Scalable and fast fabrication of graphene integrated micro-supercapacitors with remarkable volumetric capacitance and flexibility through continuous centrifugal coating

Microscale electrochemical energy storage devices,e.g., micro-supercapacitors(MSCs),possessing tailored performance and diversified form factors of lightweight,miniaturization,flexibility and exceptional integration are highly necessary for the smart power sources-unitized electronics.Despite the great progress,the fabrication of MSCs combining high integration with high volumetric performance remains largely unsolved.Herein,we develop a simple,fast and scalable strategy to fabricate graphene based highly integrated MSCs by a new effective continuous centrifugal coating technique.Notably,the resulting highly conductive graphene films can act as not only patterned microelectrodes but also metal-free current collectors and interconnects,endowing modular MSCs with high integrity,remarkable flexibility,tailored voltage and capacitance output,and outstanding performance uniformity.More importantly,the strong centrifugal force and shear force generated in continuous centrifugal coating process lead to graphene films with high alignment,compactness and packing density,contributing to excellent volumetric capacitance of ~31.8 F cm^(-3) and volumetric energy density of ~2.8 mWh cm^(-3),exceeding most reported integrated MSCs.Therefore,our work paves a novel way for simple and scalable fabrication of integrated MSCs and offers promising opportunities as standalone microscale power sources for new-generation electronics.

Intercalating Ultrathin MoO_3 Nanobelts into MXene Film with Ultrahigh Volumetric Capacitance and Excellent Deformation for High-Energy-Density Devices

The restacking hindrance of MXene films restricts their development for high volumetric energy density of flexible supercapacitors toward applications in miniature,portable,wearable or implantable electronic devices.A valid solution is construction of rational heterojunction to achieve a synergistic property enhancement.The introduction of spacers such as graphene,CNTs,cellulose and the like demonstrates limited enhancement in rate capability.The combination of currently reported pseudocapacitive materials and MXene tends to express the potential capacitance of pseudocapacitive materials rather than MXene,leading to low volumetric capacitance.Therefore,it is necessary to exploit more ideal candidate materials to couple with MXene for fully expressing both potentials.Herein,for the first time,high electrochemically active materials of ultrathin MoO3 nanobelts are intercalated into MXene films.In the composites,MoO3 nanobelts not only act as pillaring components to prevent restacking of MXene nanosheets for fully expressing the MXene pseudocapacitance in acidic environment but also provide considerable pseudocapacitive contribution.As a result,the optimal M/MoO3 electrode not only achieves a breakthrough in volumetric capacitance(1817 F cm-3 and 545 F g-1),but also maintains good rate capability and excellent flexibility.Moreover,the corresponding symmetric supercapacitor likewise shows a remarkable energy density of 44.6 Wh L-1(13.4 Wh kg-1),rendering the flexible electrode a promising candidate for application in high-energy-density energy storage devices.

Visualization of flow structures inside a conical spouted bed by electrical capacitance volume tomography

Electrical capacitance volume tomography (ECVT) was conducted to measure instantaneous gas–solid flow structures in a conical spouted bed. The sensor has 24 electrodes/channels and was used to make three-dimensional measurements of the solid volume fraction. Flow structures in the conical spouted bed were analyzed using quantitative ECVT images. Three-dimensional images of gas–solid flow structures and time-averaged vertical and radial solid volume fraction profiles are presented. Different fluidization regimes in spouted beds were characterized by analyzing pressure fluctuation signals and ECVT images. ECVT was shown to be robust and powerful for the three-dimensional visualization and quantitative measurement of a gas–solid fluidization system.

