Activated carbon prepared from PVDC by NaOH activation as electrode materials for high performance EDLCs with non-aqueous electrolyte

Mesoporous activated carbons with high surface area have been prepared from PVDC by NaOH activation for non-aqueous electric double layer capacitors (EDLCs). The BET surface area and pore volume of the carbon reach as high as 2675 m² g⁻¹ and 1.683 cm³ g⁻¹, respectively. The pore size of the carbon distributes mainly in small mesopore of 2∼4 nm, which is ideal for non-aqueous electrolyte EDLCs. The unique microstructure features, i.e. very high surface area and optimized pore size make the carbon present both a high capacitance of 155 F/g and outstanding rate capability in non-aqueous electrolytes. As the current density increases to 18?000 mA/g, it remains 109 F/g, an attractive value for EDLCs.     

Hydrogen storage in activated carbons produced from coals of different ranks: Effect of oxygen content

20 activated carbons (ACs) were prepared by activation of four coals of different ranks (bituminous, low-ash bituminous and sub-bituminous coals, and one anthracite) with potassium hydroxide, in order to evaluate their hydrogen storage capacities at −196 °C. The effect of surface area and oxygen content on hydrogen storage was examined. Oxygen content was determined by temperature-programmed desorption. The significance of oxygen content on hydrogen storage capacity was evaluated by Analysis of Variance (ANOVA). Apparent surface areas higher than 3000 m² g⁻¹ and hydrogen adsorption as high as 6.8 wt.% were obtained. The best results were obtained with ACs from bituminous coals. No significant effect of oxygen content on hydrogen adsorption was observed. We concluded that surface area controls hydrogen storage capacity at −196 °C.     

A novel hazelnutt bagasse based activated carbon as sodium borohydride methanolysis and electrooxidation catalyst

In this study, activated carbon is produced from defatted hazelnut bagasse at different activation conditions. The catalytic activities of activated carbons are evaluated for NaBH₄ methanolysis and electrooxidation. These materials are characterized by N₂ adsorption-desorption, FTIR, SEM-EDS and XPS and results show that these materials are prepared successfully. N₂ adsorption-desorption results reveal that activated carbon (FH3-500) has the highest BET surface area as 548 m²/g, total pore volume as 0.367 cm³/g and micropore volume as 0.205 cm³/g. On the orher hand, as a result of hydrogen production studies, FH3-500 activated carbon catalyst has the highest initial hydrogen production rate compared to other materials. At 50 °C, this metal-free activated carbon catalyst has a high initial hydrogen production rate of 13591.20 mL/min.g_cat, which is higher than literature values. Sodium borohydride electrooxidation measurements reveal that FH2-500 also has the highest electrocatalytic activity and stability. Hazelnut pulp-based activated carbons are firstly used as a metal-free catalyst in the methanolysis and electrooxidation of sodium borohydride, and its catalytic activity is good as a metal-free catalyst. The results show that the hazelnut pulp-based activated carbon catalyst is promising as a metal-free catalyst for the methanolysis and electrooxidation of sodium borohydride.     

Preparation and hydrogen storage capacity of highly porous activated carbon materials derived from polythiophene

Highly porous carbons have been successfully synthesized by chemical activation of polythiophene with KOH. The activation process was performed under relatively mild activation conditions, i. e., a KOH/polymer weight ratio of 2 and reaction temperatures in the 600-850 °C range. The porous carbons thus obtained possess very large surface areas, up to 3000 m²/g, and pore volumes of up to 1.75 cm³/g. The pore size distribution of these carbons can be tuned via modification of the activation temperature. Thus, by increasing the activation temperature from 600 to 850 °C, the nature of the carbons changes gradually from microporous to micro-mesoporous (with small mesopores of up to 2.5 nm). The polythiophene-derived activated carbons are sulfur-doped with sulfur contents in the 3-12 wt% range. The sulfur content decreases at higher activation temperature. The hydrogen storage capacity of these activated carbons, at cryogenic temperature and 20 bar, is up to 5.71 wt% with an estimated maximum hydrogen uptake of 6.64 wt%. Their ease of preparation and high uptake makes the polythiophene-derived carbons attractive hydrogen storage materials.     

