Edge-Rich Quasi-Mesoporous Nitrogen-Doped Carbon Framework Derived from Palm Tree Bark Hair for Electrochemical Applications

Deashing Strategy on Biomass Carbon for Achieving High-Performance Full-Supercapacitor Electrodes

The porous carbon materials, namely, MC700/800, PC700/800, and SC700/800, have been prepared using several biomasses (mushroom dreg, Chinese parasol leaves, and Siraitia grosvenorii leaves) as individual precursors at 700 and 800 °C activation temperatures. Among these carbon-negative electrodes, SC700 exhibits an impressive specific capacitance, nearly 2-fold that of commercial activated carbon (169.5 F g-1). When assembled with a Ni(OH)2 positive electrode in asymmetric supercapacitors, the SC700//Ni(OH)2 device can achieve a specific capacitance of 80 F g-1 and an energy density of 32.16 Wh kg-1 at 1700 W kg-1. In contrast, the MC700 electrode can display inferior performance potentially attributed to the high ash content in the biomass. To further optimize the activated process of the MC700 product, three deashing carbon negative electrodes (denoted as MC(H2O), MC(HF), and MC(Mix)) were prepared by deashing treatment using H2O, HF, and mixed acid, and then a modified composite positive electrode (MC700@MnO2(MCM)) has been prepared by doping with MnO2. Electrochemical testing demonstrates that the deashing strategy achieves a significant capacitance enhancement compared to the primary carbon material while maintaining excellent cyclic stability. The asymmetric supercapacitors, assembled from these decorated electrode materials, exhibited a maximum energy density of 21.08 Wh kg-1 and a power density of 1150 W kg-1 under a high-voltage window of 2.2 V. Additionally, this type of full device can power 28 LEDs for approximately 5 min.

Biomass-Derived Carbon Materials for Electrochemical Sensing: Recent Advances and Future Perspectives

In recent years, biomass carbon materials have received widespread attention in the field of electrochemical sensors. As a new type of renewable green energy, biomass carbon has the advantages of low cost and abundant resources. After special treatment, it can be used as an ideal electrode material. Since biomass carbon materials have diverse sources and their morphology is difficult to control, researchers have conducted in-depth research on their preparation process, morphology regulation and application. This review summarizes different biomass carbon structures and their preparation methods and explores the applications of these materials in electrochemical sensors. Modification of biomass carbon materials through pretreatment, physical and chemical activation, heteroatom doping, metal compound composite and other methods can make up for the deficiencies in its pore structure, electrical conductivity and surface wettability, thereby improving its electrochemical performance. The effects of different biomass sources, functional groups, constituent elements and modification methods on the morphology, structure and electrochemical properties of biomass carbon materials are discussed, and the applications of this type of material in biological molecules, heavy metal ions and pesticide residues are reviewed. Biomass carbon-based materials show great application potential and development prospects in the field of electrochemical sensors.

Block Copolymer-Directed Facile Synthesis of N-Doped Mesoporous Graphitic Carbon for Reliable, High-Performance Zn Ion Hybrid Supercapacitor

Ordered mesoporous carbons (OMCs) are promising materials for cathode materials of a Zn ion hybrid capacitor (Zn HC) due to their high surface area and interconnected porous structure. Graphitization of the framework and nitrogen doping have been used to improve the energy storage performance of the OMCs by enhancing electrical conductivity, pseudocapacitive reaction sites, and surface affinity toward aqueous electrolytes. Thus, when both methods are simultaneously implemented to the OMCs, the Zn HC would have improved energy storage performance. Herein, we introduce a facile synthetic method for N-doped mesoporous graphitic carbon (N-mgc) by utilizing polystyrene-block-poly(2-vinlypyridine) copolymer (PS-b-P2VP) as both soft-template and carbon/nitrogen sources. Co-assembly of PS-b-P2VP with Ni precursors for graphitization formed a mesostructured composite, which was converted to N-doped graphitic carbon through catalytic pyrolysis. After selective removal of Ni, N-mgc was prepared. The obtained N-mgc exhibited interconnected mesoporous structure with high nitrogen content and high surface area. When N-mgc was employed as a cathode material in Zn ion HC, excellent energy storage performance was achieved: a high specific capacitance (43 F/g at 0.2 A/g), a high energy density of 19.4 Wh/kg at a power density of 180 W/kg, and reliable cycle stability (>3000 cycles).

