Supercapacitor Cell Research Articles

Structural supercapacitor electrolytes based on cementitious composites containing recycled steel slag and waste glass powders

Incorporating solid wastes into cement-based materials is beneficial for the waste disposal and the conservation of natural resources. In this study, cement-based electrolyte incorporated with recycled steel slag powder (SSP) and waste glass powder (GP) was proposed as a potential candidate for assembling structural supercapacitor cells (SSCs) with multi-functionality. Compared with pure cement devices, the 28-day conductivity and areal capacitance of the SSCs containing SSP and GP increased by up to 112% and 84%, respectively, at a current density of 0.1 mA cm−2. On the one hand, the addition of SSP and GP increased the pore volume in the cement-based electrolyte, which in turn resulted in more paths for ion transport. On the other hand, the presence of SSP and GP increased the concentration of major ions, such as Na+ and OH−, in pore solution. Both the increased ion transport paths and the improved ion concentration contributed substantially to the enhancement of the energy storage performances of the SSCs. At 28 days, an additional incorporation of 10% GP made up for the strength loss caused by SSP as an appropriate amount of GP with high pozzolanic activity resulted in an increased amount of C-S-H product, a reduction of porosity, and a denser microstructure. The proposed SSCs containing the cement-based electrolyte with cement partially replaced by 20% SSP and 10% GP is competitive for the development of green building energy storage devices.

A facile one-step electrosynthesis of polypyrrole/nano-SbOx composite for supercapacitors

The study depicts a one-step electrochemical synthesis of composite based on polypyrrole (PPy) and SbOx (Sb2O3, Sb2O5) on the graphite surface for the supercapacitor electrode in an acetonitrile solution including pyrrole monomer and Sb(BF4)3. PPy/SbOx composite on graphite plate is characterized using XPS, XRD, TEM, BET, and FESEM by comparing it with PPy homopolymer prepared in the same way. SbOx forms in nano-size and homogeneously encapsulates in PPy due to their simultaneous synthesis. The average pore size of the composite coating is 23.9 nm. The coated PG electrodes are tested in an H2SO4 electrolyte using CV, EIS, and GCD methods. SbOx nanoparticles enhance the capacitive performance of PPy due to the contribution of its catalytic and pseudocapacitive properties. The specific capacitance of the PPy/SbOx-coated PG electrode is 389.5 F g−1 at 5 A g−1 for 1.0 mg cm−2 loading. PPy/SbOx is synthesized in the presence of carboxymethyl cellulose (CMC) to provide stability to the coating. An asymmetric supercapacitor cell is fabricated by assembling the PPy/SbOx/CMC-coated and activated carbon-based graphite paper electrodes (10 mg cm−2 loading). While the potential window expands to 1.4 V, it delivers an energy density of 8.3 Wh kg−1, a power density of 3.5 kW kg−1, and a coulombic efficiency of 90% at 5 A g−1. Post-mortem analysis reveals that structural degradation of PPy in the composite limits long-term stability.

Magnetic particle-filled polyaniline-doped graphene oxide nanocomposite-based electrode in application of supercapacitor

In this study, the electrochemical characteristics of magnetic particle-filled conductive polyaniline-doped graphene oxide nanocomposites (MDiPG) were investigated. The graphene oxide was chemically exfoliated from natural graphite flakes by the modified Hummer's method. The nanocomposite was characterised through thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Its electrochemical characteristics were evaluated by cyclic voltammetry and galvanostatic charge/discharge tests. The nanocomposite electrode material was obtained through in situ polymerisation of polyaniline-doped graphene oxide combined with the mixing of a magnetic substance. The supercapacitor cell was composed of symmetric magnetic-derived electrodes, polypropylene separator, and 6M KOH as an electrolyte. The cyclic voltammetry curve study showed a good relation of both materials, where a high specific gravimetric capacitance was achieved at 303 F/g.

