KOH Activation Process Research Articles

Phytoplankton derived and KOH activated mesoporous carbon materials for supercapacitors

An activated phytoplankton-derived carbon (APDC) based material was successfully synthesized from phytoplankton for the first time via a simple and low-cost method, to the best of our knowledge. The specific surface area (SBET) value of APDC is as high as 482m2g−1. In addition, the as-prepared APDC-based supercapacitor (SC) electrode displays high area capacitance of 130mFcm−2 at the current density of 2mAcm−2, and the SC device based on APDC electrode reveals good capacitance performance and prominent cycling stability (92% retention after 10,000 cycles), demonstrating a promising application for SCs. The high supercapacitor performance is attributed to the KOH activation process which brings higher surface area and mesoporous structure.

Sustainable fabrication of nitrogen activated carbon from chlorella vulgaris for energy storage devices

Porous carbons were successfully prepared from nitrogen containing microalgae by the carbonization and KOH activation processes. The materials thus synthesized showed surface areas ranging from 1210 to 2433m2/g and nitrogen contents ranging from 21.8 to 1.40wt.% due to the use of N-rich microalgae as a carbon precursor. The samples synthesized at 700°C with char: hydroxide=1: 5 exhibited excellent endurance, with specific capacitances of 117F/g at 0.5A/g.

Multiple Functional Biomass‐Derived Activated Carbon Materials for Aqueous Supercapacitors, Lithium‐Ion Capacitors and Lithium‐Sulfur Batteries

AbstractBiomass‐derived activated carbon electrode materials have been synthesized by carbonization and KOH activation processes from an agriculture waste − rice husk, composed of organic compound and silica. The surface area of activated carbon reached 1098.1 m2/g mainly including mesopores and macropores due to the template effect of silica in rice husk. Owing to the existence of mesopores and macropores, the as‐obtained activated carbon materials can be used in aqueous supercapacitors, lithium‐ion (Li‐ion) capacitors and lithium‐sulfur (Li‐S) batteries. In KOH electrolyte, fast rate performance (as high as 2 V/s) was obtained due to the existence of ideal electrical double layer capacitance. In organic electrolyte, high voltage (2.5 V) was achieved. Activated carbon electrode for Li‐ion capacitor also showed capacity of 17 mAh/g at 100 mA/g with the high voltage range of 2.5 V. The capacities of sulfur‐activated carbon in Li‐S batteries were 1230 and 970 mAh/g at the current densities of 0.1 and 0.2 C. The present results showed that activated carbon materials with mesopores were good host to immobilize polysulfides.

Hierarchical porous carbon from hazardous waste oily sludge for all-solid-state flexible supercapacitor

Rationally packed porous carbon with high ion-accessible surface area and low ion-transport resistance is proved to be an excellent candidate as electrode materials in high performance supercapacitors. However, its cost-effective fabrication still remains a significant challenge. Here, we report on a novel three-dimensional hierarchical porous carbon (HPC) synthesized via a facile and low-cost approach from hazardous waste oily sludge for the first time. Both the smart “self-template” effect and appropriate activation effect are crucial for the rational hierarchical porous structure. The “self-template” procedure is the key point for creating the skeleton of carbon, and the KOH activation process is able to regulate pore size distribution and increase specific surface area. The as-fabricated HPC possesses favorable features for supercapacitor, such as outstanding specific surface area (2561m2g−1), large pore volume (2.25cm3g−1), tunable and large range of pore size distribution. The HPC-based electrode can deliver an admirable capacitance of 348.1Fg−1 at 0.5Ag−1 and 94.3% capacitance retention at 5Ag−1 after 10,000 cycles in aqueous electrolyte. Remarkably, the all-solid-state HPC//HPC symmetric supercapacitor displays outstanding capacitance of 81.3Fg−1 at 0.5Ag−1 with high energy density of 7.22W h kg−1. It is demonstrated that the strategy developed here would provide cost-effective production of HPC electrode material for high performance supercapacitors and offer a promising avenue of large-scale fabrication of HPC from other hazardous industrial waste.

