Cube Fe3O4 nanoparticles embedded in three-dimensional net porous carbon from silicon oxycarbide for high performance supercapacitor

The porous structural tailoring of polyacrylonitrile-based carbon materials is the key to maximize capacitive performance. Herein, hierarchical porous carbons (HPC) with high specific surface area and controllable porosity are synthesized by preoxidation assisted alkali activation strategy using polyacrylonitrile as the precursor. The results show that high preoxidation temperature is beneficial to increase the specific surface area and pore volume of HPC. The optimized HPC-300 has a high BET specific surface area of 3161 m2 g-1, a micropore volume of 1.45 cm3 g-1, and an AD/AG of 3.56. Electrochemical test shows that the specific capacitances of HPC-300 in 6 M KOH electrolyte at 1 A g-1 and 10 A g-1 are 314.1 F g-1 and 213.0 F g-1, respectively, with a capacitance retention of 67.8 %. The assembled supercapacitors based on HPC-300 deliver an energy density of 11.7 Wh kg-1 at a power density of 250.0 W kg-1 in KOH electrolyte and 21.1 Wh kg-1 at 450.0 W kg-1 in Na2SO4 electrolyte and possess a capacitance retention of 98.1 % over 20,000 charge-discharge cycles. This preoxidation coupled activation method provides a potential strategy for the preparation of PAN-based porous carbon with high specific surface area and capacitance.

Facile synthesis of three-dimensional porous carbon for high-performance supercapacitors

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

This research work aims to explore the potential usage of post-consumer waste expanded polystyrene (EPS) for the fabrication of self-standing electrodes by incorporating reduced graphene oxide (rGO) into it via a facile cost-effective mechanical mixing process. The π-π interaction between the expanded polystyrene and rGO is evidenced from FT-IR and Raman analysis. The elevated thermal stability of the EPS/rGO composite from thermogravimetric analysis (TGA) further confirms the interconnection between the rGO and EPS. This π-π stacking interaction between the rGO and the polystyrene molecules present in the polymer matrix enable the composite material to be interconnected throughout which is beneficial for the charge transport process. The symmetric coin cell supercapacitor fabricated using the EPS/rGO composite electrode can be operated with a high operating voltage of 1.6 V in aqueous KOH and Na2SO4 electrolytes. The devices fabricated with KOH and Na2SO4 electrolytes deliver an areal capacitance of 11.9 mF cm-2 and 10 mF cm-2 at the discharge current density of 0.1 mA cm-2. Further, the devices fabricated with the KOH and Na2SO4 electrolytes demonstrated remarkable rate capability of 87.1% and 99.5% after 10 000 continuous charge discharge cycles. This facile method of preparation without consuming energy or polluting the environment is a novel approach which can be scaled-up to large-scale fabrication of self-standing plastic electrodes for low-cost energy storage applications.

Electrochemical performance of polyacrylamide hydrogel based nitrogen-doped porous carbon for supercapacitor

Porous carbon has been one desirable electrode material for supercapacitors, but it is still a challenge to balance the appropriate mesopore volume and a high specific surface area (SSA). Herein, a good balance between a high SSA and mesopore volume in biomass-derived porous carbon is realized by precarbonization of wheat husk under air atmosphere via a chloride salt sealing technique and successive KOH activation. Due to the role of molten salt generating mesopores in the precarbonized product, which can further serve as the active sites for the KOH activation to form micropores in the final carbon material, the mesopore–micropore structure of the porous carbon can be tuned by changing the precarbonization temperature. The appropriate amount of mesopores can provide more expressways for ion transfer to accelerate the transport kinetics of diffusion-controlled processes in the micropores. A high SSA can supply abundant sites for charge storage. Therefore, the porous carbon with a good balance between the SSA and mesopores exhibits a specific gravimetric capacitance of 402 F g−1 at 1.0 A g−1 in a three-electrode system. In a two-electrode symmetrical supercapacitor, the biomass-derived porous carbon also delivers a high specific gravimetric capacitance of 346 F g−1 at 1.0 A g−1 and a good cycling stability, retaining 98.59% of the initial capacitance after 30,000 cycles at 5.0 A−1. This work has fundamental merits for enhancing the electrochemical performance of the biomass-derived porous carbon by optimizing the SSA and pore structures.

Rational design and synthesis of high-efficient and cost-effective electrode materials are pivotal for developing high performance supercapacitors. Herein, we synthesized N, O, co-doped hierarchical porous carbon fibers (NPCFs) towards high performance symmetric supercapacitor with N-rich cocoon silk as precursor via an alkali activation and a g-C3N4 mediated strategy. By adjusting the addition of g-C3N4, the N doping content and pore structures can be regulated, and the optimized material NPCF1 (mass ratio, primary char CF: g-C3N4 = 1:1) exhibits high N doping content (6.05%) with domination of active pyridinic-N pyrrolic-N, and more abundant pores as well as higher specific surface area (2643.75 m2 g−1). Meanwhile, NPCF1 as supercapacitor electrode can deliver high specific capacitance of 392 F g−1 at 1 A g−1 and excellent rate performance (222 F g−1 at 20 A g−1) in 6 M KOH. More impressively, NPCF assembled symmetric supercapacitor with 1.0 M neutral Na2SO4 electrolyte can still achieve a high operating voltage of 1.8 V, an outstanding energy density of 20.77 W h kg−1 at a power density of 450 W kg−1. Such universal small molecule nitrogen source-mediated strategy may inspire new progress of synthesizing advanced carbons for energy-related application.

