Rationally tuning ratio of micro- to meso-pores of biomass-derived ultrathin carbon sheets toward supercapacitors with high energy and high power density

Carbon quantum Dot incorporated Xanthan gum based gel polymer electrolytes for high performance supercapacitors

In this study, a novel biodegradable gel polymer electrolyte (GPE) was developed using carbon quantum dots (CQDs)-infused xanthan gum (XG) as the polymer matrix, sodium perchlorate (NaClO4) as the ionic dopant, and glycerol as the plasticizer. The GPE was paired with activated carbon (AC) and graphene (GC) electrodes to fabricate symmetric supercapacitor cells to enhance energy storage performance. Xanthan gum underwent hydrothermal treatment to form a distinctive puffer ball-like microstructure, which was further nucleated into CQDs. This study introduced an innovative approach by incorporating carbon quantum dots into a polymer electrolyte system, with a new focus on investigating the interactions between the polymer matrix and the salt, offering new insights into their integrated performance. These CQDs functioned as stabilizers and enhanced both the ionic conductivity and electrochemical behavior of the GPE. Structural and morphological analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), confirmed a wave-like, porous surface and well-dispersed CQDs. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) revealed strong intermolecular interactions among the GPE constituents, indicating excellent thermal and chemical stability. Electrochemical studies showed that the AC electrode achieved a specific capacitance of 92 F g⁻¹ via cyclic voltammetry (CV), while the GC electrode delivered 69 F g⁻¹. Galvanostatic charge-discharge (GCD) tests at 1 mA g⁻¹ showed that the GC electrode reached specific capacitance of 75 F g⁻¹, with energy density and power density of 10.40 Wh kg⁻¹ and 0.49 kW kg⁻¹ respectively. Similarly, AC electrode-based supercapacitor was tested which showed specific capacitance, energy density and power density as 45 F g⁻¹, 5.55 Wh kg⁻¹, and 0.66 kW kg⁻¹, respectively. Both systems demonstrated good reversibility and cycling stability, highlighting the potential of CQD-integrated biodegradable GPEs and carbon-based electrodes for environmentally friendly, flexible, and high-performance supercapacitor applications.

Optimized mesopore design in ginkgo nuts-derived hyper-crosslinked porous carbon for enhancing supercapacitor capacitance performance

The capacitance performance of a co-doped carbon-based supercapacitor derived from Ginkgo nuts was significantly enhanced by optimizing the mesoporous structure through high-temperature pyrolysis combined with KOH activation. The precisely engineered GBHHPC-750-4 is characterized by a hyper-crosslinked 3D hierarchical porous structure, with an exceptionally high specific surface area of 3163.9 m2/g, a substantial mesopore proportion (Vmeso/Vt = 74.1 %), a broad pore size range of 2-10 nm, and elevated levels of heteroatom doping (3.4 at.% N, 8.3 at.% O, 1.6 at.% P). The symmetric supercapacitor based on the GBHHPC-750-4 electrode exhibits a peak specific capacitance of 256 F/g at 1 A/g, achieves an energy density of 118.2 Wh kg-1, maintains an impressive rate capability of 63.6 % across a wide current range (0.5-20 A/g) and demonstrates a prolonged cycle lifespan with 88.0 % capacitance retention after 5000 cycles in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMBF4) electrolyte, emphasizing the substantial potential of the optimized mesoporous carbon material for energy storage applications.

Ultrahigh-Power Carbon-Based Supercapacitors through Order-Disorder Balance

Although carbon-based supercapacitors (SCs) hold the advantages of high-power and large-current characteristics, they are difficult to realize ultrahigh-power density (> 200 kW kg-1) and maintain almost constant energy density at ultrahigh power. This limitation is mainly due to the difficulty in balancing the structural order related to the electrical conductivity of carbon materials and the structural disorder related to the pore structure. Herein, we design a novel super-structured tubular carbon (SSTC) with a crosslinked porous conductive network to solve the structure order-disorder tradeoff effect in carbon materials. The direct conversion of CO2 in combination with appropriate annealing treatment tailored SSTC that exhibits considerably high conductivity (≈19300 S m-1) along with an optimal mesoporous structure. Consequently, SSTC-based SCs show impressive ultrahigh-power and high-energy features as demonstrated from three aspects. First, SSTC-1000-based SCs with organic electrolytes deliver a maximum power density of 1138.8 kW kg-1. Second, the energy density retention is up to 84.6% as the power density increases from 0.7 to 280 kW kg-1. Third, SSTC-1000-based SC exhibits excellent ultrahigh-power durability as demonstrated by 93.7% capacitance retention after 100000 cycles at 200 A g-1.

Regulating the Pore Structure and Heteroatom Doping of Soybean Straw Carbon Based on a Bifunctional Template Method for the High-Performance Carbon Supercapacitor

The previous research addressed the waste problem of agriculture and forestry residues by exploring the efficient utilization of liquefied soybean straw in supercapacitor. The structures of the liquefied soybean straw were controlled by coupling microwave hydrothermal treatment with carbonization under the influence of a C3N4 bifunctional template. What's more, C3N4 could effectively regulate the pore structures and provide an effective N active site of carbon materials C3N4. The obtained N-SLR Carbon-700 possess a specific surface area of up to 1593.7 m2 g -1, and the pore size is mainly concentrated in the range of 1.8-2.5 nm, providing efficient ions transmission channels and storage space. Its specific capacitance is up to 261.5 F g-1 (current density of 0.5 A g-1), and the capacity retention is 74.04 % when the current density is expanded by 20 times. In the two-electrode system, the energy density of N-SLR Carbon-700 could reach to 31.3 W h kg-1 at a power density of 360 W kg-1, as well as the energy surface density is maintained at 69 % when the power density is increased by a factor of 20. This work enhances effectively the charging and discharging stability and capacitance value of carbon-based supercapacitor.

