Capacitor Charging Research Articles

Effect of alloying Li on lithium-ion batteries applicability of two-dimensional TiN and TiC as novel electrode materials: a first principle study

The two-dimensional structures of transition metal nitride and carbide, TiN, and TiC have been alloyed with lithium (Li) in replacement of Ti, and their Li-ion applicability has been investigated using density functional theory and general gradient approximation. The alloy composition of x=0.125, 0.25, 0.375, and 0.5 have been considered and the stability of the alloys has been proved by cohesive energy and phonon density of states results. Moreover, the bond lengths between atoms as structural properties have been studied for these alloy structures. The largest peak of quantum capacitance and the largest negative value of surface storage charge are for alloy composition of TiC with x=0.125 with the values of 909.79 upmu F/cm^{2} and -,1819.58,upmu C/cm^{2}, respectively. Moreover, the results of the quantum capacitance and surface storage charge as a function of voltage for all Li alloy compounds are in the range of excellent supercapacitors and could have good potential to use as an electrode in the capacitor of Li-ion batteries. Furthermore, the electronic density of states of this group of alloys represents metallic behavior and therefore electrode material. In addition, the diffusion coefficient at temperatures of 77 and 300 K has been calculated using molecular dynamic calculations, and its lowest and largest values are 8times 10^{-8} cm^2/s (at 77 K) and 5.6times 10^{-7} cm^2/s (at 300), respectively. Plus, the largest value of electrical conductivity per relaxation time at 300 K belongs to Li_{0.25}Ti_{0.75}C with a value of 9.8times 10^{19}/(Omega m s).

Multistage coupling water-enabled electric generator with customizable energy output

Constant water circulation between land, ocean and atmosphere contains great and sustainable energy, which has been successfully employed to generate electricity by the burgeoning water-enabled electric generator. However, water in various forms (e.g. liquid, moisture) is inevitably discharged after one-time use in current single-stage water-enabled electric generators, resulting in the huge waste of inherent energy within water circulation. Herein, a multistage coupling water-enabled electric generator is proposed, which utilizes the internal liquid flow and subsequently generated moisture to produce electricity synchronously, achieving a maximum output power density of ~92 mW m−2 (~11 W m−3). Furthermore, a distributary design for internal water in different forms enables the integration of water-flow-enabled and moisture-diffusion-enabled electricity generation layers into mc-WEG by a “flexible building blocks” strategy. Through a three-stage adjustment process encompassing size control, space optimization, and large-scale integration, the multistage coupling water-enabled electric generator realizes the customized electricity output for diverse electronics. Twenty-two units connected in series can deliver ~10 V and ~280 μA, which can directly lighten a table lamp for 30 min without aforehand capacitor charging. In addition, multistage coupling water-enabled electric generators exhibit excellent flexibility and environmental adaptability, providing a way for the development of water-enabled electric generators.

Does energy always have mass?

One of the most widespread interpretations of the mass-energy equivalence establishes that not only can mass be transformed into energy but that every type of energy also has mass (via the mass-energy equivalence formula \(m = {\cal E}/c^2\)). Here, we show that this is not always the case. By using two simple thought experiments, we show that, for instance, the electric potential energy of a charged capacitor should not contribute to the capacitor rest mass.

Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation.

The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only -1V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of ≈700 water molecules per electron-ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7MPa (1.4MPa vs dry) and a work density of ≈150kJm-3 (2MJm-3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems.

EDLC performance of plasticized NBG electrolyte inserted with Ba(NO3)2 salt: Impedance, electrical and electrochemical properties

