High Micropore Volume Research Articles

Carbide-derived carbon obtained via bromination of titanium carbide: Comparative analysis with chlorination and hydrogen storage studies

Carbide-derived carbons (CDCs) are synthesized from TiC micropowder via gas phase bromination at the temperature range of 350–1150 °C. The resultant carbon materials demonstrate high specific surface areas and micropore volumes of up to 1745 m2 g−1 and 0.64 cm3 g−1 respectively. Successful bromination of TiC in a wide temperature range permitted the first in-depth comparative study of CDCs produced by Br2 and Cl2 thermochemical extraction. Although minor, some structural differences between TiC-CDCs obtained via bromination and chlorination reactions are observed. It is concluded that it is not the size of halogen and evolving titanium halide molecules but the reactivity of the halogen that affects the microporosity of TiC-CDCs. The structural similarity of materials obtained via Br2 and Cl2 extraction proves that the extractive step does not determine the final structure of CDCs. Cryogenic high-pressure hydrogen storage studies show that the maximum excess hydrogen uptake of TiC-CDCs strongly correlates to the volume of micropores below 1.75 nm in size.

Synthesis of polypyrrole (PPy) based porous N-doped carbon nanotubes (N-CNTs) as catalyst support for PEM fuel cells

In this study, it was aimed to synthesize catalytically active, high surface area carbon nanotubes (CNTs) by means of nitrogen doping (N-doping). The synthesized nitrogen doped carbon nanotubes (N-CNTs) were used as Pt catalyst support in order to improve oxygen reduction reaction (ORR) kinetics at the cathode electrode in PEM fuel cell. Polypyrrole (PPy) was served as both carbon and nitrogen source and FeCl3 solution was used as oxidizing agent in the synthesis procedure of N-CNTs. Chemical activation of the materials was made with potassium hydroxide (KOH) solution during 12 and 18 h time periods. It was considered that activation period is of great importance on the properties of the synthesized PPy based N-CNTs. 12 h activated N-CNTs gave higher surface area (1607.2 m2/g) and smaller micropore volume (0.355 cm3/g) in comparison to 18 h activated N-CNTs having smaller surface area (1170.7 m2/g) and higher micropore volume (0.383 cm3/g). PEM fuel cell performance results showed that 12 h activated N-CNTs are better catalyst supports than 18 h activated N-CNTs for Pt nanoparticle decoration.

Study on the characteristics of matrix compressibility and its influence factors for different rank coals∗

To thoroughly understand the mechanism of permeability change and improve production in coalbed methane development, it is important to clarify the evolution characteristics and influencing factors of matrix compressibility for various coal ranks. This paper presents calculations of matrix compressibility coefficients of different rank coals through mercury intrusion porosimetry (MIP) and N2 adsorption. Furthermore, the evolution of coal material and pores based on coal rank is analyzed to study their effect on matrix compressibility coefficients. The results show that the relationship between matrix compressibility coefficients and coal rank is a cubic polynomial function, in which two inflection points are situated in the maximum vitrinite reflectance (Ro,max) = 1.3% and 2.5%. For coals with Ro,max < 1.3%, matrix compressibility coefficients increase as vitrinite and volatile matter contents increase, which may be related to the lower microhardness of vitrinite and the more random structure of aromatic carbon micells surrounded or linked by carbon functional groups, such as aliphatic chains, methoxyl and carboxylic functional groups. Moreover, the regular change of moisture content with coal rank is similar to matrix compressibility coefficients and it also plays a positive role in matrix compressibility. However, the inertinite and mineral content has a rather opposite effect on matrix compressibility. For the pore structure, the larger porosity and micropore volume in coals, the greater matrix compressibility. The coals Ro,max < 1.0%, which have a loose chemical structure and high micropore volume, can bear a greater intrusion pressure than the coals with Ro,max > 1.0%, in which the micropore structure will be broken when pressure exceeds 150 MPa. The coals with greater fractal dimension are more sensitive to stress. The matrix compression can lead to reduction of micropore volume and can make the micropore structure more irregular. It indicates that the increasing of effective stress with gas discharge could reduce the permeability of the reservoir and enhance the adsorption of micropore.

