Electric Double Layer Supercapacitors Research Articles

Janus molybdenum di-chalcogenides based van der Waals bilayers for supercapacitor electrode design- effects of interlayer stacking orientations on quantum capacitance

In this work, for the first time, the quantum capacitance of an artificial two-dimensional (2D) material system based on van der Waals (vdW) bilayer heterostructures of Janus Molybdenum Di-chalcogenides, MoXY (X≠Y, X/YS, Se, Te) have been extensively investigated for electrode design of electrical double-layer (EDL) supercapacitor. The effects of different interlayer stacking orientations on local charge distribution, interlayer charge transfer, energy band structure, and density of states (DOS) have been comprehensively analyzed and correlated with the excess charge density and quantum capacitance variation with local electrode potential. Furthermore, the total capacitance reduction with respect to EDL capacitance has been analyzed over a wide range of EDL capacitance, and the performance of vdW Janus bilayers has been systematically benchmarked against the natural monolayers/bilayers and Janus monolayers of Molybdenum Di-chalcogenides. The results demonstrate that the large interlayer charge transfer induced built-in interlayer electric field significantly reduces the energy band gap of vdW Janus bilayers for S–Te and Se–Te interlayer stacking, thus leading to a significantly superior quantum capacitance. Finally, the favorable valley-dependent effective mass and band-degeneracy in MoSTe/MoSeTe have greatly enhanced quantum capacitance in S–Te and Se–Te stacking, rendering these bilayers a highly attractive candidate for supercapacitor electrode design.

Differential capacitance of curved electrodes: role of hydration interactions and charge regulation.

The functioning of supercapacitors relies on establishing electrostatic double-layer capacitance across a larger surface area, offering numerous advantages over conventional batteries, such as an extended lifespan and elevated safety standards. The differential capacitance is a fundamental property within the electrical double layer, playing a pivotal role in the advancement of electrical double-layer supercapacitors. In addition to electrostatic interactions, multiple theoretical and experimental studies have indicated that the differential capacitance is influenced by factors such as the physical structure of the electrode, solvent-mediated hydration interactions, and the specific type of electrolyte utilized. In this work, we incorporate hydration interactions into the Poisson-Boltzmann theory to explore curved electrodes whose surfaces can be covered by either acidic or basic groups. We examine how the electrostatic interaction, charge regulation, hydration effects, and the finite size of ions collectively modify the differential capacitance. Furthermore, we explore different scenarios of electrode curvature and how it may be used to achieve larger capacitance depending on the electrolyte type and pH.

