Nitrogen-enriched porous carbon nanofiber networks for binder-free supercapacitors obtained by using a reactive surfactant as a porogen

Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm3 g-1) and specific surface area (1162 m2 g-1), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g-1 @ 1 A g-1 and a high capacitance retention of 62.7 % @ 80 A g-1. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg-1 @ 250 W kg-1. Moreover, the sample still exhibits a specific capacitance of 165 F g-1 @ 1 A g-1 at a high mass loading of 10 mg cm-2, resulting in a high areal capacitance of 1.65 F cm-2. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.

Preparation of N/O co-doped porous carbon by a one-step activation method for supercapacitor electrode materials

Heteroatom-doped carbon materials used in supercapacitors are low in cost and demonstrate extraordinary performance. Here, ethylenediamine tetraacetic acid (EDTA) with intrinsic N and O elements is selected as a raw material for the preparation of heteroatom self-doped porous carbon. Furthermore, N/O self-doped porous carbon with a large surface area has been successfully prepared using K₂CO₃ as the activator. The derived sample with a 1 : 2 molar ratio of EDTA to K₂CO₃ (EK-2) demonstrates a porous structure, rich defects, a large surface area of 2057 m² g⁻¹ and a micropore volume of 0.25 cm³ g⁻¹. Benefiting from high N content (2.89 at%) and O content (10.75 at%), EK-2 exhibits superior performance, including high capacitance of 325 F g⁻¹ at 1 A g⁻¹ and outstanding cycling stability with 96.8% retention after 8000 cycles at 10 A g⁻¹, which strongly confirms its immense potential toward many applications. Additionally, the maximum energy density of EK-2 reaches was 17.01 W h kg⁻¹ at a power density of 350 W kg⁻¹ in a two-electrode system. This facile and versatile strategy provides a scalable approach for the batch synthesis of N/O co-doped carbonaceous electrode materials for energy storage.

Heteroatom-doped carbon materials used in supercapacitors are low in cost and demonstrate extraordinary performance.

Key issues facing electrospun carbon nanofibers in energy applications: on-going approaches and challenges

Electrospun carbon nanofibers (CNFs), with one-dimensional (1D) morphology, tunable size, mechanical flexibility, and functionalities by themselves and those that can be added onto them, have witnessed the intensive development and extensive applications in energy storage and conversion, such as supercapacitors, batteries, and fuel cells. However, conventional solid CNFs often suffer from a rather poor electrical conductivity and low specific surface area, compared with the graphene and carbon nanotube counterparts. A well-engineered porous structure in CNFs increases their surface areas and reactivity, but there is a delicate balance between the level and type of pores and mechanical robustness. In addition, CNFs by themselves often show unsatisfactory electrochemical performance in energy storage and conversion, where, to endow them with high and durable activity, one effective approach is to dope CNFs with certain heteroatoms. Up to now, various activation strategies have been proposed and some of them have demonstrated great success in addressing these key issues. In this review, we focus on the recent advances in the issue-oriented schemes for activating the electrospun CNFs in terms of enhancing the conductivity, modulating pore configuration, doping with heteroatoms, and reinforcing mechanical strength, in close reference to their applications in supercapacitors. The basic scientific principles involved in these activation processes and their effectiveness in boosting the electrochemical performance of CNFs are examined. Finally, some of the on-going challenges and future perspectives in engineering CNFs for better performance are highlighted.

Nacre-like laminate nitrogen-doped porous carbon/carbon nanotubes/graphene composite for excellent comprehensive performance supercapacitors

A nitrogen-doped porous carbon/carbon nanotubes/graphene (PGMC) composite was prepared through a process of hydrothermal treatments, polymerization of o-phenylenediamine (OPD), and pyrolysis. The as-prepared PGMC composite was found to be of a nacre-like laminate porous structure, constructed with alternatively stacked two-dimensional (2D) graphene sheets and porous carbons, and also interspersed within one-dimensional (1D) multi-walled carbon nanotubes (MWNTs). The MWNTs effectively suppressed agglomeration of graphene sheets during the hydrothermal process and were interspersed in PGMC to help construct more networks with excellent conductivity. The PGMC possessed an enriched nitrogen doping ratio of 15.67 at% and relative high density of 1.39 g cm-3. The electrode composed of PGMC provided high gravimetric capacitance of 562.9 F g-1 and volumetric capacitance of 782.4 F cm-3 at current density of 1 A g-1, as well as excellent rate capability and cycling stability. The symmetric supercapacitors mounted with the as-prepared PGMC electrode were stably operated in a wide potential range of 0-1.3 V and demonstrated a superb gravimetric energy density of 19.79 W h kg-1 at high power density of 650 W kg-1, and a high volumetric energy density of 27.51 W h L-1 with a power density of 904 W L-1. The outstanding electrochemical performance enables this as-prepared nacre-like laminate PGMC composite to be a promising candidate for energy storage application.

Electrospinning preparation of a large surface area, hierarchically porous, and interconnected carbon nanofibrous network using polysulfone as a sacrificial polymer for high performance supercapacitors

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization. Addition of PSF as a sacrificial polymer leads to CNFMs with high surface area, large numbers of micropores and mesopores, good degree of carbonization, and interconnected fibrous network, due to the high decomposition temperature, release of SO₂ during decomposition, and large amount of carbon residue of PSF during carbonization. The electrochemical characterization shows that the CNFM electrode has a specific capacitance of 272 F g⁻¹ at a current density of 1 A g⁻¹ with 74% of the specific capacitance retained at 50 A g⁻¹ in 2.0 M KOH electrolyte. The CNFM electrodes have excellent cycling durability with 100% capacitance retention after 10 000 cycles.

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization.

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage

Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.

Dendritic unzipped carbon nanofibers enable uniform loading of surfactant-free Pd nanoparticles for the electroanalysis of small biomolecules

Illustration of the mechanisms of SCNF and preparation of Pd/GNF composites and Pd/GNF sensors for the simultaneous determination of small biomolecules.

Fabrication of N-doped and shape-controlled porous monolithic carbons from polyacrylonitrile for supercapacitors

N-doped and shape-controlled porous monolithic carbon (PMC) was easily fabricated and displayed excellent electrochemical performance as an electrode for supercapacitors.