Ultramicroporous Carbon Research Articles

Facile synthesis of ultramicroporous carbon adsorbents with ultra‐high CH4 uptake by in situ ionic activation

AbstractWe introduce a straightforward method for the preparation of novel starch‐based ultramicroporous carbons (SCs) that demonstrate high CH4 uptake and excellent CH4/N2 selectivity. These SCs are derived from a combination of starch and 1–6 wt.% of acrylic acid, and the resulting materials are amenable to surface cation exchangeability as demonstrated by the formation of highly dispersed K+ in carbon precursors. Following activation, these SCs contain ultramicropores with narrow pore‐size distributions of <0.7 nm, leading to porous carbon‐rich materials that exhibit CH4 uptake values as high as 1.86 mmol/g at 100 kPa and 298 K, the highest uptake value for CH4 to date, with the IAST‐predicted CH4/N2 selectivity up to 5.7. Both the potential mechanism for the formation of the narrow pores and the origin of the favorable CH4 adsorption properties are discussed and examined. This work may potentially guide future designs for carbon‐rich materials with excellent gas adsorption properties.

An Ultra-microporous Carbon Material Boosting Integrated Capacitance for Cellulose-Based Supercapacitors

HighlightsAn ultra-microporous carbon material simultaneously with high specific surface area (1554 m2 g−1) and packing density (1.18 g cm−3) is designed and fabricated.The resulting carbon material integrates the high gravimetric and volumetric capacitance (430 F g−1 and 507 F cm−3 at 0.5 A g−1) and thereof provides the robust all-solid-state cellulose supercapacitor with high areal and volumetric density.

Rapid, simple and sustainable synthesis of ultra-microporous carbons with high performance for CO2 uptake, via microwave heating

A one step microwave pyrolysis-activation method has been developed for the preparation of activated carbons from biomass with high CO2 capture efficiency (5.3 mmol g−1) by employing a low impregnation ratio (1) of KOH and K2CO3. The high microwave susceptibility identified by the dielectric properties enabled the preparation of a series of activated carbons in short processing times (<6 min), and the pyrolysis-activation simultaneously enhanced the formation of ultra-micropores leading to high CO2 uptake at 15 and 100% CO2 in the temperature range of 0–100 °C. The high CO2/N2 selectivity of up to 36 the adsorptive capacities were directly correlated to a pore size of ~0.7 nm, which favoured CO2 uptake up to 5.3 and 4.5 mmol g−1 at 1.1 bar and 0 °C and an uptake of 3.7 and 3.3 at 25 °C for activated samples with KOH and K2CO3, respectively. The activated carbons presented in this study are the first examples of samples that have been prepared by this simple and rapid method, which represents a 96.66% reduction in the processing times in comparison to conventional heating routes, and the CO2 uptake is comparable to the largest reported in literature for activated carbons. The outstanding uptake and selectivity, the simple synthesis using microwave technology in addition to the utilisation of a waste biomass as a carbon precursor, satisfy the requirements for the development of new and more sustainable energy environmental processes.

Electrochemical behaviors of graphene decorated sulfurized polyurethane foam-based ultra-microporous carbon

Polyurethane foam is a typical commercial polymer with a large production quantity and its waste needs to be recycled. This work reports a facile method to prepare ultra-microporous carbon from the polyurethane foam (PUF) waste and use it as a reservoir to impregnate sulfur for Li-S batteries. The raw PUF was carbonized and then activated with KOH. By controlling the activation temperatures, four carbon materials (PUFC-T) with different textures and N-doping levels were obtained. PUFC-800 shows the highest BET surface area, microporous volume, and quaternary N and pyridine N-oxide species. The electrochemical test results showed that higher microporous volume is beneficial to increase the uniform distribution of sulfur, as a result, the cycle stability and rate capacity is improved significantly. A large reversible capacity of 542 mAh g-1 can be retained at a large current of 0.5 C after 200 cycles with high sulfur loading of 70%.

