Porous Carbon Samples Research Articles

Synthesis of porous carbon nanostructure formation from peel waste for low cost flexible electrode fabrication towards energy storage applications

Abstract Porous activated nanostructure carbon is prepared by feasible two steps method utilizing naturally available bio-wastes such as jack fruit peel waste (JFW) and studied the effect of pyrolysis condition for porosity formation. X-ray analysis and BET pore size analysis confirmed the formation of graphitic nature carbon with micro and mesoporous existence. HR-SEM and TEM images of Jack fruit (JF) derived porous carbon samples are shown spherical nanoball and tiny nanotube morphology. High resolution SEM images further confirms that the, increase in the activation temperature increase the uniform hexagon shape porous structure formation. The superior electrochemical activity and recycling stability was achieved for our method prepared (phohphoric acid activation method using graphite crucible mold) porous carbon materials. The Cs (specific capacitance) of the JF-9 (porous carbon prepared Jack fruit at 900 °C) sample was shown 324 F/g at the scan rate of 5 mV/s using Na2SO4 electrolyte. The JF carbon sample exhibits a higher capacitance retention of 93% for upto 5000 cycles. We found that the JF derived porous carbon sample shows higher recycling capacity by Galvano static charge-discharge analysis. The effect of current density and scan rate on specific capacitance property are analyzed in detailed by cyclic-voltammetry , Galvano static charge-discharge method and electrochemical impedance spectroscopy analysis.

Templating synthesis of hierarchical porous carbon from heavy residue of tire pyrolysis oil for methylene blue removal

A simple and regulatable strategy was proposed to synthesis hierarchical porous carbon from heavy residue of waste tire derived pyrolytic oil (TPO). Magnesium acetate powder was adopted as a pore creator and adjustor which was mixed with heavy residue and tetrahydrofuran (THF) by grinding. Subsequently, the various pore structure carbons were obtained after evaporation, carbonization and MgO removal. The change in pore size was significantly observed with the magnesium acetate dosage. In this method, the addition of magnesium acetate could result in higher carbon yield. Remarkably, the carbon prepared at optimum condition exhibited higher specific surface area and micro-mesopore structure leading to an excellent performance towards dye contaminant removal. The prepared porous carbon sample exhibited best adsorption capacity (843.5 mg/g) at 298 K for methylene blue (MB). Furthermore, the effect of pH and temperature on adsorption capacity of prepared porous carbon were also investigated. The adsorption process of MB onto porous carbon was favorable according to the Freundlich model parameter (1/n < 0.5). This study highlighted a great potential of using the heavy residue of TPO as a low-cost precursor for porous carbon and simultaneously offered a value-added way to treat the heavy residue of waste tire derived pyrolytic oil.

Pore structure control of porous carbon via the synergistic effect of boric acid and divalent metal iron salt

Abstract Homogeneous porous carbons were obtained from phenolic resin/ethylene glycol resin mixtures based on polymerization-induced phase separation (PIPS) by the addition of boric acid and divalent metal iron salt. The mechanism of boric acid and divalent metal iron salt promoting pore formation was studied. The research indicates: the resulting porous carbon sample has a bigger pore size and a more uniformly distributed pore structure under the synergistic action of boric acid and a divalent metal iron salt, and its carbon matrix morphology is in the form of spherical particles. Under the synergistic effect, the average pore size of the porous carbon sample is increased to 1226 ± 48 nm. The reaction of the boric acid with the resin mixture promotes an increase in the molecular chain of the monomer, which is polymerized around the divalent metal iron salt to form a spherical polymer.