Development of highly microporous activated carbon from the alcoholic beverage industry organic by-products

This work has the aim to employ the agave bagasse, a waste from Tequila and Mescal industries, to obtain a product of high commercial value such as activated carbon. The activated carbon production methodology was based on a chemical activation, by using ZnCl₂ and H₃PO₄ as activating agent and agave bagasse as a natural source of carbon. The activation temperature (150-450 °C), activation time (0-60 min) and weight ratio of activating agent to precursor (0.2-4) were studied. The produced carbon materials were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and nitrogen physisorption at −196 °C. In addition, the activating agent recovery was evaluated. We were able to obtain highly microporous activated carbons with micropore volumes between 0.24 and 1.20 cm³/g and a surface area within 300 and 2139 m²/g. These results demonstrated the feasibility to treat the industrial wastes of the Tequila and Mescal industries, being this wastes an excellent precursor to produce highly microporous activated carbons that can be processed at low activation temperatures in short times, with the possibility of recycling the activating agent.     

A study on optimal pore range for high pressure hydrogen storage behaviors by porous hard carbon materials prepared from a polymeric precursor

In this study, activated polymer-based hard carbons were prepared using various steam activation conditions in order to enhance their hydrogen storage ability. The structural characteristics of the activated carbons were observed by X-ray diffraction and Raman spectroscopy. The N₂ adsorption isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and non-local density functional theory equations. The hydrogen storage behaviours of the activated carbons at 298 K and 10 MPa were studied using a Pressure-Composition-Temperature apparatus. From the results, specific surface areas and total pore volume of the activated carbons were determined to be 1680–2320 m²/g and 0.78–1.39 cm³/g, respectively. It was also observed that various pore size distributions were found to be dependent on the functions of activation time. In the observed result, the hydrogen adsorption of APHS-9-4 increased about 30% more than that of as-prepared hard carbon. This indicates that hydrogen storage capacity could be a function not only of specific surface area or total pore volume, but also of micropore volume fraction in the range of 0.63–0.78 nm of adsorbents.     

Optimization and characterization of sliced activated carbon prepared from date palm tree fronds by physical activation

Sliced activated carbons were prepared from palm tree fronds, a biomass material, using a single step physical method. Effect of the synthetic parameters on the surface area, pore size and pore volume of the activated carbon were studied, pursuing by the optimization of studied parameters. The activation temperature, heating ramp rate, reaction vessel pressure and the CO₂ flowrate were found to be the influential parameters for the synthesis of sliced activated carbon with larger porosity and surface area. The optimum conditions to synthesize the porous activated carbon bearing high pore volume and surface area were studied and identified. Highest surface area of 1094 m² g⁻¹ was achieved under the optimum conditions. Scanning electron microscopy (SEM) for the porosity and Fourier transform infrared spectroscopy (FTIR) for surface functional groups and transmission electron microscopy (TEM) confirms the presence of uniform nanoparticles of 2.1385 nm.     

Scope of doped mesoporous (<10 nm) surfactant‐modified alumina templated carbons for hydrogen storage applications

Metal (Ni/Pd) and nitrogen codoped mesoporous templated carbons were synthesized using low‐cost surfactant‐modified mesoporous alumina as a hard template via chemical vapor deposition for hydrogen storage application. Initially, high surface area (1508 m²/g) nitrogen‐doped templated carbon was successfully prepared. Pore volume was also significant (1.64 cm³/g). The codoping with metals (Ni or Pd) reduced both the area and pore volume. All the codoped carbons were mesoporous (2‐8 nm). Aggregated morphology was observed for nitrogen‐doped carbon; tubular or noodle shape appeared on codoping with metals. The dispersion of Pd metal within the carbon framework was highest. The 2 wt% Pd codoped carbon showed the highest hydrogen uptake of 5 wt% (?196°C; 25 bar). This may be attributed to its most number of active sites corresponding to the highest metal dispersion and amount of nitrogen present. The cyclic stability of the samples was also good with only 3% to 5% loss in storage capacity up to 10 cycles.     

Preparation and characterization of activated carbon from pistachio nut shells via microwave-induced chemical activation

In this work, pistachio nut shell, a biomass residue abundantly available from the pistachio nut processing industries, was utilized as a feedstock for the preparation of activated carbon (PSAC) via microwave assisted KOH activation. The activation step was performed at the microwave input power of 600 W and irradiation time of 7 min. The porosity, functional and surface chemistry were featured by means of low temperature nitrogen adsorption, scanning electron microscopy and Fourier transform infrared spectroscopy. Result showed that the BET surface area, Langmuir surface area, and total pore volume of PSAC were 700.53 m² g⁻¹, 1038.78 m² g⁻¹ and 0.375 m³ g⁻¹, respectively. The adsorptive property of PSAC was tested using methylene blue dye as the targeted adsorbate. Equilibrium data was best fitted by the Langmuir isotherm model, showing a monolayer adsorption capacity of 296.57 mg g⁻¹. The study revealed the potentiality of microwave-induced activation as a viable activation method.     

