Gravimetric Specific Capacitance Research Articles

Application of N/P-rGO composite electrode materials and novel electrolytes in high-performance supercapacitors

Traditional graphene-based electrode materials often can not have excellent gravimetric and volumetric electrochemical properties at the same time. Furthermore, the gel electrolyte widely used at present has the disadvantages of poor water retention, easy solidification, low ionic conductivity, and narrow working temperature range during the working process. In this paper, nanocellulose/N, P co-doped reduced graphene oxide composites (NC-NPrGOs) were synthesized via a simple approach using graphene oxide (GO), ammonium dihydrogen phosphate, and nanocellulose (NC) as raw materials. Meanwhile, a new type of gel electrolyte (SNG) with renewable, wide working temperature range and ultra-high water retention properties was prepared using sodium alginate (SA), NC, GO, and potassium hydroxide as precursors. Benefiting from the unique physical and chemical properties of NC-NPrGOs, the assembled aqueous symmetric supercapacitors assembled by NC-NPrGOs present high gravimetric (303.9 F/g) and volumetric specific capacitance (416.5 F cm−3), large gravimetric (10.5 Wh kg−1) and volumetric energy density (14.6 Wh/L). Due to the multiple interactions of several components in SNG, the flexible solid-state supercapacitors (ASSC) assembled by NC-NPrGO55 and SNG deliver high specific capacitance (240.0 F/g), ultra-long cycling life, excellent bending resistance, a wide range of operating temperatures, and good regenerative performance. In summary, NC-NPrGOs and SNGs are ideal for the investigation of new energy storage devices.

Manipulating the overall capacitance of hierarchical porous carbons via structure- and pore-tailoring approach

Herein, we present pore architecture-tailorable porous carbons through a time-adjustable hydrothermal reaction and subsequent KOH chemical activation method. Accordingly, platanus spiky (Ps) fruits, taro (T) roots, and green bell peppers (Pp) biowaste substrates were utilized as sustainable precursors to construct novel hierarchical porous carbons (HPCs) with highly interconnected porous frameworks and smart micro/meso/macroporous architecture for supercapacitors. The heterogeneous feedstocks were pre-carbonized under hydrothermal conditions for different hold durations (12 h, 24 h, 36 h) at 200 °C. The optimized Ps-24h material exhibits a high capacitance of 371.6 F g−1 at 1 A g−1 in an aqueous Na2SO4 electrolyte and an outstanding rate performance (94% capacitance retention after 10,000 charge-discharge cycles). Surprisingly, the specific gravimetric capacitance of HPCs can be significantly manipulated by establishing a high-performance redox electrolytic system. In particular, the tailored Ps-24h-based electrode delivers a superior capacitance of 843 F g−1 at 1 A g−1 with an exceptional rate capability (64.7% capacitance retention from 1 to 20 A g−1 in K3[Fe(CN)6]/Na2SO4 electrolyte). Consequently, the as-integrated Ps-24h//Ps-24h symmetric supercapacitor device with a working voltage of 1.8 V presents enhanced energy/power outcomes (63.8 Wh kg‒1/900.2 W kg‒1) with remarkable long-term cyclic durability (90.4% capacitance retention after 15,000 cycles) in a redox electrolytic system.

Mass scale synthesis of graphene nanosheets using waste cardboard for application in perovskite solar cells and supercapacitors

Advanced graphene-based materials have been proficiently incorporated into next-generation solar cells and supercapacitors because of their high electrical conductivity, large surface area, excellent charge-transport ability, and exceptional optical properties. Herein, we report the synthesis of graphene nanosheets (GNs) from waste cardboard via pyrolysis, with ethyl alcohol as the growth initiator. Additionally, we demonstrated the use of GNs in energy conversion and storage applications. Using the GN electrode in perovskite solar cells resulted in an excellent power conversion efficiency of ∼10.41 % for an active area of 1 cm2, indicating an enhancement of approximately 27 % compared to conventional electrodes. Furthermore, the GNs were used as active electrode materials in supercapacitors with excellent electrochemical performance and a high gravimetric specific capacitance of 167.5 F/g at a scan rate of 2 mV/s. The developed GNs can be efficiently used for energy storage, conversion, and electrochemical sensing applications.

