specific capacitance of 45.3 mF cm–2 at the current density of 0.4 mA cm–2 and maintain a capacitance retention rate of 93.6% after 10,000 charge–discharge tests. This study presents a strategy to prepare carbon electrode materials with both high performance and excellent stability.

Effect of Polypyrrole on the Capacitance Enhancement of the Spherical ZnS–ZnO/g-C3N4 Nanocomposite for Supercapacitor Applications

Effect of Polypyrrole on the Capacitance Enhancement of the Spherical ZnS–ZnO/g-C3N4 Nanocomposite for Supercapacitor Applications

Miniaturized lumped‐element low‐temperature co‐fired ceramic balun using capacitance‐enhanced capacitors

SummaryA capacitance‐enhanced capacitor (CEC) is proposed and applied to build a low‐temperature co‐fired ceramic (LTCC) balun for miniaturization. The capacitance enhancement is by adding horizontal fingers to traditional vertically interdigital capacitor (VIC) for capacitance increasing without size enlargement. The proposed CEC increased 7.2% capacitance comparing with that of traditional VIC. The balun using the proposed CEC is only 9.5 × 8.4 × 1 mm3, which is equivalent to 0.0034 × 0.0031 × 0.0004 λg3. The measured inband S11, S21, and S31 are better than −15, −3.6, and 3.5 dB from 46 to 58 MHz, respectively. A wide fractional bandwidth (FBW) of 24% based on 15 dB return loss is also reached. The proposed balun has widely applications in maritime navigation, aircraft navigation, and 1–1.5 Tesla (T) magnetic resonance imaging (MRI) applications.

High‐Yield Exfoliation of Large MXene with Flake Sizes over 10 µm Using Edge‐Anchored Carbon Nanotubes

AbstractThe exceptional properties of 2D transition metal carbides and nitrides (MXene) have led to numerous promising applications. However, the performance of MXene is often dependent on the size of the flakes, and obtaining large‐sized, high‐quality MXene flakes remains challenging. Herein, a carbon nanotube (CNT)‐assisted exfoliation strategy is introduced, which significantly improves the yield of large‐flake MXene while entirely transforming the centrifugation residues into small‐flake MXene, resulting in waste‐free synthesis of MXene. The average size of the obtained MXene flakes can reach over 10 and 0.7 µm for the two populations, respectively. Additionally, the capacitive performance of MXene can be greatly enhanced with a small amount of CNTs. As a proof of concept, a planar interdigital micro‐supercapacitor with heterogeneous layers assembled by large‐ and small‐flake MXene simultaneously exhibits outstanding synergistic enhancement in volumetric capacitance (1072 F cm⁻3) and energy density (53.5 mWh cm⁻3). This CNT‐assisted method provides explicit directions for achieving the ideal utilization of MXene, improving the yield of large flakes while making judicious use of waste, to meet specific application needs.

Experimental and Theoretical Findings of the Concerted Effect of Dual Quantum Dots on a Graphene Matrix for Energy Storage Applications

The construction of composite electrode materials that exhibit superior energy and power densities has stirred rigorous research on supercapacitors. Herein, we have successfully designed nitrogen-doped carbon dots (CDs) and hematite dots (HtDs) functionalized reduced graphene (RG) hybrid ternary composites (RG@CDs/HtDs) by liquid exfoliation followed by the solvothermal method. The hybrid electrode material, RG@CDs/HtDs, exhibits a high specific capacitance of 1566 F/g at a scan rate of 2 mV s–1 and excellent stability up to 10,000 cycles. The DFT calculations have been performed to investigate the capacitance enhancement in the hybrid structure. The enhanced quantum capacitance and intense electronic states near the Fermi level for the ternary structure RG@CDs/HtDs justify the superior charge storage. When HtDs and CDs are introduced into RG, charge transfers from the Fe 3d orbital to the C 2p orbital of RG occur. An asymmetric aqueous supercapacitor device has been fabricated using RG@CDs/HtDs as a cathode and Mn3O4/C as an anode. Remarkably, the assembled aqueous asymmetric supercapacitor operates in a stable and wide potential window of 2.5 V with an ultrahigh energy density (134 Wh kg–1) along with extraordinary rate capability and is stable at 10,000 cycles performance that was validated on powering of the red light-emitting diode (LED).