Surface texture, chemistry and adsorption properties of acid blue 9 of hemp (Cannabis sativa L.) bast-based activated carbon fibers prepared by phosphoric acid activation

Hemp (Cannabis sativa L.) bast was used to prepare activated carbon fibers by phosphoric acid activation at 400-600 °C. The pyrolysis process, textural and chemical properties for the samples were investigated by means of TG/DTA, SEM, cryogenic N₂ adsorption, FTIR and XPS. Dye adsorption on the resultant sample was also measured. The textural properties of the activated carbon fibers were found to be strongly dependent on the activation temperature. Activated carbon fibers exhibited narrow pore size distributions with maxima in the micropore and small mesopore regions. BET surface area, total pore volume, micropore volume and mesopore volume increased with the increase of activation temperature up to 450 °C and then decreased with further heating, and a sample with maximum surface area of 1142 m² g⁻¹ and total pore volume of 0.67 cm³ g⁻¹ was obtained. Phosphoric acid facilitated the conservation of porous structure, led to the creation of tremendous porosity, and resulted in various P-containing functional structures on the surface and in the bulk phase of the resultant samples. The adsorption of acid blue 9 on the sample could be favorably described by Langmuir isotherm, and the adsorption kinetics was found to be well fitted by the intraparticle diffusion model.     

A simple method for the production of highly ordered porous carbon materials with increased hydrogen uptake capacities

The synthesis, characterization and hydrogen uptake of porous carbons generated by heat treatment was investigated using various zeolites and mesoporous silicas as hard templates. The effect of heat treatment on the structural order, textural properties and hydrogen uptake capacities of porous carbons templated from the model zeolite EMC-2 in a temperature range of 600–800 °C during chemical vapour deposition were studied in details. The heat treatment improved the structural order of replicated microporous carbons, significantly increased both total and microporous surface area and pore volume, and remarkably increased the hydrogen uptake capacity. The optimized heat treatment conditions were at 900 °C for 3 h. The heat treatment at high temperatures was found to be a simple and general approach to synthesize well-ordered microporous carbons from different zeolite templates, using various carbon precursors and through different synthesis methods. The microporous carbons possessed a high surface area and pore volume with increased microporosity and therefore exhibited improved hydrogen storage capacities up to 5.85 wt% at 20 bar and −196 °C. The heat treatment, however, has no obvious effect on the textural properties and hydrogen uptake capacities for mesoporous carbons templated from mesoporous silicas.     

The comparison of two activation techniques to prepare activated carbon from corn cob

We report on the preparation of biomass-based activated carbons by the steam physical activation and KOH chemical activation methods. In addition, we also investigate their adsorption performance. By adjusting the reaction parameters, different carbon materials are prepared from corn residues and characterized using instrumental analyses such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer–Emmett–Teller (BET). It is found that the synthesized activated carbons exhibit high surface area (1600 m² g⁻¹) and large pore volume (2.01 cm³ g⁻¹). Furthermore, the high methylene blue and iodine adsorption value and a considerable CO₂ uptake (exceeding 1.5 mmol g⁻¹) are attained with the activated carbons, showing their potential usage for the CO₂ adsorbent.     

Effect of physical activation/surface functional groups on wettability and electrochemical performance of carbon/activated carbon aerogels based electrode materials for electrochemical capacitors

Polymeric carbon/activated carbon aerogels were synthesized through sol-gel polycondensation reaction followed by the carbonization at 800 °C under Argon (Ar) atmosphere and subsequent physical activation under CO₂ environment at different temperatures with different degrees of burn-off. Significant increase in BET specific surface area (SSA) from 537 to 1775 m²g⁻¹ and pore volume from 0.24 to 0.94 cm³g⁻¹ was observed after physical activation while the pore size remained constant (around 2 nm). Morphological characterization of the carbon and activated carbons was conducted using X-ray diffraction (XRD) and Raman spectroscopy. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to investigate the effect of thermal treatment (surface cleaning) on the chemical composition of carbon samples.Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to analyse the capacitive and resistive behaviour of non-activated/activated/and surface cleaned activated carbons employed as electroactive material in a two electrode symmetrical electrochemical capacitor (EC) cell with 6 M KOH solution used as the electrolyte.CV measurements showed improved specific capacitance (SC) of 197 Fg⁻¹ for activated carbon as compared to the SC of 136 Fg⁻¹ when non-activated carbon was used as electroactive material at a scan rate of 5 mVs⁻¹. Reduction in SC from 197 Fg⁻¹ to 163 Fg⁻¹ was witnessed after surface cleaning at elevated temperatures due to the reduction of surface oxygen function groups.The result of EIS measurements showed low internal resistance for all carbon samples indicating that the polymeric carbons possess a highly conductive three dimensional crosslinked structure. Because of their preferred properties such as controlled porosity, exceptionally high specific surface area, high conductivity and desirable capacitive behaviour, these materials have shown potential to be adopted as electrode materials in electrochemical capacitors.     