Tailoring the structure and acid site accessibility of mordenite zeolite for hydroisomerisation of n-hexane

Mordenite zeolites with diffusion-restricted access to the acid sites located in mono-dimensional 12-ring channels and 8-ring side pockets have found broad applications as catalysts for hydroisomerisation of linear C5 and C6 alkanes and other highly relevant acid-catalysed processes. The accessibility of the porous structure of mordenite (MOR) zeolite is traditionally enhanced by dealumination, but this is invariably connected with a dramatic reduction in the aluminium content and corresponding concentration of the acid sites in the zeolites. Here we describe the preparation of MOR zeolite with high micropore volume, three-dimensional supermicropores (d ∼ 7.5 Å) and good acid site accessibility by concurrent extraction of Si and Al using postsynthesis fluorination-alkaline-acid treatment. The concurrent extraction of Si and Al enables formation of more developed supermicroporous structure and preservation of the molecular Si/Al. The procedure yields MOR with a crystalline structure in which the Si/Al ratio and the micropore volume can be tailored (Si/Al from ∼ 6, VMI up to 0.25 cm3.g−1) by the chemical conditions of the treatment. The Al-rich 3D supermicroporous structure with accessible Brønsted and Lewis active sites provides strongly enhanced activity, selectivity and long-term catalytic stability in the transformation of n-hexane into the corresponding branched isomers.

A combined strategy of acid-assisted polymerization and solid state activation to synthesize functionalized nanoporous activated biocarbons from biomass for CO2 capture

Novel acid treated porous activated biocarbons (APABs) are synthesized from biomass waste, Arundo donax, through sulphuric acid polymerization followed by a single step solid state activation using KOH at a fixed carbonization temperature of 600 °C. The specific surface area and the pore volume of the prepared materials is controlled by varying the ratio of KOH to biomass from 1 to 4. The sample prepared with the KOH/biomass ratio of 3 is found to be the best as it exhibits the specific surface area of 2232 m2 g−1 and a pore volume of 1.01 cm3 g−1 which is much higher than those of other samples prepared in this study. Interestingly, XPS and FT-IR studies confirm the presence of oxygen rich functional groups on the surface of the samples, which play an important role in enhancing the CO2 capture performance of the materials. Among the samples studied, the sample with the highest specific BET surface area exhibits the highest CO2 adsorption capacity of 21.2 mmol g-1 at 0 °C and 30 bar and a moderately high value of 4.1 mmol g-1 at 0 °C and 1 bar. The high CO2 adsorption capacity is attributed to the presence of excellent textural parameters coupled with high micropore volume and the oxygen functional groups. The samples are highly stable and do not show any change in the adsorption capacity even after repeated adsorption experiments. The combination of high adsorption capacity, stability and low cost makes these materials as a potential alternative to other expensive commercially available CO2 adsorbents.

Exploring the effect of ultramicropore distribution on gravimetric capacitance of nanoporous carbons

The capacitive performance of activated carbons of similar volume of ultramicropores but of marked differences in their pore size distributions was tested in aqueous electrolytes. Dramatic differences in the capacitive behavior were measured in H2SO4, KOH, or in Na2SO4. In the case of the carbon activated with CO2, the sterical hindrances limited the access of Na+ ions to pores resulting in a small capacitance. The results indicated that even though the high volume of micropores is required for a good capacitive behavior, it is not a sufficient condition for granting a high capacitance. It was found that even subtle differences in the ultramicropore distribution can affect dramatically the capacitive behavior and, for a given carbon, the electrolyte type needs be adjusted, if the optimum performance is targeted. That adjustment should be made based on the size of the large ion and its compatibility/similarity with/to the predominant ultramicropore size. Carbon surface chemistry does not play a marked role for carbons with a high degree of microporosity when used as supercapacitor electrodes. Since the size of pores are critical for ion accessibility, it is suggested that enhanced adsorption potential in small pore might also contribute to the high capacitive performance in pores similar in size to ions.

