Mesopore Content Research Articles

Spherical mesoporous Fe–N–C catalyst for the air cathode of membrane-less direct formate fuel cells

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm−2, significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs.

Effect of Pyrolysis Conditions on the MOFs-Derived Zinc-Based Catalysts in Acetylene Acetoxylation

The preparation method and calcination temperature of metal-organic framework (MOFs)-derived materials are critical factors affecting catalytic performance. In this work, the preparation conditions of MOFS precursors were optimized, and zinc-based catalysts with different activities (MOF5-700, MOF5-750, and MOF5-800) were obtained by pyrolysis of MOFS precursors under nitrogen, which were then applied to an acetylene acetoxylation reaction system. According to the results, the conversion rate of acetic acid under catalysis was significantly different. (MOF5-700 (48%), MOF5-750 (62%), and MOF5-800 (22%)). Comparing the activity of the catalyst with the industrial catalyst Zn(OAc)2/AC (20%), MOF5-750 showed higher activity, and the acetic acid conversion rate remained around 60% after 50 h of stability testing. By characterization analysis, MOFs-derived materials were obtained after proper temperature pyrolysis. They have high mesoporous content, defects, and oxygen-containing functional groups and can maintain a good crystal structure, greatly reducing the loss of active components. This is the main reason for the good performance of the MOF5-750 catalyst in acetylene acetoxylation. Thus, the preparation conditions and favorable pyrolysis temperature of MOF derivative catalysts play a key role in the catalytic performance of acetylene acetoxylation.

Uniaxial tensile properties of multi-scale fiber reinforced rubberized concrete after exposure to elevated temperatures

With the rapid development of transportation and population growth, there is a surge hike in demand for automobile tires. Waste rubber disposal has become a big environmental concern worldwide due to the non-biodegradability of waste rubber. Based on the previous literature, waste rubber has great potential to make green concrete. However, the mechanical behavior of concrete, especially the tensile strength after being heated, will be reduced by adding waste crumb rubber. To improve the residual tensile behavior of rubberized concrete, steel fibers, PVA fibers (or PE fibers), and CaCO3 whiskers were added to make green concrete with better fire resistance. This study investigated the influences of the crumb rubber and multi-scale fibers on the failure mode, first cracking strength and strain, ultimate strength and strain, and the stress-strain relationships of MSFRRC subjected to elevated temperatures (up to 800 °C). In addition, the damage evolution of rubberized concrete under uniaxial tension was studied by the acoustic emission (AE) technique. Results show that specimens without fibers exhibited a single straight crack and a brittle failure. Adding crumb rubber could not improve the brittleness of concrete and eliminate explosive spalling. However, the brittleness of rubberized concrete could be improved and a multi-cracking behavior could be achieved by incorporating multi-scale fibers. Meanwhile, the ultimate strength decreased significantly when the crumb rubber volume replacement ratio increased from 0% to 30% since the increase in the porosity of the concrete specimen. The incorporation of multi-scale fibers could mitigate the strength loss and contribute to the first cracking strength, ultimate strength, and strain-hardening capability. The tensile strength of MSFRRC was enhanced by 54.4%–64.3% and the ultimate strain increased by 26.9–50.4 times. Nevertheless, the strain-hardening capability was eliminated owing to the weakened interfacial bond between the steel fiber and the matrix and the decomposition of PVA fibers when the temperature reached 400 °C. In addition, the large and medium capillary pores were reduced due to the additives of multi-scale fibers and the content of mesopores increased. Furthermore, the empirical formulas to predict the residual uniaxial tensile stress-strain relationship of MSFRRC considering parameters of crumb rubber, multi-scale fibers, and elevated temperatures were proposed based on the test results.