Agricultural residues as precursors for activated carbon production—A review

A review of the production of activated carbons from agricultural residues is presented. The effects of various process parameters on the pyrolysis stage are reviewed. Influences of activating conditions, physical and chemical, on the active carbon properties are discussed. Under certain process conditions several active carbons with BET surface areas, ranging between 250 and 2410 m²/g and pore volumes of 0.022 and 91.4 cm³/g, have been produced. A comparison in characteristics and uses of activated carbons from agricultural residues with those issued from tires, and commercial carbons, have been made. A review is carried out of the reaction kinetic modelling, applied to pyrolysis of agricultural wastes and activation of their pyrolytic char.     

Development of activated carbon pore structure via physical and chemical activation of biomass fibre waste

Biomass waste in the form of biomass flax fibre, produced as a by-product of the textile industry was processed via both physical and chemical activation to produce activated carbons. The surface area of the physically activated carbons were up to 840 m² g⁻¹ and the carbons were of mesoporous structure. Chemical activation using zinc chloride produced high surface area activated carbons up to 2400 m² g⁻¹ and the pore size distribution was mainly microporous. However, the process conditions of temperature and zinc chloride concentration could be used to manipulate the surface area and porosity of the carbons to produce microporous, mesoporous and mixed microporous/mesoporous activated carbons. The physically activated carbons were found to be a mixture of Type I and Type IV carbons and the chemically activated carbons were found to be mainly Type I carbons. The development of surface morphology of physically and chemically activated carbons observed via scanning electron microscopy showed that physical activation produced activated carbons with a nodular and pitted surface morphology whereas activated carbons produced through chemical activation had a smooth surface morphology. Transmission electron microscopy analysis could identify mesopore structures in the physically activated carbon and microporous structures in the chemically activated carbons.     

Thermochemical method for controlling pore structure to enhance hydrogen storage capacity of biochar

Developing new carbon-based hydrogen storage materials can significantly promote solid-state hydrogen storage technology. Biochar with high hydrogen storage capacity can be prepared by KOH melt activation, which has a high proportion of micropores (96.56%) compared with the porous carbon in the existing literature. Its specific surface area and pore volume are 2801.88 m²/g and 1.44 cm³/g, respectively. The size of the nanopores is affected by the activation ratio, but the temperature has little effect at the low activation ratio. SEM results show that the KOH activation process gradually shifts from the biochar's inside to the outside. A low KOH/char ratio (less than 2:1) can promote the formation of small aromatic rings. Due to its high specific surface area and microporosity, the absolute adsorption capacity of hydrogen in biochar is 2.53 wt% at −196 °C and 1 bar, rising to 5.32 wt% at 50 bar. The hydrogen adsorption process conforms to the Langmuir model. Microporous, mesoporous, and macroporous exhibit different hydrogen adsorption characteristics in various pressure ranges. However, ultramicroporous (<0.7 nm) always plays a decisive role in the hydrogen storage of biochar.     

Data-driven modelling and optimization of hydrogen adsorption on carbon nanostructures