Green synthesis of carbon and cobalt oxide composites by 1–Watt laser sintering for flexible supercapacitors

Transition metal oxides, as well as multivalent metal oxides like Co3O4, have attracted huge attention for energy-storing materials. Combining Co3O4 with carbon materials is of interest to improve the limited electrical conductivity and electrochemical performance of Co3O4 composites. However, most synthesis methods of those Co3O4 and carbon composites commonly need plenty of chemicals with long calcination and release many harmful byproducts. Thus, our green strategy based on laser sintering to synthesize a carbon-Co3O4 composite from a single source – cobalt acetate – is proposed. With a low-power laser, our method is applicable to making flexible devices. A demonstration of flexible supercapacitor cells formed on a silver-nanowires-coated polyimide substrate is presented. Furthermore, the effects of laser pulse duration and current collector conductance on the device performance are investigated. As tested in Na2SO4 and KOH electrolytes, these cells can deliver specific capacitances of 13.2 F g−1 (at 0.08 A g−1) and 48.2 F g−1 (at 1 A g−1), respectively, with a remarkable cycling behavior of 90% after 3000 cycles. Notably, the usability of our composite with the neutral Na2SO4 electrolyte is worth exploring for eco-friendly energy storage. Altogether, our study shows opportunities to create green composites of carbon and multivalent metal oxides quickly and cost-effectively.

The Self-Adhesive Properties of Carbon Activated-Like Shape Coin Derived From Palmae Plant Waste and Used as High-Performance Supercapacitor Electrodes

Abstract Synthesized biomass-based carbonaceous materials from Palmae plant wastes with self-adhesive properties, converted into coin-like shapes, are used as supercapacitor electrodes with high power and energy density, high specific capacitance, excellent electrical conductivity, low cost, and environmentally friendly. Therefore, this study aims to investigate a simple and cost-effective method to generate porous carbon activation from Palmae plant waste biomass, namely areca leaf midrib (ALM). Activated carbon (AC) material derived from ALM was obtained through precarbonization, alkaline chemical activation, and two-step pyrolysis, namely carbonization and physical activation at 600 °C and 700 °C in the N2 as well as CO2 atmosphere, respectively. Its physical properties show an sp2 structure with high graphitization or amorphousness and two sloping peaks in the hkl plane at an angle of 2θ, approximately 24 deg and 44 deg. The electrochemical properties of AC supercapacitor cells derived from ALM biomass have the highest specific capacitance value of 216 F g−1 at a scan rate of 1 mV s−1 in a two-electrode system. Furthermore, the cell obtained a maximum energy density of 11 W h kg−1 and a power density of 196 W kg−1, respectively. Therefore, this study recommends an innovative and environmentally safe approach for producing high-performance supercapacitor cell electrodes for energy storage without adding nanomaterials and externally doped heteroatoms.

Vanadium oxide nanorods as an electrode material for solid state supercapacitor

The electrochemical properties of metal oxides are very attractive and fascinating in general, making them a potential candidate for supercapacitor application. Vanadium oxide is of particular interest because it possesses a variety of valence states and is also cost effective with low toxicity and a wide voltage window. In the present study, vanadium oxide nanorods were synthesized using a modified sol–gel technique at low temperature. Surface morphology and crystallinity studies were carried out by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy analysis. To the best of our knowledge, the as-prepared nanorods were tested with magnesium ion based polymer gel electrolyte for the first time. The prepared supercapacitor cell exhibits high capacitance values of the order of ~ 141.8 F g−1 with power density of ~ 2.3 kW kg−1 and energy density of ~ 19.1 Wh kg−1. The cells show excellent rate capability and good cycling stability.

Activation of nipah fruit coir-derived carbon material with KOH and NH3 for supercapacitor cell applications

Chemical impregnation is a simple and low-cost activated carbon activation method that can engineer the electrochemical properties of supercapacitor cell electrodes. The carbon material was derived from nipah fruit coir biomass by optimizing chemical activator reagents (without activating agents, KOH, NH3). The carbon material derived from nipah fruit coir is synthesized through of pre-carbonization, chemical activation, carbonization-activation physics in an integrated manner. The carbonization process uses N2 gas flow at a temperature of 600℃ with a flow rate of 1.5 l/min and a heating rate of 3ºC/min, as well as physical activation using CO2 gas at a temperature of 800°C with a flow rate of 1 l/min and a heating rate of 10ºC/min. Electrochemical properties were analyzed using Cyclic Voltametry (CV) and Galvanostatic Charge-Discharge (GCD) methods. The symmetrical supercapacitor based on SBN electrode material has an optimum specific capacitance of 224 Fg-1 at a scan rate of 1mV/s in an aqueous electrolyte (H2SO4 1M) operated at a potential of 1V. These results provide a clear, simple and easy synthesis strategy for the large-scale conversion of sustainable waste biomass into activated carbon materials for energy storage and conversion applications.