Carbamide-mediated facile sol-gel synthesis of porous flower-like ZnCo2O4 microspheres for high-performance asymmetric coin cell supercapacitors

The design and development of ultrahigh-performance nanomaterials possessing novel characteristics are needed to achieve reliable energy storage performance. To satisfy the needs, diverse electrode materials are explored. Even though carbon-based materials hold high surface area and conductivity, their specific capacitance value fails to deliver high-performance applications. Therefore, pseudocapacitive transition metal oxide is adopted to overcome these issues. Among all Zinc Cobaltite, a binary transition metal oxide is widely explored owing to its fascinating electrochemical properties. As most of the synthesis of these kinds of materials requires the hydro/solvothermal method, herein, we have proposed the concept of a facile sol-gel method to prepare this class of materials by using Carbamide as both structure director and fuel to achieve the porous flower-like Zinc Cobaltite. The prepared material delivers the notable gravimetric specific capacitance of 513.3 F g−1. Owing to its unique morphology and porous structure, ion channelization is feasible, which will enhance the electrochemical reaction. Constructed asymmetric coin cell supercapacitor showed an extraordinary specific capacitance of 106.5 F g−1 and energy density of 56.2 Wh kg−1, demonstrating an impressive ability to retain 89.6 % of its capacitance after 4000 cycles at a current density of 6 A g−1. Due to the remarkable electrochemical behavior, this work can act as a guiding tool for designing efficient and cost-effective energy storage devices that will hold prodigious potential in commercial energy storage applications.

Silicon Solid State Battery: The Solid‐State Compatibility, Particle Size, and Carbon Compositing for High Energy Density

AbstractSolid‐state battery research has gained significant attention due to their inherent safety and high energy density. Silicon anodes have been promoted for their advantageous characteristics, including high volumetric capacity, low lithiation potential, high theoretical and specific gravimetric capacity, and the absence of lethal dendritic growth. Addressing concerns such as low conductivity, pulverization, fracture, dense solid electrolyte interface layer, and low coulombic efficiency has substantially improved the use of silicon electrodes in solid‐state batteries. Researchers have explored carbon additions, solid electrolyte suitability for Si anodes, pressure optimization, and particle size effects (nano/micro) to enhance energy density. Recent studies have investigated the conductivity mechanism, stack pressure, and anode‐solid electrolyte compatibility to improve energy density. Micro‐ and nano‐sized silicon have attracted attention in carbon‐based composites due to their exceptional conductivity, uniform distribution, efficient electron migration, and diffusion channels. The development of solid‐state batteries with high energy density, safety, and extended lifespan has been a major focus. This review sheds light on significant insights and strategic approaches for researchers working on solid‐state silicon‐based systems to overcome existing challenges.

Dual regulation of particle size and surface structure of SrVO3 for high volumetric capacity

Perovskite SrVO3 stands out as a promising anode material for lithium-ion batteries due to its inherent redox activity, excellent electrical conductivity, and structural adaptability. Despite these advantages, challenges persist, such as in achieving high tap density and volumetric specific capacity. In this study, we overcome these challenges by finely regulating particle size and constructing a tailored surface structure for SrVO3. The implementation of ball milling during the synthesis process proves to be a simple yet highly efficient method for simultaneously tailoring particle size and in-situ creating an amorphous layer on SrVO3 particles. The reduction in particle size not only facilitates enhanced electron and ion transport but also significantly improves the tap density of SrVO3, increasing it from 2.61 to 3.15 g cm−3. The in-situ construction of an amorphous layer introduces a multitude of defects and high valence V5+. These defects serve as active sites for lithium ions, while the V5+ species contribute to increased electron transfer, collectively resulting in a high gravimetric specific capacity. The engineered SrVO3 anode delivers an impressive volumetric capacity of 1134 mAh cm−3 at 0.1 A g−1, surpassing both pristine SrVO3 (733 mAh cm−3) and commercial graphite anode (∼460 mAh cm−3).