Recent Advances and Synergistic Effects of Non-Precious Carbon-Based Nanomaterials as ORR Electrocatalysts: A Review

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal-air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field.

Selective removal of Pb(II) from yellow rice wine using magnetic carbon-based adsorbent

BACKGROUND

The non-distilled property and prolonged production period of yellow rice wine have significantly increased the metal residue problem, posing a threat to human health. In this study, a magnetic carbon-based adsorbent, named magnetic nitrogen-doped carbon (M-NC), was developed for the selective removal of lead(II) (Pb(II)) from yellow rice wine.

RESULTS

The results showed that the uniformly structured M-NC could be easily separated from the solution, exhibiting a high Pb(II) adsorption capacity of 121.86 mg g-1 . The proposed adsorption treatment showed significant Pb(II) removal efficiencies (91.42-98.90%) for yellow rice wines in 15 min without affecting their taste, odor, and physicochemical characteristics of the wines. The adsorption mechanism studied by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) analyses indicated that the selective removal of Pb(II) could be attributed to the electrostatic interaction and covalent interaction between the empty orbital of Pb(II) and the π electrons of the N species on M-NC. Additionally, the M-NC showed no significant cytotoxicity on the Caco-2 cell lines.

CONCLUSION

Selective removal of Pb(II) from yellow rice wine was achieved using magnetic carbon-based adsorbent. This facile and recyclable adsorption operation could potentially address the challenge of toxic metal pollution in liquid foods. © 2023 Society of Chemical Industry.

Iron Carbide Nanoparticles Embedded in Edge-Rich, N and F Codoped Graphene/Carbon Nanotubes Hybrid for Oxygen Electrocatalysis

Rational design of cost-effective and efficient bifunctional oxygen electrocatalysts for sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently desired for rechargeable metal–air batteries and regenerative fuel cells. Here, the Fe3C nanoparticles encapsulated in N and F codoped and simultaneously etched graphene/CNTs architecture catalyst (Fe3C@N-F-GCNTs) was synthesized by a simple yet cost-effective strategy. The as-prepared Fe3C@N-F-GCNTs exhibited excellent ORR and OER performances, with the ORR half-wave potential positive than that of Pt/C by 14 mV, and the OER overpotential lowered to 432 mV at the current density of 10 mA·cm−2. In addition, the ΔE value (oxygen electrode activity parameter) increased to 0.827 V, which is comparable to the performance of the best nonprecious metal catalysts reported to date. When it was applied in a Zn–air battery as a cathode, it achieved a peak power density of 130 mW·cm−2, exhibiting the potential for large-scale applications.

Applications of graphene-based composites in the anode of lithium-ion batteries

Limited by the disadvantages of low theoretical capacity, sluggish lithium ion deintercalation kinetics as well as inferior energy density, traditional graphite anode material has failed to meet the ever-increasing specific energy demand for lithium-ion battery technologies. Therefore, constructing high-efficiency and stable anodes is of great significance for the practical application of lithium-ion batteries. In response, graphene-based composite anodes have recently achieved much-enhanced electrochemical performance due to their unique two-dimensional cellular lattice structure, excellent electrical conductivity, high specific surface area and superior physicochemical stability. In this review, we start with the geometric and electronic properties of graphene, and then summarize the recent progresses of graphene preparation in terms of both methods and characteristics. Subsequently, we focus on the applications of various graphene based lithium-ion battery anodes and their inherent structure-activity relationships. Finally, the challenges and advisory guidelines for graphene composites are discussed. This review aims to provide a fresh perspective on structure optimization and performance modulation of graphene-based composites as lithium-ion battery anodes.

