High Quantum Capacitance Research Articles

Combined experimental and density functional theory approaches to address different mechanisms of nitrogen and sulfur doping on the enhancement of capacitive performance of hierarchical porous biochars

Activated carbon derived from biomass as hierarchical porous biochars (HPB) has been developed as electrode materials for supercapacitors. Nitrogen is known as the doping element that enhances quantum capacitance, but the mechanisms of sulfur doping on the quantum capacitance enhancement remain ambiguous. In this study, conventional approaches to assess the characteristics and capacitive performance of biochars were combined with density functional theory (DFT) calculations to assess different mechanisms of nitrogen and sulfur doping. The Bbiochar samples were prepared from the pyrolyzed fish bone powder at 800 °C without additional doping possessed a specific capacitance of 240 F g−1 at 1 A/g within 1 M H2SO4. Interestingly, additional nitrogen doping through urea mixing and additional sulfur doping through thiosulfate mixing prior to the pyrolysis enhanced the specific capacitance of biochar samples to exceed 400 F g−1 under the same condition. The urea mixed sample possessed low porosity but high charge transfer resistance, while the thiosulfate mixed sample possessed high porosity but low charge transfer resistance. The different underlying mechanisms were discussed through DFT calculations on graphene models designed based on the x-ray photoelectron spectroscopy (XPS) results. Nitrogen-doped configurations with topological defects mainly stored charge at the dangling atoms and possessed a relatively high quantum capacitance. Meanwhile, doped configurations of oxidized sulfur groups required relatively low formation energy and possessed large bond dipoles, corresponding to larger pore size and surface area of the thiosulfate mixed biochars. Understanding the contrary between effects of nitrogen and sulfur doping could resolve the bottleneck on enhancing the performance of electronic double layer supercapacitors.

Envisaging quantum capacitance in modified germanene: a first principle investigation

Two-dimensional (2D) nanomaterials with enhanced quantum capacitance have been in high demand over the past few years due to super capacitors application. A number of 2D nanosheet, including MoS2, arsenene, antimonene, and germanene, have also been explored for the same reason. The present investigation aims to explore modified germanene such as monovacant germanene/divacant germanene(MVG/DVG) and their derivatives, such as Ns substituted MVG/DVG and transition metal incorporated MVG. It is observed that 1N-MVG/3N-MVG shows the characteristics of a p-type semiconductor, while 3N-MVG/4N-DVG is considered as semiconductor. A robust binding of under-coordinated Ge to transition metals (TMs) at MVG surfaces suggests such functionalization can be accomplished. Except Ti and Co other studied TMs-MVG show metallic nature. Furthermore, it is revealed that there is an asymmetric CQ dispersion in 1N-MVG, 2N-MVG, 3N-MVG, and 4N-DVG, as opposed to the pristine germanene/MVG/DVG. Additionally, it is predicted that TMs such as Ti, V, Cr, Mn, Fe and Co incorporated MVG can provide high quantum capacitance (CQ). Enormous amount of CQ is noticed for 3N-MVG with maximum of 726 μF cm−2 in the positive biased region. Among TM-MVG, V-MVG and Mn-MVG are well suited to serve as anodes for asymmetric super capacitors due to their CQ peak of 978 μF cm−2 and 1180 μF cm−2, respectively, in negative bias region.

Effect of surface functionalization on the quantum capacitance of M2CF2 (M = Ti, V, Cr, Zr, Nb, Mo) as supercapacitor electrodes

