Fabrication of nitrogen-doped hierarchically porous carbons through a hybrid dual-template route for CO2 capture and haemoperfusion

Hierarchically porous carbon materials have many important technological applications; however, most of them were fabricated using either expensive materials or complicated procedures. Based on a general chelate-assisted multi-component co-assembly strategy, nitrogen-doped hierarchically porous carbon materials were fabricated by using Al-based composite and commercial triblock copolymer Pluronic F127 as co-templates, and natural banana peel as precursor. This versatile strategy allowed to easily achieve tunable surface area (700–2100 m² g⁻¹), pore volume (0.38–1.65 cm³ g⁻¹) and a narrow average mesoporous size of ca. 2.72–4.03 nm by simply varying the dosages of Al³⁺ and F127, and to attain high N content (4.54 wt%) in a large-scale fabrication system (2 L). X-ray photoelectron spectroscope characterization of the as-prepared sample revealed nitrogen atoms are mainly in the form of pyridinic nitrogen, quaternary nitrogen and pyridine-N-oxide. Importantly, these as-obtained carbon materials showed excellent performance in CO₂ capture and bilirubin removal with high adsorption capacities and selectivities. The present fabrication strategy is also applicable to the design of porous carbons doped with other elements by choosing appropriate biomass precursors.     

Preparation of porous carbons from petroleum coke by different activation methods

Porous carbons were prepared from Shengli petroleum coke (SPC) and Minxi petroleum coke (MPC) by different activation methods with H₂O, KOH and/or KOH+H₂O as active agents. The porous carbons were characterized by nitrogen adsorption at 77 K. It has been found that activation method and component of petroleum coke, of which different kinds of transitional metals on petroleum coke are crucial for preparing high quality porous carbons. Under the identical experimental conditions, the co-activation with KOH and H₂O as active agents in the same activation process, which has been rarely reported in literature, is the easiest method for the preparation of porous carbons with high surface area. The sequence of active agents in terms of difficulty in the preparation of porous carbons with high surface area is as follows: KOH+H₂O>KOH>H₂O. A drawback of KOH+H₂O activation in the preparation of porous carbon in this work is found to be its low carbon yield in comparison to KOH activation. Compared with the SPC coke, the MPC coke with higher contents of transitional metal and carbon and lower content of nitrogen is more suitable for making high surface area porous carbons, which is believed to be mainly due to the difference in the contents of transitional metals. Porous carbon with surface area around 2500–3000 m²/g and carbon yield about 25–30% has been obtained from MPC coke by KOH+H₂O activation with less KOH and shorter activation time in comparison to the traditional methods.     

N‐doped porous carbons for CO2 capture: Rational choice of N‐containing polymer with high phenyl density as precursor

N‐doped porous carbons (NPCs) are highly promising for CO₂ capture, but their preparation is severely hindered by two factors, namely, the high cost of N‐containing polymer precursors and the low yield of carbon products. Here we report for the first time the fabrication of NPCs through the rational choice of the polymer NUT‐4, with low cost and high phenyl density, as precursor. For the material NPC‐600 obtained from carbonization at 600°C, the yield is as high as 52.1%. The adsorption capacity of CO₂ on NPC‐600 reaches 6.9 mmol/g at 273 K and 1 bar, which is obviously higher than that on the benchmarks, including 13X zeolite (4.1 mmol/g) and activated carbon (2.8 mmol/g), as well as most reported carbon materials. Our results also demonstrate that the present NPCs can be completely regenerated under mild conditions. The abundant microporosity and “CO₂‐philic” (N‐doped) sites are responsible for the adsorption performance. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1648–1658, 2017     

New mesoporous carbon materials synthesized by a templating procedure

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀). SBA-15/cryogel carbon composites were obtained by sol–gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533–771 m² g^?1), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated.     

Synthesis and characterization of the SBA-15/carbon cryogel nanocomposites

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520 m² g^?1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution.     