Solvent-free and one-pot synthesis of ultramicroporous carbons with ultrahigh nitrogen contents for sulfur dioxide capture

• Porous carbon materials were synthesized by a solvent-free and one-pot route. • Rich ultramicropores and ultrahigh N contents are present in synthesized carbons. • Synthesized carbons display very high SO 2 capacities, especially at low pressures. • Impressive selectivities for SO2/CO2/N2 and good reversibility are also achieved. Recycling SO 2 from industrial tail gas is of great significance to control the environmental issues potentially induced by SO 2 emission. In the present work, porous carbons with rich ultramicropores and ultrahigh N contents (11.5–17.3 wt%) were synthesized by directly pyrolyzing the mixtures of glucose and urea at 700 ℃, without the use of any solvents. The synthesized porous carbons were characterized for porosity, morphology and elemental compositions, and also systematically investigated for SO 2 capture performance. It is found that the adsorption of SO 2 on synthesized porous carbons shows chemical behavior, owing to the strong acid-based interaction between SO 2 and pyridinic N. As consequence, the SO 2 capacities of synthesized porous carbons are very high, especially at low pressures (4.16 mmol/g at 296.2 K and 10 kPa). The synthesized porous carbons also display impressive adsorption selectivities for SO 2 /CO 2 /N 2 mixed gas, and good reversibility for SO 2 adsorption. Thus, it is believed that the synthesized porous carbons are promising candidates for selective and reversible SO 2 capture.

Evaluation of the textural properties of ultramicroporous carbons using experimental and theoretical methods

Spherical carbon molecular sieves (CMS) have selective adsorptive properties which are suitable for separation and purification of gas mixtures. Precise methods of characterization are needed to understand the performance of CMS in separation processes. To this end, the pore size distribution (PSD) of four carbon molecular sieves were evaluated experimentally using immersion calorimetry and complemented with gas adsorption measurements at cryogenic temperatures for N2, O2 and Ar, and at 273 K for CO2. Theoretical pore size distributions were estimated using two-dimensional non-local Density Functional Theory (2D-NLDFT) models. Calorimetry results showed that B and C samples had a narrow pore size distribution with pores below 0.7 nm. Meanwhile, the pore size distributions calculated from O2 and Ar adsorption isotherms, gave an apex in the 0.5–0.6 nm region for all the carbons together with a growing development of porosity at around 0.8 nm and above for carbons A and D. The agreement observed between experiments and theory confirmed the validity of the theoretical 2D-NLDFT models to anticipate the PSD. Carbon C with pores exclusively below 0.7 nm separated CO2 and CH4 while carbon D with pores in the supermicroporous region separated propane and propylene chromatographically.

Carbon-Supported Palladium–Cobalt Catalysts in Chlorobenzene Hydrodechlorination

Bimetallic and monometallic composite materials containing ultra-microporous carbon, the structure of which is similar to that of activated carbon, Pd0, CoO, and possibly PdCoO2 nanoparticles are synthesized via the pyrolysis of sawdust impregnated with a solution of palladium nitrate and cobalt nitrate. According to TEM, the size distribution of metal-containing particles in the bimetallic catalysts is slightly broader than the one in monometallic catalysts, and the average particle size of the former is larger than that of the latter. Some metal-containing particles are localized on the support surface, while others are pressed into the support matrix or coated with a carbon shell. Bimetallic catalysts exhibit high stability and activity in gas-phase chlorobenzene hydrodechlorination (HDC) to form mostly benzene; in the presence of all cobalt-containing catalysts, chlorobenzene conversion is greater than 85% throughout the investigated range of temperatures (150–300°C). XPS shows that during HDC, the metals are chlorinated and the carbon shells of the metal particles are partially degraded under the action of hydrogen chloride. This is accompanied by the emergence of active metal particles on the catalyst’s surface. Introducing cobalt helps reduce the deactivation of the catalysts’ palladium-containing sites and ensures the formation of additional active sites based on CoO.

Biomass-Tar-Enabled Nitrogen-Doped Highly Ultramicroporous Carbon as an Efficient Absorbent for CO2 Capture

As a notorious hazardous waste, biomass tar has for a long time been recognized as one of the key challenges throughout the progress in biomass gasification for renewable energy and chemical purpos...