The surface charge storage capacity, atomic structures, and quantum capacitance of M2CF2 (M=Ti, V, Cr, Zr, Nb, Mo) are investigated using density functional theory (DFT). The influence of different surface functionalization methods on the capacitance performance of M2CF2 is also examined, including the introduction of vacancy defects (C-, F-, M-vacancy) and nonmetal doping (N, O, and S). The findings show that both defects and doping reduce the quantum capacitance of V2CF2, Cr2CF2, and Mo2CF2, but they have a negligible impact on the capacitance behavior of Ti2CF2, Zr2CF2 and Nb2CF2. Furthermore, the pristine Cr2CF2 system exhibits relatively high quantum capacitance and surface charge storage capacity under both positive and negative bias. However, the presence of vacancies and dopants significantly decreases its capacitance. Among the structures studied, pristine and nonmetal-doped V2CF2 demonstrate the highest quantum capacitance values (1302.02–1517.56 μF/cm2), suggesting its potential as an effective positive electrode material. Overall, the findings of this study are expected to boost the development of high-capacitance electrodes in the future.

Quantum capacitance behavior of Ti2CO2/MoS2 heterostructures with 3d and 4d transition-metal doping

The storage capacity of capacity, quantum capacitance behavior, and atomic stability of O-defected, S-defected, 3d and 4d transition-metal (3d-TMs: Sc, Ti, V, Cr, Mn, Fe, Co, and Ni; 4d-TMs: Y, Zr, Nb, Mo, Ru, Rh, Pd, and Ag) doped Ti2CO2/MoS2 heterostructures were studied by density functional theory (DFT). Pristine Ti2CO2/MoS2 exhibited a high quantum capacitance of 1038.62 μF/cm2 at the positive potential. The appearance of O-vacancy in Ti2CO2-layer enhanced the capacitance of Ti2CO2/MoS2 at negative bias, and S-vacancy induced an obvious improvement of quantum capacitance at 0 V. After introducing various transition metals into modified Ti2CO2/MoS2 heterostructures, the doping in pristine structures increased the capacitance value to be 1182.71 μF/cm2 (Y-doping), while TM-doping in S-vacancy defected Ti2CO2/MoS2 systems induced a slight decrease of capacitance at positive potentials. For TM-doped O-defected Ti2CO2/MoS2, only Sc- and Y-doped systems exhibited higher quantum capacitance than the pristine Ti2CO2/MoS2, which were 1093.60 and 1096.26 μF/cm2. Due to the obvious advantage of capacitance of pristine Ti2CO2/MoS2 than Ti2CO2 or MoS2 single-layer at the positive bias, it can be used as effective anodes for high-capacitance supercapacitors, while 3d or 4d TM-doping had no significant enhancement in capacitance behaviors. The findings in this study were supposed to be theoretical data base to design high-performance supercapacitors.

Three-Dimensional Ni-MOF as a High-Performance Supercapacitor Anode Material; Experimental and Theoretical Insight.

A three-dimensional (3D) Ni-MOF of the formula [Ni(C4H4N2)(CHO2)2]n, has been reported, which shows a capacitance of 2150 F/g at a current density of 1A/g in a three-electrode setup (5.0 M KOH). Post-mortem analysis of the sample after three-electrode measurements revealed the bias-induced transformation of Ni-MOF to Ni(OH)2, which has organic constituents intercalated within the sample exhibiting better storage performance than bulk Ni(OH)2. Afterward, the synthesized MOF and reduced graphene (rGO) were used as the anode and cathode electrode material, respectively, and a two-electrode asymmetric supercapacitor device (ASC) setup was designed that exhibited a capacitance of 125 F/g (at 0.2 A/g) with a high energy density of 50.17 Wh/kg at a power density of 335.1 W/kg. The ASC further has a very high reversibility (97.9% Coulombic efficiency) and cyclic stability (94%) after 5000 constant charge-discharge cycles. Its applicability was also demonstrated by running a digital watch. Using sophisticated density functional theory simulations, the electronic properties, diffusion energy barrier for the electrolytic ions (K+), and quantum capacitance for the Ni(OH)2 electrode have been reported. The lower diffusion energy barrier (0.275 eV) and higher quantum capacitance (1150 μF/cm2) are attributed to the higher charge storage performance of the Ni-MOF-transformed Ni(OH)2 electrode as observed in the experiment.