Preparation and carbon dioxide uptake capacity of N-doped porous carbon materials derived from direct carbonization of zeolitic imidazolate framework

The preparation, characterization and CO₂ uptake performance of N-doped porous carbon materials and composites derived from direct carbonization of ZIF-8 under various conditions are presented for the first time. It is found that the carbonization temperature has remarkable effect on the compositions, the textural properties and consequently the CO₂ adsorption capacities of the ZIF-derived porous materials. Changing the carbonization temperature from 600 to 1000 °C, the composites and the resulting porous carbon materials possess a tuneable nitrogen content in the range of 7.1–24.8 wt%, a surface area of 362–1466 m² g⁻¹ and a pore volume of 0.27–0.87 cm³ g⁻¹, where a significant proportion of the porosity is contributed by micropores. These N-doped porous composites and carbons exhibit excellent CO₂ uptake capacities up to 3.8 mmol g⁻¹ at 25 °C and 1 bar with a CO₂ adsorption energy up to 26 kJ mol⁻¹ at higher CO₂ coverages. The average adsorption energy for CO₂ is one of the highest ever reported for any porous carbon materials. Moreover, the influence of textural properties on CO₂ capture performance of the resulting porous adsorbents has been discussed, which may pave the way to further develop higher efficient CO₂ adsorbent materials.     

Superior carbon-based CO2 adsorbents prepared from poplar anthers

A series of renewable nitrogen-containing granular porous carbons with developed porosities and controlled surface chemical properties were prepared from poplar anthers. The preparation conditions such as pre-carbonization and activation temperatures and KOH amount significantly influence the structures and chemical compositions of the porous carbons, the CO₂ adsorption capacities of which are highly dependent on their pore structures, surface areas, nitrogen contents and adsorption conditions. The sample with developed microporosity, especially with the pores between 0.43 and 1 nm and high nitrogen content shows high CO₂ adsorption capacity at 1 bar and 25 °C. In contrast, when the adsorption pressure is higher than 5 bar, its CO₂ adsorption capacity is dominated by its surface area, and more accurately by its pore volume. Irrespective of this, if the pressure was decreased to 0.1 bar, its CO₂ capture ability is closely correlated to its nitrogen content but not to its porosity. By optimizing the preparation conditions, a porous carbon with a surface area of 3322 m² g⁻¹ and a CO₂ adsorption capacity as high as 51.3 mmol g⁻¹ at 50 bar and 25 °C was prepared.     

Low thermal conductivity in porous SiC–SiO2–Al2O3–TiO2 ceramics induced by multiphase thermal resistance

The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO₂–Al₂O₃–TiO₂ (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO₂, Al₂O₃, and TiO₂ compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO₂, Al₂O₃, and TiO₂ ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm³/g.     

Preparation and properties of porous SiC–Al2O3 ceramics using coal ash

In this paper, we first reported that porous SiC–Al₂O₃ ceramics were prepared from solid waste coal ash, activated carbon, and commercial SiC powder by a carbothermal reduction reaction (CRR) method under Ar atmosphere. The effects of addition amounts of SiC (0, 10, 15, and 20 wt%) on the postsintering properties of as-prepared porous SiC–Al₂O₃ ceramics, such as phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal shock resistance, and thermal diffusivity have been investigated. It was found that the final products are β-SiC and α-Al₂O₃. Meanwhile, the SEM shows the pores distribute uniformly and the body gradually contacts closely in the porous SiC–Al₂O₃ ceramics. The properties of as-prepared porous SiC–Al₂O₃ ceramics were found to be remarkably improved by adding proper amounts of SiC (10, 15, and 20 wt%). However, further increasing the amount of SiC leads to a decrease in thermal shock resistance and mechanical properties. Porous SiC–Al₂O₃ ceramics doped with 10 wt% SiC and sintered at 1600°C for 5 hours with the median pore diameter of 4.24 μm, room-temperature compressive strength of 21.70 MPa, apparent porosity of 48%, and thermal diffusivity of 0.0194 cm²/s were successfully obtained.     

