KOH Activation Process Research Articles

Environmentally Friendly Biological Activated Carbon Derived from Sugarcane Waste as a Promising Carbon Source for Efficient and Robust Rechargeable Zinc–Air Battery

China is one of the largest sugarcane industrial countries in the world, and the annual output of bagasse waste is abundant. Classical incineration, landfill, and other treatment methods are inefficient and seriously harmful to the environment, so it is urgent to develop a new comprehensive utilization of agricultural waste. In this work, the sugarcane waste residue is converted to biological activated carbon (BAC) through a simple pre-carbonization and KOH activation process, which is then mixed with perovskite oxide BaCo0.5Fe0.5O3−δ (BCF) to form BAC/BCF composite air electrode. BAC/BCF assembled rechargeable zinc–air battery (ZAB) exhibits a relatively good output maximum power density of 96 mW·cm−2 and considerable long-term charge–discharge cycle stability over 250 h operation. These results indicate that the BAC derived from sugarcane waste is a promising potential carbon material candidate for ZAB application, which can realize the high-value utilization of agricultural waste in the field of efficient and durable energy storage and conversion devices.

Ultralight activated carbon/polyimide foam with heterogeneous interfaces for improved thermal stability, mechanical properties, and microwave absorption

AbstractThe activated carbon (AC) has been widely used in the field of electromagnetic protection because of its porous, hollow microstructure and excellent electrical conductivity. In this paper, AC was prepared through KOH activation process. The ACs/polyimide foam (PIF) composite was prepared in situ during the synthesis of PI and the ACs. In this paper, AC was prepared using the potassium hydroxide (KOH) activation process. The AC/PIF composites were prepared by mixing ACs and pyromellitic dianhydride (PMDA) with methylene diphenyl diisocyanate (MDI). The pore structure and surface morphology of the ACs were observed using nitrogen adsorption–desorption isotherms and scanning electron microscopy (SEM). After KOH activation with KOH, the surface area and total pore volume of ACs significantly increased by 79.31% and 0.9539 cm3/g, respectively, mainly were the microporous structure. X‐ray photoelectron spectroscopy (XPS) results confirmed an increase in the oxygen content of ACs after KOH activation, indicating an increase in the relative hydroxyl content on the surface. The SEM resulting of the ACs/PIF composite has a well‐developed open cell structure. Thermal gravimetric analysis (TGA) revealed that ACs significantly improved the thermal stability of the ACs/PIF composite. The compressive strength of the ACs/PIF‐3 increased from 518 to 834 KPa, significantly enhancing its mechanical properties. Simultaneously, the microwave absorption performance can be controlled and regulated by optimizing the impedance gradient of the skeleton. Results showed that when ACs constituted 8 wt% of the PIF, the real permittivity (ɛ′) and imaginary permittivity (ɛ″) of ACs‐PIF‐5 were approximately 2.03 and 0.025, respectively.

Nanoarchitectonics of hydrothermal carbonized sugarcane juice-derived biochar for high supercapacitance and dye adsorption performance

Here, we report the exfoliation of micron-sphere biochar to a few layers using the conventional KOH activation process. Micron-sphere biochar is obtained from hydrothermal carbonization (HTC) of sugarcane juice (Saccharum officinarum). HR-TEM and Raman spectroscopy studies revealed the conversion of micron-sphere biochar (MSB) to a few layers of biochar (FLB) in the activation process. BET characterization revealed FLB with a high surface area of 681.21 m2/g having mesopores. Consequently, an electrochemical study demonstrated excellent supercapacitor performance with a specific capacitance of 964.5 F/g and an energy density of 33.11 Wh/kg at a maximum power density of 936 W/kg. Batch adsorption studies showed rapid Methylene blue (MB) dye adsorption in 10 min. The equilibrium data analysis indicated the Langmuir adsorption isotherm with a correlation coefficient of 0.99. Evaluation of the kinetic models suggests that pseudo-second-order kinetics is the most appropriate model, implying that the adsorption of MB dye is primarily due to chemisorption. These findings suggest a Nanoarchitectonics of biochar into a few layers using traditional KOH activation, suitable for various applications.