Monolithic Self-Charging Storage Device with Stable 3 V Operation

Monolithic self-charging storage device with Stable 3 V Operation The energy paradigm has been changing from the traditional power plant system to micro-gride system based on renewable energy. However, renewable energy including wind, solar, and vibration, is intermittent and influenced by time, weather, and location. Thus, the suitable storage device is required for efficient utilization of renewable energy. The representative combination of renewable energy and energy storage device is an energy storage system (EES) consisting of photovoltaic systems and Lithium-ion batteries. The EES is mainly applied to social infrastructure system that generate large amounts of energy. As the Fourth Industrial Revolution progresses, the rechargeable power supply including Lithium-ion batteries is widely applied to wireless system such as sensor network, wearable device, and electric vehicles. However, the batteries have only storage function, so periodic charging is required. Thus, it is necessary to develop technologies for portable and small energy generation/storage as standalone power sources that can continuously supply power to various electronic devices. Large-scale energy production/storage system has entered the maturity stage, but the development of portable and small energy generation/storage systems based on IoT is in its early stages. To date, research on this system is conducted by simply connecting energy harvesting and energy storage device to external wires after manufacturing them independently. However, the introduction of additional wires is complicated in system design and manufacturing and has difficulty in miniaturization. These problems have motivated the integration of both functions into one device. The integrated device is fabricated by sharing one electrode, called a common electrode between the energy harvesting and storage components. Currently, research on a monolithic photo-charging storage device that integrates solar cells and energy storage devices into one device has been developed. This structure can miniaturization and flexible design, thereby it is suitable for the wearable and smart device. Although the importance of an integrated device is emphasized, the current research of monolithic device is limited to the fabrication of an integrated device without considering their practicability. In other words, most studies focus on simply connecting two devices to achieve the highest overall efficiency. In this case, since the open circuit voltage of single solar cell is under 1 V, the operation of photo-charging storage device is limited to 1 V. Thus, we proposed the monolithic photo-charging storage device operating at 3 V. We fabricated the multiple series-connected perovskite solar cell to increase the operating voltage. Since the secondary batteries are difficult to be charged by the high current density of 20 mA cm−2 solar cell owing to their storage mechanism, we choose the supercapacitor with the rapid response to an applied electric field change. We select the silver paste as the common electrode owing to its strong adhesion, high electric conductivity, and lack of chemical/mechanical damage to the solar cell and supercapacitor. Based on density functional theory (DFT) calculation, we prove the common electrode exhibits good compatibility with our supercapacitor and solar cell. For this reason, the proposed photo-charging storage device exhibits an ultra-fast charging time of less than 3 sec under AM 1.5 G illumination and high overall efficiency of 13.17 % at 1 mA cm−2 and 9.87 % at 20 mA cm−2. For electric double layer supercapacitors integrated with a solar cell, higher discharging current densities that 20 mA cm−2 have not been reported so far. We firstly demonstrate the behavior of photo-charging storage device under light/dark state by the impedance analysis. By the impedance analysis, we demonstrated that the solar cell provides a stable power supply to the supercapacitor under light condition. Further, the additional encapsulation ensures the long-term stability of photo-charging storage device and demonstrate the indoor cycling performance. We prove the photo-charging storage device has high potential as an IoT sensor power source. Figure 1

(Best Student Poster Award) Energy Harvesting from Carbon Dioxide Capture through an Ionic Liquid Based Supercapacitor

Nowadays, Earth is undergoing effects of climate change due to the exponential increase of greenhouse gasses's emissions. The main component of greenhouse emissions is carbon dioxide (CO2), which is estimated responsible for about 60% of global warming generated by human activities, and its concentration is increased by 40% with respect to the concentration at the beginnings of industrial era. This increase is due to several factors such as the combustion of coal, oil and gas and the progressive deforestation: this last phenomenon generates a sort of bottleneck in the so called biogeochemical "carbon cycle". Deforestation causes the lack of one of the natural regulating sources of carbon dioxide concentration.Scientific community set an increase of 2°C (with respect to the pre-industrial global temperature) as the threshold beyond which there is a much higher risk that dangerous and possibly catastrophic changes in the global environment will occur. At the moment the increase of the temperature has reached about +0,85°C thanks to greenhouse gasses. All technologies developed in CO2 capturing have to be intended in the reduction of global warming.The goal of the presented work is to develop a device able to cut down greenhouse emissions by reusing human produced carbon dioxide. This can be done exploiting the free energy released each time two solutions with different compositions are mixed. Even if this phenomenon holds true both for liquids and gases, in last decades it was deeply investigated for what concerns liquid sources (CapMix), while few technologies are available to harvest free energy coming from gas sources. The adopted structure is an electrical double layer super-capacitor based on ionic liquid electrolyte. Special attention should be paid to the choice of the electrolyte which should work both as an electrolyte and CO2 absorbing medium in a CapMix cell. Among the tested ionic liquids, the choice fell on an Imidazole based ionic liquid, which showed excellent absorption rates of gas, being able to capture 15.67% of CO2 over the total mass.This work is a proof of concept of a novel not yet studied mechanism, which is able to work without any imposed external bias. When a CO2 gas stream is flushed through the supercapacitor, the gas strongly affects the electrode/IL interface and the IL physico-chemical properties, producing a change in the potential difference between the electrodes. In this way it is possible to convert the mixing energy into electrical energy. Figure 1

(Best Poster Award - 2nd Place) Energy Harvesting from CO2 Emission Exploiting an Ionic-Liquid Based Electrochemical Capacitor