Tannic acid-Fe coordination derived Fe/N-doped carbon hybrids for catalytic oxidation processes

Abstract Novel nano-sized iron carbides and/or iron‑nitrogen clusters embedded into porous N-doped carbon (CP-Fe-N) samples were derived from a Fe-tannic acid coordination compound and used as highly reactive Fenton-like catalysts to oxidize recalcitrant organics via peroxymonosulfate (PMS) activation. The CP-Fe-N hybrids possessed superior catalytic activity, benefiting from uniformly distributed Fe3C and Fe-Nx active sites into N-doped graphitic carbon in a hierarchically porous structure, which not only provided the channels for rapid mass transfer but also guaranteed the exposure of the highly catalytic active sites. The effects of several important factors, such as reaction temperature, initial pH and inorganic anions, on the removal of recalcitrant organics have been elucidated. Radical quenching and electron paramagnetic resonance experiments demonstrated that a large number of reactive oxygen species (ROS: 1O2 and O2•−) were responsible for the contaminant degradation. The Fe-tannic acid coordination compound was a renewable source for the synthesis of magnetic CP-Fe-N hybrids, which favored magnetic separation for reuse. This work demonstrated the great potential of metal-tannic acid coordination as effective precursors to fabricate novel functional materials and their excellent application for environmental remediation.

Investigation on the Impact of Carbon Porosity in the Microporous Layer of PEM Fuel Cells

In recent years, the PEMFC has seen tremendous progress in terms of reliability, durability and performance. The cathode performance in particular, greatly influences the overall performance. Issues such as water management remains a huge issue that must be addressed particularly in cases under high current density operating conditions as the occurrence of flooding is prevalent. The microporous layer (MPL) is pivotal in improving water management in PEMFCs. The layer which generally consists of carbon particles and a hydrophobic agent, functions as an intermediate layer between the catalyst layer and the more porous substrate layer. In MPL research, different types of carbon particles (BLACKPEARLS, XC-72R, acetylene black, graphite, etc.) have been compared and key relationships between the carbon porosity and overall PEMFC performance have been reported. However, it is difficult to delineate the impact of porosity from parameters such as particle size and agglomeration packing which are intrinsic to each type of carbon. This study focuses on the application of porous carbons that have been systematically modified in terms of porosity in the MPL to establish a clearer comparison. The first approach involves the modification of the porosity of carbon black to different degrees through physical activation. Carbon black particles were activated under CO2 ­for different durations to induce different levels of porosity. In the second approach, colloid-imprinted carbons (CIC) were synthesized with various pore sizes and used to study the impact of pore size in carbons on overall MPL performance in PEMFCs. Both approaches utilize the same type of carbon material but with varying porosities. The wettability of the carbon materials will also be studied as it also impacts the interaction between water and the carbon surface. To fabricate the MPL, the carbon was made into a slurry before being applied on a carbon fiber paper followed by sintering. The newly fabricated gas diffusion layer (GDL) was incorporated in a membrane electrode assembly (MEA) before being tested in a single cell PEMFC. The Pt loadings on the anode and cathode were 0.04 mgPt/cm2 and 0.4 mgPt/cm2 respectively. Polarization tests were used to study the electrochemical properties of the GDL during operation. Bulk powder samples were also characterized using N2 sorption, x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The wettability and through-plane resistance of the fabricated GDLs were also examined. This study attempts to elucidate the impact of the porosity of carbons in the MPL on the mass transport losses in PEMFC. By establishing a further understanding on the effect of carbon porosity, improved microporous layer designs through material selection and design can be achieved leading to greater PEMFC operational robustness. Synthesis and characterization results of the porous carbon samples and the fabricated GDL along with their electrochemical results will be presented.

Nitrogen-doped microporous carbon derived from a biomass waste-metasequoia cone for electrochemical capacitors

Naturally nitrogen-doped porous carbon is acquired from the fruit of Metasequoia (dawn redwood cone) by two facile steps of pre-carbonization and chemical activation. Current collectors coated with the porous carbon as electrodes are evaluated in 6.0 M basic electrolyte for the application of electrochemical capacitors. Results show that the porous carbon obtained with an activated temperature of 700 °C keeps the highest specific surface area (1,831 m2 g−1) and the largest pore volume (0.92 cm3 g−1). In three-electrode test, the carbon based electrode not only possesses an outstanding capacitive performance up to 326 F g−1 and 236 F g−1 at current densities of 0.5 A g−1 and 10 A g−1, respectively, but also shows a stable cycling characteristic. The two-electrode symmetric device also harvests a specific capacitance of 197 F g−1 at a current density of 1.0 A g−1 and an excellent energy density as high as 7.6 W h kg−1. Our study suggests that the cone can be applied as a promising and almost zero-cost precursor in fabricating porous carbon samples for supercapacitor, thanks to the abundance of resources.