Machine learning techniques for prediction of capacitance and remaining useful life of supercapacitors: A comprehensive review

Supercapacitors are appealing energy storage devices for their promising features like high power density,outstanding cycling stability,and a quick charge–discharge cycle.The exceptional life cycle and ultimate power capability of supercapacitors are needed in the transportation and renewable energy generation sectors.Hence,predicting the capacitance and lifecycle of supercapacitors is significant for selecting the suitable material and planning replacement intervals for supercapacitors.In addition,system failures can be better addressed by accurately forecasting the lifecycle of SCs.Recently,the use of machine learning for performance prediction of energy storage materials has drawn increasing attention from researchers globally because of its superiority in prediction accuracy,time efficiency,and costeffectiveness.This article presents a detailed review of the progress and advancement of ML techniques for the prediction of capacitance and remaining useful life(RUL)of supercapacitors.The review starts with an introduction to supercapacitor materials and ML applications in energy storage devices,followed by workflow for ML model building for supercapacitor materials.Then,the summary of machine learning applications for the prediction of capacitance and RUL of different supercapacitor materials including EDLCs(carbon based materials),pesudocapacitive(oxides and composites)and hybrid materials is presented.Finally,the general perspective for future directions is also presented.

Structure-guided Capacitance Relationships in Oxidized Graphene Porous Materials Based Supercapacitors

Supercapacitors formed from porous carbon and graphene-oxide(GO)materials are usually dominated by either electric double-layer capacitance,pseudo-capacitance,or both.Due to these combined features,reduced GO materials have been shown to offer superior capacitance over typical nanoporous carbon materials;however,there is a significant variation in reported values,ranging between 25 and 350 F g^(−1).This undermines the structure(e.g.,oxygen functionality and/or surface area)-performance relationships for optimization of cost and scalable factors.This work demonstrates important structure-controlled charge storage relationships.For this,a series of exfoliated graphene(EG)derivatives are produced via thermal-shock exfoliation of GO precursors and following controlled graphitization of EG(GEG)generates materials with varied amounts of porosity,redox-active oxygen groups and graphitic components.Experimental results show significantly varied capacitance values between 30 and 250 F g^(−1)at 1.0 A g^(−1)in GEG structures;this suggests that for a given specific surface area the redox-active and hydrophilic oxygen content can boost the capacitance to 250–300%higher compared to typical mesoporous carbon materials.GEGs with identical oxygen functionality show a surface area governed capacitance.This allows to establish direct structure-performance relationships between 1)redox-active oxygen functional concentration and capacitance and 2)surface area and capacitance.

Design optimization of a silicon-germanium heterojunction negative capacitance gate-all-around tunneling field effect transistor based on a simulation study

The steep sub-threshold swing of a tunneling field-effect transistor(TFET)makes it one of the best candidates for lowpower nanometer devices.However,the low driving capability of TFETs prevents their application in integrated circuits.In this study,an innovative gate-all-around(GAA)TFET,which represents a negative capacitance GAA gate-to-source overlap TFET(NCGAA-SOL-TFET),is proposed to increase the driving current.The proposed NCGAA-SOL-TFET is developed based on technology computer-aided design(TCAD)simulations.The proposed structure can solve the problem of the insufficient driving capability of conventional TFETs and is suitable for sub-3-nm nodes.In addition,due to the negative capacitance effect,the surface potential of the channel can be amplified,thus enhancing the driving current.The gateto-source overlap(SOL)technique is used for the first time in an NCGAA-TFET to increase the band-to-band tunneling rate and tunneling area at the silicon-germanium heterojunction.By optimizing the design of the proposed structure via adjusting the SOL length and the ferroelectric layer thickness,a sufficiently large on-state current of 17.20μA can be achieved and the threshold voltage can be reduced to 0.31 V with a sub-threshold swing of 44.98 mV/decade.Finally,the proposed NCGAA-SOL-TFET can overcome the Boltzmann limit-related problem,achieving a driving current that is comparable to that of the traditional complementary metal-oxide semiconductor devices.