A novel approach to fabricate carbon sphere intercalated holey graphene electrode for high energy density electrochemical capacitors

Desirable porous structure and huge ion-accessible surface area are crucial for rapid electronic and ionic pathway electrodes in high-performance graphene-based electrochemical capacitors. However, graphene nanosheets tend to aggregate and restack because of van der Waals interaction among graphene sheets, resulting in the loss of ion-accessible surface area and unsatisfactory electrochemical performance. To resolve this daunting challenge, a novel approach is developed for the self-assembly of holey graphene sheets intercalated with carbon spheres (H-GCS) to obtain freestanding electrodes by using a simple vacuum filtration approach and a subsequent KOH activation process. Through the introduction of carbon spheres as spacers, the restacking of reduced graphene oxide (rGO) sheets during the filtration process is mitigated efficiently. Pores on rGO sheets produced by subsequent KOH activation also provide rapid ionic diffusion kinetics and high ion-accessible electrochemical surface area, both of which favor the formation of electric double-layer capacitance. Furthermore, a higher degree of graphitization of CSs in H-GCS thin film improves the electrical conductivity of the H-GCS electrode. The H-GCS electrode exhibits 207.1Fg−1 of specific capacitance at a current density of 1Ag−1 in 6MKOH aqueous electrolyte. Moreover, the symmetric electrochemical capacitor assembled with H-GCS electrodes and organic electrolyte is capable of delivering a maximum energy density of 29.5Whkg−1 and a power density of 22.6kWkg−1.

Synthesis of Bamboo-Based Activated Carbons with Super-High Specific Surface Area for Hydrogen Storage

Activated carbons (ACs) were developed from the agricultural by-products of moso bamboo by pyrolysis carbonization and the KOH activation process. N2 adsorption-desorption at 77 K, thermogravimetric analysis (TG), X-ray photoelectron spectrometry (XPS), element analysis (EA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high- resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FTIR) were used to investigate the synthesis process, the impact of the weight ratio of KOH/bamboo charcoal (BC), and the characteristics of the bamboo charcoal and ACs produced. The results showed that the developed bamboo ACs achieved surface areas (SBET) as high as 3208 m2/g and micropores volumes (VDR) as high as 1.01 cm3/g. The carbonation and activation of the bamboo resulted in the enhancement of the microstructure of the bamboo ACs, and hence improvements in the sorption behavior and storage capacity. The highest hydrogen storage capacities achieved were 6.6 wt.% at 4 MPa and 2.74 wt.% at 1 bar, both at 77 K, which were much higher than those of a well-known commercial activated carbon.

Resin-derived activated carbons with in-situ nitrogen doping and high specific surface area for high-performance supercapacitors

Nitrogen-doped porous carbons (NPCs) for high-performance supercapacitors have been fabricated from urea formaldehyde microspheres via a one-step carbonization and KOH activation process. The NPCs possess a nitrogen content of 2.08at.% and an ultra-high specific surface area of 3318m2g−1 with abundant micropores. When used as electrode materials for supercapacitors, the NPCs exhibit excellent electrochemical performance with a high specific capacitance of 343Fg−1 at 0.5Ag−1 in 1M H2SO4 aqueous electrolyte and a good rate capability of 234Fg−1 (68% capacitance retention) at 30Ag−1. Furthermore, the NPCs electrode demonstrates a robust long-term stability without capacitance fading after 5000 cycles.

KOH-activated carbon aerogels derived from sodium carboxymethyl cellulose for high-performance supercapacitors and dye adsorption

In this paper, we present a facile and eco-friendly approach for the synthesis of porous carbon aerogels by sol–gel processing, freeze-drying, and pyrolysis of sodium carboxymethyl cellulose aerogels. The obtained carbon aerogels were further treated via a KOH activation process. The results showed that the as-prepared carbon aerogels exhibited a high specific surface area of 428m2/g after KOH activation for 3h. The highly porous and interconnected three-dimensional nanostructure provided efficient migration of electrolyte ions and electrons, and thus the activated carbon aerogels exhibited excellent electrochemical performance for supercapacitors. The specific capacitances reached 152.6F/g at a current density of 0.5A/g within a potential window of −1.0 to 0V in a 6M KOH solution. In addition, the carbon aerogels showed excellent adsorption capacity for methylene blue and malachite green, which reached 249.6mg/g and 245.3mg/g, respectively. The excellent electrochemical performance and adsorption capacities showed the carbon aerogels to be a high-performance and promising material for supercapacitors and adsorbents.