Synergistic Modulation of Carbon-Based, Precious-Metal-Free Electrocatalysts for Oxygen Reduction Reaction

Developing alternatives to noble-metal-based catalysts toward the oxygen reduction reaction (ORR) process plays a key role in the application of low-temperature fuel cells. Carbon-based, precious-metal-free electrocatalysts are of great interest due to their low cost, abundant sources, active catalytic performance, and long-term stability. They are also supposed to feature intrinsically high activity and highly dense catalytic sites along with their sufficient exposure, high conductivity, and high chemical stability, as well as effective mass transfer pathways. In this Review, we focus on carbon-based, precious-metal-free nanocatalysts with synergistic modulation of active-site species and their exposure, mass transfer, and charge transport during the electrochemical process. With this knowledge, perspectives on synergistic modulation strategies are proposed to push forward the development of Pt-free ORR catalysts and the wide application of fuel cells.

Ultrasound-assisted transformation from waste biomass to efficient carbon-based metal-free pH-universal oxygen reduction reaction electrocatalysts

Efficient carbon-based nitrogen-doped electrocatalysts derived from waste biomass are regarded as a promising alternative to noble metal catalysts for oxygen reduction reaction (ORR), which is crucial to fuel cell performance. Here, coconut palm leaves are employed as the carbon source and a series of nitrogen-doped porous carbons were prepared by virtue of a facile and mild ultrasound-assisted method. The obtained carbon material (ANDC-900-10) conveys excellent pH-universal catalytic activity with onset potentials (E_onset) of 1.01, 0.91 and 0.84 V vs. RHE, half-wave potentials (E_1/2) of 0.87, 0.74 and 0.66 V vs. RHE and limiting current densities (J_L) of 5.50, 5.45 and 4.97 mA cm^-2 in alkaline, neutral and acidic electrolytes, respectively, prevailing over the commercial Pt/C catalyst and, what's more, ANDC-900-10 displays preeminent methanol crossover resistance and long-term stability in the broad pH range (0-13), thanks to its abundant hierarchical nanopores as well as effective nitrogen doping with high-density pyridinic-N and graphitic-N. This work provides sonochemical insight for underpinning the eco-friendly approach to rationally designing versatile metal-free carbon-based catalysts toward the ORR at various pH levels.

Dual potassium salt-assisted lyophilization of natural fibres for the high-yield synthesis of one-dimensional carbon microtubes for supercapacitors and the oxygen reduction reaction

Natural fibre-derived carbon microtubes exhibit excellent performances as supercapacitor electrodes and oxygen reduction electrocatalysts via dual-potassium-salt-assisted freeze-drying and post-nitrogen doping.

Template-free preparation of anthracite-based nitrogen-doped porous carbons for high-performance supercapacitors and efficient electrocatalysts for the oxygen reduction reaction

The conversion of coal into high-performance electrochemical energy materials, exemplified by electrodes and electrocatalysts for supercapacitors and fuel cells, is currently crucial to the advancement of high value-added, clean and non-fuel utilization of coal resources. In this work, anthracite-based nitrogen-doped porous carbon (ANPC) materials with well-defined pore architectures and adjustable nitrogen concentrations were prepared without any template: ANPC-1 by a one-step activation/doping process and ANPC-2 by a two-step process. The specific capacitance value of the ANPC-1 materials could attain a maximum of 346.0 F g-1 at the current density of 0.5 A g-1 in 6 M KOH. Supercapacitors composed of the ANPC-1 electrodes were able to achieve high energy densities up to 10.3 W h kg-1 and 20.8 W h kg-1, together with good charge/discharge stabilities of 95.4% and 91.3% after 5000 cycles, in KOH and Na2SO4 aqueous electrolytes, respectively. The ANPC-2 materials are more associated with the oxygen reduction reaction (ORR): one possessed a comparable ORR electrocatalytic activity to the commercial JM Pt/C (20% Pt) catalyst, and, moreover, its onset potential (0.96 V vs. RHE), half-wave potential (0.85 V vs. RHE), catalyst durability (95.9% activity retained after 40 000 s) and methanol tolerance were all superior to the benchmark electrocatalyst. This study provides a feasible route to rational design of coal-based multifunctional materials towards electrochemical energy storage and conversion.

