Multi-heteroatom-doped porous carbon with high surface adsorption energy of potassium derived from biomass waste for high-performance supercapacitors

N-doped porous carbon derived from different lignocellulosic biomass models for high-performance supercapacitors: the role of lignin, cellulose and hemicellulose

Biomass-derived porous carbon (PC) has been widely studied in the field of supercapacitors due to its low cost, sustainability and developed pore structure, but how to screen the precursors of high-performance PC is still a major difficulty. Herein, six lignocellulosic biomass models based on different compositions were innovatively constructed and prepared into high-performance PC by a synergistic activation-doping strategy. The results show that the synergistic activation-doping strategy has a certain universality for biomass models. Meanwhile, cellulose and hemicellulose mainly contribute to the formation of micropores, resulting in high specific surface area (SSA), specific capacitance and energy density. While lignin provides some micropores and most mesopores for PC, which enables PC to exhibit excellent rate and cycling performance. Specifically, the MF prepared from the biomass model constructed based on wheat bran has the optimized specific capacitance (474 F g-1 at 1 A g-1), due to its largest SSA (2773 m2 g-1) and high proportion of micropores (76.6%). At 5 A g-1, the coulombic efficiency during 5000 cycles is maintained at 98.8-99.4%, and the final capacity retention is 95.89%. Impressively, an aqueous symmetric supercapacitor based on MF assembled in 1 M Na2SO4 electrolyte delivers an energy density of 27.66 Wh kg-1 at a power density of 82.03 W kg-1. This study provides a reference for the precursor screening of high-performance PC at the composition level, and also contributes an operational idea for PC performance regulation.

One-Step Hydrothermal Synthesis of Glucose-Induced Low Crystallinity NiCo-Based Layered Double Hydroxides for High-Performance Asymmetric Supercapacitors

In order to improve the electrochemical performance of NiCo-based layered double hydroxide (NiCoLDH), the synthesis of low-crystallinity NiCoLDH was induced by the adsorption of glucose and NiCoLDH. The results showed that glucose could not only effectively regulate the pore structure and morphology of NiCoLDH, but also had a regular effect on crystallinity. Pure phase NiCoLDH had higher crystallinity. When the mass of glucose is 0.05 g, the prepared NiCoLDH-0.05 is a short-range ordered structure embedded in the amorphous matrix. The crystallinity of the product decreases further with the further increase of glucose mass. Since the ordered structures have higher electrical conductivity, and amorphous structures have more defects and active sites, the structure of NiCoLDH-0.05 is conducive to achieving the best electrochemical performance. Electrochemical test results show that NiCoLDH-0.05 has a high specific capacitance, about 12 times that of the pure phase NiCoLDH, the mass of glucose is higher than or below 0.05 g, the specific capacitance will be further reduced. NiCoLDH-0.05 and activated carbon assembled into an asymmetric supercapacitor have a power density of 400 W kg-1 at an energy density of 32.7 Wh kg-1. This study provides a new idea for obtaining excellent electrochemical properties by adjusting LDH crystallinity.

Microwave-modulated graded porous carbon for supercapacitors: Pore size matching and operating voltage expansion

Optimizing the pore structure and its interaction with the electrolytes was vital for enhancing the performance of supercapacitors based on the electrical double layer mechanism. In this study, graded porous carbon material (STP) with outstanding properties was prepared by adjusting the activation temperature and KOH dosage in the microwave pyrolysis process of sargassum thunbergii. The results demonstrated that better electrochemical performance was obtained when 1 M NaNO3 was used as electrolyte and STP-800-3 was employed as electrode material, attributed to its excellent specific surface area (SSA) of 2011.8 m2 g-1, high micropore ratio, and the optimal matching degree between micropore size and electrolyte ion diameter. Moreover, the operating voltage window was expanded to 2.0 V in supercapacitors assembled with 6 M NaNO3 high-concentration electrolyte. Simultaneously, the symmetric supercapacitors exhibited a remarkable specific capacitance of 290.0 F g-1, a high energy density of 39.0 W h kg-1, and outstanding capacity retention at 70.9% after 10,000 charge/discharge cycles based on 6 M NaNO3 electrolyte. Consequently, the results provided valuable technical support and theoretical basis to foster progress of novel and high-performance supercapacitors.

Acid-modified biomass-based N-doped O-rich hierarchical porous carbon as a high-performance electrode for supercapacitors

In contemporary society, the conversion and efficient utilization of waste biomass and its derivatives are of great significance. Carbonized wood (CW) is an easily accessible and cost-effective green resource, but it has limitations as an electrode material due to its low specific surface area, limited active sites and poor conductivity. Therefore, it is crucial to improve the performance of biomass-based materials by using activation, heteroatom doping and modification methods to enhance the specific surface area and active sites. In this study, we developed acid-modified urea-doped activated carbonized wood (AUACW) with a three-dimensional (3D) porous structure and porosity, achieving a high specific surface area of 1321.3 m2 g-1. In addition, the degree of graphitization (ID/IG = 1.0) provides good conductivity and a large number of active sites, which are conducive to charge transfer and ion diffusion. The increase of nitrogen and oxygen elements enhances the surface wettability of the material and provides additional pseudocapacitance. The specific capacitance of AUACW reaches 435.84 F g-1 at 0.8 A g-1 with a 93.6% capacitance retention after 10 000 cycles in a 1 M KOH electrolyte. More attractively, a symmetrical supercapacitor (SSC) based on AUACW delivers an energy density of 22.61 W h kg-1 at a power density of 533.26 W kg-1. This work demonstrates the promising potential of utilizing waste biomass to develop green and valuable carbon materials for supercapacitors.

Three-dimensional NiCoS nanotubes@NiCo-LDH nanosheets core-shell heterostructure for high-rate capability alkaline zinc-based batteries

Aqueous alkaline zinc-based batteries (AAZBs) are promising for large-scale applications due to their high working voltage, safety, and low cost. However, the further development of AAZBs has been significantly hindered by the low electronic conductivity and poor cycling stability of traditional nickel/cobalt-based cathode materials. In this work, a binder-free electrode was successfully designed by electrodepositing NiCo-LDH nanosheets on NiCoS nanotube arrays that were grown on nickel foam (NiCoS@NiCo-LDH). The unique three-dimensional core-shell heterostructures not only enhance electrical conductivity but also offer abundant active sites and rapid ion/electron transport channels, thereby improving its electrochemical performance. The as-fabricated NiCoS@NiCo-LDH electrode delivers a capacity of 312 mA h g-1 (0.624 mA h cm-2) at 2 mA cm-2 and exhibits high rate capability with 90% capacity retention at 10 mA cm-2. Additionally, the assembled NiCoS@NiCo-LDH//Zn battery exhibits a high energy density of 435.3 W h kg-1 at a power density of 4.1 kW kg-1 and maintains 95.9% of its capacity after 3000 cycles at a current density of 20 mA cm-2.