Structural Transformation of Hydrated WO3 into SnWO4 via Sn Incorporation Enables a Superior Pseudocapacitor and Aqueous Zinc-Ion Battery

The strategy of crystal structure transformation tunes the electrochemical properties favoring the energy storage performance of the electrode material. Herein, we prepared SnWO4 nanoflakes through Sn incorporation into the tungsten oxide matrix by a single-step wet chemical method. The crystal structure tuning occurs from the orthorhombic structure of hydrated tungsten oxide (WO3·H2O, i.e., HWO) to the hexagonal (SnWO4, i.e., SWO) structure. Simultaneously, the morphology tailoring from nanodisks of HWO to nanoflakes of SWO is realized as a result of the Sn ion exchange mechanism. Further, the electrochemical supercapacitor of SWO nanoflakes demonstrates almost 2-fold enhancement in the specific capacitance of 622 F g–1 at 0.5 A g–1 over HWO nanodisks (255 F g–1). Moreover, the asymmetric supercapacitor (ASC) of SWO//activated carbon (AC) exhibits the specific capacitance of 50 F g–1 at 1 A g–1, with the maximum energy density and power density of 18 Wh kg–1 and 7000 W kg–1, respectively. Furthermore, superior performance of the aqueous zinc-ion battery (AZIB) demonstrates the specific capacity of 75 mA h g–1 at 0.3 A g–1 along with 106% stability and 101% coulombic efficiency after 70 cycles. The improved performance of SWO nanoflakes in the pseudocapacitor and AZIB is attributed to crystal structure tuning, increasing conductivity, enhanced surface area, and Sn redox sites. Therefore, the SWO nanoflakes are favorable cathode materials for commercial energy storage devices.

Hierarchical Columnar Cactus-like Co-MOF@NiCo-LDH Core–Shell Nanowrinkled Pillar Arrays for Supercapacitors with Ultrahigh Areal Capacitance

The design of metal–organic framework/layered double hydroxide (MOF/LDH) heterogeneous hybrids is crucial to the enhancement of areal capacitance for supercapacitor electrodes. Herein, the NiCo-LDH nanowrinkles are evenly epitaxially grown on the surface of self-supported Co-MOF nanoneedles to form aligned nanopillar arrays by a facile electrodeposition. Thanks to the high porosity of the Co-MOF, excellent redox activity of NiCo-LDH, and interfacial synergy of the core–shell multicomponent heterostructure, the Co-MOF@NiCo-LDH composite has an extraordinary areal capacitance (44.1 F cm–2 at 5 mA cm–2), which is 7.6 and 2.6 times higher than that of the bare NiCo-LDH and Co-MOF, respectively. Furthermore, the constructed asymmetric supercapacitor with activated carbon demonstrates a satisfactory energy density of 0.89 mWh cm–2 at the power density of 7.5 mW cm–2 and superior cycling stability (97.6% capacitance retention after 10,000 cycles).

Aestivum-inspired photothermal 3D-MXene-unity membrane-aerogel for flexible supercapacitor with solar enhanced performance

Designing high gravimetric capacitance, flexible, and functional structural electrodes based on 2D nanomaterials is crucial for wearable electronics, however, it is still limited by serious restacking problems and uncontrollable assembly processes. Herein, inspired by a specialized network of rigidity-flexible integration in aestivum, an effective half-dry 2D-1D-2D pre-assembly combined with an “ice templating” strategy was proposed to construct a novel 3D-MXene-unity membrane-aerogel for the desirable supercapacitor substrate with energy harvesting capacity, addressing the incompatible contradiction between electrochemical properties and desirable mechanical strength. With cellulose nanofiber serving as a 1D structural modifier as well as black-phosphorus nanosheets applied as a 2D restacking reliever and electron-conductive network jointer, the multi-leveled mimicked topology facilitated the configured complexity of the membrane-aerogel can be achieved to be utilized in multifunctional composite electrodes. The resulting super-flexible and net-shaped 3D-MXene-unity membrane-aerogel showed low-tortuosity topology, superior electron-conductive network (870 S/cm), outstanding mechanical strength (53.2 MPa), and favorable electrochemical property (215 F/g), hardly achieved in a single system. Because of the synergistic photo-thermal capability from MXene and BP, assembled supercapacitors can harvest energy from sunlight and result in a 196% enhancement in capacitance. This work would lay a significant foundation for the construction of high-performance flexible energy storage devices.