Straw-based biochar prepared from multi-step KOH activation and its structure-effect relationship of CO2 capture under atmospheric/pressurized conditions via experimental analysis and MD/DFT calculations

Porous carbon-based CO2 capture holds great promise. However, the preparation process, pore structure and oxygen/nitrogen functional groups of porous carbon on CO2 adsorption still remain unclear. Herein, we develope straw-based biochar with ultra-high specific surface area(SSA), high micropore ratio and different O/N content by modifying the two-step KOH activation procedure and confirm the KOH activation mechanism, CO2 adsorption characteristics, and the structure-effect relationship of CO2 capture. The KOH activation process is controlled by the activation temperature and is divided into five temperature zones. The pickling treatment enhanced the activation effect of biochar, with a SSA of 3567.33 m2/g and a microporous ratio of 96.05 %. The potassium-containing active components reacts with the defective carbon structure above 800 °C catalyzed by alkali and alkaline earth metals(AAEMs), but reacts with the aliphatic hydrocarbon group after pickling. H-4–9-4-m has a maximum CO2 adsorption capacity of 24.77 mmol/g (25 °C/30 bar), whereas 4–9-2-m has a maximum capacity of 3.46 (25 °C/1 bar) and 5.42 mmol/g (0 °C/1 bar) and outstanding CO2/N2 selectivity (123 at 0.02 bar). The pressurized CO2 adsorption capacity is positively correlated with total pore volume. While under atmospheric pressure, the optimal adsorption site of biochar at 25 °C is ultramicroporous(0.5 nm) and oxygen-containing functional groups, and transforms into ultramicroporous(0.7 nm) and N-5 groups at 0 °C. The simulation results show that 0.5 nm is the pore size of CO2 adsorption from monolayer to bilayer, and both oxygen/nitrogen-containing groups could increase the CO2 adsorption capacity of biochar. This study provides guidance for the preparation of excellent carbon-based CO2 adsorbents according to application scenarios.

Nanoporous Carbon Materials Derived from Zanthoxylum Bungeanum Peel and Seed for Electrochemical Supercapacitors.

In order to prepare biomass-derived carbon materials with high specific capacitance at a low activation temperature (≤700 °C), nanoporous carbon materials were prepared from zanthoxylum bungeanum peels and seeds via the pyrolysis and KOH-activation processes. The results show that the optimal activation temperatures are 700 °C and 600 °C for peels and seeds. Benefiting from the hierarchical pore structure (micropores, mesopores, and macropores), the abundant heteroatoms (N, S, and O) containing functional groups, and plentiful electrochemical active sites, the PAC-700 and SAC-600 derive the large capacities of ~211.0 and ~219.7 F g-1 at 1.0 A g-1 in 6 M KOH within the three-electrode configuration. Furthermore, the symmetrical supercapacitors display a high energy density of 22.9 and 22.4 Wh kg-1 at 7500 W kg-1 assembled with PAC-700 and SAC-600, along with exceptional capacitance retention of 99.1% and 93.4% over 10,000 cycles at 1.0 A g-1. More significantly, the contribution here will stimulate the extensive development of low-temperature activation processes and nanoporous carbon materials for electrochemical energy storage and beyond.

Preparation and comparison of polyaniline composites with lotus leaf-derived carbon and lotus petiole-derived carbon for supercapacitor applications

Biomass carbon is a class of economical and sustainable materials for supercapacitor electrode materials, while the low energy density restricts its development. Herein, lotus leaf-derived carbon (LLDC) and lotus petiole-derived carbon (LPDC) were prepared via carbonization and KOH activation processes. Then LLDC and LPDC were further modified with polyaniline to synthesize the polyaniline@lotus leaf-derived carbon (PANI@LLDC) and polyaniline@lotus petiole-derived carbon (PANI@LPDC) composites by the in-situ polymerization approach. The synthesized PANI@LPDC exhibited an ultra-large specific capacitance of 1332.5 F·g−1 at 0.3 A·g−1 and outstanding electrochemical stability of 89.2 % after 5000 cycles in the KI active electrolyte (1 M H2SO4 + 0.05 M KI), showing better electrochemical performance than PANI@LLDC (1190.3 F·g−1 at 0.3 A·g−1; 87.1 % after 5000 cycles). This is mainly due to the natural tubular structure of LPDC being more conducive to the movement of electrons, the introduction of Faradic capacitance by PANI and KI, and the porous structure of LPDC providing enough space for performing redox reactions. Moreover, a symmetric supercapacitor device assembled with two PANI@LPDC electrodes showed a superb energy density of 75.7 Wh·kg−1 at the power density of 540 W·kg−1. This study provides guidance for selecting different parts of biomass to prepare high-performance supercapacitor electrode materials.