Global warming is one of the most serious problems that the humanity is facing in his history.Since 1900 to nowadays, the global temperature has risen by 1 °C and, according to the scientificcommunity, the cause is related to the climate-changing emissions due to anthropogenic activities.In order to avoid an environmental disaster, 196 countries have signed the Paris agreement thataims to maintain global warming below 1.5 °C compared with pre-industrial levels.The reduction of greenhouse gas emissions is a key issue in contemporary science, and in thiscontext, the ability of certain ionic liquids (ILs) to capture carbon dioxide has attracted a lot ofinterest. The idea presented in this work is to design an electric double layer supercapacitor whichis able to harvest energy by exploiting the reaction between an ionic liquid and carbon dioxide. Inparticular, the system consists of two carbon-based electrodes and a polymeric separator soakedin ionic liquid. The use of carbon electrodes ensures a high surface area and excellent electricalconductivity while imidazole-based ionic liquid acts and as electrolyte and as capture media.The operating principle of this system is a novel mechanism which exploits the formation of avoltage drop across the device when the electrode-IL interfaces are different; the two differentinterfaces are ensured by the presence of imidazole carbamate in a part of the cell (Im − CO2reaction’s product) and just imidazole in the other part.Unfortunately the high viscosity of ionic liquids affects a lot the carrier transport and consequentlythe device’s performance too; this aspect worsens when imidazole reacts with CO2. Improved ionmobility is achieved by reducing the ion pairing through the use of high dielectric solvents capableto screen the ions’ electric field. Polar aprotic solvents tend to have large dipoles making themsuitable for the solvation of charged species.Several mixtures have been analyzed to detect the best dilution which guarantees high ionic mobilitystill maintaining a large amount of active species.A further performance improvement has been achieved through the engineering of the electrodes,namely the capacitance of the supercapacitor has been enhanced by exploiting the huge specificsurface area of the activated carbon.The results show that all the upgrades mentioned lead to an improvement of 500 times in terms ofharvested energy.Acknowledgement: This result is part of a project that has received funding from the European Research Council(ERC) under the European Union’s ERC Starting Grant Grant agreement No. 949916 Figure 1

Construction of activated-CNT/carbon composite aerogel for supercapacitor electrode with ultra high cycle stability

Double layer supercapacitors are widely used for energy storage devices due to their excellent characteristics such as high stability and good cycling performance. In this work, a novel carbon aerogel doped with activated short multi-walled carbon nanotube (CA/AMWCNT composite aerogel) was constructed by sol-gel and carbonization process. The effects of the activated short multi-walled carbon nanotube (AMWCNT) addition amount on the microstructure and electrochemical properties of the composite aerogels were investigated. The composite aerogels with appropriate AMWCNT addition amount exhibited improved specific surface area, pore diameter and pore volume. In particular, the composite aerogel CA/AMWCNT-2.5, with higher specific surface area (640 m2 g−1) and pore volume (1.985 cm3 g−1), exhibited improved electrochemical performance with the equivalent series resistance and specific capacitance at a current density of 1 A g−1 being 0.36 Ω and 115.11 F g−1, respectively. Moreover, the composite aerogel CA/AMWCNT-2.5 electrode showed excellent cycle stability, with the retention rate maintaining 99.9 % even after 10,000 cycles, and three prepared symmetrical supercapacitors could supply power for a light emitting diode bulb for a long time. This work provides a new strategy for developing electric double layer supercapacitors with ultra high cycling stability, and the obtained CA/AMWCNT composite aerogels will have promising applications in the field of energy storage devices that require a long service lifetime.

