Facile in Situ Synthesis of Multiple-Heteroatom-Doped Carbons Derived from Polyimide Precursors for Flexible All-Solid-State Supercapacitors

Effective approaches to co-dope lignin based concave shaped carbon nanofibers with multiple elements for supercapacitors

High-value utilization of lignin to fabricate carbon nanofibers for supercapacitors has drawn much attention due to its sustainability. However, the heterogeneity of crude lignin structure led to the comparatively poor performance of lignin-based carbon nanofibers (LCNF) as electrodes in supercapacitors. Herein, flexible and porous LCNF simultaneously doped with N, S and Zn were firstly synthesized by electrostatic spinning followed by carbonization. The obtained L-NS20-Zn15 fibers showed optimum specific capacitance of 328.6 F g-1 at current density of 0.5 A g-1 in the three-electrode system. The assembled supercapacitor exhibited specific capacitance of 46.8 F g-1 at current density of 0.5 A g-1, and energy density of 25.8 W h kg-1 with power density of 200 W kg-1, which outperformed most of the reported LCNF-based materials. After 3000 charge-discharge cycles, the capacitance retention remained 86 % of the initial value. The remarkable electrochemical performance supports the use of co-doped lignin as a promising material for energy storage.

Dual heteroatoms doped SBA-15 templated porous carbon for symmetric supercapacitor in dual redox additive electrolyte

Porous carbon (PC) based materials is a proficient impetus for upgrading supercapacitor thanks to its traits of high surface area, meso, micropores, and replication morphology. Mainly, single and dual heteroatom doping in PC material is one of the amazing strategies for enhancing the supercapacitor activity due to the interaction of carbon and heteroatom material along with the excessive contribution of by functional groups. Here, we have synthesized nitrogen (N) and boron (B) dual doped PC (NBPC) with the assistance of Santa Barbara Amorphous (SBA-15) silica material and afterward investigated their doping impact of the heteroatom which is investigated for supercapacitor application. Among all, NBPC material delivered a high specific capacitance of 375 F/g at 2 A/g current density in 1 M H₂SO₄ electrolyte with excellent rate capability and capacitance retention. Such an attractive property of NBPC is a reflection of its high specific surface area (809 m²/g) rendered by N and B functional groups. In addition, the introduction of dual redox additive materials to the electrolyte synergistically enhanced the specific capacity of the symmetric supercapacitor cell. An unprecedented high specific capacity of 929 C/g at 3 A/g current density is observed and a 56% of initial specific capacity was retained when current density increased to 20 A/g. The fabricated symmetric cell using NBPC electrode in 1 M H₂SO₄ + 0.01 M ammonium metavanadate + Ferrous (II) sulfate dual redox additive electrolyte delivered an energy density of 48.4 W h/kg which is five folds higher than the bare electrolyte (10.1 W h/kg). Similarly, the NBPC electrode delivered a power density of 15 kW/kg in the redox additive electrolyte which is three folds higher than the bare electrolyte (5 kW/kg).

High-performance supercapacitor based on highly active P-doped one-dimension/two-dimension hierarchical NiCo2O4/NiMoO4 for efficient energy storage

Multi-dimensional metal oxides have become a promising alternative electrode material for supercapacitors due to their inherent large surface area. Herein, P-doped NiCo₂O₄/NiMoO₄ multi-dimensional nanostructures are synthesized on carbon clothes (CC) with a continuous multistep strategy. Especially, P has the best synergistic effect with transition metals, such as optimal deprotonation energy and OH^- adsorption energy, which can further enhance electrochemical reaction activity. For the above reasons, the P-NiCo₂O₄/NiMoO₄@CC electrode exhibits an ultra-high specific capacitance of 2334.0 F g^-1 at 1 A g^-1. After 1500 cycles at a current density of 10 A g^-1, its specific capacity still maintains 93.7%. Besides, a P-NiCo₂O₄/NiMoO₄@CC//activated carbon device (hybrid supercapacitor or device) was also prepared with a maximum energy density of 45.1 Wh kg^-1 at a power density of 800 W kg^-1. In particular, the capacity retention rate is still 89.97% after 8000 cycles due to its excellent structural stability. Our work demonstrates the vast potential of multi-dimensional metal oxides in energy storage.

Three-dimensional tellurium and nitrogen Co-doped mesoporous carbons for high performance supercapacitors

Tellurium-doped mesoporous carbon composite materials (Te/NMC) have been prepared by a facile intercalation method in the presence of nitrogen-doped mesoporous carbon (NMC) with tellurium powder, for the first time. The effects of the co-doped N and Te in the mesoporous carbon matrix on the physical/chemical properties and capacitance performances were investigated via the use of various characterization methods and electrochemical studies. The as-prepared NMC and Te/NMC materials were found to mainly be composed of mesopores and maintained the 3D hierarchical graphite-like structure with lots of defect sites. By intercalation of Te atoms into the NMC materials, 2.12 at% (atom%) of Te was doped into NMC and the specific surface area of Te/NMC (261.07 m2 g-1) decreased by about 1.5 times compared to that of NMC (437.96 m2 g-1). In electrochemical measurements as a supercapacitor (SC) electrode, the Te/NMC based electrode, even with its lower porosity parameters, exhibited a higher capacitive performance compared to the NMC-based electrode. These results for Te/NMC arise due to the pseudo-capacitive effect of doped Te and the increase in the capacitive area available from the formation of interconnections in the mesoporous carbons through Te-O bonds. As a result, the synergetic effect of the Te and N atoms enables Te/NMC to exhibit the highest specific capacitance of 197 F g-1 at a current density of 0.5 A g-1. Moreover, remarkable long-term cycling stability with the retention of more than 95% of the initial capacitance is observed for Te/NMC at a current density of 5 A g-1 and also for 1000 charge-discharge cycles.