N-Doped rGO-Like Carbon Prepared from Coconut Shell:Structure and Specific Capacitance

An rGO−like carbon compound has been synthesized from biomass,i.e.,old coconut shell,by a carbonization process followed by heating at 400°C for 5 h.The nitrogen doping was achieved by adding the urea(CH4N2O)and stirring at 70°C for 14 h.The morphology and structure of the rGO-like carbon were investigated by electron microscopies and Raman spectroscopy.The presence of C-N functional groups was analyzed by Fourier transform infrared and synchrotron X-ray photoemission spectroscopy,while the particle and the specific capacitance were measured by particle sizer and cyclic voltammetry.The highest specific capacitance of 72.78 F/g is achieved by the sample with 20%urea,having the smallest particles size and the largest surface area.The corresponding sample has shown to be constituted by the appropriate amount of C–N pyrrolic and pyridinic defects.

Integration of pore structure modulation and B,N co-doping for enhanced capacitance deionization of biomass-derived carbon

Biomass-derived carbon has demonstrated great potentials as advanced electrode for capacitive deionization(CDI),owing to good electroconductivity,easy availability,intrinsic pores/channels.However,conventional simple pyrolysis of biomass always generates inadequate porosity with limited surface area.Moreover,biomass-derived carbon also suffers from poor wettability and single physical adsorption of ions,resulting in limited desalination performance.Herein,pore structure optimization and element co-doping are integrated on banana peels(BP)-derived carbon to construct hierarchically porous and B,N co-doped carbon with large ions-accessible surface area.A unique expansionactivation(EA)strategy is proposed to modulate the porosity and specific surface area of carbon.Furthermore,B,N co-doping could increase the ions-accessible sites with improved hydrophilicity,and promote ions adsorption.Benefitting from the synergistic effect of hierarchical porosity and B,N co-doping,the resultant electrode manifest enhanced CDI performance for NaCl with large desalination capacity(29.5 mg g^(-1)),high salt adsorption rate(6.2 mg g^(-1)min^(-1)),and versatile adsorption ability for other salts.Density functional theory reveals the enhanced deionization mechanism by pore and B,N co-doping.This work proposes a facile EA strategy for pore structure modulation of biomass-derived carbon,and demonstrates great potentials of integrating pore and heteroatoms-doping on constructing high-performance CDI electrode.

Compensation of Parasitic Capacitance of Quartz Tuning Fork in AFM

We have built an atomic force microscope using a quartz tuning fork as sensor. The excitation method we adopted, the electrical excitation, introduces stray capacitance into the signal-processing circuit. In this report, we demonstrated a simple but effective method to compensate for this parasitic capacitance by adding a compensator circuit consisting of an inverting amplifier and a capacitor. The capacitor is connected in series with the inverting amplifier and the compensator is connected in parallel with the quartz tuning fork. The resonance curve of the system measured after adding the homemade compensator resembles that of a pure RLC circuit, meaning that the stray capacitance is successfully eliminated. Furthermore, we tried to use our equipment to measure PDMS sample and got clean data. This system can be further combined with confocal microscope and diamond with NV defect to build scanning NV magnetometry.

Kinetic-Thermodynamic Promotion Engineering toward High-Density Hierarchical and Zn-Doping Activity-Enhancing ZnNiO@CF for High-Capacity Desalination

Despite the promising potential of transition metal oxides(TMOs)as capacitive deionization(CDI)electrodes,the actual capacity of TMOs electrodes for sodium storage is significantly lower than the theoretical capacity,posing a major obstacle.Herein,we prepared the kinetically favorable Zn_(x)Ni_(1−x)O electrode in situ growth on carbon felt(Zn_(x)Ni_(1−x)O@CF)through constraining the rate of OH^(−)generation in the hydrothermal method.Zn_(x)Ni_(1−x)O@CF exhibited a high-density hierarchical nanosheet structure with three-dimensional open pores,benefitting the ion transport/electron transfer.And tuning the moderate amount of redox-inert Zn-doping can enhance surface electroactive sites,actual activity of redox-active Ni species,and lower adsorption energy,promoting the adsorption kinetic and thermodynamic of the Zn_(0.2)Ni_(0.8)O@CF.Benefitting from the kinetic-thermodynamic facilitation mechanism,Zn_(0.2)Ni_(0.8)O@CF achieved ultrahigh desalination capacity(128.9 mgNaCl g^(-1)),ultra-low energy consumption(0.164 kW h kgNaCl^(-1)),high salt removal rate(1.21 mgNaCl g^(-1) min^(-1)),and good cyclability.The thermodynamic facilitation and Na^(+)intercalation mechanism of Zn_(0.2)Ni_(0.8)O@CF are identified by the density functional theory calculations and electrochemical quartz crystal microbalance with dissipation monitoring,respectively.This research provides new insights into controlling electrochemically favorable morphology and demonstrates that Zn-doping,which is redox-inert,is essential for enhancing the electrochemical performance of CDI electrodes.