Double Reinforced Energy Storage of Graphene By KOH Activation and Nitrogen Doping

For the goal of synthesizing high performance supercapacitor electrode materials to meet the pressing requirements of energy storage, nitrogen doped activated graphene (N-AG) was successfully synthesized by employing two steps as KOH activating and following nitrogen doping using a hydrothermal method. Continuously increased ID/IG ratios were observed in Raman spectra after KOH activation and N-doping process, indicating increased defects due to the etching effect of KOH and the introduced nitrogen defects on graphene sheet. Stacked graphene with damaged sheets on the surface was clearly seen in transmission electron microscopy (TEM) image after the KOH etching. The successful dopant of N was demonstrated by X-ray photoelectron spectroscopy (XPS) spectra and energy-dispersive X-ray spectroscopy (EDS) mapping, confirming this effective hydrothermal N doping method. The N-AG exhibited largely enhanced capacitance (186.63 F/g) and cycling stability compared with that of nitrogen doped graphene (N-G, 50.88 F/g) and activated graphene (AG, 58.38 F/g) due to the combined positive effects of KOH activation and N-doping. This facile hydrothermal method is of great significance of scaling the production and the synthesized N-AG through combining the KOH activation and nitrogen doping processes represents a promising alternative candidate to commonly used electrode materials in supercapacitor. Experimental Graphite oxide (GO) was synthesized following the modified Hummers method.1 For the synthesis of nitrogen doped graphene (N-G) and KOH activated graphene (AG), 26.0 g homogeneous GO solution (0.338 g GO) was first transferred to a 40 mL teflon lined hydrothermal autoclave, 3 mL NH4OH solution or well dissolved KOH solution (4.05 g KOH, mass KOH : GO = 12:1) was added, the solution was diluted to 40 mL by DI water and sealed maintaining at 150 ºC for 3 hrs. After cooling down, the precipitates were collected by filtration and washed with water for 3 times, the products were dried naturally for 72 hours. Reduced graphene oxide (RGO) was also obtained following the same procedure using simple GO solutions as a control experiment. For the synthesis of N-AG, 0.2 g synthesized AG powders were uniformly grinded and dissolved in 30 mL water, which undergo a 30 min sonication to achieve a uniform distribution, the AG solution was then transferred to a 40 mL autoclave added with 1.80 mL NH4OH solution (same NH4OH/AG ratio as that of NH4OH/GO). Similar procedures were following proceeded to obtain the N-AG powder products. Results and Discussion The Raman spectroscopy and TEM have successfully demonstrated the increased defects and edge parts on graphene after the activation with KOH. Typical N peaks deconvoluted from XPS and uniform distribution of N observed from EDS mapping clearly indicate the successful doping of N using this facile hydrothermal method. Activation and N-doping processes can both contribute to the enhancement of energy storage through increasing active electronic sites and surface area. Increased capacitance, energy and power densities as well as cycling stability after the activation and N-doping processes are confirmed by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements,2demonstrating the effectiveness of this hydrothermal method and potential of this N-AG for practical energy storage applications. Conclusion A facile hydrothermal synthesis method combining KOH activation and N-doping was successfully employed to synthesize nitrogen doped activated graphene, which is economically and effectively at a very high yield, implying feasibility for mass production. The synthesized N-AG exhibited relatively decreased oxygen containing groups with increased defects due to the etching nature of KOH and N containing defects were also introduced with this effective N doping method. These unique properties endow them as promising electrodes for supercapacitors with high capacity, excellent rate capability, and long-term stability. Due to the possibility of scalable synthesis and prominent properties, the N-AG can offer attractive opportunities for both fundamental study and potential industrial applications in catalysis, adsorption, energy storage, and energy conversion systems. Acknowledgments The financial supports from University of Tennessee Knoxville are kindly acknowledged. Figure 1. Charge−discharge of RGO, N-G, AG and N-AG with a current density as 1 A/g. Background is a schematic representation of the synthesis process.