The great challenge in front of energy storage devices is to reduce the microplastics in the ocean and their potential harm to human health through drinking. The microplastics topic mainly results from the increasing usage of electronic devices and their components. Developing green electrolytes based on natural polymers and plasticizers is unique in overcoming microplastic issues. Natural beef gelatin (NBG) based plasticized polymer electrolyte films doped with barium nitrate (Ba(NO3)2) and glycerol (Gly) were fabricated using a solution casting process. The NBG electrolyte containing 12 wt.% Ba(NO3)2 and 50 wt.% Gly-has the maximum ionic conductivity, 4.87 × 10−5 S cm−1, at room temperature. The electrochemical performance of plasticized NBG:Ba(NO3)2 was examined utilizing impedance spectroscopy, with an emphasis on the dielectric characteristics and electric modulus parameters. With electrochemical stability up to 2.65 V, the plasticized specimen with the highest conducting demonstrated eligibility for use in energy storage devices. Transference number measurement (TNM) proved the dominancy of ions as a charge carrier in the plasticized NBG:Ba(NO3)2 system, yielding an electron transference number of 0.045 and an ion transference number of 0.955. The absence of redox peaks in the cyclic voltammograms suggests a capacitive charge accumulation in the plasticized electrolyte near to the electrode surface other than the Faradaic process. The triangle-shaped galvanostatic charge-discharge (GCD) plot shows a comparatively low drop voltage. The constructed electric double layer capacitor (EDLC) using activated carbon displays energy and power densities of 3.41 W/kg and 336.4 Wh/kg, respectively, at the first cycle. The EDLC performances of plasticized NBG:Ba(NO3)2 demonstrated the cell has potential industrial use as an energy storage device.

Analysis and Design Considerations of Input Parallel Output Series-Phase Shifted Full Bridge Converter for a High-Voltage Capacitor Charging Power Supply System

Capacitor charging power supply (CCPS) is used for impulse-power applications such as electromagnetic rail guns, flash lamps, medical sterilization, and rock crushing, among many other application fields. This paper describes the design and analysis of an Input Parallel Output Series-Phase Shifted Full Bridge converter for CCPS. The proposed system has a low output current ripple to improve the lifetime of the high-voltage pulsed capacitor. Design considerations of topology's electrical parameters such as HF transformer's leakage inductor and output inductor for the CCPS application are presented. The intermediate DC-link capacitance is provided as an energy storage element to minimize the disturbances (power variation) on the source for the CCPS application. Analysis and sizing of the capacitance for two different charging methods are analyzed and compared. A controller design procedure for the Active Front End Converter (AFEC) is also included to ensure near-constant power drawn, rejecting the load disturbances. Finally, a complete design procedure for the whole CCPS system is presented. Design and simulation results are presented for a rated system, followed by experimental results from a scaled-down hardware prototype to validate the design.

A simple practical to measure energy stored when stretching a spring

After deriving the equations for energy stored in a stretched spring which obeys Hooke’s Law (E= ½Fx = ½kx 2), a practical demonstration was required to show that the energy stored in the spring was proportional to the square of the spring’s extension. Using existing equipment in the school laboratory, a bank of charged capacitors was discharged into a motor which wound a string to extend the spring. Measurements taken showed the required proportionality convincingly.

Highly Flexible Tribovoltaic Nanogenerator Based‐on P‐N Junction Interface: Comparative Study on Output Dependency Dominated by Photovoltaic Effect in Freestanding‐Mode

AbstractThe emergence of tribovoltaic nanogenerators (TVNGs) paves the way for developing a new kind of semiconductor‐based energy harvester that overcomes the restriction of low output current in a conventional approach. The traditional TVNG generally depends on the frictional pair between two rigid semiconductors (or metal‐semiconductor), limiting the practicability of flexible and portable electronics. Recent developments require the fundamental understanding of charge generation in diverse operating modes and structures. Here, a flexible TVNG based on the p‐Cu2O/n‐g‐C3N4 interface is presented. Operating in a freestanding mode, the proposed TVNG can generate a stable signal in any optical conditions including UV illumination, dark, and ambient. Under UV illumination, the electrical outputs of the TVNG reach 0.43 V and 2.1 µA cm−2, which are significantly larger than those obtained from dark and ambient conditions. The results demonstrate the coupling effect of three phenomena: tribovoltaic, photovoltaic, and triboelectric effects, and the unique mechanism to the observed signal is proposed. Additionally, the TVNG shows the practical feasibility of energy harvesting with capacitor charging and charge‐boosting circuits. This study showcases the unique concept with potential for developing a novel flexible nanogenerator in many aspects, including material, structure, and fundamental mechanism.