Investigating the effect of porosity level and pore former type on the mechanical and corrosion resistance properties of agro-waste shaped porous alumina ceramics

The strength integrity and chemical stability of porous alumina ceramics operating under extreme service conditions are of major importance in understanding their service behavior if they are to stand the test of time. In the present study, the effect of porosity and different pore former type on the mechanical strength and corrosion resistance properties of porous alumina ceramics have been studied. Given the potential of agricultural wastes as pore-forming agents (PFAs), a series of porous alumina ceramics (Al₂O₃-xPFA; x=5, 10, 15 and 20 wt%) were successfully prepared from rice husk (RH) and sugarcane bagasse (SCB) through the powder metallurgy technique. Experimental results showed that the porosity (44–67%) and the pore size (70–178 µm) of porous alumina samples maintained a linear relationship with the PFA loading. Comprehensive mechanical strength characterization of the porous alumina samples was conducted not just as a function of porosity but also as a function of the different PFA type used. Overall, the mechanical properties showed an inverse relationship with the porosity as the developed porous alumina samples exhibited tensile and compressive strengths of 20.4–1.5 MPa and 179.5–10.9 MPa respectively. Moreover, higher strengths were observed in the SCB shaped samples up to the 15 wt% PFA mark, while beyond this point, the silica peak observed in the XRD pattern of the RH shaped samples favored their relatively high strength. The corrosion resistance characterization of the porous alumina samples in hot 10 wt% NaOH and 20 wt% H₂SO₄ solutions was also investigated by considering sample formulations with 5–15 wt% PFA addition. With increasing porosity, the mass loss range in RH and SCB shaped samples after corrosion in NaOH solution for 8 h were 1.25–3.6% and 0.44–2.9% respectively; on the other hand, after corrosion in H₂SO₄ solution for 8 h, the mass loss range in RH and SCB shaped samples were 0.62–1.5% and 0.68–3.3% respectively.     

The use of aliphatic alcohol chain length to control the nitrogen type and content in nitrogen doped carbon nanotubes

Nitrogen doped carbon nanotubes (N-CNTs) were synthesized using acetonitrile/alcohol mixtures as the nitrogen, carbon and oxygen sources using the chemical vapor deposition (CVD) method. XPS analysis of the CNTs produced from an acetonitrile/ethanol mixture using different CVD temperatures (700–1000 °C), revealed that nitrogen incorporation in N-CNTs decreased with an increase in CVD temperature and that the type of nitrogen species incorporated also varied. Molecular nitrogen and a low content of pyridinic nitrogen was obtained in N-CNTs grown at 700 and 800 °C, while quaternary nitrogen was noted in all N-CNTs grown. Use of 20% acetonitrile/ROH (R = CH₃, C₂H₅, C₄H₉, C₅H₁₁, C₇H₁₅ and C₈H₁₇) mixtures allowed the C/O ratio to be changed whilst the N content in the precursor mixture was kept constant. The N content in the N-CNTs grown at 850 °C increased with the alcohol chain length and also controlled the nitrogen species incorporated, an effect related to the oxygen content of the reactant mixtures.     

Processing of biomorphic porous TiO2 ceramics by chemical vapor infiltration and reaction (CVI-R) technique

Porous biomorphic TiO₂ ceramics were manufactured from paper preforms by chemical vapor infiltration and reaction (CVI-R) in a three-steps process. First, the cellulose fibers of the paper were converted into carbon (C_b) by pyrolysis in an inert atmosphere. Then, C_b-template was infiltrated with a precursor system consisting of TiCl₄, CH₄ and H₂ to produce porous TiC ceramics, which were oxidized in a final step with air at temperatures in the range of 400–1200 °C. Depending on the conversion degree, TiC/TiO₂ or TiO₂ ceramics were obtained. The kinetics of the oxidation process was studied by thermal gravimetric analysis (TGA) and activation energies of 63 and 174 kJ mol⁻¹ were estimated for the lower (400–800 °C) and higher (950–1200 °C) temperature regions, respectively. The TiO₂ ceramics were characterized by Raman spectroscopy (anatase/rutile ratio), SEM/EDX (morphology, composition) and nitrogen gas adsorption (pore structure). It was shown, that the anatase/rutile ratio as well as the pore structure of the resulting TiO₂ ceramics could be controlled varying the oxidation temperature. The TiO₂ samples obtained by oxidation of TiC biomorphic porous ceramics are lightweight but nevertheless have very good mechanical performances. Their bending strength varies between 30 and 40 MPa at a porosity of 65–70%. These structures have many potential applications, e.g. light structured materials, implants because of their bio-compatibility, catalyst support or catalyst for photo catalytic applications.     