Superior Lithium-Ion Storage at Room and Elevated Temperature in an Industrial Woodchip Derived Porous Carbon

An industrial pyrolysis process converted loblolly pine tree woodchips into porous carbonaceous particles that are tested as a promising lithium ion battery anode. SureCarbon, a Tennessee company, demonstrated scalability for the KOH activation and pyrolysis process by producing hundreds of kilograms of carbon from the sustainable wood precursor. Material characterization reveals amorphous carbon structure, with 1580 m2/g BET surface area and 0.883 cc/g pore volume. Galvanostatic cycling was performed at a C/10 rate in a half cell (carbon vs Li+/Li), achieving a stable capacity of 700 mAh/g and 1000 mAh/g at 22 and 50 °C, respectively. Cycling at 50 °C increases lithium ion diffusion rates into the electroactive carbon but lowers the Coulombic efficiency and long-term cell cyclability due to electrolyte degradation. Electrochemical impedance spectroscopy studies reveal the decreased charge transfer and diffusional resistance in a porous carbon electrode compared to conventional graphite, making it an attr...

Hierarchically Porous N-Doped Carbon Nanosheets Derived From Grapefruit Peels for High-Performance Supercapacitors

In this work, the low-cost hierarchically porous nitrogen-doped carbon nanosheets (PNCNs) were prepared via one-step carbonization and KOH activation process of grapefruit peels. The prepared PNCNs exhibit higher specific surface area due to the inducement of the KOH-assisted carbonization compared to directly carbonized grapefruit peels (DCGPs). The PNCNs exhibit excellent electrochemical performances with high specific capacitance up to 311 F g−1, superior cycling stability over 10000 cycles with only 5.95 % capacitance degradation, high energy density of 17.7 W h kg−1 and power density of 1100 W kg−1 in 1 mol L−1 H2SO4 electrolyte. All these electrochemical data are significantly better than the comparative DCGPs material. Moreover, the assembled symmetric supercapacitor in 1 mol L−1 Na2SO4 aqueous electrolyte exhibits a high energy density of 34.05 W h kg−1 at a power density of 180 W kg−1 and retains 14.25 W h kg−1 even at 5400 W kg−1.

Remarkable adsorption capacity of Ni-doped magnolia-leaf-derived bioadsorbent for congo red

A novel high-performance porous carbon material, nickel-doped magnolia-leaf-derived porous carbon (Ni/MPC), is synthesized by a KOH activation process and nickel-doping strategy. The morphology, microstructure, and element composition of Ni/MPC are characterized by scanning electron microscopy, nitrogen adsorption and desorption, and X-ray photoelectron spectroscopy, respectively. Removal of anionic dye congo red (CR) from contaminated water was performed in a batch reactor system to obtain adsorption kinetics and isotherms. The results showed that pseudo-second-order kinetic model and Langmuir adsorption isotherm matched well for the adsorption of CR onto Ni-doped MPCs. Compared with previously reported adsorbents, Ni/MPCs demonstrated a superior CR dye adsorption capability. The results of the present study substantiate that Ni/MPC is a promising adsorbent for the removal of the anionic dyes from wastewater.