Use of a hypercrosslinked triphenylamine polymer as an efficient adsorbent for the enrichment of phenylurea herbicides

A hypercrosslinked triphenylamine polymer (HCTPA) was prepared through a simple one-step Friedel-Crafts alkylation reaction. The HCTPA had an extended π-conjugated system, large specific surface area and high micropore volume. In order to evaluate its extraction performance, the HCTPA was used as the adsorbent for the solid-phase extraction of the phenylurea herbicides (monuron, chlortoluron, isoproturon, monolinuron and buturon) from watermelon, tomato and cucumber samples. The main parameters that could affect the extraction efficiency including the sample volume, sample solution pH, sample solution loading rate and desorption conditions were investigated and optimized. Under the optimized conditions, the HCTPA showed a good extraction performance for the target analytes. The linear range for the quantification of the analytes was in the range of 0.4–160.0 ng g−1 with the correlation coefficients of 0.9996–0.9999. The limits of detection (S/N = 3) of the analytes by the method ranged from 0.06 to 0.12 ng g−1 for watermelon and tomato, and 0.06–0.15 ng g−1 for cucumber samples. The recoveries of the analytes for the method were between 83.1% and 112.5% with the relative standard deviations below 5.5%. These results indicate that the HCTPA can be used for the enrichment of phenylurea herbicides from complex matrix samples like watermelon, tomato and cucumbers.

High performance capacitive deionization using modified ZIF-8-derived, N-doped porous carbon with improved conductivity.

Zeolitic imidazolate framework (ZIF) composite-derived carbon exhibiting large surface area and high micropore volume is demonstrated to be a promising electrode material for the capacitive deionization (CDI) application. However, some inherent serious issues (e.g., low electrical conductivity, narrow pore size, relatively low pore volume, etc.) are still observed for nitrogen-doped porous carbon particles, which restrict their CDI performance. To solve the above-mentioned problems, herein, we prepared gold-nanoparticle-embedded ZIF-8-derived nitrogen-doped carbon calcined at 800 °C (Au@NC800) and PEDOT doped-NC-800 (NC800-PEDOT). The newly generated NC800-PEDOT and Au@NC800 electrodes exhibited notably increased conductivity, and they also achieved high electrosorption capacities of 16.18 mg g-1 and 14.31 mg g-1, respectively, which were much higher than that of NC800 (8.36 mg g-1). Au@NC800 and NC800-PEDOT can be promisingly applicable as highly efficient CDI electrode materials.

Ordered Mesoporous Carbons with High Micropore Content and Tunable Structure Prepared by Combined Hard and Salt Templating as Electrode Materials in Electric Double‐Layer Capacitors

AbstractSynthesis of high surface area carbon materials with hierarchical pore structure is reported. Combined salt templating with ZnCl2 and hard templating with SBA‐15 is used to produce ordered mesoporous and microporous hard–salt‐templated carbons (OM‐HSTCs) from simple sucrose as carbon precursor. OM‐HSTCs achieve specific surface areas of more than 2600 m2 g−1 and total pore volumes up to 2.2 cm3 g−1. In comparison to purely hard‐templated ordered mesoporous carbons, the additional salt template leads to high micropore volume and provides control over the size/distribution of micro‐ and mesopores and over the carbon microstructure. This method combines carbonization and the formation of well‐defined micropores in one step and is more versatile in terms of resulting pore structure than previously reported routes toward ordered mesoporous/microporous carbons. When applied as electrode materials in electric double‐layer capacitors with 1 m tetraethylammonium tetrafluoroborate in acetonitrile organic electrolyte, OM‐HSTCs combine high gravimetric capacitance (133 F g−1 at 0.1 A g−1) resulting from high micropore volume with high capacitance retention under high‐power conditions (126 F g−1 at 40 A g−1), exceeding the purely microporous or purely ordered mesoporous reference materials.