THE INVESTIGATION OF THE POROUS STRUCTURE OF CARBON SORBENTS BASED ON β-CYCLODEXTRIN FOR USE IN ENVIRONMENTAL PROTECTION TECHNOLOGIES

In this paper, the porous structure of three types of β-cyclodextrin (β-CD) carbons was synthesized and investigated. The first carbon was obtained from pure β-CD, the second carbon was synthesized from β-CD using the KOH activator, and the third carbon was synthesized from pure β-CD with additional ultrasonic treatment in the non-cavitation mode at the last stage. It was found that the carbon from pure β-CD has a micromesoporous structure with a small specific surface area (~35 m2/g). Activation with KOH causes a significant increase in the specific surface area (~654 m2/g) due to an increase in the content of micropores with an average size of 1,25 nm. The ultrasonic treatment causes mechanical grinding and oxidation of the carbon surface. It has been shown that such treatment increases the mesopore content and significantly changes the mesopore size distribution. It has been established that the oxidation of the β-CD carbon surface after ultrasonic treatment causes an increase in its hydrophilicity of up to 83,1%. The increase in hydrophilicity will allow more efficient use of synthesized carbon and composites based on it in solving the problems of environmental safety in water environments.

Research on double template agents to regulate the grain growth behavior of SAPO-34

The effects of different template ratios on the physicochemical properties of SAPO-34 molecular sieve and the catalytic performance of methanol to olefin (MTO) were investigated using tetraethylammonium hydroxide (TEAOH) and morpholine (Mor) as mixed templates. It was found that when the amount of Mor was more, the grains were smooth and regular cubes, and the acidity was stronger, and the mesoporous content was more. With the increase of TEAOH, the grain surface gradually changed into a multi-grain stacking structure, the acidity decreased slightly, and the large-sized mesopores slowly disappeared, replaced by small-sized mesopores with a diameter of 3–4 nm. It can be seen from the MTO reaction that the molecular sieve with stronger acidity deactivates faster, and the mesoporous size is too large to affect the shape-selective catalytic ability of the catalyst, which is not conducive to the formation of light olefins. Combined with the reaction and characterization, when the template ratio R = 4, the acidity distribution in the molecular sieve is moderate, and the average pore size is small, which improves the selectivity of low olefins.

Construction of hierarchical porous carbon with mesopores-enriched from sodium lignosulfonate by dual template strategy and their diversified applications for CO2 capture, radioactive iodine adsorption, and RhB removal

Lignosulfonate, as the large-scale by-products from the sulfite pulping, converting them to porous carbon is an alternative potential path. However, most sodium lignosulfonate (LS-Na) derived porous carbon all belonged to the dominated microporous carbon materials, and had poor graphitization degree and low heteroatoms content. Here, a series of hierarchically porous carbon with rich and controllable mesopores were firstly prepared from LS-Na by two dual template strategies. These carbon materials showed high Brunauer-Emmett-Teller (BET) surface areas (SBET) of 230.6–1483.3 m2/g, hierarchical porous structure (mesopore content up to 84.5%), rich heteroatoms (N, O, S) doping (9.22–22.53%), and good graphitization structure. The incorporation of SBA-15 and Ni species as the nano-templates not only brought the unique micro-structure, but also enhanced mesoporous properties. SLS-C had the largest CO2 uptake (206.2 mg/g) due to the largest micropore volume (Vmicro) and ultramicropore volume (Vultra) by micropore filling mechanism. SLS-S-Ni-C possessed effective iodine capacity (∼2.2 g/g) and good recycling (∼90.9%), the adsorption process was based on the dominated physical adsorption, meanwhile, also along with the weak chemical interaction for some iodine molecules by little strong binding sites. SLS-Ni-C had the largest equilibrium capacity of RhB (350.6 mg/g) and the fast adsorption kinetic (about 50 min) due to the large SBET, suitable micro-mesopores size and proportion. This work provided a kind of hierarchical porous carbon from LS-Na by dual template routes, and matched adsorbents for the removal of targeted contaminants.