The use of some sulfonic acids for improving aluminum current collector resistance

The corrosion behavior of aluminum current collectors in the standby and high-load modes was investigated by simulating via immersion and anodization experiments in electrolyte environments. The immersion experiments were carried out using aluminum alloy (AA5754) in camphorsulfonic (CSA), p-toluenesulfonic (PTSA), trifluoromethanesulfonic (TFMSA), and fluorosulfonic (FSA) acid solutions, and the results were compared with those of H 2 SO 4 and methanesulfonic acid (MSA). Corrosion resistance increased in the order of FSA, MSA, TFMSA, PTSA, H 2 SO 4 , and CSA. Thin-film XRD and XPS results revealed sulfonic acid adsorption to Al 2 O 3 . From AFM, the least rough and highest crystalline oxide layer was obtained with CSA, while FSA yielded the opposite. In addition, AA5754 was anodized in 0.1 M CSA, PTSA, and H 2 SO 4 solutions, and its corrosion behavior was examined. R ct values were about one hundred times higher than in the immersion experiments; besides, less rough and thicker layers were obtained on the surface owing to the controlled dissolution. The mixture of CSA:H 2 SO 4 (1:1) was used as an anodization solution, and the maximum resistance (5652 Ω.cm 2 ) was obtained at 20 V, which was a better corrosion behavior according to individual electrolytes. This could be due to the optimum combination of the high acidity of H 2 SO 4 and the ability of CSA to block the surface sites thanks to its larger cyclic structure. Finally, a symmetric supercapacitor cell prepared using a carbon-coated Al current collector in PVA/H 2 SO 4 :CSA gel electrolyte was tested by cyclic voltammetry and GCD. The cell provided 26 Wh.kg -1 and 10.2 kW.kg -1 with 89% efficiency and 64% retention after 5000 cycles over a wide potential range of 1.6 V, exhibiting better capacitive performance than the gel electrolyte without CSA. This increase could be because CSA contributes to the growth of the protective aluminum oxide layer as an anionic surfactant. • Sulfonic acids are adsorbed on aliminum alloy surface during immersion and anodization • Al 2 O 3 has the least rough and highest crystalline in the presence of camphorsulfonic and p-toluenesulfonic acids • The corrosion resistance of AA5754 significantly improves by anodization in the mixtures of sulfonic acids with H 2 SO 4 • Supercapacitor with Al current collector operates in a wide potential range of 1.6 V in PVA/H 2 SO 4 :CSA • The cell provides 26 Wh.kg -1 and 10.2 kW.kg -1 with 89% efficiency

Investigation on the synthesis of Mn3O4 nanoparticles embedded on nano rods as an electrode material for supercapacitor application

. • Facile synthesis of Mn 3 O 4 (Hausmannite) was performed via simple Co-precipitation method. • Fabricated Electrode reveals excellent specific capacitance of 499 F/g at 1mV/s in 1M Na 2 SO 4. • 75% of specific capacitance is retained even after 5000 cycles. Many studies are being conducted in the field of energy storage devices to improve the performance of electrode materials for future application. In recent years, numerous research have been published that fully define Nano level synthesis techniques, dopant and composite-based work for improving the charge storing capability and long cycle life of energy storage devices, particularly in supercapacitors. In this current era, researchers prefer eco-friendly synthesis techniques to rectify unnecessary hazardous issues. Since, environmental friendly technic along with good cyclic stability was one of the major focuses in scientific society. Here, the present paper concentrates on the synthesis of Trimanganese Tetroxide / Mn 3 O 4 (Hausmannite) under a facile co-precipitation technique. Upon Co-precipitation based technique the formations of nanoparticles cramped on nanorods occur simultaneously. The three electrode supercapacitor cell system composed of Mn3O4 shows high capacitance and capacity retention. The highest specific capacitance of 499 F/g is achieved at a scanning rate of 1 mV/s, with 75% of retention after 5000 cycles in 1M Na 2 SO 4 aqueous electrolyte.