Porous N-doped carbon microfibres derived from cattail as high-performance electrodes for supercapacitors

Nitrogen-doped carbon microfibres were produced by carbonisation of cattail seeds and subsequent KOH activation. The KOH activation process produces a large surface area of 2,486 m2 g−1. The carbon derived from cattail contains N heteroatom with a content of 1.6%. Benefiting from the large surface area and unique microstructure of the nitrogen-doped carbon microfibres material, these materials demonstrate superior capacitive properties with a large capacitance of 214 F g−1 at the current density of 1 A g−1 and excellent cycle stability. When current densities is increased to 10 and 90 folds from 1 A g−1, capacitance retention is about 87 and 52%, implying excellent rate performance and high power densities. Based on the nitrogen-doped carbon microfibres, a symmetrical and aqueous supercapacitor device was also assembled, which show a considerable capacitance of 105 F g−1 at the current density of 1 A g−1 and perfect long ability. Such excellent performance is at least comparable to the best reports in the literature for two-electrode configuration under aqueous system. The facile method and excellent capacitive properties of nitrogen doped carbon fibres suggest promising applications as advanced supercapacitors.

Low-cost, green synthesis of highly porous carbons derived from lotus root shell as superior performance electrode materials in supercapacitor

Facile production of high quality activated carbons from biomass materials has greatly triggered much attention presently. In this paper, a series of interconnected porous carbon materials from lotus root shells biomass are prepared via simple pyrolysis and followed by a KOH activation process. The prepared carbons exhibit high specific surface areas of up to 2961 m2/g and large pore volume ∼1.47 cm3/g. In addition, the resultant porous carbons served as electrode materials in supercapacitor exhibit high specific capacitance and outstanding recycling stability and high energy density. In particular, their specific capacitance retention was almost 100% after 10500 cycles at a current density of 2 A/g. Remarkabely, the impact of the tailored specific surface areas of various carbon samples on their capacitive performances is systematically investigated. Generally, it was believed that the highly-developed porosity features (including surface areas and pore volume and pore size-distributions), together with the good conductivity of activated carbon species, play a key role in effectively improving the storage energy performances of the porous carbon electrode materials in supercapacitor.

Adsorption and removal of tetracycline from water by petroleum coke-derived highly porous activated carbon

Herein, petroleum coke (PC) derived activated carbons (ACs) were prepared via KOH activation process. The as-prepared ACs exhibited a large surface area (2800–2900m2/g) and total pore volume (1.4–2.1cm3/g). In addition, the oxygen-correlated functional groups endow the resultant ACs with an acid surface. Combining the structural characters with the surface properties, these ACs were successfully applied for the effective removal of a commonly-used antibiotics (tetracycline) from drinking water for the first time. As a typical example, the maximum adsorption capacities of 897.6, 961.5 and 1121.5mg/g were obtained at the temperature of 303, 313 and 323K, respectively, for tetracycline removal, which was higher than that of other reports. Furthermore, the adsorption parameters, including the initial concentration, contact time, pH of solution, ionic strength and temperature, were investigated. The adsorption isotherms and kinetics were also discussed in detail. It was observed that the adsorption isotherms were well fitted to Freundlich model, the kinetics studies implied the adsorption process was attributed to pseudo-second-order model. The above-mentioned results proved the successful application of the as-synthesized ACs for effective removal of tetracycline.

Adsorptive efficacy analysis of lignocellulosic waste carbonaceous adsorbents toward different mercury species

Adsorptive efficacy of lignocellulosic waste char (LW-CHAR) and activated carbon (LW-AC) toward inorganic (Hg2+) and organic (MeHg+) mercury ions was studied. The LW-CHAR and LW-AC were, respectively, prepared by carbonization and KOH activation processes of lignocellulosic waste (LW) carried out at 700°C. The Hg2+ adsorption onto the LW-CHAR was lower than LW-AC, however, an opposite result was observed for the MeHg+ indicating the nature of the surface interactions of both mercury ions to respective adsorbent surfaces was significantly different. The adsorption data analysis of both mercury ions was found however to only follow the Langmuir isotherm and pseudo-second order kinetic models whereby a combination of chemisorption and diffusional process was the governing mercury ions adsorption mechanism.