Electrocapacitive removal of malachite green and methylene blue using green-synthesized NiBi2O4 nanospinels

Bismuth based spinels are new spinels which possess special features for advanced material applications. In this study, NiBi2O4 was synthesized through a green sol-gel method using plant extract reductant for capacitive removal of malachite green dye. Parameters like effect of concentration, applied voltage, electrode spacing, and cycle were investigated. The NiBi2O4 spinel showed 91 % malachite green removal and followed the Elovich model at R2 of 0.99413. This confirms that the capacitive removal is chemisorption and depends on surface chemistry of the green NiBi2O4. This work confirms that high temperature destabilizes the surface chemistry of green bismuth-based spinels. XRD confirms the NiBi2O4 crystallized as a cubic spinel, the FTIR confirms the presence of Bi2O3 octahedron and NiO tetrahedron. XPS confirms Bi 2p1/2 and 2p3/2 at 798 and 776 eV respectively. Over the first five cycles, a charge capacitance and charge recovery kept at 214 to 212 and 99 to 97 % respectively confirms its capacitive stability over the spinels that were prepared at higher temperatures. The green NiBi2O4 spinels also showed 83 % removal efficiency for malachite green and methylene blue binary mixtures in the presence of an acidified iodine ion carrier. This work shows that green NiBi2O4 maintains good structural stability and shows good capacitive behavior at room temperature than spinels synthesized at higher temperatures.

Electrochemical Impedance Spectroscopy of Amorphous TiO2 Protected Photocathodes Under Hydrogen Evolution Conditions

Despite widespread use of electrochemical impedance spectroscopy (EIS) to study multi-layer photoelectrochemical (PEC) cells, the appropriate equivalent circuits describing these devices under hydrogen evolution conditions are not commonly investigated.1 This creates ambiguity with respect to the pathways of charge recombination and ionic movement within layers of the device during operation, therefore limiting rational development of future PEC devices. In this study, amorphous TiO2 (a-TiO2) protected silicon photocathodes have been investigated using EIS to show that these devices behave according to the Maxwell circuit during hydrogen evolution, which occurs when the semiconductor is in depletion. Therefore, there are two simultaneous processes occurring in parallel and on different timescales. While the high frequency component is the result of the depletion region in the semiconductor, the low frequency component of this circuit is found to originate from the a-TiO2 itself, implying a capacitive charging process of this protective overlayer during PEC cell operation. Studies to isolate the physical mechanism of capacitive charging in the a-TiO2 from a range of possibilities such as proton intercalation and vacancy migration have been carried out. This result is important for the development of future PEC devices using emerging semiconductors which heavily rely on the a-TiO2 overlayer in acidic electrolytes, such as Cu2O and Sb2Se3, where this low frequency process has previously been observed.1 Using the Maxwell circuit for a-TiO2 protected photocathodes under hydrogen evolution conditions, one can independently determine properties of the semiconductor, such as the depletion capacitance and doping density, and the protective overlayer in these PEC devices under hydrogen evolution conditions. With this baseline, EIS can continue to aid the development of PEC cells as additional overlayers are developed and tested for further performance improvements. Yang, W. et al. Operando Analysis of Semiconductor Junctions in Multi-Layered Photocathodes for Solar Water Splitting by Impedance Spectroscopy. Adv. Energy Mater. 11, 2003569 (2021). Figure 1

Modeling Mesoporous 3D-Printed Lattice Electrodes for Energy Storage

3D printing could offer the versatility to design and manufacture energy storage devices on demand. The precision and material flexibility of 3D printing is ideal for integrating porous electrodes that can enhance electrochemical performance[1]. This work analyzes the electrical conductivity of 3D-printed mesoscale strut lattices at the 100 μm – 1 mm scale with 40 – 90 % volumetric porosity to develop optimal electrodes for energy storage devices. We use a graph-theory-based model[2] to compute the conductivity of multiple 3D lattice types with either solid conducting struts or struts coated with conductive material. These structures show 3 – 5X higher conductivity than random conductive foams that lack an internal periodic mesostructure[3]. Using microstereolithography, we 3D print samples with high-resolution struts (< 70 µm) that maintain their shape and achieve high conductivity after carbonization at 700 ˚C. By tuning the lattice architecture, we manipulate the tradeoff between conductivity, weight, and porosity, validating our simulations with experimental measurements. These results demonstrate that that body-centered cubic (BCC) strut lattices have optimal conductivity per weight compared with other lattice types. Implementing these 3D-printed conductive lattices as supercapacitor electrodes, we see that the lattice architecture impacts the gravimetric capacitance of the devices as well as the mechanical strength, with octet structures outperforming both cubic and BCC lattices. Electrochemical impedance spectroscopy (EIS) shows that 3D-printed electrodes with higher porosity exhibit higher gravimetric double layer capacitance and lower charge transfer resistance, making them ideal candidates for use in supercapacitor electrodes as free-standing 3D hosts for active materials. CV characterization of the electrodes also illustrates how our graph theory-based model for 3D lattices can predict the optimal structure for energy storage. This model can also serve to predict electrode performance and tailor design for integration of higher surface area nanoporous materials on these conductive 3D printed scaffolds. This allows us to guide the design of 3D printed electrodes to minimize charge transfer resistance and achieve an optimal balance between gravimetric and volumetric energy density for device applications.[1] J. Zhao, Y. Zhang, X. Zhao, R. Wang, J. Xie, C. Yang, J. Wang, Q. Zhang, L. Li, C. Lu, Y. Yao, Advanced Functional Materials 2019, 29, 1900809.[2] J. E. Huddy, M. S. Rahman, A. B. Hamlin, Y. Ye, W. J. Scheideler, Cell Reports Physical Science 2022, 3, 100786.[3] F. G. Cuevas, J. M. Montes, J. Cintas, P. Urban, J Porous Mater 2008, 16, 675. Figure showing (a) designed octet (blue), cubic (orange), and BCC (red) lattice types as well as (b) SEM images of their experimental 3D-printed counterparts and (c) measured electrical resistance. Figure 1