Soft-templating synthesis of partially graphitic Fe-embedded ordered mesoporous carbon with rich micropores from bayberry kernel and its adsorption for Pb(II) and Cr(III)

An eco-friendly promising strategy for the synthesis of biomass-derived ordered mesoporous carbon (BOMC) and Fe-doped BOMC (Fe/BOMC) using bayberry kernel as carbon precursor have been developed via liquidation and subsequent soft-templating synthesis. The obtained BOMC presents a 3D interconnected ordered mesoporous framework with big surface area. Spectroscopy analysis shows various Fe nanoparticles including zero Fe, Fe2O3 and Fe3O4 are successfully embedded, penetrating the interconnected micro/mesopore framework. Fe/BOMC still remains the ordered structure with high surface area (1012m2/g), mesopore volume (0.95cm3/g) and micropore volume (0.35cm3/g). Interestingly, the introduction of Fe increases the oxygen content and generates more oxygen-containing functional groups such as CO group and CO bands, which further enhances the active of adsorption sites, resulting in the higher adsorption of Pb(II) and Cr(III) on Fe/BOMC. The maximum adsorption amount of Pb(II) and Cr(III) adsorption increases by 18% and 21% to 123 mg/g and 46 mg/g, respectively. Moreover, 80% of the adsorption equilibrium amount is obtained at 15 min. The results demonstrate a cost-effective and environmental-friendly strategy for synthesizing bayberry kernel-derived Fe-doped ordered OMC with rich micro/mesopores, active iron and oxygen-containing functional groups for Pb(II) and Cr(III) adsorption.

Opening the Cages of Faujasite-Type Zeolite.

Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules. As more active sites become accessible, the catalytic performances for these modified zeolites are substantially improved. The method, based on etching with NH4F, is also applicable to other cage-containing microporous molecular sieves, where some of the most industrially relevant zeolites are found.

Pore characteristics of Damodar valley shale and their effect on gas storage potential

The current global interest in fine grained sedimentary shale rock is driven by its ability to store gas in the pore spaces in them. The current study focuses on the understanding of the gas storage capacity of less explored Damodar Valley shales of India, in light of pore characteristics of organic matter and clay minerals. In this study, four samples were collected from different parts of Damodar valley basin and their geochemical composition, pore structure and adsorption capacity were investigated by XRD studies, rock-eval analyses, low-pressure N2-CO2 adsorption analyses and high-pressure methane adsorption experiment. The samples were also studied to know their hydrocarbon potential. The relationship between mineralogy, organic matter, and pore-structure was analyzed and finally, their effect on methane sorption capacity was discussed. The shale samples are found to be clay rich. The average clay content of the shale samples is 50.69% and average quartz content is 31.65%. Presence of excellent TOC content (4.8%–37.36%) with a predominance of type III organic matter and Tmax varying from 440 °C to 465 °C suggests a very good to excellent hydrocarbon generation potential in all the samples. The correlation between the TOC and VL was found to be positive indicating a positive influence of organic matter on methane sorption capacity of the studied samples. However, a lack of correlation between total clay and CH4-VL indicates that the role of clay minerals on methane sorption behavior of these shales are inconclusive. A positive correlation between CO2 micropore volume, CH4-VL and TOC suggest microporous nature of organic matter within the shale samples and their positive control on methane sorption potential. The negative correlation of clay mineral with CO2 micropore volume suggests a lack of microporosity in the clay minerals of the collected shale samples. It was also observed that thermally mature shale samples have higher micropore volume and surface area, and are prone to higher methane sorption capacity compared to that of less mature shales.

