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2019 Volume 35 Issue 7
2019, 35(7): 657-658
doi: 10.3866/PKU.WHXB201809044
Abstract:
2019, 35(7): 659-660
doi: 10.3866/PKU.WHXB201809045
Abstract:
2019, 35(7): 661-662
doi: 10.3866/PKU.WHXB201809053
Abstract:
2019, 35(7): 663-664
doi: 10.3866/PKU.WHXB201811042
Abstract:
2019, 35(7): 665-666
doi: 10.3866/PKU.WHXB201812001
Abstract:
2019, 35(7): 667-683
doi: 10.3866/PKU.WHXB201806062
Abstract:
The global energy shortage has led to vigorous research for the development of new energy technologies in all countries to cope with the energy crisis and to meet the demand for green energy. In this regard, the development of new battery systems with high energy densities has become the current research hotspot. Lithium-sulfur battery is considered as a promising candidate due to its high energy density and low cost. However, it suffers from the insulating nature of sulfur and the shuttle effect of polysulfide, which hinder its practical application. Selenium (Se), as a congener element of sulfur, possesses electrochemical properties similar to sulfur. Lithium-selenium batteries have attracted considerable research attention due to the high electronic conductivity of selenium and high volumetric capacity. The conductivity of Se (1 × 10-3 S·m-1) is ~24 orders of magnitude higher than that of sulfur (5 × 10-28 S·m-1), providing much better electron transportation in cathode, leading to fast electrochemical reaction and high utilization of Se. Moreover, Se is compatible with cheap carbonate-based electrolytes, which could greatly reduce the cost. Lithium-selenium batteries also have much higher theoretical volumetric and gravimetric capacities (3253 mAh·cm-3 and 675 mAh·g-1, respectively) than those of commercial lithium-ion batteries such as LiCoO2/graphite and LiFePO4/graphite systems. Volumetric capacity is a more important requirement than gravimetric capacity for a battery, especially for applications in electric vehicles and portable electronic devices, because they have limited space for accommodating batteries. Thus, research on lithium-selenium batteries with high volumetric capacities is of great significance for these volume-sensitive applications. However, the electrochemical performance of current lithium-selenium batteries is not satisfactory. Several key problems must be solved, including shuttle effect, electrolyte compatibility, volume change during cycling, capacity fading, and low coulombic efficiency. In recent years, widespread research has been conducted to address these problems and considerable progress has been made. This review summarizes the status of research on lithium-selenium batteries, and focuses on the recent progress in the research of selenium-carbon cathode materials. The advantages and disadvantages of lithium-selenium batteries are discussed in detail. The performance-structure relationship is analyzed from the perspective of different dimensional structures, including one-dimensional nanofibers and nanowires, two-dimensional nanosheets, composite films and scaffolds, three-dimensional hollow structures, solid structures, and freestanding structures (spheres, nanobelts, nanotubes, microcubes etc.). Other types of selenium-based cathodes, including metal selenides and heterocyclic selenium-sulfur (SexSy), are also described. The compatible electrolytes and functional interlayers for lithium-selenium batteries are also discussed. The reaction mechanisms of lithium-selenium batteries and their relationship with various electrolytes are summarized. Finally, the future perspective of lithium-selenium batteries is proposed. ![]()
The global energy shortage has led to vigorous research for the development of new energy technologies in all countries to cope with the energy crisis and to meet the demand for green energy. In this regard, the development of new battery systems with high energy densities has become the current research hotspot. Lithium-sulfur battery is considered as a promising candidate due to its high energy density and low cost. However, it suffers from the insulating nature of sulfur and the shuttle effect of polysulfide, which hinder its practical application. Selenium (Se), as a congener element of sulfur, possesses electrochemical properties similar to sulfur. Lithium-selenium batteries have attracted considerable research attention due to the high electronic conductivity of selenium and high volumetric capacity. The conductivity of Se (1 × 10-3 S·m-1) is ~24 orders of magnitude higher than that of sulfur (5 × 10-28 S·m-1), providing much better electron transportation in cathode, leading to fast electrochemical reaction and high utilization of Se. Moreover, Se is compatible with cheap carbonate-based electrolytes, which could greatly reduce the cost. Lithium-selenium batteries also have much higher theoretical volumetric and gravimetric capacities (3253 mAh·cm-3 and 675 mAh·g-1, respectively) than those of commercial lithium-ion batteries such as LiCoO2/graphite and LiFePO4/graphite systems. Volumetric capacity is a more important requirement than gravimetric capacity for a battery, especially for applications in electric vehicles and portable electronic devices, because they have limited space for accommodating batteries. Thus, research on lithium-selenium batteries with high volumetric capacities is of great significance for these volume-sensitive applications. However, the electrochemical performance of current lithium-selenium batteries is not satisfactory. Several key problems must be solved, including shuttle effect, electrolyte compatibility, volume change during cycling, capacity fading, and low coulombic efficiency. In recent years, widespread research has been conducted to address these problems and considerable progress has been made. This review summarizes the status of research on lithium-selenium batteries, and focuses on the recent progress in the research of selenium-carbon cathode materials. The advantages and disadvantages of lithium-selenium batteries are discussed in detail. The performance-structure relationship is analyzed from the perspective of different dimensional structures, including one-dimensional nanofibers and nanowires, two-dimensional nanosheets, composite films and scaffolds, three-dimensional hollow structures, solid structures, and freestanding structures (spheres, nanobelts, nanotubes, microcubes etc.). Other types of selenium-based cathodes, including metal selenides and heterocyclic selenium-sulfur (SexSy), are also described. The compatible electrolytes and functional interlayers for lithium-selenium batteries are also discussed. The reaction mechanisms of lithium-selenium batteries and their relationship with various electrolytes are summarized. Finally, the future perspective of lithium-selenium batteries is proposed.