Wide-range and area-selective threshold voltage tunability in ultrathin indium oxide transistors

The scaling of transistors with thinner channel thicknesses has led to a surge in research on two-dimensional (2D) and quasi-2D semiconductors. However, modulating the threshold voltage (VT) in ultrathin transistors is challenging, as traditional doping methods are not readily applicable. In this work, we introduce a optical-thermal method, combining ultraviolet (UV) illumination and oxygen annealing, to achieve broad-range VT tunability in ultrathin In2O3. This method can achieve both positive and negative VT tuning and is reversible. The modulation of sheet carrier density, which corresponds to VT shift, is comparable to that obtained using other doping and capacitive charging techniques in other ultrathin transistors, including 2D semiconductors. With the controllability of VT, we successfully demonstrate the realization of depletion-load inverter and multi-state logic devices, as well as wafer-scale VT modulation via an automated laser system, showcasing its potential for low-power circuit design and non-von Neumann computing applications.

(Invited) Unification of Bulk Storage and Supercapacitive Storage

In typical insertion electrodes for batteries, the capacity is determined by bulk storage within the electroactive particles, which is comparatively well investigated and understood. In contrast, supercapacitor electrodes are dominated by interfacial storage at interfaces, which is well addressed experimentally. However the charge carrier chemistry (defect chemistry) especially in the latter case is not taken seriously. Consequently a bridge between the two important fields is absent. Following and extending our quantitative concept of job-sharing storage, a generalized description that includes bulk and space charge storage (electrochemical and supercapacitive storage) is possible. In other words the treatment of defect chemistry as a function of the degree of storage as well as of position is key to a unification. The experimental part of our research uses TiO2 and Nb2O5 thin films. The precise measurement of the storage capacity of thin films as a function of thickness allows us to deconvolute bulk and interfacial contributions. We discuss the results in terms of bulk and space charge capacitance. The generalized treatment that comprises both contributions shows also how the ratio of both varies with the degree of storage. Meanwhile exploiting various techniques (bias dependent impedance, TEM and EELS) electric field and charge distributions from bulk to the interface region are investigated. In the same context we study the space charge behavior in a discretized manner rather than by using the analytical Poisson-Boltzmann function. In this way a more precise definition and demarcation of electrode and double layer capacity is achieved. In terms of application we expect this work to provide a better understanding of energy and power densities of storage devices which becomes particularly important for nanoionic systems.

MgCo2O4 nanosheets//NF as a potential electrode with enhanced cycling performance for symmetric supercapacitor

Transition metal oxides were noticed as advanced electrodes in supercapacitors because of their superurb theoretical capacitance and effective charge transfer kinetics properties. In this research work, we have strongly estimate the charge storage activities of the binder-free MgCo2O4 nanosheets as a positive material for high-performance supercapacitor applications. Herein, the MgCo2O4 nanosheet electrode attained the manifest capacitance of 1460 F/g at a current value of 2 mA cm−2 and along with good cycling retention of 87 % after 5000 cycles. Moreover, the MgCo2O4 based symmetric supercapacitor device delivered an impressive energy and power densities of 16.06 W h kg−1 and 1500 W kg−1, respectively, Interestingly, the assembled SSC device was well-retained the stability retention upto 96.2 % even after 4000 GCD cycles. Overall, the better electrochemical studies were concludes the simple approach towards an emerging the positive materials in the area of energy storage applications.