Preparation of walnut shell-based activated carbon and its properties for simultaneous removal of H2S, COS and CS2 from yellow phosphorus tail gas at low temperature

Walnut shell-based activated carbon (WSBAC) was prepared used to simultaneously remove H2S, COS and CS2 from yellow phosphorus tail gas and closed carbide furnace tail gas. The influences of different preparation conditions (carbonization temperature, activating agent species, activating agent content, activation temperature) on the simultaneous removal efficiency of H2S, COS and CS2 were investigated. The results showed that the WSBAC carbonizated at 600 °C, then activated with 0.5 times KOH at 700 °C had the highest sulfur capacity (52.67 mgS/gWSBAC). The structure and surface properties of the catalysts were characterized by Brunauer–Emmett–Teller (BET) method, and the results showed that the high BET surface area (484.26 m2/g), high micropore volume (0.261 cm3/g) and more pore sizes of 0.3–1.8 nm were conducive to the simultaneous removal of H2S, COS and CS2. X-ray photoelectron spectroscopy results showed that the most of products on the exhausted WSBAC were S/SO4 2− species which accumulated on the WSBAC’s surface and had a negative effect on the adsorption activity.

Rational Design of High-Loading Cathodes for Lithium Sulphur Batteries

The lithium-sulphur (Li/S) battery has been the subject of intense research and development in recent years owing to its low cost and high-capacity. Fundamental challenges of Li-S batteries originate from the insulating properties of elemental sulphur and lithium sulfides, the dissolution of lithium polysulfides (LiPS) in the electrolyte, the cathode volume changes, and corrosion of lithium anodes.1-2 It is now widely realized that high sulphur loading and low electrolyte to sulphur (E/S) ratios are critical for Li-S technology in the marketplace. 3 These problems are exacerbated due to the difficulties in creating a continuous electron/ Li+ pathway over thick cathodes, 2 severely inhomogeneous distribution of LiPS within thick cathodes and resultant shuttle effect on both electrodes 4-5 and presence of internal inherent mesoscale porosities 2. To address these two imperative challenges, the concept of sparingly solvating electrolytes was proposed to control the dissolution of LiPS.6 Herein, we propose a new strategy on rational design of high-loading cathodes under lean operation for Li-S batteries by spatial homogeneity control. An activated carbon fiber cloth (ACFC) has been selected as both a sulphur-hosting material and the current collector. ACFC possesses a high micropore volume (ca. 0.8 cc/g) with a narrow pore distribution (< 2 nm), high surface area (ca. 1800 m2/g) but with the absence of mesopores which is common in conventional carbon matrices. The microporous nature of the ACFC allows sulfur to be confined, yet the macro-surface area (< 10 m2/g; excluding micropores) is low, which potentially allows high utilization electrolytes (i.e. complete wetting at low E/S ratios). An adsorptive impregnation method was developed successfully and achieved the theoretical sulphur loading (i.e. 100 % occupation of micropores) based on the empirical relationship. Preliminary cycling experiments indicate there is an optimum sulphur pore-loading range (5-7 mg cm-2) for this method if penetration of electrolytes, volumetric expansion upon lithiation, and escape of resultant LiPS from micropores into bulk electrolytes are taken into account. After sulphur loading, the effective sulphur to carbon (excluding the average weight contribution from Al current collector) weight ratio is approximate 58:42. The cell with sulphur loading of 5.4 mg cm-2 exhibits the best cycling retention, compared to cells with lower sulphur loading and the cell with comparable sulphur loading using melt-infusion method. After 16 cycles, the cell can deliver a favorable areal capacity of 5.2 mAh cm-2 with the E/S ratio of 7.3 along with decreasing nucleation barrier for the first liquid-solid discharge reaction. These results suggest encapsulation of most liquid LiPS in the micropores can be achieved under lean electrolyte condition using an optimum sulphur loading and a hybrid cycling protocol, which also shed light on approaches of delivering high areal capacities (6 mAh cm-2) in a lean electrolyte (E/S < 3). Others factors that affect the cell cycling performance will be discussed in terms of E/S ratios, different kinds of ACFC, temperature and cycling parameters. [1] J-G. Zhang, W. Xu, and W.A. Henderson. Springer Series in Materials Science,vol. 249, Springer International Publishing, Cham, Switzerland, DOI: 10.1007/978-3-319-44054-5 (2017) [2] Q. Pang, X. Liang, C.Y. Kwok and L.F. Nazar, Nat. Energy, 16132 (2016) [3] D. Eroglu, K. R. Zavadil and K. G. Gallagpher, J. Electrochem. Soc.,162 (6) A982-A990 (2015) [4] Y. V. Mikhaylik and J. R. AkridgeJ. Electrochem. Soc., 151 (11) A1969-A1976 (2004) [5] H. J. Peng, J.Q. Huang, X.Y. Liu, X.B. Cheng, W.T. Xu, C.Z. Zhao, F. Wei and Q. Zhang, J. Am. Chem. Soc., DOI:10.1021/jacs.6b12358 (2017) [6] L. Cheng, L.A. Curtiss, K.R. Zavadil, A.A. Gewirth, Y.Y. Shao and K.G. Gallagher, ACS Energy Lett., 1503-509 (2016)