In Ukrainian

The paper considers an approach to the processing of waste of agro-industrial raw materials due to chemical activation. To obtain a sorption material, waste was used, which is the shell of Juglansregia walnuts. The aim of the work was to develop adsorbents from walnut shells with a large proportion of mesopores, to determine the parameters of the porous structure and to study their adsorption capability to absorb egg albumin as a marker of medium molecular toxins of a protein nature. Activated carbon samples with a high mesopore content (550 m2/g) were obtained by combined activation of the feedstock. The sorption of one of the obtained samples and, for comparison, the medical product SORBEX was studied by the spectrophotometric method, and its effectiveness was proved in the absorption of egg albumin from aqueous solutions. The significant capability of the obtained sample to sorb protein (35–38 mg/g) was shown, it has been assumed that in the process of sorption, macromolecules are concentrated near the inlets into the pores of the adsorbent. It can be stated that the adsorption of albumin increases in proportion to the increase in the specific surface area of the mesopore. Using the obtained sorption isotherms, the parameters of adsorption processes were calculated. Adsorption isotherms were calculated using the Langmuir and Freundlich equations. It is shown that the maximum adsorption values calculated using the Langmuir equation are in good agreement with the experimental data.

Enhanced supercapacitor performance of Camellia oleifera shell derived hierarchical porous carbon by carbon quantum dots

Biomass-derived porous carbons have great potential as electrode materials for supercapacitors. However, their amorphous and micropore-dominated structures are unfavorable for the electrochemical kinetics, which will limit their rate capability and cycle stability. In this work, we reported a facile strategy to improve the capacitive behavior of porous carbons derived from Camellia oleifera shell by introducing carbon quantum dots (CQDs) with highly graphitization degree into the skeleton of porous carbons. Benefiting from the unique surface property of CQDs, the obtained CQD/hierarchically porous carbon composites (CQDs/HPC) possessed a well-developed porous structure with high mesopore content and moderate surface heteroatom doping. Furthermore, their charge/ion transfer kinetics were improved due to the formation of the conductive channels in the carbon skeleton as well as optimized pore structure and surface doping. Consequently, the optimized CQDs/HPC-2 presented a high capacitance of 259 F g−1 at 1 A g−1 and a high rate capability in 1 M H2SO4, which is much better than bare HPC. The assembled symmetric supercapacitors delivered an energy density of 8.61 (17.86) Wh kg−1 at the power density of 477 (954) W kg−1 in 1 M H2SO4 (1 M Na2SO4) solution and high long-term stability with 94 % capacitance retention after 20,000 cycles at 5 A g−1.

Facile 3D Nitrogen‐Doped Hierarchical Porous Carbon for High‐Performance Supercapacitors

A novel activated nitrogen‐doped hierarchically porous carbon (ANPC) material has been synthesized using polyurethane foam as the supporting template, phenolic resin with a high carbonization ratio, and low‐cost ammonium polyphosphate as the carbon and nitrogen sources, respectively. The preparation process comprises curing and carbonization combined with KOH activation. Despite the simplicity of the process, the obtained ANPC‐4 exhibits a high specific surface area (1452 m2 g−1), a well‐developed specific pore volume (0.799 cm3 g−1), moderate mesoporous content (32.7%), good electrolyte ions transport property, and appropriate nitrogen dopant content. When used as a material for fabricating supercapacitor electrodes, the ANPC‐4 exhibits a significantly high capacitance value of 356 F g−1 at 0.2 A g−1 in a 6 M KOH electrolyte with outstanding rate performance. In addition, the symmetrical capacitors assembled by ANPC‐4 have good specific capacitance (175 F g−1 at 0.2 A g−1), high energy density up to 24.3 Wh kg−1, and good cycling stability (94.5% capacitance retention after 10 000 cycles of testing).