Flexible capacitive pressure sensor based on interdigital electrodes with porous microneedle arrays for physiological signal monitoring

Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stability have hindered their large-scale commercial application.Herein,aflexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays(MNAs)is pro-posed.The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3.Due to its porous and interdigital structure,the maximum sensitivity(0.07 kPa-1)of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor,and it was much greater than that of aflat pressure sensor without a porous MNA structure.Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sen-sor.In addition,the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure.Most importantly,it was found that the sensor could accurately monitor the motion of afinger,wrist joint,arm,face,abdomen,eye,and Adam’s apple.Furthermore,preliminary semantic recognition was achieved by monitoring the movement of the Adam’s apple.Finally,multiple pressure sensors were integrated into a 33 array to detect a spatial pressure distribu-×tion.Compared to the sensors reported in previous works,the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.

Plasma density enhancement in radio-frequency hollow electrode discharge

The plasma density enhancement outside hollow electrodes in capacitively coupled radio-frequency(RF) discharges is investigated by a two-dimensional(2D) particle-in-cell/Monte-Carlo collision(PIC/MCC) model. Results show that plasma exists inside the cavity when the sheath inside the hollow electrode hole is fully collapsed, which is an essential condition for the plasma density enhancement outside hollow electrodes. In addition, the existence of the electron density peak at the orifice is generated via the hollow cathode effect(HCE), which plays an important role in the density enhancement. It is also found that the radial width of bulk plasma at the orifice affects the magnitude of the density enhancement, and narrow radial plasma bulk width at the orifice is not beneficial to obtain high-density plasma outside hollow electrodes.Higher electron density at the orifice, combined with larger radial plasma bulk width at the orifice,causes higher electron density outside hollow electrodes. The results also imply that the HCE strength inside the cavity cannot be determined by the magnitude of the electron density outside hollow electrodes.

Progress of Proximity Sensors for Potential Applications in Electronic Skins

Recently,electronic skins and fl exible wearable devices have been developed for widespread applications in medical monitoring,artifi cial intelligence,human–machine interaction,and artifi cial prosthetics.Flexible proximity sensors can accurately perceive external objects without contact,introducing a new way to achieve an ultrasensitive perception of objects.This article reviews the progress of fl exible capacitive proximity sensors,fl exible triboelectric proximity sensors,and fl exible gate-enhanced proximity sensors,focusing on their applications in the electronic skin fi eld.Herein,their working mechanism,materials,preparation methods,and research progress are discussed in detail.Finally,we summarize the future challenges in developing fl exible proximity sensors.

3D N,O-Codoped Egg-Box-Like Carbons with Tuned Channels for High Areal Capacitance Supercapacitors

Functional carbonaceous materials for supercapacitors(SCs)without using acid for post-treatment remain a substantial challenge.In this paper,we present a less harmful strategy for preparing three-dimensional(3D)N,O-codoped egg-box-like carbons(EBCs).The as-prepared EBCs with opened pores provide plentiful channels for ion fast transport,ensure the e ective contact of EBCs electrodes and electrolytes,and enhance the electron conduction.The nitrogen and oxygen atoms doped in EBCs improve the surface wettability of EBC electrodes and provide the pseudocapacitance.Consequently,the EBCs display a prominent areal capacitance of 39.8μF cm-2(340 F g-1)at 0.106 m A cm-2 in 6 M KOH electrolyte.The EBC-based symmetric SC manifests a high areal capacitance to 27.6μF cm-2(236 F g-1)at 0.1075 m A cm-2,a good rate capability of 18.8μF cm-2(160 F g-1)at 215 m A cm-2 and a long-term cycle stability with only 1.9%decay after 50,000 cycles in aqueous electrolyte.Impressively,even in all-solid-state SC,EBC electrode shows a high areal capacitance of 25.0μF cm-2(214 F g-1)and energy density of 0.0233 m Wh cm-2.This work provides an acid-free process to prepare electrode materials from industrial by-products for advanced energy storage devices.