Evolution of the novel C/SiO2/SiC ternary aerogel with high specific surface area and improved oxidation resistance

A novel C/SiO2/SiC ternary aerogel is derived from catechol-formaldehyde/silica hybrid aerogel (CF/SiO2) via a one-step sol-gel method followed by carbonization and carbothermal reduction processes under flowing argon. The effects of the carbon/silica molar ratios on the physicochemical properties of the C/SiO2 binary and C/SiO2/SiC ternary aerogel are investigated. The mechanism of the textural and structural evolution for the novel C/SiO2/SiC ternary aerogel is further discussed based on the experimental results and the calculated Gibbs free energy changes at different SiO partial pressure. The SiC layer is first formed on the surface of the composite aerogel via the solid-vapor reaction at 1400°C while SiC nanoparticles form at 1500°C. The C/SiO2/SiC ternary aerogel possesses a rather high specific surface area (746.87m2/g), a high micropore volume (0.2279cm3/g) and a high porosity (89.10%). The oxidation resistance is improved for 100°C when compared with the carbon based aerogel. The ternary aerogel obtains a high compressive strength (1.86MPa) and a low thermal conductivity (0.053W/m*K), which is suitable for high efficient thermal insulation uses both in inert and oxidative atmosphere.

Highly porous carbons obtained by activation of polypyrrole/reduced graphene oxide as effective adsorbents for CO2, H2 and C6H6

A series of highly porous carbon materials has been prepared from polypyrrole/reduced graphene oxide composite by one step carbonization and activation process. Two activation agents were used in this study potassium hydroxide and potassium citrate. The resulting samples exhibited high BET surface areas ranging from 1650 to 2780 m2/g, large total pore volumes in the range of 0.73–1.66 cm3/g, and high micropore volumes in the range of 0.43–0.78 cm3/g. The most porous material was synthesized by using KOH impregnation and featured hydrogen adsorption capacity of 11.3 mmol/g (2.3 wt% H2) at −196 °C under 760 mmHg and C6H6 capacity of 15.8 mmol/g at 20 °C and pressure close to the saturation vapor pressure. Also, highly ultramicroporous carbon was obtained by activation of the aforementioned composite with potassium citrate, which was confirmed by very high adsorption (6.8 mmol/g) of CO2 at 0 °C and 760 mmHg. The excellent adsorption properties of the synthesized carbons for CO2, H2 and benzene vapor were achieved by adjusting activation procedure specifically for each adsorbate used.

Studies on the correlation between nanostructure and pore development of polymeric precursor-based activated hard carbons: II. Transmission electron microscopy and Raman spectroscopy studies

Abstract In a previous study, we reported on activated polymer-based hard carbons (APHCs), which were prepared using CO 2 activation and characterized according to activation conditions, including textural properties such as specific surface area and pore volume. This paper was focused on the correlation between nanostructure and pore development of APHCs by using Cs-corrected-field emission transmission electron microscopy (Cs-corrected FE-TEM) and Raman spectroscopy to supplement the in-depth explanation. In the TEM analysis, the APHCs were observed to contain slit-shaped pores (SPs) and little cylindrical pores (CPs). And Raman spectroscopy was used in order to determine the degree of development of the crystal size (L a ) in the APHCs. The size of L a increased with increasing activation time until it was nearly 3 nm. These small crystallites might cause the SPs development, resulting in the high micropore volume of the APHCs. From a result of Raman analysis, it was confirmed that the L a value and the ratio of I D /I G value were in a proportional relation. The reason for this relation is that the L a value has grown up to about 3 nm, which is consistent with the Ferrari equation.