Unpredictable Electrochemical Processes in Ti Dental Implants: The Role of Ti Ions and Inflammatory Products.

Peri-implantitis is a substantially prevailing condition. A potential risk factor for peri-implantitis is Ti implant corrosion. During inflammation, substantial quantities of reactive oxygen species (ROS) secretion and local acidification occur. Little is known about the interaction between the inflammatory and corrosion products on Ti surface corrosion. Therefore, the objective of the current study was to evaluate the synergistic effect of hydrogen peroxide (H2O2), lactic acid, and Ti ions on Ti corrosion. Twenty-seven commercially pure Ti samples were polished (Ra ≈ 45 nm) and divided into 9 groups as a function of electrolyte: (1) artificial saliva (AS) as control (C), (2) AS + Ti ions 20 ppm (Ti), (3) AS + lactic acid (pH = 5.5) (L), (4) AS + lactic acid + Ti ions 20 ppm (TiL), (5) AS + H2O2 0.5 mM (HP0.5), (6) AS + H2O2 1.0 mM (HP1.0), (7) AS + H2O2 0.5 mM + Ti ions 20 ppm (HP0.5Ti), (8) AS + H2O2 0.5 mM + lactic acid (HP0.5L), and (9) AS + H2O2 0.5 mM + Ti ions 20 ppm + lactic acid (HP0.5TiL). Electrochemical tests were performed following ASMT guidelines. Based on Tafel's method, current density (icorr) and corresponding potential (Ecorr) were acquired from potentiodynamic curves. Using electrochemical intensity spectroscopy (EIS), Nyquist and Bode plots were derived. Using a modified Randles circuit, charge transfer resistance (Rct) and capacitance (Cdl) were estimated. Based on open-circuit potential data, groups C and Ti had the lowest potentials (around -0.3 and -0.4 V vs SCE, respectively), indicating a lower passivation tendency compared to the other groups. From potentiodynamic curves, groups HP0.5 and HP1.0 increased icorr the most. From EIS data, groups HP0.5 and HP1.0 demonstrated the lowest impedance and phase angle on the Bode plot, indicating the highest corrosion kinetics. Based on EIS modeling, the combination of Ti ions, lactic acid, and H2O2 (group HP0.5TiL) significantly decreased Rct (p < 0.05). In conclusion, the concurrent presence of Ti ions, lactic acid, and H2O2 in the vicinity of the Ti surface increased the corrosion kinetics. High corrosion may produce more Ti products in the peri-implant tissues, which may increase the potential risk of peri-implantitis.

Detection of preexisting quantum entanglements between dipole–photon discrete observables

We performed measurements of laser beam power polarized in different angles as 0^circ , 45^circ and 90^circ passing close to a symmetric shielded capacitor with parallel plates and through a polaroid filter configured with angles as 0^circ , 45^circ and 90^circ . An unusual light power variation was detected during the charging and discharging of the high voltage capacitor even considering the suppression of known electromagnetic interaction between laser beam and capacitor. The light power variation curves also indicated a typical pattern of charge and discharge of capacitors. The combination of the angles of the laser beam polarization and polaroid filter surprisingly indicated the measurement of correlations between the polarizations of photons and electric dipoles of the capacitor dielectric. These novel results can only be explained supposing the preexisting condition of quantum entanglements between discrete observables of electric dipoles and photons.

Organic-inorganic hybrid crystal-assisted etching of nickel foam for the collectively exhaustive electrochemical performance of oxygen evolution reaction.

An organic-inorganic hybrid crystal, violet-crystal (VC), was used to etch the nickel foam (NF) to fabricate a self-standing electrode for the water oxidation reaction. The efficacy of VC-assisted etching manifests the promising electrochemical performance towards the oxygen evolution reaction (OER), requiring only ~356 and ~376 mV overpotentials to reach 50 and 100 mA cm-2, respectively. The OER activity improvement is attributed to the collectively exhaustive effects arising from the incorporation of various elements in the NF, and the enhancement of active site density. Furthermore, the self-standing electrode is robust, exhibiting a stable OER activity after 4,000 cyclic voltammetry cycles, and ~ 50 h. The anodic transfer coefficients (aa) show that the first electron transfer step is the rate-determining step on the surface of NF-VCs-1.0 (NF etched by 1 g of VCs) electrode, while the chemical step involving dissociation following the first electron transfer step is identified as the rate-limiting step in other electrodes. The lowest Tafel slope value observed in the NF-VCs-1.0 electrode indicates the high surface coverage of oxygen intermediates and more favorable OER reaction kinetics, as confirmed by high interfacial chemical capacitance and low charge transport/interfacial resistance.