Enhancing Capacitance Performance of Ti3C2Tx MXene as Electrode Materials of Supercapacitor: From Controlled Preparation to Composite Structure Construction

Ti3C2Tx,a novel two-dimensional layer material,is widely used as electrode materials of supercapacitor due to its good metal conductivity,redox reaction active surface,and so on.However,there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance,such as restacking,re-crushing,and oxidation of titanium.Recently,many advances have been proposed to enhance capacitance performance of Ti3C2Tx.In this review,recent strategies for improving specific capacitance are summarized and compared,for example,film formation,surface modification,and composite method.Furthermore,in order to comprehend the mechanism of those efforts,this review analyzes the energy storage performance in different electrolytes and influencing factors.This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors.

Effect of tunnel structure on the specific capacitance of etched aluminum foil

The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The maximum of specific capacitance and the cor- responding optimum values for tunnel sizes at various anodization voltages were predicted. The increased size distribution and taper of tun- nels were demonstrated to decrease the specific capacitance, whereas the addition of polymeric additive into the ttmnel widening solution was demonstrated to increase the capacitance. The formation of merged tunnels on the etched aluminum surface, irrespective of the presence of row-merged tunnels or cluster-merged tunnels, resulted in a dramatic decrease in the specific capacitance. It is concluded that, enhancing the uniformity of turmel size and distribution and avoiding the formation of merged tunnels are the effective approach to achieving the higher capacitance for the tunnel etched and formed aluminum foil.

Band gap control of phononic beam with negative capacitance piezoelectric shunt

Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.

Reconstruction of electrical capacitance tomography images based on fast linearized alternating direction method of multipliers for two-phase flow system

Electrical capacitance tomography(ECT)has been applied to two-phase flow measurement in recent years.Image reconstruction algorithms play an important role in the successful applications of ECT.To solve the ill-posed and nonlinear inverse problem of ECT image reconstruction,a new ECT image reconstruction method based on fast linearized alternating direction method of multipliers(FLADMM)is proposed in this paper.On the basis of theoretical analysis of compressed sensing(CS),the data acquisition of ECT is regarded as a linear measurement process of permittivity distribution signal of pipe section.A new measurement matrix is designed and L1 regularization method is used to convert ECT inverse problem to a convex relaxation problem which contains prior knowledge.A new fast alternating direction method of multipliers which contained linearized idea is employed to minimize the objective function.Simulation data and experimental results indicate that compared with other methods,the quality and speed of reconstructed images are markedly improved.Also,the dynamic experimental results indicate that the proposed algorithm can ful fill the real-time requirement of ECT systems in the application.

Hydrothermal Synthesis and Capacitance Property of Cobalt Sulfide/Graphene Oxide Nanocomposite

The cobalt sulfide/graphene oxide（CoS/GO） nanocomposite was synthesized by a simple hydrothermal reaction.The products as-synthesized were characterized by XRD,SEM,TEM,BET-BJH and TG.The electrochemical property and impedance of the CoS/GO nanocomposite were studied by cyclic voltammetry and EIS analysis,respectively.The results show that the presence of the GO enhances the electrode conductivity,and then improves the capacitance property of the CoS/GO nanocomposite.The galvanostatic charge/discharge measurement results show that the CoS/GO nanocomposite has a high specific capacitance（550Fg^-1） and long cycle life（over 1 000 cycles）.