Decoupling electrolyte strategy for a high-voltage Na-ion hybrid capacitor based on NaFeO2 and activated carbon

Sodium iron dioxide (NaFeO2) with high specific capacity, has been widely used as a kind of electrode materials for Na-ion batteries. When NaFeO2 is used as the battery-type electrode for aqueous Na-ion hybrid capacitors, there are a lot of technical challenges to meet, especially the narrow voltage window limited by the thermodynamic decomposition of water. We propose a novel decoupling electrolyte strategy to suppress the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on the NaFeO2 anode and the activated carbon (AC) cathode respectively, in order to expand the voltage window of the aqueous AC//NaFeO2 Na-ion hybrid capacitor. The alkaline anolyte (2 M NaOH) and the neutral catholyte (1 M Na2SO4) can be decoupled by the cation exchange membrane, which selectively allows the Na+ ions through the membrane to carry the electric currents in the charge/discharge process. The NaFeO2 sample with the stable crystal structure and oxygen vacancy defects, can provide a gravimetric specific capacitance of 101.1 F g−1 at 1 A g−1. Electrochemical kinetic analysis indicates that the capacitor-type behaviour is predominant in the electrochemical energy storage process of the AC//NaFeO2 Na-ion capacitor at the scan rates higher than 40 mV s−1. The AC//NaFeO2 Na-ion capacitor with the stable voltage window of 2 V, can provide an energy density of 12.6 Wh kg−1 at 1 kW kg−1. Due to its inhibiting effects on HER and OER, this decoupling electrolyte strategy holds great potential for constructing high-voltage aqueous energy storage devices.

Synthesis of graphene nanocomposites integrated with 3D bimetallic magnesium/cobalt metal-organic framework as anodic material for solid-state asymmetric supercapacitors

In this study, we have grown 3D porous bimetallic Mg/Co MOF in the presence of exfoliated graphene nanoplates (EGNPs) via a one-step in-situ hydrothermal process, where 1,3,5-benzenetricarboxylic acid (BTC) was used as an effective organic linker since it is cost-effective and EGNPs served as a conductive component. Morphological characterization of Mg/Co-BTC MOF@EGNP nanohybrid confirmed the homogeneous growth of ball-shaped Mg/Co-BTC MOF around the graphene nanoplates, while nitrogen adsorption-desorption analysis revealed large surface area with a high volume fraction of mesopores. This surface features is highly favorable for rapid ion/electron transportation that ensures high specific gravimetric capacitance (838 F/g) and noticeable rate capability (81 % capacitance retention). As-synthesized nanohybrid was used as anode material to construct a prototype all-solid-state asymmetric supercapacitors (ASC) device with a significantly high energy density of 73.82 Wh kg−1, a wide potential window of 0–1.7 V, admirable capacitance retention of 95.1 % after 8000 cycles, and long self-discharge time. Moreover, these capacitance performances also demonstrates the reliability of the as-synthesized poly vinyl alcohol (PVA)-Li2SO4 membrane as a separator-cum-electrolyte for fabrication of future leakage-proof ASCs for wearable electronics. This work can lead to manufacting innovation in the future.

The influence of polyurethane precursor density on the electrochemical performance of supercapacitor composed of activated porous carbon