Sub-Ångström-level engineering of ultramicroporous carbons for enhanced sulfur hexafluoride capture

Ultramicroporous carbon materials are realized by exploiting nitrogen-doping and alkali ions activation strategies on classical carboxylic phenolic resins. Through tuning the nitrogen-doped content as well as activation strength and size of the alkali ions, carbon materials present pore sizes that are controlled at the sub-Ångström level from 5.8 to 7.7 Å with precision between 0.1 and 0.4 Å. The fine-tuning of the ultramicropore size using melamine as the sacrificial templating agent improves the practicality of the carbon materials for the recovery of SF6 which are larger than conventional molecules such as CO2. Resultantly, the optimized carbon material at 1 bar and 25 °C saw a >16-fold increase in SF6 adsorption from 0.39 to 6.55 mmol g−1 while the SF6/N2 selectivity reached as high as 78.8. We attribute this to the fine-tuning of ultramicropores, leading to optimizable pore sizes that allow easy access to the large surface areas of carbon materials by the SF6 molecules. Furthermore, owing to its high adsorption performance, a 1.5-fold higher breakthrough SF6 adsorption capacity alongside a 2-fold increase in SF6/N2 selectivity were realized under dynamic breakthrough conditions. The stability and recyclability of the carbon materials were also demonstrated with a long-term performance evaluation of up to 10 consecutive adsorption-desorption cycles.

Ultramicroporous carbons with extremely narrow pore size distribution via in-situ ionic activation for efficient gas-mixture separation

Developing highly selective, cycle reliable, and moisture resistant adsorbents is of great importance for gas separation. It is very challenging to control and optimize pore sizes within the ultramicroporous ranges (<0.7 nm), especially for biomass-derived carbons. Moreover, porous carbons featured with random micropore sizes usually exhibited inferior gas separation performances. Herein, we developed an in-situ ionic activation method, in which the chemically bonded K+ ions that are uniformly distributed in the carbon precursor are able to create ultramicroporous carbons with uniform and narrow pore size distributions. Thus, the obtained carbons exhibited high CO2 uptakes (4.17 mmol g−1) and selectivities (333.2 and 34.9) for CO2/N2 (15v/85v) and CO2/CH4 (40v/60v) separation at ambient conditions. The dynamic breakthrough experiments clearly demonstrate their superior and applicable gas-mixture separation performances. Upon the detailed evaluation of vacuum swing adsorption (VSA) working parameters, a record-high adsorbent selective parameter (S) of 1906.4 is obtained. Hence, the in-situ ionic activation approach is an effective method for preparing ultramicroporous carbons with narrow and uniform pore size distributions.

Using Ultramicroporous Carbon for the Selective Removal of Nitrate with Capacitive Deionization.

The contamination of water resources with nitrate is a growing and significant problem. Here we report the use of ultramicroporous carbon as a capacitive deionization (CDI) electrode for selectively removing nitrate from an anion mixture. Through moderate activation, we achieve a micropore-size distribution consisting almost exclusively of narrow (<1 nm) pores that are well suited for adsorbing the planar, weakly hydrated nitrate molecule. Cyclic voltammetry measurements reveal an enhanced capacitance for nitrate when compared to chloride as well as significant ion sieving effects when sulfate is the only anion present. We measure high selectivities (S) of both nitrate over sulfate (SNO3/SO4 = 17.8 ± 3.6 at 0.6 V) and nitrate over chloride (SNO3/Cl = 6.1 ± 0.4 at 0.6 V) when performing a constant voltage CDI separation on 3.33 mM/3.33 mM/1.67 mM Cl/NO3/SO4 feedwater. These results are particularly encouraging considering that a divalent interferant was present in the feed. Using molecular dynamics simulations, we examine the solvation characteristics of these ions to better understand why nitrate is preferentially electrosorbed over sulfate and chloride.

Toward Improving the Areal Energy Density of Lithium–Sulfur Batteries with Ultramicroporous Carbon–Sulfur Composite Electrodes

Sulfur possesses high specific capacity (1672 mA h g−1) and high specific energy (2600 Wh kg−1), which makes it attractive as a cathode material for lithium–sulfur batteries. However, the areal energy density of sulfur electrodes is usually low due to an excess amount of inactive materials, mostly carbon, in the electrode composite. Typically, the electrode layers must be thin to achieve good specific capacity and cyclic stability. This further reduces the areal capacities, and it is challenging to design high areal density sulfur electrodes. Herein, the possibility of achieving high areal energy density by using ultramicroporous carbon–sulfur (UMC‐S) composite electrodes is investigated. For this purpose, the weight of sulfur per area is systematically varied by varying the amount of UMC‐S, and its electrochemical performance with respect to current density, cycling voltage window, electrolyte amount, and effect of temperature on cycling is investigated. A sulfur loading of up to 9.7 mg cm−2 and areal capacities above 4.5 mAh cm−2 are attained. The results indicate that a high areal energy density can be achieved with UMC‐S electrodes, however, at lower current rates. Higher current rates can be achieved by reducing the particle size and by improving the intrinsic electronic conductivity of the UMC host.