Facile preparation of porous carbons derived from orange peel via basic copper carbonate activation for supercapacitors

Enzymatic hydrolysis lignin (EHL) is a common biomass that is difficult to use for the synthesis of porous carbon (PC) via direct microwave heating because it absorbs very little microwave energy. In this study, a novel method was developed to synthesize high‐performance PC directly from EHL using only 8 min of microwave heating. The resulting PC exhibits a high specific surface area of 2482 m2 g−1 and a hierarchical pore distribution with a high mesopore content of 35.6 % and oxygen content of 17.1 %. Nitrogen (as a protecting gas) passes through water molecules provided by steam to absorb microwave energy and acts as a physical porogen to form mesopores. Using solid KOH allows one to bypass the time‐consuming drying process and generate sufficient micropores. Additionally, fast self‐pyrolysis and a high heating rate lead to the generation of both mesopores and macropores in a PC framework. Furthermore, multiple active centers can be formed during microwave heating and subsequently stabilized by oxidation once the PC is exposed to an air atmosphere, resulting in the attachment of oxygen functional groups to the PC surface. Based on these desirable physicochemical characteristics, the PC electrodes fabricated in this study exhibit a high specific capacitance of 338 F g−1 at 1 A g−1 and high capacitance retention of 86 % at 10 A g−1. The final PC‐based supercapacitor delivers a maximum energy density of 17.1 Wh kg−1 in a Na2SO4 electrolyte and 8.6 Wh kg−1 in a KOH electrolyte.

A mild method to prepare nitrogen-rich interlaced porous carbon nanosheets for high-performance supercapacitors

We introduce a facile integrated oxidation polymerization and catalytic carbonization method to prepare three-dimensional porous nitrogen-doped carbon networks (3D N-CNWs) with high nitrogen content (about 8.4 wt %) directly from poly(p-phenylenediamine). In the synthesis process, the FeCl3 serves not only as an oxidant for oxidative polymerization of p-phenylenediamine monomers but also as the carbonization catalyst to promote porous carbon network formation. The 3D N-CNWs prepared at 700 °C exhibit an interconnected porous framework with high specific surface area and show remarkable performance as an electrode material for supercapacitors. The maximum specific capacitance of 304 F g–1 at a current density of 0.5 A g–1, which retains the high values of 226 F g–1 even at a high current density of 20 A g–1, is obtained for the N-CNW electrode in 6 M KOH aqueous solution. Moreover, the as-assembled N-CNW symmetric supercapacitor exhibits a considerably high energy density of 15.8 Wh kg–1 at a power density...

This investigation addresses increasing interest in advanced composite materials, combining capacitive properties and spontaneous magnetization for energy storage applications in supercapacitors. The capacitive properties of ferrimagnetic NiFe2O4 (NFO) spinel nanoparticles with magnetization of 30 emu g−1 were enhanced using high-energy ball-milling and the use of advanced dispersant, which facilitated charge transfer. NFO electrodes with an active mass of 40 mg cm−2 showed a capacitance of 1.46 F cm−2 in 0.5 M Na2SO4 electrolyte in a negative potential range. The charging mechanism in the negative potential range in Na2SO4 electrolyte was proposed. NFO was combined with conductive polypyrrole polymer for the fabrication of composites. The analysis of the capacitive behavior of the composites using cyclic voltammetry, chronopotentiometry and impedance spectroscopy at different electrode potentials revealed synergy of contributions of NFO and PPy. The highest capacitance of 6.64 F cm−2 was obtained from cyclic voltammetry data. The capacitance, impedance, and magnetic properties can be varied by variation of electrode composition. Composite electrodes are promising for application in anodes of asymmetric magnetic supercapacitors for energy storage and magnetically enhanced capacitive water purification devices.

A comparative investigation of normal and stripping forms of voltammetry was undertaken at single and random array microdisc, macrodisc and composite carbon electrodes using dc, derivative dc, square-wave and differential-pulse waveforms. Studies on the reduction of [Fe(CN)6]3– in 0.05 M KNO3 revealed that the dc waveform with derivative readout is superior to the use of square-wave or differential-pulse waveforms at both single disc and random array carbon fibre electrodes. Analytical superiority to that obtained at a conventional glassy carbon macrodisc electrode was also observed. The detection limit for the determination of [Fe(CN)6]3– was 4 × 10–6 M at the carbon fibre random array microdisc electrode and 6 × 10–6 M when using a single disc microelectrode (scan rate = 200 mV s–1). For the determination of Pb and Cd in 0.1 M HCl by stripping voltammetry, the ideal combination of high sensitivity (1 ppb detection limit), avoidance of the need to remove oxygen or utilise solution stirring or electrode rotation could be achieved at mercury-plated thin film single disc or random array microelectrodes or composite electrodes. Furthermore, under these thin film conditions, the analytical performance of each of these three electrode types improved with respect to signal-to-background current ratio as the scan rate increased. Consequently, short potential scanning times as well as optimum sensitivity are achieved with scan rates in the 1–50 V s–1 range. All of the results obtained demonstrate that highly sensitive field-based voltammetric analysis may be accomplished using the combination of an inherently simple two-electrode battery operated instrument, the dc waveform and random array or single carbon fibre microdisc working electrodes. An interface which enables voltammetric studies to be undertaken with a battery operated personal computer is described for this purpose.

Single-pot hydrothermal synthesis of manganese phosphate microrods as a cathode material for highly stable flexible solid-state symmetric supercapacitors

One-step fabrication of N/O self-doped porous carbon derived from 2-MeIM for high-performance supercapacitor electrode