In this work, we studied the relationship between the electrochemical performance, the specific gravimetric capacitance, and the specific volumetric capacitance as the density of the polyurethane-derived porous carbon (PPC) was varied by adjusting the amount of water used during KOH activation-carbonization synthesis process. We characterized PPCs made using five different mass ratios of water to precursor (X) of 0.4, 0.5, 0.6, 0.7, and 0.8 and found that X of 0.6 (PPC-0.6) gave the most developed porous structure and the right amount of N and O heteroatoms. As the X increased from 0.4 to 0.8, the precursor density decreased. Among the five PPCs synthesized, PPC-0.6 showed the highest specific gravimetric capacitance of 458.2 F g−1 at a current density of 1 A g−1 in a 1 M H2SO4 electrolyte. Notably, a two-electrode SC device based on PPC-0.6 operated in a 1 M H2SO4 electrolyte could generate the highest energy density of 13.12 Wh kg−1 at a corresponding power density of 50 W kg−1 and maintain 97.55 % of its initial capacitance at the end of 10,000 cycles. The highest specific volumetric and gravimetric capacitances were 242.8 F cm−3 and 458.2 F g−1, respectively, achieved by PPC-0.8 and PPC-0.6. This study serves as a guide that demonstrates how the bulk density of porous carbon supercapacitor electrodes can be adjusted by changing the polymer precursor density, whereby the trade-off relationship was observed between the specific gravimetric capacitance and the specific volumetric capacitance.

High-performance supercapacitors based on compact graphene composite hydrogels

Because of its ultra-high specific surface area and outstanding electrochemical performance, graphene has become a study focus of electrode materials for supercapacitors. However, severe agglomeration and poor volumetric electrochemical properties greatly reduce its potential for practical applications. Here, we proposed a simple hydrothermal strategy to synthesize L-glutamic acid functionalized nanocellulose/reduced graphene oxide composite hydrogels (GNGHs) with compact porous structures and plentiful heteroatom functional groups. In the hydrothermal process, a high concentration of graphene oxide solution (GO) was employed to boost the packing density of the samples. Nanocellulose (NC) and the molecular chains of L-glutamic acid were used as spacers to modulate the porous structure of GNGHs. At the same time, NC and heteroatomic groups can also boost the surface wettability of GNGHs, thereby increasing their ion-available specific surface area. The GNGH-15 based symmetric aqueous supercapacitors (SASC) deliver high gravimetric (282.0 F g−1) and volumetric (329.9 F cm−3) specific capacitance, remarkable rate capacity, and good cycling durability. Moreover, the all-solid-state flexible supercapacitors (ASSC) assembled by GNGH-15 also exhibit prominent specific capacitance (154.7 F g−1) and good rate performance. These brilliant electrochemical properties make GNGHs a strong contender for electrode materials of energy storage devices.

The electrochemical effects of pitch stabilization for supercapacitor-grade activated carbon precursors

Petroleum pitch (PP) is a by-product generated during the petroleum refining process, characterized by its high carbon content, tunable structure, and cost-effectiveness. These attributes have spurred extensive research into its potential as a carbon material. In this study, we prepared both untreated PP and oxidative stabilized PP (sPP) to explore the influence of pitch structural modifications on physical and electrochemical properties following carbonization and activation. Stabilizing the pitch above its softening point introduced oxygen functional groups on the surface, reaching levels of up to 19.6 at.%. These structural changes concurrently reduced aromaticity while increasing the coking value. Two types of activated carbons suitable for supercapacitors were derived from these distinct pitches, and their energy storage capacities were correlated with precursor pitch structural properties. The sPP-derived activated carbon exhibited a remarkable gravimetric specific capacitance of 39.6 F g−1, owing to its high specific surface area of 2508 m2 g−1. Conversely, PP-derived activated carbon exhibited a relatively lower specific surface area of 1122 m2 g−1. However, it demonstrated an increased electrode density and shallow ion intercalation within its graphitic structure, resulting in a notable volumetric capacitance of 26.0 F cc−1. This research not only sheds light on the electrochemical effects of pitch stabilization but also provides a foundation for the development of high-performance activated carbon materials through tailored modifications to the PP structure.