Preparation of macadamia nut shell porous carbon and its electrochemical performance as cathode material for lithium–sulfur batteries

Biomass carbon material as the sulfur storage matrix of lithium–sulfur batteries is one of the research hotspots. In this paper, the macadamia nut shells are used as the precursor to prepare porous carbon material. By exploring the effect of temperature on the microstructure and electrochemical performance of porous carbon materials during activation, it is found that the porous carbon material prepared under the activation condition of 900 °C has a developed pore structure, super high specific surface area (3552.7 m2•g−1), larger pore volume (2.2 cm3•g−1) and higher mesoporous content (23.85%). And the composite cathode material with the sulfur content of 70.1% has the highest specific capacity, and the initial discharge specific capacity for 0.2 C can reach 942.4 mAh•g−1. The composite material S/OCNT@OPC-1:1 obtained by compounding it with carbon nanotubes at a mass ratio of 1:1 has higher specific capacity, better rate performance and cycle performance. At 0.2 C, the initial discharge specific capacity is as high as 1252.6 mAh•g−1, and it remains at the level of 717.3 mAh•g−1 after 200 cycles. Even at 1 C, the specific capacity is still 984.3 mAh•g−1, and it remains at 690.9 mAh•g−1 after 200 cycles, and the capacity retention rate is 70.2%. Our work shows that the composite material obtained by combining low-cost biomass carbon materials and carbon nanotubes as the cathode material for lithium-sulfur batteries has obvious advantages.

Effect of different ice contents on heat transfer and mechanical properties of concrete

With annually decreasing shallow mineral resources, development and utilization of deep mineral resources are critical. However, heat hazards in deep mines pose hidden dangers to health and safe operation of equipment. Therefore, a suitable cooling method is an urgent concern in deep high-temperature mines. This study proposes a cooling method that introduces ice into concrete for phase change cooling and improved strength characteristics. It can be used in deep high-temperature mines, and is known as iced-concrete technology. Based on temperature monitoring, mechanical strength tests, and microstructure tests, this study explores the influence of different ice contents (0 %, 10 %, 20 %, 30 %, 40 %, 50 %, 60 %) on heat transfer and mechanical properties of concrete, and analyzes the mechanism of heat transfer and the mechanical properties of concrete under the action of ice particles. The results show that: (1) the temperature evolution law of concrete with different ice contents takes 18 h–26 h and has a temperature change inflection point interval that first increases and then decreases. With an increase in ice content, the lower the initial temperature, the greater the rate of temperature change. (2) Ice particles have an obvious positive effect on the uniaxial compressive strength and splitting strength of concrete; the final mechanical properties of concrete are positively correlated with the ice content with a constant water (ice)–cement ratio. (3) Compared with ordinary concrete, the initial low-temperature water storage capacity of iced concrete promotes formation of hydration products in the later stage to some extent, improving the content of hydration products in the curing stage, promoting the full filling of internal concrete pores, reducing the content of harmful macropores and mesopores, optimizing the pore structure, and improving the compactness and mechanical strength of the concrete. (4) The cooling efficiency of concrete was increased with an increase in ice content. The cooling efficiency of concrete with 60 % ice content was six times that of ordinary concrete. When the ice content exceeded 20 %, the cooling capacity generated by ice–water phase change was greater than the heat absorbed by the temperature change of the water.

Highly graphitized porous biocarbon nanosheets with tunable Micro-Meso interfaces and enhanced layer spacing for CO2 capture and LIBs

• Generation of porosity cum graphitization in carbon materials. • Controlled tuning of the porous features and degree of graphitization. • Easily manipulated content of micropores and mesopores. • High CO 2 adsorption of 5.9/16.7 mmol g −1 at 0 °C and 1/30 bar. • Graphitization and porosity led to a good specific capacity of 646 mAh g −1 in LIBs. Porous carbon materials with tunable micro and mesoporous structure, graphitic wall structure, and enhanced layer spacing are considered attractive materials for several applications, including adsorption and energy storage and conversion. However, it is challenging to design porous carbon with all these properties in a single system. Here, we present a facile and rational synthesis route to fabricate graphitized porous biocarbon nanosheets from a low-cost precursor through a simple integration of simultaneous “activation and graphitization” process using iron acetate and potassium acetate at a high temperature. The prepared materials show tunable micro and mesoporosity with an enhanced layer spacing and high crystallinity. These sophisticated materials exhibit a smooth switch over the micro and mesopores for either low (5.9 mmol g −1 / 0 °C/ 1 bar) or high pressure (16.7 mmol g −1 / 0 °C/ 30 bar) CO 2 capture. The careful manipulation of the porous texture and the graphitization degree also allows for enhanced performance as LIB anodes (646 mAh g −1 ), which show good cycling and surpass the specific capacity of conventional graphite anode (372 mAh g −1 ). These findings exemplify the importance of designing intriguing materials for addressing climate change by reducing greenhouse gases as well as providing low-cost alternative energy storage resources.