Co-hydrothermal carbonization of polystyrene waste and maize stover combined with KOH activation to develop nanoporous carbon as catalyst support for catalytic hydrotreating of palm oil

Plastic waste is massively generated daily from households, mainly as packaging material, causing serious surrounding ecological problems. The development of plastic waste for higher value-added applications instead of landfilling and incineration has received consideration interest in bioenergy and material science research. Herein, a nanoporous carbon support of nickel phosphide catalyst for palm oil hydrotreating was developed from blended polystyrene waste and maize stover via the Co-hydrothermal carbonization (HTC) coupled with the KOH activation process. The Co-HTC parameters, such as temperature, reaction time, and PS percentage, were studied on the properties of co-hydrochar feedstocks for further activation using the Box behnken design. From the comprehensive characterization results, response surface methodology (RSM) results showed that the rising polystyrene proportion significantly exhibited the higher production yield and fixed carbon of co-hydrochar products, an essential characteristic for porous carbon manufacturing. After activation step, the final nanoporous carbon derived from the co-hydrochar (PMPC) exhibited the highest specific surface area of 1033.58 m2/g with total pore volume of 0.45 cm3/g. Moreover, the PCMC-supported nickel phosphide catalysts were successfully synthesized and tested for the catalytic hydrotreating of palm oil as alternative catalyst. The NiP-PMPC catalyst represents an impressive liquid hydrocarbon yield of 74.68 % with a high green diesel selectivity of 85.92 % at 100 % palm oil conversion. The findings of this study might help develop and utilize blended plastic waste and agricultural waste as an alternate catalytic support for various processes in biofuel and biochemical synthesis.

Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm3 g−1) and specific surface area (1162 m2 g−1), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g−1 @ 1 A g−1 and a high capacitance retention of 62.7 % @ 80 A g−1. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg−1 @ 250 W kg−1. Moreover, the sample still exhibits a specific capacitance of 165 F g−1 @ 1 A g−1 at a high mass loading of 10 mg cm−2, resulting in a high areal capacitance of 1.65 F cm−2. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.

Biochar for supercapacitor electrodes: Mechanisms in aqueous electrolytes

AbstractThe utilization of biomass materials that contain abundant carbon–oxygen/nitrogen functional groups as precursors for the synthesis of carbon materials presents a promising approach for energy storage and conversion applications. Porous carbon materials derived from biomass are commonly employed as electric‐double‐layer capacitors in aqueous electrolytes. However, there is a lack of detailed discussion and clarification regarding the kinetics analysis and energy storage mechanisms associated with these materials. This study focuses on the modification of starch powders through the KOH activation process, resulting in the production of porous carbon with tunable nitrogen/oxygen functional groups. The kinetics and energy storage mechanism of this particular material in both acid and alkaline aqueous electrolytes are investigated using in situ attenuated total reflectance‐infrared in a three‐electrode configuration.

Changing the potassium-based activation path to prepare coal-based porous carbon with more graphitic or graphene structures for high-performance organic supercapacitors

Graphitic porous carbon is becoming an excellent platform for high-performance supercapacitors due to its unique structural characteristics, especially the combination of high specific surface area and long-range ordered sp2 carbon framework, which can synergistically improve the ion transfer/storage capability and the structural stability during long-term cycling. However, the trade-off contradiction between porosity and graphitization of carbon materials is difficult to circumvent by traditional chemical or physical activation strategies. Herein, we changed the conventional potassium-based activation pathway by introducing a pre-carbonization process, thus transforming low-rank coal precursors into graphitic porous carbon with more graphite or graphene structures. Raman mapping characterization was introduced to comprehensively reveal the distribution of crystalline carbon within the obtained carbon materials, confirming that enhancing the structural maturity of carbon-based precursors by introducing a pre-carbonization process promotes the deep and uniform development of graphitized structures during the KOH activation process. Typical reaction intermediate characterization indicates that the reason for this structural transformation is due to a change in the primary form of potassium species under the changed activation pathways, leading to a solid-liquid phase reaction environment mediated by molten K2CO3. The obtained graphitic porous carbon possesses simultaneously a hierarchically porous structure with specific surface area of 2456 m2 g−1 and well-developed graphitic carbon crystalline by which the constructed organic supercapacitor delivers excellent capacitance and rate performance, along with a high energy-power density, and a lifespan exceeding 10,000 cycles. The elucidated potassium-based activation mechanism facilitates the easy adjustment of carbon porosity and crystalline structures to meet varying requirements in different application scenarios.