Activation-induced layered structure in NiCoAl by atomic modulation for energy storage application

The surface activation of alloys favors their electrochemical interactions, ion diffusivity, and the rapid kinetics of ions and electrons, leading to the formation of self-supported layered double hydroxides (LDHs) in them. However, the formation of LDHs at different depths in the alloy upon activation, their electronic/atomic structures, and their electrochemical charge storage mechanism, have not been thoroughly explored. Herein, Ni ion-substituted CoAl alloys are prepared by arc melting and activated by KOH electrolyte, which is responsible for the modulation of the atomic configuration as confirmed by XRD. Raman depth mapping demonstrates how the LDHs vary with depth upon activation and that the octahedral and tetrahedral symmetry sites of CoO and Co3O4 are responsible for the formation of the layered structures of CoOOH and Co(OH)2, respectively. The activated Ni10Co85Al5 has a superior volumetric capacitance of 4.15 F/cm3 at 0.5 mA/g, which is 38.6 times that of an unactivated one, and excellent cyclic stability up to 5000 cycles, and a voltage of 0.54 V generated from a fabricated supercapacitor cell. X-ray Absorption Spectroscopy (XAS) analysis indicates greater charge transfer by Co than by Ni and the modulation of the local atomic structures facilitates electrochemical charge storage in Ni10Co85Al5. This work presents an easy route for the development of advanced LDHs, and the mechanism of electrochemical charge storage in them.

Temperature estimation method for supercapacitor cell and module with less sensors

Temperature monitoring is of great significance for the safe operation and state estimation of supercapacitors in practical applications. As excessive temperature can even cause thermal runaway, it is quite necessary to monitor the temperature of each cell, especially in transportation area. However, there are two problems in the temperature distribution estimation. Firstly, the hot-spot temperature is usually distributed inside the cell and is hard to be measured by sensors. Secondly, applying sensors to each cell in a module requires a large number of sensors, which are difficult and expensive to install. In this paper, aiming at difficulty in cell internal temperature measurement, the closed-loop observer is established which measures the surface and ambient temperature online; aiming at difficulties to reduce sensors in the module, a Long Short-Term Memory (LSTM) network is established to measure a small number of cells to predict the temperature distribution of the whole module, thus a method of hot-spot temperature estimation of supercapacitor is proposed. The result from experiment and estimation shows that the RMSE and MAE of the H-∞ and NN joint filter is <0.4 °C in most situations, and the absolute error of LSTM for module temperature distribution is <0.8 °C, the MAE and RMSE is <0.5 °C.

Tailoring of ZnFe2O4-ZrO2-based nanoarchitectures catalyst for supercapacitor electrode material and methanol oxidation reaction

Herein, a simple hydrothermal approach was employed to synthesize a homogeneous and compact ZnFe2O4 nanoparticles on the surface of ZrO2 (ZnFe2O4-ZrO2), and it was utilized as a supporting-material for Pt nanoparticles. The fabricated ZnFe2O4-ZrO2 and ZnFe2O4-ZrO2/Pt nanoarchitectures were employed as an electrode material for the supercapacitor cells, and an electrocatalyst for the methanol oxidation reaction, respectively. The Pt nanoparticles were electrochemically deposited on the ZnFe2O4-ZrO2 support. The electrochemical characterizations illustrated that ZnFe2O4-ZrO2 supported Pt was of a peak current density of 104.74 mA/cm2, which was 1.73 more than the peak current density of Pt without the use of nanocomposite support and strong cycling stability of 110 percent after 150 cycles for the methanol oxidation reaction. As a supercapacitor electrode, ZnFe2O4-ZrO2 offered a high specific capacitance of 193.76F/g at a current density of 1.0 A/g, an appropriate rate efficiency (102.4 F/g at current density of 8 A/g), and strong cycling stability of 93 % after 250 galvanostatic charge–discharge revealing the high cycle stability of the nanocomposite. The superb electrochemical behavior of the ZnFe2O4-ZrO2 electrode was ascribed to the low internal charge resistance and ion diffusion resistance. The more ion/electron pathways of diffusion and a suitable contact area with the electrolyte, and the strong synergistic interaction between the components conferred exceptional conductivity and structural durability on the electrode. The results paved the new avenues for nanoengineering of up-and-coming metal-based nanoarchitectures to be utilized in energy storage and conversion systems.