Improvement of the ability of graphene by simultaneous cobalt (Co) and nitrogen (N) doping as an electrode for supercapacitor application

Thanks to its high electronic conductance and large surface, many research studies have investigated the application of graphene (Gr) in supercapacitors as an electrode material. The properties of Gr can change efficiently through the doping of specific elements and by designing various morphologies. In the current piece of research, DFT calculations are undertaken to investigate the impact of doping cobalt (Co) and nitrogen (N) atoms, and a monovacancy (MV)-added Gr structure upon the quantum capacitance (QC), electronic attributes and stability. Based on the calculations, doping Co and N and the presence of the MV radically changed the QC of the electrode. Nevertheless, achieving structural stability can be a challenge. A high QC of ∼77 μF/cm2 was obtained in the CoN3 system by the association of N-doping and the existence of the MV. The present piece of research provides insights into the viable impact of combined doping upon increasing the QC of Gr-based electrodes.

Electrochemistry at 2D and 3D nanoelectrodes: The interplay between interface kinetics and surface density of states

Heterogenous Electron Transfer (HET) at electrode-electrolyte interfaces depends strongly on the morphological features or geometry of the nanostructure used for modifying the electrode surface. A swift HET results in faster interface kinetics, which has significant impact on the development/calibration of electrochemical devices like biomolecular sensors, supercapacitors, batteries and electrochromic platforms. The interface electrochemistry depends strongly on the electronic Density of States (DOS) of electrode materials. Over the past years, the 2D electron gas nanomaterials - primarily graphene, Graphene Oxide (GO) and Reduced Graphene Oxide (RGO), have garnered significant interest in electrochemical applications due to promising DOS features. However, the electroanalytical dependency on DOS of 3D nanostructures such as Zinc Oxide Tetrapods (ZnOT) is yet unexplored. The current work focusses on a comparative electrochemical analysis of interface kinetics at RGO (2D) and ZnOT (3D) coated screen printed electrodes, with the intention of selecting the suitable material geometry. The analyses were performed using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). While the dependence of HET on DOS of RGO and ZnOT nanomaterials were studied using both DFT analysis and impedance-derived capacitance spectroscopy – the latter giving insights on quantum capacitance. It was observed that, the 2D RGO nanostructures exhibit higher surface DOS near the Fermi level, along with a high quantum capacitance (∼345 nF) as compared to 3D ZnOT (∼276 nF). This results in enhanced HET at the former, thereby indicating its suitability in developing futuristic electrochemical devices for various applications as desired.

Experimental and theoretical insights into the supercapacitive performance of interconnected WS2 nanosheets.

Transition metal dichalcogenides (TMDs) are fascinating and prodigious considerations in the electrochemical energy storage sector because of their two dimensional chemistry as well as heterogeneous characteristics. Herein, we synthesized interconnected WS2 nanosheets by a hydrothermal method followed by sulphuration at 850 °C in an argon atmosphere. The ultrathin WS2 nanosheet array is endowed with an excellent specific capacitance of 74 F g-1 at the current density of 3 A g-1 up 7000 cycles. Moreover, a symmetric supercapacitor was fabricated using WS2 nanosheets, which provided the admirable high specific capacity of 6.3 F g-1 at 0.05 A g-1 with the energy and power density of 5.6 × 102 mW h kg-1 and 3.6 × 10 5 mW kg-1, respectively. Density functional theory (DFT) simulations revealed the presence of populated energy states near the Fermi level resulting in a high quantum capacitance value, which supports the experimentally achieved high capacitance value. The attained results recommend interconnected WS2 nanosheets as a novel, robust, and low-cost electrode material for supercapacitor energy storage devices.