Post-treatment strategies for pyrophoric KOH-activated carbon nanofibres.

The effect of two atmospheric post-treatment conditions directly after the KOH activation of polyacrylonitrile-based nanofibres is studied in this work. As post-treatment different N2 : O2 flow conditions, namely high O2-flow and low O2-flow, are applied and their impact on occurring reactions and carbon nanofibres' properties is studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Raman spectroscopy, elemental analysis and CO2 and Ar gas adsorption. At high O2-flow conditions a pyrophoric effect was observed on the KOH-activated carbon nanofibers. Based on the obtained results from the TGA and DSC the pyrophoric effect is attributed to the oxidation reactions of metallic potassium formed during the KOH activation process and a consequent carbon combustion reaction. Suppression of this pyrophoric effect is achieved using the low O2-flow conditions due to a lower heat formation of the potassium oxidation and the absence of carbon combustion. Compared to the high O2-flow samples no partial destruction of the carbon nanofibers is observed in the SEM images. The determination of the adsorption isotherms, the surface area, the pore size distribution and the isosteric enthalpies of adsorption show the superior properties under low O2-flow conditions. The present micropore volume is increased from 0.424 cm3 g-1 at high O2-flow to 0.806 cm3 g-1 for low O2-flow samples, resulting in an increase of CO2 adsorption capacity of 38% up to 6.6 mmol g-1 at 1 bar. This significant improvement clearly points out the importance of considering highly exothermic potassium oxidation reactions and possible post-treatment strategies when applying KOH activation to electrospun carbon nanofiber materials.

N-doped CNTs wrapped sulfur-loaded hierarchical porous carbon cathode for Li-sulfur battery studies.

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage devices due to their low cost and high energy density (2600 W h kg-1). However, the practical applicability of Li-S batteries is hindered by the insulating nature of sulfur cathodes, and the high solubility of polysulfides (Li2Sx, 3 < x ≤ 8) which are formed during the electrochemical process. Integrating sulfur into the carbon host is an effective way to enhance the conductivity of the electrode which hampers the shuttling effect of the polysulfides. Here in this study, hierarchical porous carbon structures (HPC) are prepared from spent coffee waste (SCW) by the KOH activation process and are encapsulated with sulfur (SHPC) which increases the interaction between sulfur and carbon and enhances both the electronic and ionic conductivities. Further wrapping of SHPC with N-doped multi-walled carbon nanotubes (NCNTs) gives a SHPC-NCNT composite, which alleviates the shuttling of polysulfides by trapping them and ensures the required conductivity to the sulfur cathode during the Li+ reactions. When studied as a cathode material for Li-S batteries, the prepared cathode showed 664 and 532 mA h g-1 specific capacities after 150 cycles at 0.2C and 0.5C, respectively. The stable cyclability and rate capability properties of SPHCNCNT suggest that the prepared sulfur composite is suitable as a cathode material for Li+ energy storage applications.