Enhanced inactivation of bacteria on capacitive semiconductor nanotubes by Self-Discharging triggered photoelectrocatalysis

Hospital-acquired infections and antibiotic-resistant pathogens are major threats to human health. We develop an antibacterial film that maintains the long-term stability of titania (TiO2) while minimizing the disadvantages, the low photocatalytic efficiency of TiO2, especially in visible light, that limits the application of TiO2. Here, TiO2 nanotubes are modified with capacitive materials as a visible-light-triggered antimicrobial surface; its mechanism is based on substantially increased content of reactive oxygen species produced from the photocatalytic reaction during the electrochemical capacitive process. The system is functionalized with MIL-125(Ti) nanosheets and monodispersed Fe2O3 nanoparticles, enabling a large capacitance (149.0 mF cm−2) in a neutral aqueous electrolyte and high visible-light absorption. Importantly, the photocatalytic activities of the resulting capacitive semiconductor are proportional to the bias provided by the capacitive sample in its self-discharging (SD) process. As a proof-of-concept of the SD-triggered photoelectrocatalysis, the capacitive semiconductor exhibits ≥ 99.9 % reduction in Escherichia coli and Staphylococcus aureus by only 30 min treatment and remarkably has a bacteria-free surface for recycling bacterial applications. Furthermore, the assembled asymmetric supercapacitor cell also exhibits excellent performance in bacteria inactivation, suggesting an efficient sterilization device for environmental applications.

High-performance with a high voltage aqueous supercapacitor cell from a simple hybrid electrode of manganese oxide-phenanthrenequinone-graphite sheet

The present-day energy demand is growing research interest in synthesizing new hybrid electrode materials for supercapacitor applications. The main focus is on the development of new electrode materials which could be easily available, synthesizable, low-cost, environmentally friendly, with worthy electrochemical performance. In this scenario, a simple one-step synthesis of MnO2 is carried out via the solvothermal method. This MnO2 is mixed with a molecule of phenanthrenequinone (PQ). MnO2, PQ, and MnO2-PQ composite are characterized by FT-IR, XRD, TGA, and BET techniques and confirmed the formation of MnO2-PQ composite. The electrode is made by drop-casting the electro-active materials such as MnO2, PQ, and MnO2-PQ on a graphite sheet wherein a graphite sheet acts as an electrode and a current collector. These electrodes are studied in a three-electrode and also in the symmetric cell configuration in 1 M Na2SO4 electrolyte via CV, GCD, and EIS techniques. The device is constructed in Swagelok system exhibits a high energy density of 140 W h kg−1 at a power density of 6000 W kg−1 in the voltage range of 0 to 2 V. A coin cell is built using two MnO2-PQ-GS hybrid electrodes in an aqueous Na2SO4 electrolyte. The cycle life of the coin cell showed a retention capacitance of 74 % after 5000 cycles at a high voltage of 2 V, even at a high current density of 5 A g−1. EIS results carried out before and after 5000 cycles show that the cell works even at 5000 GCD cycles.