Nitrogen-doped porous carbon embedded with cobalt nanoparticles for excellent oxygen reduction reaction

Nitrogen-doped hierarchical porous carbon (CNx-Co) samples embedded with cobalt nanoparticles are selectively prepared with polyethylenimine (PEI) as both the carbon and nitrogen sources. By processing at different temperature, CNx-Co-800 and CNx-Co-1000 are selectively prepared and the materials exhibit excellent electrocatalytic activity in the oxygen reduction reaction (ORR). The ORR measurements show that sample processed at the higher temperature delivers better performance due to the larger Co and graphitic nitrogen concentrations. CNx-Co-1000 also shows more tolerance against methanol crossover and outstanding durability towards ORR, making it a promising Pt-free electrocatalyst for ORR under alkaline conditions. The method demonstrated here is a general strategy to prepare other metal or metal alloy/porous carbon hybrid materials.

Removal of Cu(II) ions from aqueous solutions using petroleum coke-derived microporous carbon: investigation of adsorption equilibrium and kinetics

Petroleum coke (PC)-derived porous carbons were developed through chemical activation using KOH and applied to adsorb Cu(II) ions from aqueous solutions. The effects of KOH/PC mass ratio and activation temperature on the preparation and physical properties of porous carbon were studied. Also, the effects of the initial solution pH, contact time, operating temperature, dosage of adsorbent, and initial Cu(II) concentration on adsorption were investigated in detail. A maximum Cu(II) ion adsorption capacity of 89.85 mg g−1 was attained at 30 °C using PCK3-450, the porous carbon sample prepared using a KOH/PC mass ratio of 3:1 at 450 °C. Adsorption isotherms were analyzed using the Langmuir, Freundlich, and Temkin models, and the experimental data fit well with the Freundlich model. Pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion models were used to describe the adsorption kinetics, and the rate of adsorption conformed to the pseudo second-order kinetic model. The activation energy of Cu(II) ion adsorption on PCK3-450 was estimated at 29.61 kJ mol−1, and thermodynamic parameters were discussed. The porous carbon adsorbents developed in this study are inexpensive and effective for Cu(II) ion removal from aqueous solutions.

Template-free and fast one-step synthesis from enzymatic hydrolysis lignin to hierarchical porous carbon for CO2 capture

Abstract Conventional two-step synthesis (carbonization followed by activation) of porous carbon required long heating duration at high temperature, leading to high energy consumption. To obtain carbon with hierarchical porous structure, a templating method was typically used. In view of the above drawbacks, this study provided a template-free and fast one-step synthesis from enzymatic hydrolysis lignin to hierarchical porous carbon by microwave heating in humidified nitrogen. It was shown that moisture in humidified nitrogen acts as a physical activating agent combined with KOH to achieve a hierarchical porous structure consisting of abundant micropores and considerable meso-/macropores. The results show high dependency of porosity, amorphous structure, and surface chemical properties of porous carbon samples on microwave heating duration. In particular, a porous carbon with a prominent hierarchical pore structure (65.3% mesopores), high specific surface area (2870 m2/g) and total pore volume (2.02 cm3/g) was synthesized using a microwave heating duration of 30 min. Under this condition, a high content of O-C=O group (10.0%) was also achieved, implying the presence of a hydrophilic carbon surface. These properties of prepared porous carbon synergistically enhance its CO2 uptake (up to 1.31 mmol/g measured by thermogravimetric analyzer at 30 °C). This time-saving and energy efficient synthesis of hierarchical porous carbon could be an effective approach to utilize industrial lignin waste to reduce greenhouse gas emission.