Mesopore dominated capacitive deionization of N-doped hierarchically porous carbon for water purification

Under the global shortage of freshwater resources, capacitive deionization (CDI) has attracted widespread attention as an efficient and energy-saving water purification technology. Herein, N-doped hierarchically porous carbons (NPCs) with micro-meso-macropore, excellent specific capacitance (194.75 F g−1), large specific surface area (1903.0 m2 g−1), high mesoporous content, and fast ion transport capability were prepared by the pyrolysis of polyacrylonitrile using nano-silica and ZnCl2 as pore-making agents. As CDI electrode materials for desalination and heavy metal adsorption, the optimized NPC-0.75 electrode delivered a maximum electrosorption capacity of 19.61 mg g−1 at the optimum operating parameters (1.2 V, 10 mL min−1, 500 mg L-1 NaCl) and an excellent regeneration performance after continuous electrosorption-desorption cycles. The structure–activity relationship analysis indicated that the mesopore dominates the CDI performance of NPCs in water. In addition, NPC-0.75 electrode showed a high removal capacity for Cu2+ (36.3 mg g−1), Cd2+ (30.02 mg g−1) and Pb2+ (21.5 mg g−1) in water. This study provides new insight into the design of high-efficiency porous carbons toward the CDI from water.

Is early drying shrinkage still determined by the mesopore content? A case study of cement paste with minerals

Long-term drying shrinkage is deemed to be relevant with the mesopore content of cement paste, so is early drying shrinkage still determined by the number of mesopores? This was not the case. Through combining the measurement of water loss and pore size distribution (PSD), this study provides an explanation of early-age drying shrinkage of cement paste with different types/contents of minerals (i.e., blended cement paste) added, and a corresponding prediction model was proposed in terms of its early shrinkage. The results show that during hydration, instead of the mesopore content, the water loss due to evaporation in capillary pores of cement paste was well correlated with its early drying shrinkage, which could be attributed to a small portion of mesopores rather than all mesopores have lost water at an early age. Meanwhile, a parameter rs, which was defined as the radius of the pores where the meniscus formed, was calculated by combining the results of PSD and water evaporation, and its reduction led to an increment of drying shrinkage of specimens. Finally, the outcomes obtained from the proposed prediction model fitted well with experimental data, revealing the effectiveness and accuracy of the model in foreseeing early drying shrinkage of blended cement paste.

Li–Se batteries: Insights to the confined structure of selenium in hierarchical porous carbon and discharge mechanism in the carbonate electrolyte

Confining selenium in porous carbon hosts is an effective strategy to improve the performance of Li–Se batteries. The structure of confined Se and the corresponding lithiation mechanism remain to be clarified yet. In this work, Se@CISC-58 composite material was prepared based on hierarchical porous carbon CISC-58 with same content of mesopores and micropores, and then used for cathode material of Li–Se batteries. The selenium loaded in Se@CISC-58 takes Sex chain structure rather than the cyclic Se8, as evidenced by both 77Se MAS NMR and EPR experiments. In particular, the free radical signals in EPR changes adaptively with the discharge-charge cycling. Ex-stiu EPR and in-stiu 7Li NMR techniques further confirmed the stepwise reaction mechanism of Sex chains in the carbonate-based electrolytes. To better understand the discharge process of selenium, NMR in combination with DFT calculations are utilized to assign the polyselenides engaged in discharge process. We have found that polyselenides represented by Li2Se2 were generated during the discharge of selenium in the carbonate-based electrolytes.