KCl-assisted activation of macadamia nut shell-derived carbon: Unveiling enhanced pore structure, adsorption and supercapacitor performance

A novel and efficient strategy, known as one-step pyrolysis with KCl-assisted K2C2O4 activation of biomass, was employed in the preparation of porous carbon derived from macadamia nut shells. Our aim was to analyze the alterations in material morphology and pore structure during the process of KCl-assisted activation. The addition of KCl during activation introduced additional mesopores and narrow micropores, resulting in a hierarchical pore structure. Compared to activation without KCl, the specific surface area increased by 50.7% and the pore content increased by 54.5%. We further investigated the evolution of the pore structure and activation mechanism during KCl-assisted activation. Among the tested samples, K3K5 showed the best adsorption performance with 6.48 and 4.11 mmol/g at 0 and 25 °C, respectively. In our study on the adsorption properties of CO2, we found that the narrow micropores are the primary factor influencing CO2 adsorption. Additionally, nonlinear fitting of adsorption isotherms indicated that the adsorption process followed a multilayer physisorption mechanism. We also explored the effects of KCl-assisted activation on the adsorption process. Furthermore, we evaluated the electrochemical properties of the activated carbon and determined that it functioned as a capacitance-controlled electric double-layer supercapacitor, with a specific capacitance of 279.3F/g at 0.5 A/g. We investigated the effects of KCl-assisted activation on specific capacitance, rate performance, and conductivity. This research provides valuable insights into the environmentally friendly synthesis of efficient CO2 adsorbents and energy storage materials.

Quantum capacitance engineering in boron and carbon modified monolayer phosphorene electrodes for supercapacitor application: A theoretical approach using ab-initio calculation

In this work, for the first time, the effects of Boron (B) and Carbon (C) substitutional doping/co-doping on the quantum capacitance of monolayer Phosphorene (Ph) have been extensively investigated for electrode design of electrical double-layer (EDL) supercapacitor. In this context, the effects of different doping concentrations on local charge distribution, energy band structure, and density of states have been systematically correlated with the quantum capacitance variation with local electrode potential. In pristine Ph, the presence of a large energy bandgap and the absence of states therein severely compromise the quantum capacitance at lower electrode potential compared to pristine Graphene (Gr). The B and C both act as acceptor-type impurities in Ph and tend to shift the Fermi level towards the valence band edge. Specifically, the introduction of B-doping induces localized defect states near the conduction band edges. This leads to a moderate improvement in quantum capacitance for a relatively larger electrode potential. In contrast, the C doping and B/C co-doping introduce de-localized defect states around the Fermi level near the valence band edges, which ensures a significantly larger quantum capacitance compared to pristine Gr and Ph over the range of −1.0 V to 1.0 V electrode potential.

Expanded Carbon Nanotube Fiber at the Liquid-Air Interface for High-Performance Fiber-Based Supercapacitors and Electrochemical Sensors.

Carbon nanotube fibers (CNTFs) are widely utilized in flexible and wearable electronics due to their outstanding electrical and mechanical properties. However, the spinning process of CNTFs has limited the CNTs from exposure, leading to an ultralow usage efficiency of individual CNTs. Here, we propose an electrochemical expansion strategy of a single CNTF at the liquid-air interface, forming a macroscopic spindle-shaped CNTF (SS-CNTF) with an enlarged volume of up to 5000-fold upon the spindle. The obtained spindle-shaped structure endows CNTF with a high specific surface area together with excellent conductivity and good mechanical properties. Therefore, the SS-CNTF-based devices exhibit outstanding performances both in energy storage (electrical double-layer supercapacitor, energy density: 11.22 Wh kg-1, power density: 203.9 kW kg-1) and electrochemical sensing (ascorbic acid: 1.26 μA μM-1 cm-2; dopamine: 103.91 μA μM-1 cm-2; uric acid: 11.53 μA μM-1 cm-2). The novel architecture of SS-CNTF prepared by one-step electrochemical expansion at the liquid-air interface enabled its high performance in multiple applications, providing new insight into the development of CNTF-based devices.