A bimodal porous carbon with high surface area supported selenium cathode for advanced Li–Se batteries

A novel bimodal porous carbon (BPC) with high surface area was prepared by a simple hydrothermal route and KOH activation process, and the Se–BPC composite was synthesized for lithium–selenium batteries by the melt-diffusion method. It is found that the elemental selenium was dispersed inside the pores of BPC based on the analyses. Electrochemical tests reveal that the Se–BPC composite has a large reversible capacity and high rate performance as cathode materials. The Se–BPC (45.1wt.% Se) composite displays an initial discharge capacity of 552mAhg−1 and a reversible discharge capacity of 264mAhg−1 after 80cycles at 1C charge/discharge rate. In particular, the Se–BPC composite presents a durable cycling performance at high rate of 2C. These outstanding electrochemical features of Se–BPC composite cathode should be attributed to the uniform BPC with high surface area and bimodal porous structure. The bimodal porous carbon would be a promising carbon matrix to develop high performance lithium–selenium batteries.

Nano Carbon Black Powder Synthesized via Liquid Phase Plasma Process as a Supercapacitor Active Material

In this study, synthesized carbon black powder (SC) was obtained from benzene via a liquid phase plasma (LPP) process. This powder was then activated by KOH to obtain activated SC (A-SC). Both of SC and A-SC powders were compared with commercial carbon black powder (CCB) and activated commercial carbon black (A-CCB) via Brunauer–Emmett–Teller surface area analysis, Raman spectroscopy, scanning electron microscopy, and X-ray diffraction for physical and chemical investigations. SC, A-SC, CCB and A-CCB powders were used as active materials of electrochemical double-layer capacitors (EDLC), which were studied via cyclic voltammetry, galvanostatic measurements, and impedance spectroscopy. Their electrochemical performance shows that SC electrode has higher specific capacitance, capacity, and energy than CCB electrode. Non-aqueous electrolyte EDLC using A-SC electrode, especially exhibited suitable cyclic stability over 8000 cycles at various charge–discharge current densities from 250 mA g−1 to 2000 mA g−1. This study indicates that the LPP process successfully created specific nano-scaled CB particles supported by KOH activation process, which are noteworthy electrode materials for supercapacitor applications.

Porous nitrogen-doped carbon microspheres derived from microporous polymeric organic frameworks for high performance electric double-layer capacitors.

This research presents a simple and efficient method to synthesize porous nitrogen-doped carbon microspheres (PNCM) by the carbonization of microporous poly(terephthalaldehyde-pyrrole) organic frameworks (PtpOF). The common KOH activation process is used to tune the porous texture of the PNCM and produce an activated-PNCM (A-PNCM). The PNCM and A-PNCM with specific surface area of 921 and 1303 m(2) g(-1) , respectively, are demonstrated as promising candidates for EDLCs. At a current density of 0.5 A g(-1) , the specific capacitances of the PNCM and A-PNCM are 248 and 282 F g(-1) , respectively. At the relatively high current density of 20 A g(-1) , the capacitance remaining is 95 and 154 F g(-1) , respectively. Capacity retention of the A-PNCM is more than 92% after 10000 charge/discharge cycles at a current density of 2 A g(-1) .

Facile synthesis of wheat bran-derived honeycomb-like hierarchical carbon for advanced symmetric supercapacitor applications

A novel honeycomb-like hierarchical carbon (HHC) derived from wheat bran has been obtained by the facile and environmentally friendly method via hydrothermal carbonization of wheat bran followed by KOH activation process at mild conditions without any template. The prepared carbon has a large Brunauer–Emmett–Teller (BET) surface area of 2,189.2 m2 g−1 and pore volumes of up to 1.1 cm3 g−1. The performance of the HHC as electrodes for electrochemical supercapacitors was evaluated in a symmetric two-electrode cell configuration with 6 M KOH and 1 M TEABF4/AN as the electrolytes. Electrochemical studies show that the supercapacitors based on the as-prepared HHC exhibit an excellent capacitive performance in both aqueous and organic electrolytes. We attribute the outstanding capacitive behavior of HHC to their unique structure and high accessible surface area. Considering that the cost-effective and feasible process, this facile technique presented here will not only provide a promising method for the production of biomass-derived hierarchical carbon but also put forward the application of carbon materials in energy storage and conversion.