A template-assisted strategy to synthesize a dilute CoNi alloy incorporated into ultramicroporous carbon for high performance supercapacitor application.

Carbon is widely studied as an electrical double-layer capacitor (EDLC) electrode material due to its high specific surface area and good electronic conductivity. However, the low capacitance and energy density limit its further commercial applications. Herein, we report a facile and novel synthesis of dilute CoNi alloy nanoparticles embedded into ultramicroporous carbon (CoNi/UMCs) via a template-assisted strategy using SBA-15 as a template. The CoNi alloy serves as not only the electron collector to decrease the conductivity during tests, but also creates CoNi oxide/oxhydroxide on the alloy surface in an alkali solution, promoting redox reactions in pseudocapacitors, enhancing the performance of supercapacitors. Interestingly, the final morphology of the composite is not transferred from SBA-15 and the ultramicropores absolutely come from sucrose itself. However, the presence of SBA-15 can definitely enlarge the surface area of the CoNi/UMCs. After carefully tailoring the loading of CoNi, we find that 0.95% CoNi/UMCs exhibit a high surface area of 613 m2 g-1 with regular ultramicropores of 0.57 nm. Due to the synergistic effect of porous carbon and CoNi alloy, the unique 0.95% CoNi/UMCs exhibit a high specific capacitance of up to 268 F g-1 at 0.25 A g-1 in 6 M KOH aqueous solution and a high capacitance retention ratio of 97.8% after 10 000 cycles.

Biomass waste-carbon/reduced graphene oxide composite electrodes for enhanced supercapacitors

We present a simple and effective alternative which optimizes electrodes based on low-cost carbons for high-performance supercapacitors. The combination with reduced graphene oxide (rGO) greatly improves the operation of microporous carbons easily produced by one-pot activation of grape seeds. The use of composite electrodes with rGO lowers the supercapacitor resistance and enables a much higher rate capability.The mixture of rGO flakes and particles of a highly porous carbon obtained by KOH activation allows retaining the high capacitance of 260 F g−1 of the standard electrodes at 1 mA cm−2 in aqueous H2SO4 whereas the value at 200 mA cm−2 is increased by around 2.4 times. Consequently, at high current density, the capacitor assembled with these composites stores eight times more energy and the power density is multiplied by four.The synergy between rGO and an ultramicroporous carbon produced by CO2-activation results extremely profitable, the cell assembled with composite electrodes reaching three times more energy and power at 200 mA cm−2 than the best performance of the standard counterpart.More importantly, the higher density of the composite electrodes leads to a capacitance of around 200 F cm−3 which translates into a remarkable improvement in the supercapacitor operation normalized to volume.

In-situ ion-activated carbon nanospheres with tunable ultramicroporosity for superior CO2 capture

Ultramicroporous carbon materials play a critical role in CO2 capture and separation, however facile approaches to design ultramicroporous carbon with controllable amount, ratio and size of pores are still challenging. Herein, a novel strategy to design carbon nanospheres with abundant, uniform, and tunable ultramicroporosity was developed based on an in-situ ionic activation methodology. The adjustable ion-exchange capacity derived from oxidative functionalization was found capable of substantially governing the ionic activation and precisely regulating the ultramicroporosity in the resultant product. An ultrahigh ultramicropore content of 95.5% was achieved for the optimally-designed carbon nanospheres, which demonstrated excellent CO2 capture performances with extremely high capacities of 1.58 mmol g−1 at typical flue gas conditions and 4.30 mmol g−1 at 25 °C and ambient pressure. Beyond that, the CO2 adsorption mechanism in ultramicropore was also investigated through molecular dynamics simulation to guide the pore size optimization. This work provides a novel and facile guideline to engineer carbon materials with abundant and tunable ultramicroporosity towards superior CO2 capture performance, which also delivers great potential in extensive applications such as water purification, catalysis, and energy storage.