Gas storage scale-up at room temperature on high density carbon materials

In relation to the current interest on gas storage demand for environmental applications (e.g., gas transportation, and carbon dioxide capture) and for energy purposes (e.g., methane and hydrogen), high pressure adsorption (physisorption) on highly porous sorbents has become an attractive option. Considering that for high pressure adsorption, the sorbent requires both, high porosity and high density, the present paper investigates gas storage enhancement on selected carbon adsorbents, both on a gravimetric and on a volumetric basis. Results on carbon dioxide, methane, and hydrogen adsorption at room temperature (i.e., supercritical and subcritical gases) are reported. From the obtained results, the importance of both parameters (porosity and density) of the adsorbents is confirmed. Hence, the densest of the different carbon materials used is selected to study a scale-up gas storage system, with a 2.5 l cylinder tank containing 2.64 kg of adsorbent. The scale-up results are in agreement with the laboratory scale ones and highlight the importance of the adsorbent density for volumetric storage performances, reaching, at 20 bar and at RT, 376, 104, and 2.4 g l⁻¹ for CO₂, CH₄, and H₂, respectively.     

Thermal conductivity of porous Alumina-20 wt% zirconia ceramic composites

Effect of porosity and temperature on thermal conductivity of the porous Alumina-20 wt% Zirconia (3 mol.% Y₂O₃) ceramic composites with and without niobia were investigated. The ceramic powders were synthesized by the sol-gel route using alkoxide precursors. The porosity in the composites was maintained in the range of 9.5–65 vol% using starch as a space holder material. After processing, samples were compacted uniaxially and sintered at 1873 K for 3 h. The thermal conductivity of porous ceramic composites with and without niobia dopant was measured at three different temperatures of 300, 473, and 673 K using laser-flash technique. The thermal conductivity of the samples was reduced with increasing temperature and porosity. At temperature of 300 K, the thermal conductivity value of 11 W/m.K was obtained for the undoped sample S0 with 17 vol% residual porosity, dropped to 2 W/mK for the sample S40 containing 65 vol% porosity, and for the same sample it was further reduced to the lowest value of 0.68 W/m.K at 673 K. The measured conductivity values were used to determine the grain boundary thermal resistance value (R) of the samples which exhibited an ascending trend with the porosity. The obtained thermal conductivity for the different porous composites was verified and formulated with the Maxwell-Eucken and Ticha models. The results showed that the experimentally measured conductivity values follow a descending order with the models while at the higher-porosity level (57–65 vol%), it fits well with the Ticha equation with only 9% and 4.6% deviation for undoped and doped samples, respectively. Results also revealed that the addition of niobia significantly reduced thermal conductivity at the lower porosity levels, but at higher porosity level the effect of porosity was more dominant.     