Contribution of surface oxygen groups to the measured capacitance of porous carbon supercapacitors

Porous carbon is used as the electrode material in electrochemical double-layer capacitors (EDLCs) due to its high surface area and electrical conductivity. However, one of the challenges associated with porous carbon is the presence of electrochemically active surface oxygen groups, which undergo rapid charge transfer reactions in alkaline or acidic electrolytes. In this study, oxygen groups have been removed from porous carbon samples in order to quantify their contribution to the double-layer capacitance. The oxygen-free porous carbon samples have similar pore size distributions to the original sample; however, the specific surface area (SSA) is observed to increase slightly with heat treatment. The original porous carbon sample, containing oxygen, has an SSA-normalized capacitance of 12.2 ± 0.2 μF cm−2, while the oxygen-free samples have SSA-normalized capacitances of 8.8 ± 1.0 μF cm−2, regardless of total SSA. Based on these results, the relative contributions of the carboxyl and phenol oxygen groups are determined, which are the two electrochemically active oxygen groups in alkaline solutions. From this work, it is shown that the carboxyl groups and phenol groups contribute approximately 1.10 μF cm−2at.%−1. These results demonstrate the importance of oxygen groups for accurate characterization of the performance of novel porous carbons for EDLCs.

Significant Effect of Pore Sizes on Energy Storage in Nanoporous Carbon Supercapacitors.

Mesoporous carbon can be synthesized with good control of surface area, pore-size distribution, and porous architecture. Although the relationship between porosity and supercapacitor performance is well known, there are no thorough reports that compare the performance of numerous types of carbon samples side by side. In this manuscript, we describe the performance of 13 porous carbon samples in supercapacitor devices. We suggest that there is a "critical pore size" at which guest molecules can pass through the pores effectively. In this context, the specific surface area (SSA) and pore-size distribution (PSD) are used to show the point at which the pore size crosses the threshold of critical size. These measurements provide a guide for the development of new kinds of carbon materials for supercapacitor devices.

Medulla tetrapanacis-derived O/N co-doped porous carbon materials for efficient oxygen reduction electrocatalysts and high-rate supercapacitors

O/N co-doped porous carbon materials derived from biomass have become the most promising candidates for electrochemical energy conversion and storage due to their renewability and sustainability. We herein present a simple approach to fabricate O/N co-doped porous carbon materials by direct pyrolysis of medulla tetrapanacis (the stem pith of tetrapanax papyriferus). The porous carbon sample (MT-900) synthesized under optimum conditions shows outstanding electrocatalytic activity toward oxygen reduction reaction (ORR) (onset potential (Eo) = 3 mV; half-wave potential (E1/2) = −128 mV vs. Ag/AgCl), together with excellent long-term stability, and high resistance to methanol crossover and CO poisoning. Furthermore, the MT-900-based supercapacitor electrode also exhibits high-rate performance (83.6% capacitance retention from 1 to 100 A g−1) as well as excellent stability (95.2% capacitance retention after 10000 cycles) in 6 M KOH electrolyte.

Paulownia tomentosa derived porous carbon with enhanced sodium storage

Abstract

In situ vibrational spectroscopy of adsorbed nitrogen in porous carbon materials.

This study uses in situ vibrational spectroscopy to probe nitrogen adsorption to porous carbon materials, including single-wall carbon nanotubes and Maxsorb super-activated carbon, demonstrating how the nitrogen Raman stretch mode is perturbed by adsorption. In all porous carbon samples upon N2 physisorption in the mesopore filling regime, the N2 Raman mode downshifts by ∼2 cm-1, a downshift comparable to liquid N2. The relative intensity of this mode increases as pressure is increased to saturation, and trends in the relative intensity parallel the volumetric gas adsorption isotherm. This mode with ∼2 cm-1 downshift is thus attributed to perturbations arising due to N2-N2 interactions in a condensed film. The mode is also observed for the activated carbon at 298 K, and the relative intensity once again parallels the gas adsorption isotherm. For select samples, a mode with a stronger downshift (>4 cm-1) is observed, and the stronger downshift is attributed to stronger N2-carbon surface interactions. Simulations for a N2 surface film support peak assignments. These results suggest that N2 vibrational spectroscopy could provide an indication of the presence or absence of porosity for very small quantities of samples.