Quantum capacitance properties of the holes in planar germanium

Quantum capacitance of two-dimensional (2D) systems contains useful physical information. Here, we report a high sensitivity quantum capacitance measurement with an improved radio frequency superheterodyne bridge technique for probing the electronic characteristic of Ge/SiGe 2D hole gas (2DHG) at low temperatures and under a perpendicular magnetic field B⊥. At low fields, a rapid decrease in quantum capacitance following B⊥−3 dependence is observed, indicating an abrupt change in chemical potential near the gate boundary at high frequencies; at high fields, a series of capacitance oscillations are observed due to the Landau quantization and Zeeman splitting of the Ge/SiGe 2DHG, where gate-dependent effective g factor under B⊥ is extracted. These results represent implementation of the high-precision capacitance measurement for exploring the physical properties of Ge/SiGe 2DHG.

Achieving high quantum capacitance graphdiyne through doping and adsorption.

In recent years, a new two-dimensional carbon material, graphdiyne (GDY), has attracted extensive attention in the field of energy storage, due to its unique topological and electronic structures, high charge mobility, and excellent electron transport properties. However, the disappearance of the density of states near the Fermi level leads to a low quantum capacitance (CQ) of pristine GDY, which limits its application in supercapacitors. Here, we propose doping and metal atom adsorption to be efficient ways to increase the CQ of GDY. Based on first-principles density functional theory, the effects of doping B, N, P, and S atoms and adsorbing Au, Ag, Cu, Ti, and Al atoms on the CQ of GDY are systematically investigated. The results show that the CQ of GDY can be significantly improved by introducing doping/adsorption, which could be a potential cathode material and anode material for supercapacitors. Our work provides an effective way for GDY to be applied as an efficient electrode material for supercapacitors.

Graphene Chemeo‐Phononics for Biosensor Applications: An Interfacial Raman Transducer

AbstractLeveraging the phononic sensitivity and scalability of nano‐biointerfaces has accelerated the growth of unique and versatile biosensors. Graphene has the properties of a near‐ideal signal transducer, due to the strong coupling between its interfacial and phononic properties. This enables sensitive yet quick detection of surface interactions on graphene via Raman spectral analysis. The Raman‐active vibrational bands of graphene are demonstrated to be sensitive to structural, electrical, and interfacial modifications. This sensitivity is attributed to graphene's electron–phonon coupling and high quantum capacitance. The fundamental understanding of graphene phonons is crucial for developing reliable platforms for disease and infectious agent detection. This review provides a mechanistic explanation of these phenomena at the interface between graphene and various biosystems (including cancerous, bacterial, viral, and biophysical specimens) to set the foundation for next‐generation chemeo‐phononic medical devices.

Surface functionalization effect on physical properties and quantum capacitance of Ca2C MXenes

Effects of surface terminal groups on the structural, mechanical, and electronic properties, as well as the quantum capacitance of Ca2CT2 (T = F–, O–, Cl–, OH–) MXenes are studied by first-principles electronic structure computations. Ca2C(OH)2 is determined to be the most stable structure compared with Ca2C and Ca2CT2 (T = F–, Cl–) MXenes, while Ca2CO2 is mechanically unstable. The surface terminations have a strong influence on the work function of MXene as they can alter the Fermi level and the associated electron transfer. Analyzing the atom projected density of states shows the existence of localized electron states at and around the Fermi level, generating a high charge density close to the Fermi level and resulting in relatively high quantum capacitance. The quantum capacitance of Ca2CCl2 is the highest (152 μF/cm2) among the studied cases, while Ca2C(OH)2 has the lowest quantum capacitance. The observed variations in quantum capacitance are mainly attributed to the creation and annihilation of new electronic states and the shift of Fermi level in the studied MXenes. Also, presence of surface terminations of Ca2C MXenes considerably changes the electrode quantum capacitance and Ca2CCl2 is the most promising one among the studied cases.

