Waste-converted nitrogen and fluorine co-doped porous carbon nanosheets for high performance supercapacitor with ionic liquid electrolyte

Nitrogen-doped activated carbon composite electrode for deionization of phosphate removal and DFT model adsorption of phosphates

Phosphate discharge in sewage can result in water eutrophication, posing a threat to aquatic ecosystems. Membrane capacitive deionization (MCDI) has demonstrated outstanding performance and significant potential for salt removal and nutrient recovery. In this study, a nitrogen-doped activated carbon electrode material (NAC) was synthesized through one-step pyrolysis to selectively remove phosphate from MCDI. At a voltage of 1.2V, a flow rate of 20 mL/min, and a pH of 6.51, the phosphate adsorption capacity of the NAC electrode was determined to be 1.60 mg/g. The study revealed that NAC pHpzc increased from 4.14 to 6.44, effectively broadening the pH range for phosphate removal. In the presence of competing ions (NO3-, Cl-, and SO42-) at a concentration of 0.5 M, the electroadsorption capacity of phosphate decreased to 1.21 mg/g, 1.14 mg/g, and 1.02 mg/g, respectively. The kinetic parameters of adsorption indicated that NAC electroadsorbed phosphate through physical adsorption, with the maximum adsorption capacity achieved at 303K. Data from the Freundlich isothermal model suggested that phosphate adsorption by the NAC electrode involves a multilayer adsorption process. A carbon structure model of density functional theory (DFT), incorporating doped nitrogen, was constructed based on XPS analysis. Following nitrogen doping, the electrostatic potential (ESP) of unsaturated carbon atoms became more positive, enhancing the ability of nitrogen-doped activated carbon to adsorb phosphate. This study provides compelling evidence that nitrogen doping facilitates the adsorption of phosphate by carbon materials.

Unveiling Superior Capacitive Behaviors of One-Pot Molten Salt-Engineered B, N Co-Doped Porous Carbon Sheets

Heteroatom-doped porous carbon materials with distinctive surface properties and capacitive behavior have been accepted as promising candidates for supercapacitor electrodes. Currently, the researches mainly focus on developing facile synthetic method and unveiling the structure-activity relationship to further elevate their capacitive performance. Here, the B, N co-doped porous carbon sheet (BN-PCS) is constructed by one-pot pyrolysis of agar in KCl/KHCO3 molten salt system. In this process, the urea acts as directing agent to guide the formation of 2D sheet morphology, and the decomposition of KHCO3 and boric acid creates rich micro- and mesopores in the carbon framework. The specific capacitance of optimized BN-PCS reaches 361.1 F g-1 at a current density of 0.5 A g-1 in an aqueous KOH electrolyte. Impressively, the fabricated symmetrical supercapacitor affords a maximum energy density of 43.5 Wh kg-1 at the power density of 375.0 W kg-1 in 1.0 mol L-1 TEABF4 /AN electrolyte. It also achieves excellent long-term stability with capacitance retention of 91.1% and Columbic efficiency of 100% over 10 000 cycles. This study indicates one-pot molten salt method is effective in engineering advanced carbon materials for high-performance energy storage devices.

Recent Advances in Porous Carbon Materials as Electrodes for Supercapacitors

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors.

Facile synthesis of crumpled nitrogen-doped porous carbon nanosheets with ultrahigh surface area for high-performance supercapacitors

Porous carbon nanosheets are currently considered excellent electrode materials for high-performance supercapacitors. However, their ease of agglomeration and stacking nature reduce the available surface area and limit the electrolyte ion diffusion and transport, thereby leading to low capacitance and poor rate capability. To solve these problems, we report an adenosine blowing and KOH activation combination strategy to prepare crumpled nitrogen-doped porous carbon nanosheets (CNPCNS), which exhibit much higher specific capacitance and rate capability compared to flat microporous carbon nanosheets. The method is simple and capable of one-step scalable production of CNPCNS with ultrathin crumpled nanosheets, ultrahigh specific surface area (SSA), microporous and mesoporous structure and high heteroatom content. The optimized CNPCNS-800 with a thickness of 1.59 nm has an ultrahigh SSA of 2756 m² g^-1, high mesoporosity of 62.9% and high heteroatom content (2.6 at% for N, 5.4 at% for O). Consequently, CNPCNS-800 presents an excellent capacitance, high rate capability and long cycling stability both in 6 M KOH and EMIMBF₄. More importantly, the energy density of the CNPCNS-800-based supercapacitor in EMIMBF₄ can reach up to 94.9 W h kg^-1 at 875 W kg^-1 and is still 61.2 W h kg^-1 at 35 kW kg^-1.

Pyrolysis characteristics, kinetics, and biochar of fermented pine sawdust-based waste

The objective of current study is to explore the energy recovery potential of fermentation residues. In this perspective, pyrolysis characteristics, kinetics, and modified biochar derived from pine sawdust after fermentation (FPD) were determined, and comparison was established with pine sawdust (PD). The variation range of comprehensive pyrolysis index (CPI) values of FPD was found 6.51 × 10^-7-16.38 × 10^-7%²·min^-2·°C^-3, significantly higher than that of untreated samples determined under the same experimental conditions. The average activation energy of FPD was 367.95 kJ/mol, 389.45 kJ/mol, and 346.55 kJ/mol calculated by Flynn-Wall-Ozawa (FWO) method, Kissinger-Akahira-Sonuse (KAS), and Starink method respectively, and importantly, these values are much higher than those of PD. Additionally, fermentation could enhance the adsorption capacity for methylene blue of biochar from 0.76 mg/g to 1.6 mg/g due to the abundant surface functional groups and three-dimensional internal pore structure. The adsorption pattern of fermented pine wood shifted from chemisorption dominated to the synergetic adsorption of surface functional groups adsorption and intragranular filling. These results show that FPD has favorable pyrolytic properties, and the derived biochar has adsorption properties, which is the basis for designing pyrolysis process and reusing fermentation residues. HIGHLIGHTS: The FPD has higher values of CPI and activation energy than the PD. FPD-derived biochar has higher adsorption capacity than PD-derived biochar. The fermentation improves the pyrolysis performance. The fermentation enhances adsorption capacity due to unique structure of biochar.