Erythritol-strengthen electrolytes effectively improve the electrochemical stability window of aqueous symmetric supercapacitor

Due to the advantages of high safety, high conductivity and low cost, the supercapacitor with aqueous electrolytes exhibits the great prospects in the future energy storage market. However, the narrow electrochemical stability window (ESW) of electric double-layer supercapacitor leads to its low energy density, which seriously limits its application. Herein, we demonstrate erythritol (Et) additive could efficaciously decrease the water molecules in the solvation sheath and break the hydrogen bond network of aqueous electrolytes, which resulting in expanded ESW. Especially, symmetric supercapacitor based on 37.9% Et additive to 1 M LiTFSI electrolyte expands ESW from 1.8 to 2.1 V, and the energy density increased to 13.3 Wh kg−1 with high specific capacitance of 86.6F g−1 and the capacitance retention rate of 73.8% after 10,000 cycles. Therefore, this study affords an efficient strategy to achieve high energy density aqueous supercapacitor.

Development of supercapacitor hybrid electric vehicle

Hybrid electric vehicle needs dedicated energy storage system suitable for its special operating conditions. The nickel-metal hydride batteries and lithium-ion batteries dominate this market, but they also have some drawbacks. The electric double layer supercapacitors have been employed in passenger vehicles, but the drawbacks of those supercapacitors prevent them from the application of energy storage system for hybrid electric vehicles. A technical route of hybrid supercapacitor-based energy storage systems for hybrid electric vehicles is proposed, this kind of hybrid supercapacitor battery is composed of a mixture of supercapacitor materials and lithium-ion battery materials. We developed a supercapacitor battery cell dedicated for energy storage system of hybrid electric vehicles. The advantages of those supercapacitor cells are low cost, long life cycle, high safety, wide working temperature range, high power density and high energy density. The supercapacitor battery pack and supercapacitor hybrid electric vehicle with the developed supercapacitor cells showed great performance improvements.

Fomes fomentarius as a Bio-Template for Heteroatom-Doped Carbon Fibers for Symmetrical Supercapacitors

Nowadays, commercial electric double-layer supercapacitors mainly use porous activated carbons due to their high specific surface area, electrical conductivity, and chemical stability. A feature of carbon materials is the possibility of obtaining them from renewable plant biomass. In this study, fungi (Fomes fomentarius) were used as a bio-template for the preparation of carbon fibers via a combination of thermochemical conversion approaches, including a general hydrothermal pre-carbonization step, as well as subsequent carbonization, physical, or chemical activation. The relationships between the preparation conditions and the structural and electrochemical properties of the obtained carbon materials were determined using SEM, TEM, EDAX, XPS, cyclic voltammetry, galvanostatic measurements, and EIS. It was shown that hydrothermal pretreatment in the presence of phosphoric acid ensured the complete removal of inorganic impurities of raw fungus hyphae, but at the same time, saved some heteroatoms, such as O, N, and P. Chemical activation using H3PO4 increased the amount of phosphorus in the carbon material and saved the natural fungus’s structure. The combination of a hierarchical pore structure with O, N, and P heteroatom doping made it possible to achieve good electrochemical properties (specific capacitance values of 220 F/g) and excellent stability after 25,000 charge/discharge cycles in a three-electrode cell. The electrochemical performance in both three- and two-electrode cells exceeded or was comparable to other biomass-derived porous carbons, making it a prospective candidate as an electrode material in symmetrical supercapacitors.

Molecular insights into the electric double-layer structure at a polymer electrolyte-electrode interface

Polymer electrolyte-based electric double-layer supercapacitors (EDLCs) have been increasingly studied for flexible, wearable, and multifunctional energy storage applications. Although the phenomenon that electrode materials present significantly lower EDL capacitances in polymer electrolytes than in liquid electrolytes has been widely observed, it has not been well studied and explained. Here we present the molecular dynamics simulation of a representative polymer electrolyte-based EDLC to reveal the atomic structure of such a polymer electrolyte-electrode interface for the first time. The polymer electrolyte composed of polyethylene oxide and lithium perchlorate is simulated between graphene electrodes and compared with an aqueous electrolyte-based system with the same lithium salt. We find that the polymer-based system shows unique EDL structures in the inner and outer Helmholtz layers that are not seen in the aqueous one. Statistical analyses along with ab initio calculations show that the disparities mainly come from the different interaction strengths between ions, polymer or water molecules, and graphene electrodes. Despite these disparities, the intrinsic interfacial capacitances calculated from various simulated charge states of different EDLCs show very close values. Combined with experimental measurements, we conclude that the reduced capacitances with polymer electrolytes reported in the literature come from the poor interface between electrode and electrolyte, which can be significantly improved through proper thermal treatments.