Phase dependent electrochemical characteristics of bismuth ferrite: A bifunctional electrocatalyst for Supercapacitors and Dye‐Sensitized Solar Cells

Different phases of bismuth ferrite (BiFeO3, Bi2Fe4O9, Bi25FeO40) have been synthesized hydrothermally with the assistance of polyethylene glycol (PEG) and employed as an electrocatalyst for supercapacitor and dye-sensitized solar cells (DSSC). The impact of PEG on the crystal structure and phases is analyzed using X-ray diffraction (XRD). More experimental measurements are done to analyze phase dependence on the shape, vibration, and optical response. Cyclic voltammetry and galvanostatic charge-discharge (GCD) results show the phase-dependent electrochemical characteristics and the sillenite phase Bi25FeO40 (BFO-10) of 10 mL PEG has a higher specific capacitance (CS) of 351 F g−1 at 4 A g−1 due to the increment of Bi stoichiometry. In addition, an asymmetric supercapacitor (ASC) is assembled by BFO-10//AC and observed with a higher energy density of 70 Wh kg−1, the corresponding power density is 3240 W kg−1, and an excellent life cycle. The same samples are used as a counter electrode (CE) in DSSCs, Bi25FeO40 CE assisted cell delivering a maximum short circuit current (JSC) of 4 mA cm−2 than the other phases of BFO. The higher electrocatalytic activity, conductivity, and lower charge transfer resistance are responsible for the improvement. These investigations reveal that the sillenite phase of Bi25FeO40 is a better choice for future energy storage and conversion devices.

Irradiated rGO electrode-based high-performance supercapacitors: Boosting effect of GO/rGO mixed nanosheets on electrochemical performance

Supercapacitors are seemed to be one of the most promising choices as an energy storage system. However, there is still a gap in enhancing its energy density values and cyclic stabilities throughout a facile approach. Herein, it was aimed to propose a facile and effective way to fabricate high-energy supercapacitor electrode material based on reduced graphene oxide (rGO) nanostructure. Bearing this in mind, the bulk rGO powder was irradiated by various beam sources including Co-60, Am-241, Na-22, and Sr-90, and the resultant irradiated rGO samples were utilized as the electrode active material to fabricate symmetrical supercapacitor cells. The irradiated rGO samples were characterized both physicochemically and electrochemically. The physicochemical characterizations revealed that as a consequence of the irradiation, both GO and rGO nanosheets were formed in the resultant powder and the d-spacing of the graphene nanosheets were expanded. The highest electrochemical performance metrics were acquired for Sr-90 irradiated rGO electrode-based supercapacitor cell with the specific capacitance value of 585.44F.g−1 at 0.2 A.g−1, and outstanding capacitance retention performance of 97.14% for the 5000th CV cycles at 200 mV.s−1. Moreover, the energy density and power density values were comparable to other commercial energy storage systems such as lead-acid and nickel-metal hybrid batteries. Hence, it can be speculated that these pioneering breakthroughs could pave the way for cutting-edge high-energy supercapacitors based on rGO-derivatives with superior electrochemical performance metrics, as well as engineering of high-performance rGO-based materials to be employed in various energy applications.

SOC, SOH and RUL Estimation for Supercapacitor Management System: Methods, Implementation Factors, Limitations and Future Research Improvements

The development of a supercapacitor management system (SMS) for clean energy applications is crucial to addressing carbon emissions problems. Consequently, state of charge (SOC), state of health (SOH), and remaining useful life (RUL) for SMS must be developed to evaluate supercapacitor robustness and reliability for mitigating supercapacitor issues related to safety and economic loss. State estimation of SMS results in safe operation and eliminates undesirable event occurrences and malfunctions. However, state estimations of SMS are challenging and tedious, as SMS is subject to various internal and external factors such as internal degradation mechanism and environmental factors. This review presents a comprehensive discussion and analysis of model-based and data-driven-based techniques for SOC, SOH, and RUL estimations of SMS concerning outcomes, advantages, disadvantages, and research gaps. The work also investigates various key implementation factors such as a supercapacitor test bench platform, experiments, a supercapacitor cell, data pre-processing, data size, model operation, functions, hyperparameter adjustments, and computational capability. Several key limitations, challenges, and issues regarding SOC, SOH, and RUL estimations are outlined. Lastly, effective suggestions are outlined for future research improvements towards delivering accurate and effective SOC, SOH, and RUL estimations of SMS. Critical analysis and discussion would be useful for developing accurate SMS technology for state estimation of a supercapacitor with clean energy and high reliability, and will provide significant contributions towards reducing greenhouse gas (GHG) to achieve global collaboration and sustainable development goals (SDGs).