Study of Quantum Capacitance of Pure and Functionalized Nb2c and Ti2c Mxenes for Supercapacitor Applications

Supercapacitors in combination with renewable energy sources can provide environment friendly and sustainable energy devices. But due to their lower energy density, they are not able to replace batteries for all commercial applications. Their energy density can be increased by using high quantum capacitance electrodes. MXenes have potential to be used for such electrodes. In present work, density of states, band structure and quantum capacitance (QC) of bare and functionalized niobium carbide and titanium carbide MXenes are studied using DFT simulations. The calculated quantum capacitances of Nb2C and Ti2C show significant values of 324.1 and 246.2 µF/cm2 respectively. Nb2C shows higher value for QC in comparison to Ti2C for both positive as well as negative electrodes. These calculations are also performed for functionalized MXenes using =O, -F and –OH as functional group. Functionalization of MXenes with these groups reduces the QC of Nb2C and Ti2C MXenes at Fermi level.

Design principle of MoS2/C heterostructure to enhance the quantum capacitance for supercapacitor application

1T Molybdenum disulfide (1T-MoS2) has been widely studied experimentally as an electrode for supercapacitors due to its excellent electrical and electrochemical properties. Whereas the capacitance value in MoS2 is limited due to the lower density of electrons near the Fermi level, and unable to fulfill the demand of industry i.e. quantum capacitance preferably higher than 300 μF/cm2. Here, we investigated the performance of 2H, 1T, and 1T′ phases of MoS2 in its pristine form and heterostructures with carbon-based structures as an electrode in the supercapacitors using density functional theory. Specifically, we reported that the underneath carbon nanotube (CNT) is responsible for the structural phase transition from 1T to 1T′ phase of MoS2 monolayer in 1T′-MoS2/CNT heterostructure. This is the main reason for a large density of states near Fermi level of 1T′-MoS2/CNT that exhibits high quantum capacitance (CQ) of 500 μF/cm2 at a potential of 0.6 V. Also, we observed that the nitrogen doping and defects in the underneath carbon surface amplify the CQ of heterostructure for a wider range of electrode potential. Therefore, the 1T′-MoS2/N doped CNT can be explored as an electrode for next-generation supercapacitors.

First-principle study of electronic properties and quantum capacitance of lithium adsorption on pristine and vacancy-defected O-functionalized Ti2C MXene

The electronic structure, surface charge storage and quantum capacitance of lithium adsorption on pristine and vacancy-defected Ti2CO2 MXene are theoretically investigated by density functional theory. Negative adsorption energies (Eads) of pristine Ti2CO2 (PT) and C-vacancy Ti2CO2 (VT) monolayers adsorbed by Li atom indicate that the adsorption processes of Li atom on systems are exothermic and favorable to adsorption. The most stable configurations are confirmed for the Li-adsorbed PT and VT monolayers. Pristine Ti2CO2 (PT) monolayer is a semiconductor with the bandgap of 0.2035 eV, while C-vacancy Ti2CO2 (VT) monolayer has the metallic nature. The adsorption of Li atom on PT monolayer makes the system undergo the semiconductor-metal transition, while the adsorption of Li atom on VT monolayer doesn’t change the metal nature. The magnetism is observed for the system with Li atom directly adsorbed on top of hollow site (VT-LH), and the total magnetic moments is 0.18 μB. Charge density differences of the adsorption of Li atom on PT and VT monolayers are further explored. The introduction of C-vacancy improves the quantum capacitances of the Li-adsorbed systems at 0 V, and Li-adsorbed PT and VT monolayers have high quantum capacitance because of the large density of states near Fermi level, and are suitable for cathode material.

Theoretical investigation of quantum capacitance in the functionalized MoS2-monolayer

In this work, we investigated the electronic structure and the quantum capacitance of a set of functionalized MoS2 monolayers. The functionalizations have been done by using different ad-atom adsorption on MoS 2 monolayer. Density functional theory calculations are performed to obtain an accurate electronic structure of ad-atom doped MoS2 monolayer with a varying degree of doping concentration. Subsequently, the quantum capacitance in each functionalized system was estimated. A marked quantum capacitance above 200 μF cm−2 has been observed. Our calculations show that the quantum capacitance of MoS2 monolayer is significantly enhanced with substitutional doping of Mo with transition metal ad-atoms. The microscopic origin of such enhancement in quantum capacitance in this system has been analyzed. Our DFT-based calculation reveals that the generation of new electronic states at the proximity of the band-edge and the shift of Fermi level caused by the ad-atom adsorption results in a very high quantum capacitance in the system.