Lignin-derived electrode materials for supercapacitor applications: progress and perspectives

Lignin is one of the most abundant natural polymers and is affordable, has high carbon content and abundant active functional groups. It has been utilized as electrode materials in electrical double-layer supercapacitors and pseudo-supercapacitors.

Effect of modulation by adsorption and doping on the quantum capacitance of borophene.

Electric double-layer supercapacitors (EDLCs) have attracted much attention in the energy storage field due to their advantages such as high output power, long service life, safety and high efficiency. However, their low energy density limits their application. Aiming at the problem of the low energy density of EDLCs, improving quantum capacitance (CQ) of electrode materials is an effective strategy. In this paper, we systematically studied the effects of vacancy, doping, and metal atom adsorption on the CQ of borophene using first-principles calculations. The results show that S and N doping greatly enhance the charge accumulation of borophene at positive and negative potential, respectively. The maximum CQ values of S-doped and N-doped borophene are 157.3 μF cm-2 (0.38 V) and 187.8 μF cm-2 (-0.24 V), respectively. Both of them can serve as ideal candidates for the positive (S-doped one) and negative (N-doped one) electrodes of EDLCs. Besides, metal Al atom-adsorbed borophene can also effectively enhance the CQ, with a maximum value of 109.1 μF cm-2.

A MXene-BiFeO3-ZnO nanocomposite photocatalyst served as a high-performance supercapacitor electrode.

MXenes have attracted considerable attention in the field of energy storage and conversion due to their high surface area, excellent electrical conductivity, and ability to intercalate various ions. However, simultaneously achieving high capacitance, rate capability, cycling stability, and mechanical flexibility is a significant challenge for designing MXene-based supercapacitors. In this article, we explored MXene-BiFeO3-ZnO nanocomposites for both photocatalytic and electric double-layer supercapacitor applications. While the BiFeO3-ZnO nanohybrid heterostructure improves the charge separation properties in nanocomposite photocatalysts, it was applied as an interlayer spacer between the MXene layers to prevent the stacking effect of electrodes in the supercapacitor. Furthermore, the optimization of MXene content in the nanocomposite was established by photocatalytic studies on methylene blue dye, which revealed a maximum of 98.72% degradation under direct sunlight with superior stability. The electrochemical studies on the best composition material reveal a maximum areal capacitance (Ccv) of 142.8 mF cm-2, an energy density (E) of 1.65 μW h cm-2, and a capacitive retention of 99.98% after 8000 cycles at 7 μA cm-2. Additionally, the flexible solid-state supercapacitor fabricated with the same material demonstrates an areal capacitance of 47.6 mF cm-2 and a capacitive retention of 66% after 8000 cycles at 7 μA cm-2, with potential for high-performance flexible supercapacitors.

From energy storage to pathogen eradication: unveiling the antibacterial and antiviral capacities of flexible solid-state carbon cloth supercapacitors.