Ultramicroporous Carbons Puzzled by Graphene Quantum Dots: Integrated High Gravimetric, Volumetric, and Areal Capacitances for Supercapacitors

AbstractPorous carbons integrated with high gravimetric/volumetric/areal capacitances, especially at high mass loadings (&gt;10 mg cm−2), are important for practical applications in supercapacitors. Here, a strategy is developed for the synthesis of ultramicroporous carbons puzzled by graphene quantum dots as the building units through chemical welding and in situ activation. The resulted carbon has unique ultramicroporous structure (≈0.5 nm) with both high surface area (1730 m2 g−1) and packing density (0.97 g cm−3), providing high gravimetric and volumetric capacitances of 270 F g−1 and 262 F cm−3 at 1 A g−1, respectively. More importantly, such carbon achieves an ultrahigh areal capacitance of 5.70 F cm−2 with a high mass loading of 25 mg cm−2 at 1 A g−1, which is one of the best among the previously reported porous carbons. Furthermore, a two‐electrode supercapacitor exhibits an ultrahigh areal capacitance of 3 F cm−2 at 0.5 A g−1, rapid charge–discharge ability, and long lifespan. This work paves an avenue for developing advanced porous carbons with integrated capacitive performances for supercapacitors.

Unraveling the Operation Mechanisms of Lithium Sulfur Batteries with Ultramicroporous Carbons

Quasi-solid-state lithium–sulfur batteries (QSS-LSBs) constitute a new type of lithium sulfur batteries having a cathode usually based on ultramicroporous carbon and presenting only one voltage pla...

Facile and Controllable Preparation of Ultramicroporous Biomass-Derived Carbons and Application on Selective Adsorption of Gas-mixtures

It is very challenging to prepare biomass-derived porous carbons with well-confined ultramicropores. Traditionally, biomass-derived carbons, via a chemical activation process, possess wide pore size distributions from micropores to macropores. Outstanding BET surface area of 2676 ± 107 m2 g–1 was obtained with excellent CO2 uptake of 6.15 and 2.26 mmol g–1 under 1 and 0.15 bar at 273 K. Furthermore, the outstanding CO2/N2, CO2/CH4, and CH4/N2 selectivities of 43.5, 7.4, and 5.9 were obtained on an OTS-1-550 at 298 K and 1 bar. The pore size effect on CO2 capture and gas-separation performance was carefully investigated, indicating that the ultramicropores (<1 nm) governed the CO2 adsorption capacity at 1 bar. Also, the vacuum swing adsorption (VSA) processes and breakthrough experiments have confirmed their practical application potential.

Insight into Sulfur Confined in Ultramicroporous Carbon.

Here, we provide a deeper insight into the state of sulfur confined in ultramicroporous carbon (UMC) and clarify its electrochemical reaction mechanism with lithium by corroborating the results obtained using various experimental techniques, such as X-ray photoelectron spectroscopy, electron energy loss spectroscopy, in situ Raman spectroscopy, and in situ electrochemical impedance spectroscopy. In combination, these results indicate that sulfur in UMC exists as linear polymeric sulfur rather than smaller allotropes. The electrochemical reactivity of lithium with sulfur confined in UMC (pore size ≤0.7 nm) is different from that of sulfur confined in microporous carbon (≤2 nm, or ultramicroporous carbon containing significant amount of micropores) and mesoporous carbon (>2 nm). The observed quasi-solid-state reaction of lithium with sulfur in UMC with a single voltage plateau during the discharge/charge process is due to the effective separation of solvent molecules from the active material. The size of carbon pores plays a vital role in determining the reaction path of lithium with sulfur confined in UMC.

Nitrogen Codoped Unique Carbon with 0.4 nm Ultra-Micropores for Ultrahigh Areal Capacitance Supercapacitors.

A full understanding of ion transport in porous carbon electrodes is essential for achieving effective energy storage in their applications as electrochemical supercapacitors. It is generally accepted that pores in the size range below 0.5 nm are inaccessible to electrolyte ions and lower the capacitance of carbon materials. Here, nitrogen-doped carbon with ultra-micropores smaller than 0.4 nm with a narrow size distribution, which represents the first example of electrode materials made entirely from ultra-microporous carbon, is prepared. An in situ electrochemical quartz crystal microbalance technique to study the effects of the ultra-micropores on charge storage in supercapacitors is used. It is found that ultra-micropores smaller than 0.4 nm are accessible to small electrolyte ions, and the area capacitance of obtained sample reaches the ultrahigh value of 330 µF cm-2 , significantly higher than that of previously reported carbon-based materials. The findings provide a better understanding of the correlation between ultra-micropore structure and capacitance and open new avenues for design and development of carbon materials for the next generation of high energy density supercapacitors.