Synthesis of 2D bi-metallic Zn/Cu metal-organic framework integrated graphene nanocomposites for all-solid-state asymmetric supercapacitors

In this work, a novel two-dimensional (2D) bi-metallic metal-organic frameworks (MOFs) consisting of zinc and copper metal centers with 1,3,5-tricarboxylic acid as a chief and efficient organic linker (Zn/Cu-BTC) and its composite with exfoliated graphene nanosheets (EGNSs) have been investigated for supercapacitor applications. The composites were synthesized via facile in-situ solvothermal process. Different spectroscopic, microscopic, and surface analyses confirmed the successful formation of porous electroactive composites, where 2D MOF nanosheets were vertically grown on the EGNS surfaces. In the two-electrode symmetric system, the as-synthesized Zn/Cu-BTC MOF@EGNS electrode achieved an enhanced specific gravimetric capacitance and equivalent volumetric capacitance of 1284.9 F/g and 813.3 F/cm3 at 0.5 A/g. It exhibits high-rate performance and prolonged cycling stability with >90 % retention after 8000 cycles. All-solid-state asymmetric supercapacitor (ASC) device was constructed with Zn/Cu-BTC MOF@EGNS composite and EGNS electrodes, where PVA-KOH membrane served as a separator-cum-electrolyte. The ASC device delivered a satisfactory energy density of 60.55 Wh kg−1 and a maximum power density of 10 kW kg−1 with an admirable cycling stability of 92 % after 10,000 charge-discharge cycles. In the future, this work can encourage manufacturing innovation.

Electrochemical Characteristics of Li‐Ion Battery Anodes Based on Titanium Oxyfluoride

The properties of titanium oxyfluoride‐based anodes are studied by galvanostatic cycling and galvanostatic intermittent titration technique in a TiOF2—Li half‐cells. This anode material is shown to have a high degradation resistance and a specific gravimetric capacity comparable to that of carbon and Li4Ti5O12. The chemical diffusion coefficient of Li+ in TiOF2 varies by two orders of magnitude in the range from 2.3 × 10−13 to 2.5 × 10−15 cm2 s−1 depending on the degree of lithiation and the direction of charge or discharge process. The electrode electrical resistance changes with cycling and its value is always lower in the lithiated state than in the delithiated state. The phenomenon of superreversibility inherent in this material has been studied. This phenomenon consists in the excess of the discharge capacity (Li extraction) over the charge capacity (Li insertion), that is, the Coulomb efficiency (CE) exceeds 100%. In the first few tens of cycles, the phenomenon is due to the extraction of excess lithium, which was previously stored in the electrode during the first cycle. On subsequent cycles, the CE stabilizes at a level above or below 100%, depending on the ratio between the charge and discharge currents, and is not related to the accumulation or spending of Li.

Hydrothermal synthesis of graphene oxide interspersed in non-uniform tungsten oxide nanorod and its performance towards highly efficient hybrid supercapacitor

In this study, hybrid graphene oxide/tungsten oxide nanostructures (GO/WO3 NSs) are synthesized using an eco-friendly and efficient hydrothermal method. Physicochemical analysis reveals the presence of a monoclinic phase with characteristic diffraction peaks, as indicated by the crystallinity degree. Using a field emission scanning electron microscope, heterogeneous non-uniform agglomerated nanosheets with non-uniform nanorods are observed in the GO/WO3 hybrid NSs. Results of transmission electron microscopy and X-ray photoelectron spectroscopy provide comprehensive details regarding the morphological, structural, and electronic state characteristics of the GO/WO3 hybrid NSs. Electrochemical data for GO/WO3 are obtained using an aqueous 2 M KOH electrolyte. The maximum specific capacity (Csp) and gravimetric capacitance (Cg) of the GO/WO3 are observed under 10% GO. The values of Csp and Cg are 123 mAh/g and 738 F/g, respectively, whereas the maximum energy (Ed) and power densities (Pd) are 37 Wh/kg and 500 W/kg at 5 mA/cm2, respectively. Furthermore, the optimized sample (GO-W2) shows superior capacitive retention of 88% over 7000 cyclic voltammetry cycles at a scan rate of 100 mV/s. A GO-W2-NF//GO-NF (where NF represents Ni-foam) asymmetrical hybrid liquid state device is fabricated using a two-electrode system, which demonstrates favorable electrochemical properties, i.e., Csp and Cg values of 94 mAh/g and 213 F/g at 5 mV/s respectively, and Ed and Pd values of 25 Wh/kg and 1000 W/kg at 4 mA/cm2, respectively. These findings indicate that GO/WO3 hybrid NSs are effective electrode materials for future research pertaining to energy storage systems.