Enhancement of capacitance and widening of the operating voltage window of flexible supercapacitors by adding Li2TiO3/BN on their electrodes

The electrochemical performance of flexible carbon-nanotube (CN) based supercapacitors (SCs) is reported in this research. A mixture of Boron nitride (BN), graphene (G) and lithium titanate (Li2TiO3, LiTi) was added on the SC electrodes to enhance their capacitance/energy-density. SC devices were fabricated with the names of CN-SC, CN/BNG-SC and CN/BNG + LiTi-SC and generated a capacitance/energy density of 329.7 F g−1/7.3 Wh kg−1, 890.2 F g−1/35.2 Wh kg−1 and 1662.6 F g−1/124.2 Wh kg−1, respectively. From those last values, we realize that adding BN, G and LiTi (CN/BNG + LiTi-SC), enhanced the capacitance and the energy density by ~ 4 and ≈ 16 times, respectively. Interestingly, the output voltage of the SCs also increased from 0.1 to 0.4 V after adding these three compounds to their electrodes. The SC electrodes were analyzed by UV–vis absorbance, Raman and XPS and found the presence of defects (oxygen vacancies) and Ti3+/Ti4+ species, which worked as redox centers for the charge storage. Moreover, the best CN/BNG + LiTi-SC device was subjected to 500 bending/charging-discharging cycles and maintained a capacitance of 86–97% despite the mechanical deformations. Finally, we demonstrated that the incorporation of the BN and LiTi materials on the SC electrodes produced a widening of the operating voltage window from 1.2 to 2.2 V, which is of particular interest to increase the lifetime of portable energy sources.

Enhancing quantum capacitance of iron sulfide supercapacitor through defect-engineering: A first-principles calculation

Quantum capacitance (CQ) has recently emerged as a solution for the saturated growth of supercapacitor performances. The CQ depends on the density of states of the electrode materials, which could be tuned by several approaches (i.e., introducing dopants). In this case, a transition metal sulfide material with a narrow band gap, such as hexagonal iron sulfide (h-FeS), has enormous advantages. In this study, we predict p-type defect importance in the h-FeS structure on capacitance enhancement through the quantum capacitance mechanism. From the first-principle calculation, the Cr-doped h-FeS (FeS:Cr) anode results in integrated quantum capacitance (CQint) of 1043 F/g, or 27 times more than pristine h-FeS. From the formation energy calculation, the Cr-doped structure has a lot of stable charged states enabling additional redox-related capacitance. As dopant concentration increased, the CQint is found to increase but then saturate due to delocalized state appearances. These findings imply that a first-principles understanding is essential to predict the enhanced capacitance properties on h-FeS and TMS supercapacitors.

Shape Evolution of Indium Sulfide Heterostructures via Carbon Nanotube Scrambling: Towards Reliable Sustainability and Mitigating Leakage Current in Supercapacitors

For sustainable energy storage devices with long-term endurance, exploring novel electrode materials can be a realistic focus in the areas of robust structures, surface area control, high channel conductivity, and others. A composite of a hierarchical series of single-walled carbon nanotubes (SWNTs) with In2S3 was synthesized by applying a simple one-step solvothermal method. A SWNT scaffold yields a good conductive pathway, leading to the improved electron transportation and catalytic behaviors. This promotes the robust formation of materials and their enhancement in surface activity and specific capacitance. Herein, the nucleated nanocomposites based on SWNT-mediated In2S3 improve the specific capacitance (1268 F·g−1 at 10 mVs−1) to a remarkable 92.4% of its capacitance even after 10,000 cycles, and furthermore, the robust cocoon-like structure of INS5 (5 mL SWNT doped in In2S3) shows an excellent 97.8% of cyclic retention (10,000 cycles). As a conceptual demonstration of system integration, the as-fabricated symmetric supercapacitor (SSC) device is successfully integrated into the Bluetooth/photoplethysmography (BLE/PPG) module for a wireless sensor network. These findings, through indium sulfides with SWNT scrambling, are expected to contribute to the next-generation solid-state-supercapacitor (SSC)-integrated module in the wireless health monitoring system.