With the emergence of deadly viral and bacterial infections, preventing the spread of microorganisms on surfaces has gained ever-increasing importance. This study investigates the potential of solid-state supercapacitors as antibacterial and antiviral devices. We developed a low-cost and flexible carbon cloth supercapacitor (CCSC) with highly efficient antibacterial and antiviral surface properties. The CCSC comprised two parallel layers of carbon cloth (CC) electrodes assembled in a symmetric, electrical double-layer supercapacitor structure that can be charged at low potentials between 1 to 2 V. The optimized CCSC exhibited a capacitance of 4.15 ± 0.3 mF cm-2 at a scan rate of 100 mV s-1, high-rate capability (83% retention of capacitance at 100 mV s-1 compared to its value at 5 mV s-1), and excellent electrochemical stability (97% retention of the initial capacitance after 1000 cycles). Moreover, the CCSC demonstrated outstanding flexibility and retained its full capacitance even when bent at high angles, making it suitable for wearable or flexible devices. Using its stored electrical charge, the charged CCSC disinfects bacteria effectively and neutralizes viruses upon surface contact with the positive and negative electrodes. The charged CCSC device yielded a 6-log CFU reduction of Escherichia coli bacterial inocula and a 5-log PFU reduction of HSV-1 herpes virus. Antibacterial and antiviral carbon cloth supercapacitors represent a promising platform technology for various applications, including electronic textiles and electronic skins, health monitoring or motion sensors, wound dressings, personal protective equipment (e.g., masks) and air filtration systems.

Boosting the crystallinity of novel two-dimensional hexamine dipyrazino quinoxaline-based covalent organic frameworks for electrical double-layer supercapacitors

A novel and conjugated 2D 250-HADQ COF exhibits a high specific surface area and excellent thermal stability yielding high values of gravimetric capacitance and energy density in two-electrode double-layer supercapacitor cells.

Pore structure regulation of hierarchical porous agaric-derived carbon via boric acid activation for supercapacitors

The development of sustainable carbon materials from biomass for electric double-layer supercapacitors is a promising solution to alleviate energy and environmental pressures. The electrochemical performance of biomass-derived carbon materials is greatly affected by their hierarchical porous structure. In general, the pore structure of biomass-derived carbon activated using chemical method is dominated by micropores with few mesopores. This hinders the transmission of electrolyte ions, thus limiting the electrochemical properties. Here we have designed a green unique boric acid-assisted method to synthesize hierarchical porous agaric-derived carbon. Benefiting from the unique hygroscopic recovery characteristics of agaric, boric acid can enter the interior of the agaric and act as a novel activator to effectively adjust the pore structure of porous carbon. During the carbonization process, the melted boron oxide with high viscosity and excellent wetting properties adheres to the agaric matrix as a template, which plays a key factor for increasing the mesopores (<4 nm) and promoting ions transport. The synthesized porous carbon has a high specific surface area (2279.5 cm 2 g −1 ), more reasonable hierarchical porous structure, abundant nitrogen atom doping (4.69 at.%) and high capacitance (502 F g −1 @ 0.5 A g −1 ). The symmetric supercapacitor tested in 1 M Na 2 SO 4 electrolyte has excellent performances. This optimization strategy provides a new idea to design more reasonable hierarchical porous biomass-derived carbon materials. • Synthesis of agaric-derived carbon using a green method of boric acid-assisted • The etching of boric acid increases pores in 1–4 nm. • Superior design of hierarchically porous structure promotes ions transport. • N-doped agaric-derived carbon has an excellent specific capacitance of 502 F g −1 .

Internally-externally molecules-scissored ramie carbon for high performance electric double layer supercapacitors

Ramie carbon from the massively three-harvests-one-year and naturally channel-structured ramie straw is typically emerging as the excellent waste-biomass-utilization target toward high-performance electrochemical energy storage devices. However, the traditional activation strategies less fully optimize the pore distribution for the purpose of optimal energy storage capability. Herein, we reported the hierarchically interconnected three-dimensional ramie porous carbon based on waste ramie straw by internally-externally molecules-scissored activation strategy with pre-embedded KOH and re-added KOH molecules coordinately (in-ex-RPC). Benefiting from the synergistically internal-external activation strategy, this in-ex-RPC displays an excellent specific capacitance of 300 F g–1, which is much better than that of ramie porous carbon singly through pre-embedded KOH activation (in-RPC, 194 F g–1) or directly adding KOH activation (ex-RPC, 213 F g–1). Based on it, the aqueous symmetric supercapacitors display a cyclic capacity of 90.9%-retaining after 20,000 cycles at 5 A g–1. Therefore, this work may provide an effective strategy for energy storage applications of waste ramie straw and for further promoting waste biomass utilization.