Enhanced lithium storage performance of graphene nanoribbons doped with high content of nitrogen atoms

Nitrogen doping can provide a large number of active sites for lithium-ion storage, thus can yield a higher capacity for lithium-ion batteries. However, most of the reported N-doped graphene-based materials have low nitrogen content (<10 wt%) as the introduction of nitrogen atoms prefer to be produced at edges and defects in the graphene lattices. Owing to the formation of edges and defects, the doped states or active sites can easily be located and nitrogen contents can be determined precisely. Here we present the preparation of N-doped graphene nanoribbons with high nitrogen contents (11.8 wt%) and a facile tunable configuration of doped states. The material can be used as an anode for lithium-ion batteries and shows a higher capacity (the electrode has a reversible capacity of 1100.34 mA h g^-1 at a charge/discharge rate of 100 mA g^-1, corresponds to a discharge time of about 9 h), better rate performance (the electrode has a reversible capacity of 471 mA h g^-1 at the current density of 2 A g^-1, corresponds to a discharge time of about 11.6 min) and improved cycling stability (87.37% of the initial capacity after 200 cycles). The experimental results and first-principle calculations suggest that the residual oxygen-containing functional groups of N-doped graphene nanoribbons promote the formation of pyrrolic nitrogen at edges and substantially increase the room for nitrogen doping. This work opens new strategies for designing and developing N-doped graphene anodes for high performance lithium-ion batteries.

An ultrasound-assisted approach to bio-derived nanoporous carbons: disclosing a linear relationship between effective micropores and capacitance

Ultrasound irradiation is a technique that can induce acoustic cavitation in liquids, leading to a highly interactive mixture of reactants. In pursuit of high-performance and cost-effective supercapacitor electrodes, pore size distributions of carbonaceous materials should be carefully designed. Herein, fruit skins (mango, pitaya and watermelon) are employed as carbon precursors to prepare nanoporous carbons by the ultrasound-assisted method. Large BET specific surface areas of the as-prepared carbons (2700–3000 m² g⁻¹) are reproducible with pore diameters being concentrated at about 0.8 nm. Among a suite of the bio-derived nanoporous carbons, one reaches a maximum specific capacitance of up to 493 F g⁻¹ (at 0.5 A g⁻¹ in 6 M KOH) in the three-electrode system and achieves high energy densities of 27.5 W h kg⁻¹ (at 180 W kg⁻¹ in 1 M Na₂SO₄) and 10.9 W h kg⁻¹ (at 100 W kg⁻¹ in 6 M KOH) in the two-electrode system. After 5000 continuous charge/discharge cycles, the capacitances maintain 108% in 1 M Na₂SO₄ and 98% in 6 M KOH, exhibiting long working stability. Moreover, such high capacitive performance can be attributed to the optimization of surface areas and pore volumes of the effective micropores (referred to as 0.7–2 nm sized pores). Notably, specific capacitances have been found linearly correlated with surface areas and pore volumes of the effective micropores rather than those of any other sized pore (i.e., <0.7, 2–50 and 0.5–50 nm). Consequently, the fit of electrolyte ions into micropore frameworks should be an important consideration for the rational design of nanopore structures in terms of supercapacitor electrodes.

There is a linear relationship between the effective micropore volume (surface area) and the specific capacitance of bio-derived nanoporous carbons, regardless of biomass type and activation temperature employed.