A data driven based adaptive unit protection for transmission line integrated with large penetrated wind farms

The dynamic fault current characteristics, transient behaviour, and changing output power of large-scale doubly fed induction generator-based wind farms (WFs) have severe influence on transmission line conventional current differential schemes. Under normal conditions, the current difference between two ends of transmission line grows as its length increases. The capacitive charging current then might equal load current if power output of WF is low. In the presence of WFs, Traditional differential protection techniques are experiencing challenges. In order to ascertain the possible impacts of various scenarios with substantial offshore wind farms connected to transmission lines on differential relay characteristics, a data-driven approach is proposed in this paper. The STMPM based signal reconstruction method is used to compute the per-phase differential current and then their first and second-order derivatives are estimated to find the net change in the current magnitude. Finally, the Euclidean distance between these first and second derivative components are calculated and employed as a disturbance detection index (DDI). The conducted PSCAD/EMTDC simulation studies demonstrate satisfactory operation of proposed startergy for a wide range of disturbances, including external and internal faults, fault resistance, variable fault location, change in WF penetration, and various kinds of non-fault switching events.

Self‐Powered Fire Alarm System with Layer‐by‐layer Graphene Oxide/Chitosan Nanocoating of Flame‐Retardant Nanofilms

This study develops a self‐powered fire alarm system that utilizes a sandwich‐like self‐powered fire sensor (SSFS) with a simple system to prevent room fires. The SSFS is small, flame‐retardant, and can be easily installed on furniture or doors. The SSFS uses a nanogenerator constructed by poly(vinylidenefluoride‐co‐trifluoroethylene) (PVDF‐TrFE) nanofibers and a flexible printed circuit board (FPCB) to produce electrical power by harvesting motion energy. This nanogenerator can fully charge capacitors in a few minutes and produces a maximum voltage output of 6.47 V. The SSFS also features two flame‐retardant melamine foams (MFs) coated with graphene oxide (GO) and a chitosan multilayer nanocoating that is fabricated by layer‐by‐layer technology (LBL technology). While encountering a high‐temperature situation, the electrical state of MFs changes from insulated to conductive, triggering the fire alarm light in about four seconds. The sandwich‐like design allows the SSFS to respond to a variety of fire alarm situations, especially in the case where both the top and bottom of the fire alarm sensor are exposed to flame (bilateral fire burning). It is such an innovative research to decrease the delay time of fire‐warning by using this sandwich‐like design fire sensor. The nanogenerator can keep the warning working for 22 s after the initial trigger, which produces enough time to ensure people stay clear of the fire source. All in all, this study presents a novel approach to reducing the risk of building fires through a lightweight and self‐powered fire alarm system that harvests motion energy using piezoelectric nanogenerators (PENGs).

First-principles study of quantum capacitance of transition metal oxides and nitrogen functionalized graphene as electrode materials for supercapacitor

Graphene, with many advantages, is considered an active electrode material for the supercapacitors. However, its actual utilization performance is limited by its low specific capacitance caused by the poor quantum capacitance. In this article, we explored the effects of transition metal oxides (TMOs = MnO, FeO, CoO, NiO, CuO and ZnO) on the geometric structure, electronic properties, quantum capacitance (CQ) and surface storage charge (Q) of graphene-based materials using first-principles method. The findings of this article illustrate the TMOs could stably adsorb on the surface of graphene-based materials, making the systems exhibit metallic characteristic with conducive electron transfer. Around the Fermi level, introducing the electronic states of TMOs makes the modified graphene reveal a considerable CQ and Q in the negative applied voltages, especially the NiO-G system. Furthermore, the TMOs and nitrogen atoms co-modified graphene can further increase the quantum capacitance value, and the selection of electrode materials can be controlled by the N modification. The interesting results can provide a straightforward and effective strategy for designing the selection graphene-based material electrodes applied in high-energy supercapacitor.