Finely dispersed CuO on nitrogen-doped carbon hollow nanospheres for selective oxidation of sp3 C–H bonds

Selective oxidation of sp3 C–H bonds has been demonstrated using a novel nanocomposite, CuO/N-C-HNSs, as the catalyst.

Nitrogen-Doped Hierarchical Meso/Microporous Carbon from Bamboo Fungus for Symmetric Supercapacitor Applications

We report the synthesis of nitrogen-doped hierarchical meso/microporous carbon using renewable biomass bamboo fungus as precursor via two-step pyrolysis processes. It is found that the developed porous carbon (NHPC-800) features honeycomb-like cellular framework with well-developed porosity, huge specific surface area (1708 m² g⁻¹), appropriate nitrogen-doping level (3.2 at.%) and high mesopore percentage (25.5%), which are responsible for its remarkable supercapacitive performances. Electrochemical tests suggest that the NHPC-800 electrode offers the largest specific capacitance of 228 F g⁻¹, asplendid rate capability and stable electrochemical behaviors in a traditional three-electrode system. Additionally, asymmetric supercapacitor device is built based on this product as well. An individual as-assembled supercapacitor of NHPC-800//NHPC-800 delivers the maximum energy density of 4.3 Wh kg⁻¹; retains the majority of capacitanceat large current densities; and shows terrific cycling durability with negligible capacitance drop after long-term charge/discharge for beyond 10,000 cycles even at a high current density of 10 A g⁻¹. These excellent supercapacitive properties of NHPC-800 in both three- and two-electrode setups outperform those of lots of biomass-derived porous carbons and thus make it a perspective candidate for producing cost-effective and high-performance supercapacitors

High Specific Capacitance Electrode Material for Supercapacitors Based on Resin-Derived Nitrogen-Doped Porous Carbons

Carbon-based materials, as electrodes for supercapacitors, have attracted tremendous attention. Therefore, nitrogen-doped porous carbons (NPCs) were prepared through a facile carbonization/activation strategy by treating different mass ratios of melamine-urea-formaldehyde resin and KOH. It is clearly demonstrated that because of the introduction of KOH, the resulting NPCs were shown to have increased specific surface area and a rich pore structure, and the best sample possessed a large specific surface area of 2248 m² g^-1 and high N content, which contributed to the good electrochemical performance for supercapacitors. Accordingly, a three-electrode system assembles NPCs as an electrode using aqueous KOH solution; the specific capacitance was 341 F g^-1 under the current density of 1 A g^-1 and retained a specific capacitance of almost 92% after 5000 cycles. The maximum energy output for a symmetrical solid-state supercapacitor with NPCs as the electrode material was 9.60 W h kg^-1 at 1 A g^-1. NPCs have promising applications on high-performance supercapacitors and other energy-storage devices.

Free-Standing and Heteroatoms-Doped Carbon Nanofiber Networks as a Binder-Free Flexible Electrode for High-Performance Supercapacitors

Flexible and heteroatoms-doped (N, O and P) activated carbon nanofiber networks (ACFNs) have been successfully prepared with a mixture of polyamic acid (PAA) and poly(diaryloxyphosphazene) (PDPP) as a solution through electrospinning, followed by a heat post-treatment. The resultant heteroatoms-doped ACFNs can be used as binder-free electrodes for high-performance flexible supercapacitors (SCs) due to lightweight, three-dimensional open-pore structure and good mechanical strength. Despite its surface area being lower than 130.6 m²·g^-1, the heteroatoms-doped ACFNs exhibited a high heteroatoms (N, O and P) content of 17.9%, resulting in a highly specific capacitance of 182 F·g^-1 at a current density of 1 A·g^-1 in 6 M KOH electrolyte in a two-electrode cell and an excellent rate capability of 74.7% of its initial capacitance from 1 A·g^-1 to 10 A·g^-1 under the mass loading of 1.5 mg·cm^-2. The electrical double-layer (EDL) capacitance and pseudocapacitance can be easily decoupled in the heteroatoms-doped mesoporous ACFNs. SCs device based on heteroatoms-doped ACFNs exhibited a high energy density of 6.3 W·h·kg^-1 with a power density of 250 W·kg^-1, as well as excellent cycling stability with 88% capacitance retention after 10,000 charge-discharge cycles. The excellent electrochemical performance was attributed to the mesoporous structure of ACFNs and pseudocapacitive heteroatoms.