The effects of the surface oxidation of activated carbon,the solution pH and the temperature on adsorption of ibuprofen

A commercial microporous–mesoporous granular activated carbon was modified by oxidation with either H₂O₂ in the presence or absence of ultrasonic irradiation, or NaOCl or by a thermal treatment under nitrogen flow. Raw and modified materials were characterized by N₂ adsorption–desorption measurements at 77 K, Boehm titrations, pH measurements and X-ray photoelectron spectroscopy. Ibuprofen adsorption kinetic and isotherm studies were carried out at pH 3 and 7 on raw and modified materials. The thermodynamic parameters of adsorption were calculated from the isotherms obtained at 298, 313 and 328 K. The pore size distribution of carbon loaded with ibuprofen brought out that adsorption occurred preferentially into the ultramicropores. The adsorption of ibuprofen on pristine activated carbon was found endothermic, spontaneous (ΔG° = −1.1 kJ mol⁻¹), and promoted at acidic pH through dispersive interactions. All explored oxidative treatments led mainly to the formation of carbonyl groups and in a less extent to lactonic and carboxylic groups. This then helped to enhance the adsorption uptake while decreasing adsorption Gibbs energy (notably −7.3 kJ mol⁻¹ after sonication in H₂O₂). The decrease of the adsorption capacity after bleaching was attributed to the presence of phenolic groups.     

Magnetic porous carbon microspheres synthesized by simultaneous activation and magnetization for removing methylene blue

Magnetic porous carbon microspheres (MPCMs) based on Fe₃O₄-encapsulating carbon composites for removing methylene blue (MB) in aqueous solutions were synthesized by simultaneous activation and magnetization. A series of MPCMs were prepared by combining hydrothermal and annealing treatment with α-Fe₂O₃ nanoparticles as iron source, glucose as carbon source and ZnCl₂ as porogen. The phase structure, specific surface area, porosity, thermostability, magnetic property, as well as morphology of as-prepared MPCMs were verified by X-ray diffraction, Brunauer–Emmeltt–Teller surface area analysis, thermogravimetric analysis, vibrating sample magnetometry, field emission scanning electron microscopy and high resolution transmission electron microscopy. The results indicate that the maximum specific surface area of MPCMs is up to 480.32 m²/g when the mass ratio of ZnCl₂/glucose is 0.25, which is designated as MPCMs-0.25. The saturation magnetism of MPCMs-0.25 is 30.16 emu/g. Adsorption properties of MPCMs were detected by using MPCMs-0.25 as adsorbent to remove MB from aqueous solution. The outcomes suggest that the adsorption reaches equilibrium within 35 min and physical adsorption is involved in the whole adsorption processes. The results of adsorption isotherm reveal that the adsorption process might include monolayer and porous adsorption, meanwhile, various adsorption sites exist on the surfaces of MPCMs-0.25. The reusability and stability of MPCMs-0.25 were also confirmed by five adsorption–desorption cycle experiments.     

Solid-state dechlorination pathway for the synthesis of few layered functionalized carbon nanosheets and their greenhouse gas adsorptivity over CO and N2

A simple solid-state dechlorination route has been demonstrated to synthesize few layered functionalized carbon nanosheets (FCNS) utilizing hexachloroethane as carbon source and copper as reducing agent under the autogenic pressure at 300 °C. The obtained FCNS possesses the sheet thickness of 6–12 nm as analyzed by transmission electron microscopy. The particle nature of the FCNS provides the excess porosity having the surface area 836 m²/g. The equilibrium gas adsorption study of FCNS for greenhouse gases (CO₂ and CH₄), toxic gas (CO) and light gas (N₂) showed the maximum adsorption capacity for CO₂ (2.95 mmol/g; at 288 K) with maximum capacity selectivity of 10.1 at 318 K. The very strong adsorbate–adsorbent interaction was observed in case of CO compare to other gases resulted in higher heat of adsorption for CO. The gas adsorption and FT-IR study showed that the interaction of CO with copper present in minute quantities in FCNS improves the CO adsorption due to π complexation. The FCNS obtained under present methodology showed the very high equilibrium selectivity for CO over N₂ (197) followed by CH₄ (61) and CO₂ (7.3) at 288 K.     