Facile preparation of porous N-doped carbon via a one-step carbonization/activation treatment of polyvinylpyrrolidone/melamine formaldehyde resin with ammonium carbonate and its enhanced electrochemical performances for supercapacitors

It is highly desired to introduce active nitrogen atoms and abundant pore structures for enhanced electrochemical performances of carbon materials for supercapacitors. Hence a facile one-step carbonization/activation method was adopted to treat different mass ratios of polyvinylpyrrolidone/melamine formaldehyde resin (PVP/MF) and ammonium carbonate in order to obtain porous N-doped carbon (PNC). Symmetric supercapacitors with PNC as electrodes were assembled using KOH aqueous electrolyte. It is clearly demonstrated that due to the introduction of ammonium carbonate the resulting PNC displays increased specific surface areas, enriched pore structures and increased active nitrogen concentration. The ratio-optimized PNC with 7 wt% ammonium carbonate exhibits the highest proportion of negatively charged N-6 and N-5 with the pseudocapacitance and the highest micropore volume with the electrical double-layer capacitance, which also lead to the decrease of charge transfer resistance and the increase of transfer rate of electrolyte ions in the pores, and these are beneficial effects for the improvement of the overall capacitive performances. The ratio-optimized PNC displays an enhanced specific capacitance, which is about 32% higher than that of the PNC prepared without ammonium carbonate. And the symmetric supercapacitor assembled with the ratio-optimized PNC shows superior cycling performance and its capacitance retention is 94.43% after 1500 cycles at 20 mA cm−2.

Rice straw-based activated carbons doped with SiC for enhanced hydrogen adsorption

Activated carbons (ACs) based on rice straw (RS) were synthesised using potassium carbonate as activating agent at three different K2CO3/RS weight ratios. Morphological, chemical, structural as well as textural characterisations were carried out in order to establish relationships between the physicochemical properties of the materials and their hydrogen adsorption capacities. The ACs contained potassium and silicon as the main impurities. Si was identified by XRD in both phases of silicon dioxide and silicon carbide. The presence of SiC was particularly surprising due to the rather low activation temperature, much lower than what is usually required for SiC synthesis. ACs exhibited well-developed surface areas (approximatively 2000–2100 m2 g−1) and high micropore volumes, making them suitable for hydrogen storage applications. RS-based ACs showed higher hydrogen storage capacities than those previously obtained with KOH-activated sucrose. The latter exhibited hydrogen uptakes (excess, 10 MPa, 298 K) up to 0.55 wt. %, whereas 0.65 wt. % was measured for RS-based ACs in the same conditions. The higher hydrogen capacities and isosteric heats of adsorption found here were attributed to the presence of SiC.

Crosslinked polybenzoxazine based membrane exhibiting in-situ self-promoted separation performance for pervaporation dehydration on isopropanol aqueous solutions

The performance of pervaporation dehydration of a crosslinked polybenzoxazine membrane (CR-PBz-M) on isopropanol (IPA) aqueous solutions has been studied. Compared to the feature showing in dry state, CR-PBz-M exhibits a change in micropore size distribution from a single distribution to a bimodal pattern in wet state being swollen with the feeding solutions. The presence of two groups of micropores in different sizes attributes to the high pervaporation dehydration performance of the membrane, in which the small micropores resist to the permeation of IPA molecules so as to contribute to the high membrane selectivity and the large micropores and high micropore volume fraction contribute to the high permeation fluxes. This feature of CR-PBz-M demonstrates an in situ self-promoted characteristic for pervaporation dehydration membranes. A permeation flux of 330gh−1m−2 and a 100% of water in the permeate side has been recorded on pervaporation dehydration on a 70wt% IPA aqueous solution.