Unleashing the Full Potential of Electrochromic Heterostructured Nickel-Cobalt Phosphate for Optically Active High-Performance Asymmetric Quasi-Solid-State Supercapacitor Devices.

The rational design of hybrid systems that combine capacitor and battery merits is crucial to enable the fabrication of high energy and power density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni-Co phosphate (Ni3-xCox(PO4)2·8H2O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni3-xCox(PO4)2·8H2O offered a respectable gravimetric specific capacity and marvelous capability rate (966 and 595 C g-1 at 1 and 15 A g-1) over the Ni3(PO4)2·8H2O (327.3 C g-1) and Co3(PO4)2·8H2O (68 C g-1) counterparts. Additionally, the nanoplatelets showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni3-xCox(PO4)2·8H2O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg-1 and 15998.54 W kg-1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices are capable of glowing a red LED bulb for nearly 180 s. This research paves the way to design and fabricate electroactive species via a facile approach for boosting the design of a plethora of supercapattery devices.

Heteroatom-doped layered hierarchical porous carbon electrodes with high mass loadings for high-performance supercapacitors

Electrodes with high mass loadings are the impetus for improving the energy density of supercapacitors. However, such electrodes have poor charge and ion kinetics in most cases, and rationally designing them which have high electron and ion transport rates is a major challenge. In this work, a new heteroatom-doped hierarchical porous carbon material, called LPC-2, was developed with longan shell and KOH as its precursor and an activator, respectively, through heteroatom self-doping and architecture design integration, in which heteroatoms of nitrogen, oxygen and sulfur were found. Its frequency response was excellent at a scan rate up to 5 and 0.3 V s−1 when the mass loading was set to be 1.0 and 12 mg cm−2, respectively. At a high mass loading of 12 mg cm−2, LPC-2 had gravimetric and areal specific capacitances of 171 F g−1 and 2052 mF cm−2, respectively. The assembled LPC-2//LPC-2 symmetric supercapacitor can complete charge and discharge in 0.4 s, showing a high energy density of 10.8 Wh kg−1 at a high power density of 97.4 kW kg−1 in 6 M KOH. In addition, 99.5 % of the original capacitance was retained after 20,000 cycles at 10 A g−1, which embodies the application value of biomass-derived carbon in supercapacitors.

Carbon Dot/Ti3C2Tx MXene Hybrid on Carbon Cloth as a Flexible and Binder‐Free Supercapacitor Electrode with Commercial Scale Mass Loading

Flexible and binder‐free carbon dot/titanium carbide (CD/Ti3C2Tx) MXene electrode for supercapacitor is fabricated at commercial scale mass loading. The decline in specific gravimetric capacitance due to high mass loading is compensated by the synergistic enhancement in properties of the prepared CD/Ti3C2Tx hybrid. The optimized hybrid electrode gives a specific gravimetric capacitance of 373 F g−1 at a current density of 1 A g−1. The symmetric supercapacitor developed using the electrode has a specific gravimetric capacitance of 50 F g−1, energy density of 4.4 Wh kg−1, and power density of 66.6 W kg−1 at a current density of 1 A g−1. The device retains 90.8% capacitance after 5000 cycles when operated at a current density of 1 A g−1. Raman spectroscopy analysis provides an evaluation of the evolution of the electrochemical performance of the hybrid with the CD concentration. The work will open up new avenues in textile‐based supercapacitor technology for wearable electronics applications utilizing environment‐benign techniques.