ZnFe2O4-infused hierarchically porous carbon nanofiber electrode for enhanced capacitive deionization

Highly porous carbon materials with abundant active adsorption sites are desirable for capacitive deionization (CDI). However, their limited salt adsorption capacity, slow desalination rate, and sensitivity to salt concentrations hinder practical applications in low salinity water treatment. In this study, we successfully synthesized a hierarchically porous carbon nanofiber electrode infused with ZnFe2O4 prepared by electrospinning the FeⅢ-MOF-5/benzoxazine/polyacrylonitrile (FeⅢ-MOF-5/BA-a/PAN) system, followed by high-temperature curing, KOH activation, and carbonization processes. The activated electrode material exhibited remarkable characteristics, including an exceptionally high specific surface area of 2506.73 m2 g−1 and significantly enhanced mesoporosity. Results demonstrated pseudo-capacitive behavior with a specific capacitance of 149.3 F g−1 and excellent electrochemical cycling stability. Notably, the electrode showed significant adsorption capacities in a 1000 mg L−1 NaCl solution at applied potentials of 1.2 and 1.6 V, with values of 74.27 and 88.95 mg g−1, respectively. The adsorption process followed both the Freundlich isotherm and the pseudo-second-order kinetic models. These findings highlight the promising potential of the ZnFe2O4-infused porous carbon nanofiber electrode for efficient desalination and ion removal applications.

N, O co-doped porous activated carbon derived from rotted Cucurbita Pepo as anode material for high-performance supercapacitors

Among the numerous benefits of porous carbon materials, their economic viability, abundance of availability, and environmental sustainability have made them increasingly popular in the realm of energy transformation and storage. Herein, the rotted Cucurbita pepo L. precursor was served as the starting material for the production of nitrogen (N) and oxygen (O) co-doped porous activated carbon, which was involved in high-temperature carbonization and KOH activation processes. The rotted Cucurbita pepo-derived activated carbon (RCPAC) showcases a remarkably elevated specific surface area of 2434 m2 g−1, while its micropore volume is 0.73 cm3 g−1. These inherent attributes offer a significant quantity of electroactive sites that effectively enable the electrochemical process of adsorption as well as the desorption of electrolyte ions. The RCPAC electrode demonstrates a notable specific capacitance value of 208 F g−1 when subjected to the current density of 1 A g−1. Furthermore, it retains >99 % of its original capacitance even after undergoing 10,000 cycles at a current density of 10 A g−1. Moreover, a symmetric supercapacitor (SSC) consisting of RCPAC electrodes and 6 M potassium hydroxide (KOH) electrolyte results in a significant specific capacitance of 55 F g−1 at 0.25 A g−1. The SSC demonstrates an impressive retention of capacitance, amounting to 85.6 %, even subsequent to enduring a substantial number of 8000 charge/discharge cycles. Additionally, an SSC was assembled using two undifferentiated RCPAC-6 electrodes in [BMIM]BF4/AN electrolyte. The SSC exhibits an impressive energy density of 92.25 Wh kg−1, while simultaneously maintaining a power density of 374.9 Wh kg−1. Furthermore, it demonstrates a capacitance retention surpassing 72.6 % subsequent to enduring 5000 cycles at 2 A g−1. Our research elucidates a financially feasible methodology for the fabrication of porous carbon-based compounds, which exhibit immense potential for deployment in various energy conversion and storage.

Preparation of corn straw-based carbon by “carbonization-KOH activation” two-step method: Gas–solid product characteristics, activation mechanism and hydrogen storage potential

Making excellent carbon-based hydrogen adsorbents requires thoroughly understanding the two-step activation method's reaction mechanism. This research examined the properties of gases and solids with high KOH/biochar ratios (4:1), various carbonization temperatures (400–600 °C), and activation temperatures (700–900 °C). The potential of biochar for hydrogen storage was further examined. These results demonstrate the division of the KOH activation process into four temperature-dependent reaction stages. The emission of CH4, CO, and H2 in various temperature ranges can be significantly influenced by the degree of carbonization and activation temperature. The outcome of activation is primarily determined by the volatile content and reactivity of carbon precursors. Biochar produced at 400 °C for carbonization and 900 °C for activation has a specific surface area (SSA) of 3567.33 m2/g. The oxygen concentration of H-400 decreases as the activation temperature rises, whereas the oxygen-containing structure can be built by raising the carbonization level. The hydrogen storage capacity of biochar was 2.49 wt.% at −196 °C and 1 bar, and increased to 5.51 wt.% at 50 bar, while it is 0.43 wt.% at 50 bar and room temperature. These findings can provide a novel strategy for developing carbon-based hydrogen storage materials.