Electrical Properties of B-doped homoepitaxial diamond films grown from UHP gas sources

It is confirmed that a small amount of nitrogen incorporated into chemical vapor deposited diamond films dramatically affects their electrical properties. Nitrogen can be incorporated into diamond films through the leak of vacuum system and/or from the impurity in source gases. Because a nitrogen atom can be a deep donor in diamond crystal, the p-type semiconducting properties of boron doped diamond films can be degraded even by the small amount of nitrogen. The small amount of nitrogen in chemical vapor deposited diamond films was measured by cathodoluminescence spectroscopy. For the detection of nitrogen, the N–V center was intentionally induced by defect formation through ion beam irradiation and subsequent annealing. The luminescence intensity of the N–V center was decreased by reducing the leak of the vacuum system and by upgrading the purity of the source gases. Both the carrier density and the Hall mobility of the boron doped diamond films were successfully improved by the control of nitrogen contamination. Using extremely high pure CH₄, H₂ and B₂H₆ in a tightly sealed vacuum system, the total amount of nitrogen impurity in the source gas was controlled to <80 ppm in the N/C atomic ratio resulting in a Hall mobility of 1600 cm²/Vs with a hole concentration of >10¹⁴ cm⁻³ at the room temperature in a 10-ppm-boron doped homoepitaxial diamond film.     

Characterization of highly selective microporous carbon hollow fiber membranes prepared from a commercial co-polyimide precursor

In this work, the preparation of gas separating carbon hollow fiber membranes based on a 3,3′4,4′- benzophenone tetracarboxylic dianhydride and 80% methylphenylene-diamine + 20% methylene diamine co-polyimide precursor (BTDA-TDI/MDI, Ρ84 Lenzing GmbH), their permselectivity properties as well as details of the carbon nanostructure are reported. Hollow fibers were initially prepared by the dry/wet phase inversion process in a spinning set-up, while the spinning dope consisted of P84 as polymer and NMP as solvent. The developed polymer hollow fibers were further carbonized in nitrogen at temperatures up to 1173 K. Thermogravimetric analysis was used to investigate the weight loss during the carbonization process. The nitrogen, methane and carbon dioxide adsorption capacity of the prepared materials was determined gravimetrically at 273 and 298 K and hydrogen adsorption experiments were performed at 77 K up to 1 bar. Scanning electron microscopy was used to elucidate the morphological characteristics and the nanostructure while H₂ sorption at 77 K was applied to evaluate the microporosity of the developed carbon hollow fiber membranes. In all cases, the permeability (Barrer) of He, H₂, CH₄, CO₂, O₂ and N₂ were measured at atmospheric pressure and temperatures 313, 333 and 373 K and were found higher than those of the precursor. Moreover, the calculated permselectivity values were significantly improved. The developed carbon fibers exhibit rather low H₂ permeance values (8.2 GPU or 2.74 × 10⁻⁹ mol/m²·s·Pa) with a highest H₂/CH₄ selectivity coefficient of 843 at 373 K.     

Nitrogen-doped porous carbons through KOH activation with superior performance in supercapacitors

A series of nitrogen-doped porous carbons are prepared through KOH activation of a nonporous nitrogen-enriched carbon which is synthesized by pyrolysis of the polymerized ethylenediamine and carbon tetrachloride. The porosity and nitrogen content of the nitrogen-doped porous carbons depend strongly on the weight ratio of KOH/carbon. As the weight ratio of KOH/carbon increases from 0.5 to 2, the specific surface area increases from 521 to 1913 m² g⁻¹, while the nitrogen content decreases from 10.8 to 1.1 wt.%. The nitrogen-doped porous carbon prepared with a moderate KOH/carbon weight ratio of 1, which possesses a balanced specific surface area (1463 m² g⁻¹) and nitrogen content (3.3 wt.%), exhibits the largest specific capacitance of 363 F g⁻¹ at a current density of 0.1 A g⁻¹ in 1 M H₂SO₄ aqueous electrolyte, attributed to the co-contribution of double-layer capacitance and pseudocapacitance. Moreover, it shows excellent rate capability (182 F g⁻¹ remained at 20 A g⁻¹) and good cycling stability (97% capacitance retention over 5000 cycles), making it a promising electrode material for supercapacitors.