Activated carbon derived from hydrochar of food waste for supercapacitor: Effect of components on electrochemical performance

Herein, rice, cabbage, and pork were chosen as typical starch, lignocellulose, and protein food wastes, respectively. Hydrothermal carbonization and KOH activation were used to prepared activated carbon from single and mixed food wastes, with a focus on the effect of components on the electrochemical performance of activation carbon as EDLC electrode materials. The results showed that the mesoporous and carbonyl group in activated carbon were mainly contributed by the starch in feedstocks, while the micropores, pyrrolic-N, and edge defects in activated carbon were determined by the lignocellulose and protein in feedstocks. Compared with single components, the mixed food wastes were more suitable to produce activated carbon with high specific capacitance. Among them, the three-component mixture presented the highest specific capacitance of 327 F/g at 0.5 A/g. However, the activated carbon from the rice owed high capacitance retention rate of 83.7%. In general, the co-presence of lignocellulose and protein in food wastes were conducive to the enhancement of specific capacitance for activated carbon. The starch rich food waste was feasible to produce activated carbon with well capacitance retention rate. The results could give a guide to select suitable food wastes that could produce high efficiency electrode materials.

Electrochemical behavior of NiWO4 modified by ultrasonic and laser irradiation

In this work, NiWO4 was prepared by co-precipitation and modified by ultrasonic and laser irradiation. Its electrochemical properties were investigated by potentiodynamic, galvanostatic and impedance spectroscopy methods. The results show that NiWO4 ultrasonic-modified and exposed to laser irradiation for 420 s has the highest capacitance of 520 F/g at a discharge current of 1 mA. This capacitance value is 2.5 times higher than for NiWO4 ultrasonic-modified and 3.4 times higher than for NiWO4 obtained by co-deposition. The capacitance enhancement of NiWO4 modified by ultrasonic and laser irradiation is the result of stimulation of fast redox reactions, which is confirmed by impedance studies.

High Mass Loading of Flowerlike Ni-MoS2 Microspheres toward Efficient Intercalation Pseudocapacitive Electrodes

This work reports the exploration of intercalation pseudocapacitance in a thicker electrode of flowerlike Ni-doped MoS2 microspheres that features a mass loading of ∼10 mg/cm2 without sacrificing the gravimetric capacitance (∼425 F/g at 5 mV/s). Integration of Ni atoms into MoS2 microspheres not only stabilized the structural integrity but also ameliorated the rapid intercalation and deintercalation of electrolyte ions even at a commercial-level mass loading. The energy instability by Ni doping significantly changed the local bonding behavior and the overall electronic structure of MoS2, facilitating the breaking of the MoS2 layer and generation of more active edge sites, which are responsible for faster reaction kinetics. The experiments attribute the overall capacitance enhancement in (Mo-Ni)S2 to the increased rate of electrolyte ion insertion and extraction, which is confirmed by b-values close to 0.5, at different potentials, indicating that the current response predominantly depends on the diffusive mechanism for both MoS2 and Ni-MoS2 thicker electrodes. The symmetric device constructed with Ni-MoS2 microspheres exhibited a capacitance value of 101 F/g in 1 mV/s, for which the energy density is 9 Wh/kg, as well as attained an outstanding cycling stability of 10 000 cycles with 60% retention at 2 A/g. In addition to providing insights into the development of 2D TMDs, this work explores the design of robust and highly efficient intercalation electrode material for electrochemical energy storage devices.

A metallic nickel site in a complex multimetallic design for controlled CO2 reduction and symmetric supercapacitor device