Powerful puffing carbonization pretreatment prepared porous carbon for high-performance supercapacitors

Porous carbon as a crucial role in the electrode materials of supercapacitors (SCs) has inspired wide attentions, due to their high electrical conductivity, large specific surface area, excellent electrochemistry stability, and easy availability. Herein, we report the exploration of progressive porous carbon for SCs, which is rationally synthesized using maltose as carbon source via H2O bubbles puffing carbonization assisted KOH activation process. The optimized activated carbon-based architecture exhibits a large specific capacitance of 202.5 F g−1, which is ∼160 % to that of the electrode without H2O bubbles puffing treatment (128.7 F g−1). Moreover, the as-constructed SCs possess high specific capacitance, fast charge-discharge rate, excellent rate capability, and robust cycling stability (96 % capacitance retention after 15,000 charge/discharge cycles), which are better than most of other activated carbon-based SCs ever reported, and indicating their potential application value.

Synthesis of magnetic biochar with high iron content and large specific surface area: Synergistic effect of Fe doping and KOH activation

Magnetic biochar has promising applications in environmental remediation, catalysts, electrode materials, etc. The influence of the sequence of iron doping process and KOH activation process on the properties of magnetic biochar is significant and has not been studied yet. In this work, the properties of magnetic biochar were evaluated by changing the order of iron doping and KOH activation, accompanied by the comparison of simultaneous these two processes. Following the doping of biochar with iron, the oxide clusters of iron distributed in the surface of the carbon skeleton protect the interior from etching by KOH, resulting in low specific surface area (SSA). The advantages of the synergy strategy were evident in the high surface iron content and large SSA of the synthesized magnetic biochar. Further, batch adsorption and recovery experiments were performed on Fe/KOH-C obtained by a simple and low-cost synergistic synthesis strategy, and the results showed that the maximum adsorption capacity of tetracycline was up to 375 mg g−1, with advantages in terms of recovery. Pore filling, electrostatic attraction, π-π interaction, and complexation reaction of the surface functional groups were proved to be the adsorption mechanism of Fe/KOH-C.

MnO2-modified soybean root derived porous carbon with excellent capacity deionization

Developing high-efficient capacitive deionization (CDI) systems with low-cost environmentally friendly electrode materials is one of the most effective ways to address freshwater shortage. Meanwhile, large number of soybean roots are discarded as waste with large production of soybean and contribute to enormous pressure on the environment. In this work, soybean roots are adopted to prepare activate carbon (SRKPC) by a carbonization and KOH activation process. A composite of [email protected]2 with MnO2 nanoparticles supported on SRKPC is synthesized by a low temperature hydrothermal reaction, which exhibits excellent electrochemical properties with high specific capacitance (597.9 F g−1 at 2 mV s−1) and bimode sodium storage characteristics. The dual-mode CDI system based on [email protected]2 delivers an effective desalination performance with a desalination capacity of 42.90 mg g−1, a desalination rate of 2.86 mg g−1 min−1 and relatively good desalination recoverability. Therefore, this work not only exemplifies the simple fabrication of low-cost, environmentally friendly, and efficient dual-mode CDI electrode materials for capacitive desalination, but also provides a sustainable way to turn biomass waste into functional materials.

Prediction of structural properties of activated carbons derived from lignocellulosic biomass components using mixture design of experiments

There is significant interest in using biomass to produce activated carbons for applications such as environmental remediation, energy storage, and construction. To date, the research has primarily focused on exploring the potential of individual biomass sources. There is little research on how interactions between the fundamental components of lignocellulosic biomass affect activated carbons' structural properties, and, therefore, their suitability for various applications. This investigation sought to address this knowledge gap by exploring how the relative compositions of cellulose nanofibers, cellulose nanocrystals, and lignin affected the final properties of activated carbons produced through a two-step KOH activation process. A simplex-lattice mixture design was used to understand how the composition affected activated carbon yield, specific surface area, and micropore fraction. Mixture regression models showed that the specific surface area was highest when the activated carbon was composed of 16.7% cellulose nanofibers, 16.7% cellulose nanocrystals, and 66.7% lignin by mass. In addition, the micropore fraction was largest at 76.3% while also maintaining a high surface area, with a precursor mixture of 50% cellulose nanocrystals and 50% lignin by mass. The results of this investigation provide a foundation for future efforts to be able to predict, and tune, activated carbon properties based on biomass composition.

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.