Monodisperse Porous Carbon Nanospheres with Ultra‐High Surface Area for Energy Storage in Electrochemical Capacitors

AbstractHighly porous carbon nanoparticles are very suitable materials for supercapacitor electrodes due to their combination of large surface area for ion adsorption and short pathways for fast ion diffusion. Herein we describe the synthesis of highly porous carbon nanospheres (d=90 nm) by a simple strategy that involves the preparation of monodisperse nanoparticles by the oxidative polymerization of pyrrole, followed by their direct chemical activation with KHCO3. The morphology of the nanospheres is well retained after activation, and the inorganic impurities are removed by a simple washing step with water. The porous nanospheres possess a high electrical conductivity and specific surface areas exceeding 3000 m2 g−1 due to their high content of micropores and small mesopores (<4 nm). Their highly developed and readily available porosity make these materials promising for use as supercapacitor electrodes. In the aqueous 1 M H2SO4 electrolyte, the porous nanospheres reach a capacitance of 262 F g−1 and withstand an ultrahigh current density of 80 A g−1 maintaining a capacitance above 100 F g−1. In the organic 1 M TEABF4/AN and EMImTFSI/AN electrolytes, the nanoparticles reach 175 and 155 F g−1, and the supercapacitors could be cycled up to 50 A g−1 delivering 30 Wh kg−1 at a power density of 20 kW kg−1 and 31 Wh kg−1 at a power density of 31 kW kg−1, respectively. These results demonstrate the potential of these nanoparticles for energy storage applications.

Structure-Property Correlation of Hierarchically Porous Carbons for Fluorocarbon Adsorption.

Although traditional commercially available porous carbon-fluorocarbon working pairs have shown promising applicability for adsorption cooling, advancements in engineered carbons may further improve the performance. Moreover, insights into structure-property relationships that target higher sorption capacities within these synthesized carbons may guide such materials' future design. We utilized hierarchically porous carbons (HPCs), synthesized with colossal microporous and mesoporous content characterized by high surface areas (up to 2689 m2/g) and pore volume values (up to 10.31 cm3/g) toward fluorocarbon R134a adsorption. This unique pore topology leads to exceptional R134a uptake, ∼250 wt %, outperforming the highest uptake carbon material to date, Maxsorb III (∼220 wt %). Material characterizations reveal that the outstanding R134a capacity may be attributed to textural properties and oxygen-terminated functional groups more than graphitization of the material. Most importantly, HPCs are efficiently utilized in a two-bed model chiller device, where the performance shows excellent working capacity (105 wt %, ∼2 times the value of reported carbon materials/R134a). Fluorocarbon adsorption on HPCs also displays fast kinetics (equilibrium time: ∼2 min) mainly driven by physical adsorption (Qst: ∼27 kJ/mol), characteristic of swiftly reversible behavior adsorption-desorption behaviors. This work provides a fundamental understanding of the applicability of HPCs/R134a working pair for adsorption cooling.

Pair Distribution Function Analysis and Electrochemical Performance of Mesoporous Carbon Nanomaterials Synthesized Through KOH and ZnCl2 Activation

Mesoporous carbon has been synthesized by activating carbonized biogas slurry residues with ZnCl2 and KOH simultaneously. The carbon to activating agent mass ratios were kept at 1:4, while the ZnCl2 to KOH mass ratio varied from 4:0, 3:1, 2:2, 1:3, to 0:4. The highest BET specific surface area of 361 m2 g-1, micropore surface area of 231 m2 g‒1, mesopore surface area of 125 m2 g‒1, and total pore volume of 0.23 cm3 g‒1 which amounted to 78% mesopore content, were obtained for the sample with 3:1 ZnCl2 to KOH mass ratio. Scanning electron microscope (SEM) images were acquired to determine the surface morphology and energy dispersive X-ray (EDX) was used to determine surface composition of the samples. The short, medium, and long-range orders of the synthesized materials were studied using pair distribution function (PDF) analysis. PDF showed that in addition to the locally ordered carbon and silica phase components, samples activated using combined ZnCl2 and KOH also contained crystalline Zn2SiO4 phase with the willemite structure. Electrochemical studies in three-electrode cell system revealed maximum specific capacitance of 216 F g‒1 exhibited by sample with a ZnCl2: KOH mass ratio of 3:1 at a scan rate of 5 mV s‒1.
 Keywords: Mesoporous carbon; Pair distribution function, Specific capacitance, supercapacitor