In the present study, using modelling based on experimental data, models for predicting the hydrogen adsorption isotherm were presented. The three Automatic Learning of Algebraic Models (ALAMO), feed-forward artificial neural networks (ANNs), and group method of data handling-type polynomial neural networks (GMDH-PNN) were constructed. The created models were evaluated to predict the equilibrium data of hydrogen storage on carbon nanostructures, including activated carbons doped with palladium (Pd) nanoparticles, fullerene pillared graphene nanocomposites, and nickel (Ni)-decorated carbon nanotubes. The inputs were nanostructure characteristics such as surface area, pore-volume, and thermodynamic conditions such as pressure. The generalization of the trained models was acceptable, and the models successfully predicted the hydrogen adsorption isotherm for new inputs. The relative error percentage for most data points is less than 4%, which demonstrates their applicability in determining adsorption isotherms for any operating conditions. By performing error analysis calculations, it was shown that the ALAMO model has the highest accuracy. Also, sensitivity analysis calculations show that pressure is the most influential parameter in the adsorption process. Besides, by performing Genetic Algorithm (GA) optimization using the ALAMO model, the amount of pressure and adsorbent properties were determined so that the amount of hydrogen adsorption is maximized. According to the optimization results based on the GA, the higher the pressure, the greater the amount of hydrogen adsorption. The nanotubes with a surface area of 194.15 m²/g, a total volume of 1.8 cm³/g, micropore volume of 0.097 cm³/g, and mesopore volume of 0.963 cm³/g, graphene with a surface area of 2977.13 m²/g, a total volume of 1.5134 cm³/g, density of 617.45 kg/m³, and activated carbon at pressures less than 30 bar with a surface of 2546.36 m²/g, a total volume of 1.237 cm³/g, micropore volume of 0.839 cm³/g, and activated carbon at pressures more than 30 bar with a surface of 3027 m²/g, a total volume of 1.343 cm³/g, a micropore volume of 0.9582 cm³/g, and a mesopore volume of 1.23 cm³/g, have the highest amount of stored hydrogen.     

Promising electrochemical hydrogen storage properties of nano biomass derived from walnut shell

Novel nano biomass (NBM) was synthesized using a general and simple synthetic approach. In this process, the walnut shell is used as a green carbon source. According to the transmission electron microscopy and dynamic light scattering results, the average particle size of the produced activated carbon was 2.25 nm. The surface area of the NBM was around 420.5 m²/g totally. High pore volume, high internal surface area, lightweight as well as easy availability are some features that attract research interests on activated carbon as a solid-state hydrogen storage medium. Nano biomass was deposited directly on a copper substrate by the slurry-coating method. The electrochemical properties of nano biomass were investigated in a three-electrode electrolytic cell with 6 M KOH as the electrolyte by galvanostatic charging and discharging. Several parameters such as the impact of the number of charge and discharge cycles and discharge time are studied. Different experimental results show that Cu-NBM has 1596 mAh/g discharge capacity (corresponding to a hydrogen storage capacity of 5.66 wt%) after 16 cycles at room temperature and atmospheric conditions. Due to porosity of NBM particles, the nano biomass showed reversible hydrogen storage capacities that were better than those of previously reported porous carbons.     

Structure and electrochemical properties of activated polyacrylonitrile based carbon fibers containing carbon nanotubes

Solution spun polyacrylonitrile (PAN), PAN/multi-wall carbon nanotube (MWCNT), and PAN/single-wall carbon nanotube (SWCNT) fibers containing 5 wt.% carbon nanotubes were stabilized in air and activated using CO₂ and KOH. The surface area as determined by nitrogen gas adsorption was an order of magnitude higher for KOH activated fibers as compared to the CO₂ activated fibers. The specific capacitance of KOH activated PAN/SWCNT samples was as high as 250 F g⁻¹ in 6 M KOH electrolyte. Under the comparable KOH activation conditions, PAN and PAN/SWCNT fibers had comparable surface areas (BET surface area about 2200 m² g⁻¹) with pore size predominantly in the range of 1–5 nm, while surface area of PAN/MWCNT samples was significantly lower (BET surface area 970 m² g⁻¹). The highest capacitance and energy density was obtained for PAN/SWCNT samples, suggesting SWCNT advantage in charge storage. The capacitance behavior of these electrodes has also been tested in ionic liquids, and the energy density in ionic liquid is about twice the value obtained using KOH electrolyte.     

Electrical double layer capacitors with sucrose derived carbon electrodes in ionic liquid electrolytes

Activated carbons were prepared via a pyrolysis of sucrose followed by activation in the stream of CO₂ gas for 2-6 h at 900 °C to tune the pore size distribution (PSD) and increase the specific surface area (SSA). The porosity of the activated sucrose derived carbons (ASCs) has been characterized using N₂ sorption measurements. Increasing activation time led to the significant increase in SSA and pore volume of ASCs, among which sucrose derived carbon with 6 h activation time (ASC-6 h) exhibited the highest SSA of 1941 m² g⁻¹ and the highest micropore volume of 0.87 cm³ g⁻¹. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge cycle tests have been applied to investigate the capacitive performance of the ASC electrodes in ionic liquids (ILs) at room and elevated temperatures. The ASC-6 h electrodes in ethyl-dimethyl-propyl-ammonium bis (trifluoromethylsulfonyl) imide (EdMPNTf₂N) showed specific capacitance in excess of 170 F g⁻¹ at 60 °C, whereas the same electrodes in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) showed slightly lower capacitance but significantly better rate performance.