Single metallic sites are promising for high power density with promising capacitive performance, and for low-energy chemical reduction of CO2 to formate. Here, we present a novel strategy for accessing C-ZIF-700 with metallic nickel (Ni) sites encapsulated by multiwalled nanotube shells from trimetallic imidazolate frameworks (M-ZIF). A X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis confirmed the zero-valance state of Ni, with no significant positive valance state. C-ZIF-700 showed no sign of leaching of Ni nanoparticles under aqua regia treatment for long, as evidenced from -XANES-EXAFSanalysis. It is demonstrated that the coexistence of Ni and Co in C-ZIF-700 renders more active electrochemical energy storage by regulating charge distribution to improve electronic transportation capability. C-ZIF-700 with predominantly metallic Ni-sites demonstrated superior capacitive performance, presenting a remarkable capacitance value of 262 F/g at a scan rate of 5 mV/s. In an assembled symmetric supercapacitor device , C-ZIF-700 exhibited a very high specific energy value of 21.2 Wh/kg at a current density of 0.05 A/g, which retained up to 9.7 Wh/kg at 10 A/g, and a corresponding specific power value of 25 kW/kg. C-ZIF-700 has offered facile N-formylation of the primary amine group of aniline, with the assistance of alkyl silane as a hydride source under moderate CO2 pressure (15–20 bar) and temperature (maximum 100 °C). Electronic structural evidence of metal sites in C-ZIF-700, by using XANES-EXAFS, electron microscopy, and CO2 adsorption–desorption profile supports that Ni-site is responsible for CO2 activation-reduction. The evidence also supports a possible synergistic effect of Co nanoparticles in capacitance enhancement and CO2 reduction. This strategy,thus, proves the outstanding role of encapsulated Ni sites for enhanced capacitive performance and chemical fixation of CO2.

Laser-irradiated carbonized polyaniline-N-doped graphene heterostructure improves the cyclability of on-chip microsupercapacitor.

Laser-irradiated graphene-based heterostructures have attracted significant attention for the fabrication of highly conducting and stable metal-free energy storage devices. Heteroatom doping on the graphene backbone has proven to have better charge storage properties. Among other heteroatoms, nitrogen-doped graphene (NG) has been extensively researched due to its several advanced properties while maintaining the original characteristics of graphene for energy storage applications. However, NG is generally prepared via chemical vapor deposition or high temperature pyrolysis method, which gives low yield and has a complex operation route. In this work, first a polyaniline-reduce graphene oxide (PANI-rGO) heterostructure was prepared via in situ electrochemical polymerization, followed by the deposition process. In the next step, laser-irradiation process was employed to carbonize polyaniline as well as doping of nitrogen on the graphene film, simultaneously. For the very first time, laser-irradiated carbonization of PANI on NG (cPANI-NG) heterostructure was utilized for microsupercapacitor (MSC). The as-prepared cPANI-NG-MSC shows extremely high cycling stability with a capacitance enhancement of 135% of its initial capacitance after 70 000 continuous charge-discharge cycles. It is very interesting to know the origin of the capacitance enhancement, which results from the change of pyrrolic N in NG-MSC to the pyridinic and graphitic N. An on-chip NG-MSC exhibits an excellent charge storage capacitance of 43.5 mF cm-2 at a current density of 0.5 mA cm-2 and shows impressive power delivery at a very high scan rate of 100 V s-1. The excellent rate capability of the MSC shows capacitance retention up to 70.1% with the variation of current density. This unique approach to fabricate NG-MSC can have a broad range of applications as energy storage devices in the electronics market, as demonstrated by glowing a commercial red LED.

Electrochemical Activity of Pure and Sn-Doped CeO<sub>2</sub> Nanoparticles using Simple Chemical Precipitation Method

In the present work, pure and Sn-doped CeO2 nanoparticles (NPs) were synthesized by the chemical precipitation method calcined at 400 ºC for 4 h. Characterization of NPs was done through X-ray diffraction (XRD), UV-visible, photoluminescence (PL), Fourier transform infrared (FTIR) spectroscopy and high-resolution electron microscope (HRTEM) techniques. The XRD study revealed the crystalline nature, size, and structure of the prepared NPs. The HRTEM results illustrated cubic structure. The UV–visible and PL studies were used to measure the optical behaviors of CeO2 NPs. The UV-visible showed that the bandgap value of CeO2 NPs increased from 3.61 to 3.65 eV for different doping concentrations. The XRD study exhibited that the size of the CeO2 NPs reduced from 11.03 to 7.91 nm. From the TEM analysis, the average size of undoped and 10% Sn-doped CeO2 NPs was calculated as 9.3 and 7 nm, respectively. A cyclic voltammetric study confirmed that Sn-doped CeO2 exhibited a higher specific capacitance value than the pure CeO2. The chemical precipitation method observed excellent redox and oxidation behavior were observed for Sn-CeO2 NPs by the cyclic voltammetric study. The significant enhancement in the specific capacitance suggested that Sn-doped CeO2 is a promising material for supercapacitor applications.