Highly performed nitrogen-doped porous carbon electrocatalyst for oxygen reduction reaction prepared by a simple and slight regulation in hydrolyzing process of ZIF-8

A simple and environmentally friendly method to prepare nitrogen-doped porous carbon (NPC) electrocatalysts for oxygen reduction reaction (ORR) is studied by using glucose (Glu) to regulate the hydrolyzing process and structure of ZIF-8 precursor. Compared with pristine ZIF-8, the ZIF-8 regulated by Glu (Glu/ZIF-8) has smaller particle size. NPC has a higher content of mesopores and macropores, a higher degree of graphitization, and a higher content of pyridine and graphitic nitrogen than nitrogen-doped carbon (CN) derived from prisitine ZIF-8. The onset potential, half-wave potential, and limiting current of NPC for ORR in 0.1 ​M KOH medium is 0.99 ​V, 0.88 ​V, and 5.43 ​mA ​cm−2, respectively. The electrocatalytic performance of NPC is similar to Pt/C, and better than CN. Furthermore, its stability and resistance to methanol are better than Pt/C. Its high electrocatalytic performance is attributed to the effect of Glu on the structure of ZIF-8 precursor.

Molten Salt Templated Synthesis of Covalent Isocyanurate Frameworks with Tunable Morphology and High CO2 Uptake Capacity.

The use of reactive molten salts, i.e., ZnCl2, as a soft template and a catalyst has been actively investigated in the preparation of covalent triazine frameworks (CTFs). Although the soft templating effect of the salt melt is more prominent at low temperatures, close to the melting point of ZnCl2, leading to the formation of abundant micropores, a significant mesopore formation is observed that is due to the partial carbonization and other side reactions at higher temperatures (>400 °C). Evidently, high-temperature synthesis of CTFs in various eutectic salt mixtures of ZnCl2 with alkali metal chloride salts also leads to mesopore formation. We reasoned that using the isocyanate moieties instead of cyano groups in the monomer, 1,4-phenylene isocyanate, could enable efficient interactions between carbonyl moieties and alkali metal ions to realize efficient salt templating to form covalent isocyanurate frameworks (CICFs). In this direction, the trimerization of 1,4-phenylene diisocyanate was carried out under ionothermal conditions at different reaction temperatures using ZnCl2 (CICF) and the eutectic salt mixture of KCl/NaCl/ZnCl2 (CICF-KCl/NaCl) as the reactive solvents. We observed notable differences in the morphologies of the two polymers, whereas CICF showed irregular-shaped micrometer-sized particles, the CICF-KCl/NaCl exhibited a filmlike morphology. Moreover, favorable ion-dipole interactions between alkali metal cations and oxygen atoms of the monomer facilitated two-dimensional growth and the formation of a purely microporous framework in the case of CICF-KCl/NaCl along with a near theoretical retention of the nitrogen content at 500 °C. The CICF-KCl/NaCl showed a BET surface area of 590 m2 g-1 along with a CO2 uptake capacity of 5.9 mmol g-1 at 273 K and 1.1 bar because of its high microporosity and nitrogen content. On the contrary, in the absence of alkali metal ions, CICF showed high mesopore content and a moderate CO2 uptake capacity. This study underscores the importance of the strength of the interactions between the salts and the monomer in the ionothermal synthesis to control the morphology, porosity, and gas uptake properties of the porous organic polymers.