Flexible and binder-free supercapacitor electrode with high mass loading using transition metal doped MoS2 nanostructures

Transition metal (TM) doping has been done on MoS2 to activate its inactive sites. The edge sites created on doping with nickel (Ni), cobalt (Co), and iron (Fe) provide a conductive, flexible, and binder-free electrode with high mass loading (>19 mg/cm2) over carbon cloth. The vertical flower-like morphology together with the presence of dangling bonds, imparts a high rate of adsorption and desorption process and outstanding super-capacitive properties. Due to the identical ionic radii, Ni atom will effectively replace the Mo atoms in MoS2 and also intercalate between the layers. The resultant lattice distortions, and the presence of Ni atom in the interstitial sites, provide faradaic and non-faradaic capacitance to the Ni-doped electrode, (Ni-MoS2/CC), giving it an excellent specific capacitance of 305.9 F/g compared to 170.2 F/g for the pure MoS2/CC electrode. The doping produced 180% increase in the specific capacitance of MoS2, which is the highest reported value for a high mass loading electrode. There is an enhancement in the properties of TM doped MoS2 electrodes prepared in the present study as binders and conductive additives are avoided. A symmetric supercapacitor developed using the Ni-MoS2/CC electrode gave a specific gravimetric capacitance of 50 F/g, energy density of 4.4 W h/kg, and power density of 79.1 W/kg at a current density of 0.5 A/g. The device retained 87.4% capacitance after 5000 cycles at a scan rate of 1 A/g.

Anti-Shedding Nickel-Protection-Layer Boosting an Ultrahigh Loading Carbon Fiber@Co-NiSx Electrode to Deliver Superior Areal/Volumetric/Gravimetric Capacitance.

Challenges remain to show good capacitive performance while achieving high loadings of active materials for supercapacitors. Trying to realize this version, a nickel-protecting carbon fiber paper@Co-doped NiSx (Ni-CP@Co-NiSx) electrode with high specific gravimetric, areal, and volumetric capacitance is reported in this work. This free-standing electrode is prepared by an electroplating-hydrothermal-electroplating (EHE) three-step method to achieve a high loading of almost 26.7 mg cm-2. The cobalt-doping and nickel-protection strategies effectively decrease the impedance and inhibit the active material dropping from the electrode resulting from the expansion stress, which endows the Ni-CP@Co-NiSx electrode with a high rate and good cycling performance, especially with an ultrahigh specific areal/volumetric/gravimetric capacitance of 53.3 F cm-2/2807 F cm-3/1997 F g-1 at 5 mA cm-2, respectively. Employing activated carbon functionalized with riboflavin (AC/VB2) as a negative electrode, the asymmetric supercapacitor device delivers a very high energy density of up to 60.4 W h kg-1. This work demonstrates that electrodes with a high loading density and excellent performance can be obtained by the combination of the EHE method to adjust the internal conductivity and external structural stability.

Biological treatment as a green approach for enhancing electrochemical performance of wood derived carbon based supercapacitor electrodes

Wood-derived biochar is an eco-friendly and porous carbon material that can be used to prepare supercapacitor electrodes. For the purpose of addressing the deficiencies in the specific surface area and pore structure of wood-derived carbon as the raw material of electrodes, a biological pre-treatment method was developed to construct the desirable pore structure of wood by leveraging the lignin-degrading property of white-rot fungi. First, white-rot fungi with permeability and biodegradability on lignocellulosic substrates were used to regulate the pore structure of natural paulownia wood, which was then carbonized to produce a porous hyphae/wood-derived carbon conductive substrate. Afterward, manganese dioxide (MnO2) was deposited on the substrate to fabricate the MnO2/hyphae/wood-derived carbon (HWC-3M) electrode by the hydrothermal method. The degradation of lignin by white-rot fungi broke the original pore structure of wood, strengthened effective channels in the cell walls, and facilitated the loading of MnO2 into the channels to improve the ion transport rate. The HWC-3M had richer energy storage sites, more electrolyte ion transport channels, and better electrochemical performance than the control electrode made of untreated wood-derived carbon (HWC-0), showing an excellent areal specific capacitance (3395 mF/cm2 at a current density of 1.0 mA/cm2), moderate gravimetric specific capacitance (138.3 F/g), and good cycling stability (retention of 88.6% after 2000 cycles). The results indicate that pretreating wood-derived carbon composite electrode with white-rot fungi serves as a new green approach to develop high-performance electrochemical energy storage devices.