Designing nano-heterostructured nickel doped tin sulfide/tin oxide as binder free electrode material for supercapattery

New generation of electrochemical energy storage devices (EESD) such as supercapattery is being intensively studied as it merges the ideal energy density of batteries and optimal power density of supercapacitors in a single device. A multitude of parameters such as the method of electrodes preparation can affect the performance of supercapattery. In this research, nickel doped tin sulfide /tin oxide (SnS@Ni/SnO2) heterostructures were grown directly on the Ni foam and subjected to different calcination temperatures to study their effect on formation, properties, and electrochemical performance through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and electrochemical tests. The optimized SnS@Ni/SnO2 electrode achieved a maximum specific capacity of 319 C g- 1 while activated carbon based capacitive electrode exhibited maximum specific capacitance of 381.19 Fg- 1. Besides, capacitive electrodes for the supercapattery were optimized by incorporating different conductive materials such as acetylene black (AB), carbon nanotubes (CNT) and graphene (GR). Assembling these optimized electrodes with the aid of charge balancing equation, the assembled supercapattery was able to achieve outstanding maximum energy density and power density of 36.04 Wh kg- 1 and 12.48 kW kg- 1 with capacity retention of 91% over 4,000 charge/discharge cycles.

Biomass-Derived Porous Carbon with a Good Balance between High Specific Surface Area and Mesopore Volume for Supercapacitors

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.

Novel Moringa oleifera Leaves 3D Porous Carbon-Based Electrode Material as a High-Performance EDLC Supercapacitor

Biomass-based activated carbon has great potential in the use of its versatile 3D porous structures as an excellent electrode material in presenting high conductivity, large porosity, and outstanding stability for electrochemical energy storage devices. In this study, the electrode material develops through a novel consolidated carbon disc binder-free design, which was derived from Moringa oleifera leaves (MOLs) for electrochemical double-layer capacitor applications. The carbon discs are prepared in a series of treatments of precarbonized, chemical impregnation of zinc chloride, integrated pyrolysis of N₂ carbonization, and CO₂ physical activation. The physical activation temperatures applied at 650, 750, and 850 °C optimize the precursor potential. By optimizing the 3D hierarchical pore properties of the MOL750, the carbon disc binder-free design demonstrates optimal symmetric supercapacitor performance with a high specific capacitance of 307 F g^-1 at a current density of 1 A g^-1 in an aqueous electrolyte solution of 1 M H₂SO₄. Furthermore, the extremely low internal resistance (0.006Ω) of the carbon disc initiated excellent electrical conductivity. The supercapacitors also maintain their high capacitive properties in aqueous electrolyte solutions of 6 M KOH and 1 M Na₂SO₄, respectively. The results show that a novel consolidated carbon disc binder-free design can be obtained from biomass MOLs through a reasonable approach to develop superior electrode materials to enhance high-performance electrochemical energy storage devices.

Organic Crosslinked Polymer-Derived N/O-Doped Porous Carbons for High-Performance Supercapacitor

Supercapacitors, as a new type of green electrical energy storage device, are a potential solution to environmental problems created by economic development and the excessive use of fossil energy resources. In this work, nitrogen/oxygen (N/O)-doped porous carbon materials for high-performance supercapacitors are fabricated by calcining and activating an organic crosslinked polymer prepared using polyethylene glycol, hydroxypropyl methylcellulose, and 4,4-diphenylmethane diisocyanate. The porous carbon exhibits a large specific surface area (1589 m2·g−1) and high electrochemical performance, thanks to the network structure and rich N/O content in the organic crosslinked polymer. The optimized porous carbon material (COCLP-4.5), obtained by adjusting the raw material ratio of the organic crosslinked polymer, exhibits a high specific capacitance (522 F·g−1 at 0.5 A·g−1), good rate capability (319 F·g−1 at 20 A·g−1), and outstanding stability (83% retention after 5000 cycles) in a three-electrode system. Furthermore, an energy density of 18.04 Wh·kg−1 is obtained at a power density of 200.0 W·kg−1 in a two-electrode system. This study demonstrates that organic crosslinked polymer-derived porous carbon electrode materials have good energy storage potential.

Polydopamine Doping and Pyrolysis of Cellulose Nanofiber Paper for Fabrication of Three-Dimensional Nanocarbon with Improved Yield and Capacitive Performances

Biomass-derived three-dimensional (3D) porous nanocarbons have attracted much attention due to their high surface area, permeability, electrical conductivity, and renewability, which are beneficial for various electronic applications, including energy storage. Cellulose, the most abundant and renewable carbohydrate polymer on earth, is a promising precursor to fabricate 3D porous nanocarbons by pyrolysis. However, the pyrolysis of cellulosic materials inevitably causes drastic carbon loss and volume shrinkage. Thus, polydopamine doping prior to the pyrolysis of cellulose nanofiber paper is proposed to fabricate the 3D porous nanocarbons with improved yield and volume retention. Our results show that a small amount of polydopamine (4.3 wt%) improves carbon yield and volume retention after pyrolysis at 700 °C from 16.8 to 26.4% and 15.0 to 19.6%, respectively. The pyrolyzed polydopamine-doped cellulose nanofiber paper has a larger specific surface area and electrical conductivity than cellulose nanofiber paper that without polydopamine. Owing to these features, it also affords a good specific capacitance up to 200 F g⁻¹ as a supercapacitor electrode, which is higher than the recently reported cellulose-derived nanocarbons. This method provides a pathway for the effective fabrication of high-performance cellulose-derived 3D porous nanocarbons.