Unveiling the surface dominated capacitive properties in flexible ternary polyaniline/NiFe2O4/reduced graphene oxide nanocomposites hydrogel electrode for supercapacitor applications

The 3D ternary nanocomposites hydrogel have been effectively fabricated on carbon cloth using a two-step synthesis approach. Nickel ferrite nanoparticles (NiFe2O4) prepared by template method have been dispersed onto/within rGO nanosheets leading to the formation of NiFe2O4/rGO (NFG) nanocomposites. Afterward, polyaniline hydrogel has been polymerized on NFG nanosheets to prepare ternary polyaniline/NiFe2O4/rGO hydrogel (PNFG) nanocomposites on carbon cloth that can be further utilized as a binder-free supercapacitor electrode. The resulting 3D ternary nanocomposites hydrogel achieved maximum specific capacitance of 1134.28 F/g at a current density of 1 A/g and 76.46 % of capacitive retention at 10 A/g. The supercapacitor electrode exhibited outstanding rate capability and superior cyclic stability up to 5000 successive cycles. In addition, the symmetric supercapacitor cell delivered 0.61 kW/kg of specific power and 19.29 Wh/kg of specific energy. The excellent electrochemical characteristics of PNFG is ascribed to its well-designed 3D microstructure and the synergistic effect created by the capacitive mechanism due to electric double layer capacitance (EDLC) and pseudocapacitance (surface redox reactions) as well as diffusion-controlled mechanism (faradaic redox reactions). It has been revealed that the overall electrode reaction is dominated by surface-controlled processes, with a small contribution from diffusion-controlled faradaic processes.

A Bidirectional Integrated Equalizer Based on the Sepic–Zeta Converter for Hybrid Energy Storage System

In the hybrid energy storage system (HESS), the voltages between the battery cell and the supercapacitor cell are different, increasing the circuit and control complexity of the balance system. Therefore, a bidirectional integrated equalizer based on the Sepic–Zeta converter is proposed for the HESS, which realizes both battery string and supercapacitor string balance during the energy exchange. The inductors in the Sepic–Zeta converter are used as the primary side of the balanced multiwinding transformer. The Sepic–Zeta converter generates the current ripples to drive the multiwinding transformer. The secondary side generates currents to balance the HESS, and hence, the equalizer itself is essentially switchless. Therefore, the proposed circuit can reduce the complexity of the HESS. Experimental and comparative results show that the proposed equalizer achieves the balance of the HESS.

Cassava peel derived self-doped and hierarchical porous carbon as an optimized electrode for the ultra-high energy density of supercapacitor

The development of advanced electrode materials with optimized properties, including structural morphology, high porosity, and functional group doping, is very important to enhance the energy density of solid-state supercapacitors. Here, a hierarchical 3D porous carbon self-doping obtained from cassava peel through an environmentally benign approach to optimize the supercapacitor working electrode material. The unique sponge-like interconnected pore structure and self-doping features are controlled through chemical impregnation (CIP) of ZnCl2 (CIP/Z), KOH (CIP/K), and H3PO4 (CIP/H) and high-temperature pyrolysis in an N2&CO2 gaseous environment. Furthermore, the optimized CIP/Z carbon material exhibits high content of 94.606 % and a self-doping oxygen heteroatom of about 2.672 %. The unique sponge-like morphology possessed enriches micropores of 94 %, indicating high performance as an electrode material. The electrochemical properties were assessed through a symmetric supercapacitor system assembled in a solid free-binding coin yielding an excellent specific capacitance of 257 F g−1 at 1 A g−1. Meanwhile, the optimized electrode has a high rate capability of 92.43 % and maintained a coulombic efficiency of up to 91.10 % at 10 A g−1. The best working efficiency supercapacitor cell can show a jump in energy density of 35.69 Wh kg−1 at a specific power of 167.68 W kg−1 in an aqueous electrolyte of 1 M H2SO4. These excellent results provide important insights for optimizing electrode materials derived from cassava peel-based porous carbon for symmetrically designed supercapacitors of binder-free solid coins in aqueous electrolytes with high energy density.