Boron-Decorated Pillared Graphene as the Basic Element for Supercapacitors: An Ab Initio Study

In this work, using the first-principle density functional theory (DFT) method, we study the properties of a new material based on pillared graphene and the icosahedral clusters of boron B12 as a supercapacitor electrode material. The new composite material demonstrates a high specific quantum capacitance, specific charge density, and a negative value of heat of formation, which indicates its efficiency. It is shown that the density of electronic states increases during the addition of clusters, which predictably leads to an increase in the electrode conductivity. We predict that the use of a composite based on pillared graphene and boron will increase the efficiency of existing supercapacitors.

Recent Progress in Graphene‐Based Microsupercapacitors

The fast growing field of microsized electronic devices has urgent demand for next‐generation microscale, flexible, and lightweight energy conversion and storage devices. Among the various microdevices, microsupercapacitors (MSCs) are a promising energy storage device due to their fast rechargeability, better rate capability, long cycle life, and ultrahigh power density. The 2D graphene possesses a large surface area with flexibility, better conductivity, transparency, and high quantum capacitance that lead to an ideal energy storage material for the MSCs. Therefore, this review aims to summarize recent advances in graphene‐based MSCs. A particular emphasis is put on the various fabrication technologies for MSCs such as printing, laser, wet‐spin, and photolithography technique that are discussed elaborately. Moreover, an overview of the state‐of‐the‐art on graphene‐based electrode materials and its different composite with transition metal oxides, transition metal hydroxides, conducting polymers, transition metal chalcogenides, and MXene‐based electrode materials for MSCs are discussed and their electrochemical performances are summarized. Furthermore, this review concludes with perspectives and outlooks.

Enhanced quantum capacitance in chemically modified graphene electrodes: Insights from first principles electronic structures calculations

We have carried out a systematic study of quantum capacitance in functionalized graphenes by using DFT calculations. The graphene functionalization has been done by doping with different aliphatic and aromatic molecules and their radicals. The quantum capacitance of functionalized graphenes was estimated from the accurate electronic band structures of the system obtained by using DFT calculations. Our theoretical investigation reveals that aromatic and aliphatic radicals introduce localized density of states near the Fermi level of the functionalized systems, due to a charge localization. As a result, a very high quantum capacitance (>230μF∕cm2) was observed in the system. The effects of atomic dislocation and the vacancy defect on graphene during functionalization has also been incorporated in our investigation. Our study suggests an effective way to synthesize highly efficient graphene-based supercapacitor electrode materials by using aromatic and aliphatic molecule/ radical functionalization of graphene.

B/N-doped graphdiyne as superior supercapacitor electrode with record high quantum capacitance

Last decade has witnessed a surge of research in carbonaceous nanostructures as electrode materials for supercapacitors. Herein, we propose a new type of carbon electrode by using two-dimensional (2D) graphdiyne with nonmetal dopants. By first-principles calculations, we systematically investigated the structural, energetic, electronic and capacitance properties of B/N-doped graphdiyne. Results show that B/N doping has low formation energies in graphdiyne, indicating facile experimental synthesis. Interestingly, B/N doping transforms graphdiyne from a direct-band-gap semiconductor to an excellent metal, originating from the shift of Fermi level into the valence/conduction bands. By evaluating the quantum capacitance of graphdiyne with different doping concentrations, we demonstrate that the capacitance of B (N)-doped graphdiyne as anode (cathode) can reach a record high value of 4317 F/g (6150 F/g), significantly outperforming other 2D carbon electrodes. With high specific surface area and tunable electronic properties, we expect graphdiyne and related porous structures to have great potential for supercapacitors and energy storage devices.