Synthesis of Fe, Co Incorporated in P-Doped Porous Carbon Using a Metal-Organic Framework (MOF) Precursor as Stable Catalysts for Oxygen Reduction Reaction

Heteroatom-doped porous carbon materials have recently attracted significant attention due to their superior catalytic activities for an oxygen reduction reaction (ORR). Transition metals co-doped with heteroatom are considered to have positive effects on improving ORR catalytic activity and stability. We report a series of novel Fe, Co incorporated in P-doped carbon materials, which give high ORR performance by an in-situ carbonization method. The ratios of the two metals and the carbonization temperatures are the key factors for the electrocatalytic activity. Due to the synergistic effect of the two transition metals, the Fe, Co incorporated in P-doped porous carbon sample, carbonized at 900°C, shows the highest catalytic activity and stability. Electrochemical measurements show that Fe, Co incorporated in P-doped porous carbon materials are promising electrocatalysts to substitute Pt-based catalysts for fuel cells application.

Exploring the effects of carbon meso-structure and macrostructure on the rate performance of porous carbon supercapacitors

Electrochemical double-layer capacitors are promising energy storage devices with high power density, moderate energy density, rapid charging rates, and high cycle life. In order to maximize energy density, highly porous carbon materials are often incorporated in the electrodes. The structure of the porous carbon network is critical to ensure high power delivery and charging rate. In this study, two types of oil sands petroleum cokes, from either batch or continuous industrial coking, were used to prepare porous carbon samples. The two activated petroleum coke samples have similar chemical compositions, specific surface areas, and pore size distributions, but due to the different industrial coking methods, the two samples have differing macrostructures and porous networks. Using mercury intrusion porosimetry and scanning electron microscopy, the meso-structure, macrostructure, and pore connectivity of the two samples were characterized and compared to the capacitance performance of the activated coke samples. The results show that, in order to ensure high rate performance, especially in ion depleted electrolyte scenarios, the porous carbon samples must have an interconnected network of pores between 10 and 1000 nm in diameter. These pore sizes are shown to improve the rate of ion diffusion, and allow greater capacitance values to be achieved at rapid charging rates.

Increase of porosity by combining semi-carbonization and KOH activation of formaldehyde resins to prepare high surface area carbons for supercapacitor applications

A series of porous carbon samples were prepared by combining a semi-carbonization process of acidic polymerized phenol-formaldehyde resins and a following chemical activation with KOH used in different ratios to increase specific surface area, micropore content and pore sizes of the carbons which is favourable for supercapacitor applications. Samples were characterized by nitrogen physisorption, powder X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The results show that the amount of KOH, combined with the semi-carbonization step had a remarkable effect on the specific surface area (up to SBET: 3595m2g−1 and SDFT: 2551m2g−1), pore volume (0.60–2.62cm3g−1) and pore sizes (up to 3.5nm). The carbons were tested as electrode materials for electrochemical double layer capacitors (EDLC) in a two electrode setup with tetraethylammonium tetrafluoroborate in acetonitrile as electrolyte. The prepared carbon material with the largest surface area, pore volume and pore sizes exhibits a high specific capacitance of 145.1Fg−1 at a current density of 1Ag−1. With a high specific energy of 31Whkg−1 at a power density of 33028Wkg−1 and a short time relaxation constant of 0.29s, the carbon showed high power capability as an EDLC electrode material.

The effect of KOH concentration on chemical activation of porous carbon sorbents for carbon dioxide uptake and carbon dioxide–methane selectivity: the relative formation of micro- (&lt;2 nm) versus meso- (&gt;2 nm) porosity

Porous carbon (PC) sorbents are synthesized from polymer precursors mixed with a chemical activation reagent and pyrolised (>500 °C). KOH is known to be the best activator for a wide range of precursors, as it creates PCs with a large surface area (1200–4000 m2 g−1). In order to determine the optimum KOH : polymer ratio for both CO2 adsorption and CO2/CH4 selectivity, we prepared a set of five S-containing porous carbon (SPC) samples from polythiophene (PTh) with increasing KOH : PTh ratio (1 to 5), and investigated CO2 and CH4 uptake measurements on carbonaceous SPC samples up to a pressure limit of 30 bar. The SPCs have been characterised by XPS, SEM, TEM and BET surface area analysis. Although the apparent surface area and total pore volume increased with increasing KOH concentration, the maximum CO2 uptake (5–30 bar) was demonstrated for samples with KOH : PTh = 3. This equates to SPC samples with a surface area and total pore volume of ∼2700 m2 g−1 and 1.5 cm3 g−1, respectively. Greater values for either parameter do not enhance the CO2 uptake, showing that it is not total porosity that is important. SPC samples formed with KOH : PTh = 3 show both a maximum C composition (85%), and a maximum fraction of micro-pores ( 2 nm). KOH : PTh = 3 is also the synthetic condition to maximise CH4 uptake (5–30 bar); however, the optimum CO2/CH4 selectivity occurred with KOH : PTh = 2. This correlates with a different surface area (2200 m2 g−1) and total pore volume (1.2 cm3 g−1) that are required for optimum CO2 uptake. These results suggest that process conditions that lead to high relative microporosity need to be considered rather than the total surface area or pore volume.

Preparation and Electrocapacitive Properties of Hierarchical Porous Carbons Based on Loofah Sponge.

Four porous carbon samples denoted as LSC-1, LSC-2, LCS-3, and LSC-4 were prepared by carbonization of loofah sponge pretreated by ZnCl2 activation, immersion in N,N-dimethylformamide (DMF), DMF-assisted solvothermal and melamine-assisted hydrothermal processes, and the specific surface areas were 1007, 799, 773, and 538 m2·g−1 with mainly micropores, respectively. Electrocapacitive properties of four porous carbon-based electrodes were investigated with cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy in symmetric supercapacitors. All the cyclic voltammetries of four types of supercapacitors showed a rectangular shape, even under a high scan rate of 500 mV·s−1. The capacitances of LSC-1, LSC-2, LSC-3, and LSC-4 were 107.4, 92.5, 60.3, and 82.3 F·g−1 at the current density of 0.1 A·g−1, respectively, and LSC-1 displayed the excellent capacitance retention of about 81.3% with a current density up to 5 A·g−1. All supercapacitors showed excellent electrochemical stability, and the LSC-1-based supercapacitor showed a cycle stability with 92.6% capacitance retention after 5000 cycles at 1 A·g−1. The structure–property relationship of LSC samples is discussed and analyzed on the basis of the experimental data.

A new approach to solid waste management: fabrication of supercapacitor electrodes from solid leather wastes using aqueous KOH electrolyte

Porous carbons prepared by carbonization of solid leather wastes were employed for supercapacitor applications using KOH electrolyte. Advanced instrumentation techniques were used to determine the physicochemical properties of the porous carbon samples. Three-electrode configuration was used to investigate the electrochemical properties of porous carbon electrodes through cyclic voltammetry studies, galvanostatic charge–discharge tests, electrochemical impedance spectroscopy (EIS) techniques in 1 M KOH electrolyte. Porous carbons exhibit high specific surface areas in a range of 613–716 m2 g−1, as well as superior energy storage capacity as electrodes for supercapacitors. Porous carbon electrodes activated at 900 °C exhibited specific capacitance up to 1800 F/g in alkali medium. All the solid leather waste carbons established stable cycle performance over 5000 cycles. These desirable capacitive performances enable solid leather waste-derived carbons as a source of new materials for low-cost energy storage devices as well as supercapacitors. This paper put forwards a new concept of ‘waste to value-added products’ that can be a helping hand for leather industries and its solid waste management disposal problems. The highlights of this research work suggest that leather industries could implement and make it feasible for commercialization.