2019, 35(7): 684-696
doi: 10.3866/PKU.WHXB201806056
Abstract:
Bile acid salts, which are regarded as anionic steroid biosurfactants, have been widely used in the preparation of novel nanomaterials owing to their special amphiphilic skeleton structure, unique physical and chemical properties, good biocompatibility, and environmental friendliness. They can participate in the supramolecular self-assembly to form ordered aggregates in solution, and can be used as a template for the preparation of micro and nanomaterials. In this manuscript, we present an overview of our research work based on the effect of bile salts on the self-assembly of micro and nanomaterials along with related research done worldwide. The first section introduces the effect of small biological molecules such as amino acids, on the aggregation behavior of bile salts, wherein the interaction between amino acids and cholate has been studied extensively. Many in vivo and in vitro studies have been carried out mainly focusing on solutions and interfaces. Second part of this manuscript summarizes the research progress on the construction of supramolecular gels based on bile salts, including amino acids, rare earth salts, Graphene Oxide (GO), and surfactants. Cholic acid sodium, sodium deoxycholic acid, and lithocholic acid sodium cholic acid salt have special steroidal parent skeleton, which is much more complicated than the alkane surfactant, enabling them to self-assemble to form gel via non-covalent interactions such as van der Waals force, hydrogen bonding, and hydrophobic effect. Also addition of small molecules and other organic/inorganic fillers can increase the mechanical strength of the gels. Last part describes the formation of micro and nanomaterials by self-assembly in presence of bile salts, especially about their interaction with dye molecules, wherein the formed complex usually has novel and ordered microstructures. The interaction between surfactants and dye molecules are mainly driven by electrostatic forces, hydrogen bonding, and van der Waals force. Dye molecules are considered to be an ideal substrate for constructing functional nanomaterials and as biosurfactant, bile salts are often used to assist in the synthesis of micro and nanomaterials. In order to get a more comprehensive and in-depth understanding of the preparation of micro and nanomaterials in presence of bile salts, this article provides a solid foundation to explore future applications. Although the participation of bile salts in supramolecular self-assembly and in the preparation of various functional nanomaterials has not been studied much, the current research focuses on the template function of bile salt and ionic self-assembly. However, the biological and physiological aspects of bile salts are low; therefore the function of bile salts still needs to be probed. ![]()
Bile acid salts, which are regarded as anionic steroid biosurfactants, have been widely used in the preparation of novel nanomaterials owing to their special amphiphilic skeleton structure, unique physical and chemical properties, good biocompatibility, and environmental friendliness. They can participate in the supramolecular self-assembly to form ordered aggregates in solution, and can be used as a template for the preparation of micro and nanomaterials. In this manuscript, we present an overview of our research work based on the effect of bile salts on the self-assembly of micro and nanomaterials along with related research done worldwide. The first section introduces the effect of small biological molecules such as amino acids, on the aggregation behavior of bile salts, wherein the interaction between amino acids and cholate has been studied extensively. Many in vivo and in vitro studies have been carried out mainly focusing on solutions and interfaces. Second part of this manuscript summarizes the research progress on the construction of supramolecular gels based on bile salts, including amino acids, rare earth salts, Graphene Oxide (GO), and surfactants. Cholic acid sodium, sodium deoxycholic acid, and lithocholic acid sodium cholic acid salt have special steroidal parent skeleton, which is much more complicated than the alkane surfactant, enabling them to self-assemble to form gel via non-covalent interactions such as van der Waals force, hydrogen bonding, and hydrophobic effect. Also addition of small molecules and other organic/inorganic fillers can increase the mechanical strength of the gels. Last part describes the formation of micro and nanomaterials by self-assembly in presence of bile salts, especially about their interaction with dye molecules, wherein the formed complex usually has novel and ordered microstructures. The interaction between surfactants and dye molecules are mainly driven by electrostatic forces, hydrogen bonding, and van der Waals force. Dye molecules are considered to be an ideal substrate for constructing functional nanomaterials and as biosurfactant, bile salts are often used to assist in the synthesis of micro and nanomaterials. In order to get a more comprehensive and in-depth understanding of the preparation of micro and nanomaterials in presence of bile salts, this article provides a solid foundation to explore future applications. Although the participation of bile salts in supramolecular self-assembly and in the preparation of various functional nanomaterials has not been studied much, the current research focuses on the template function of bile salt and ionic self-assembly. However, the biological and physiological aspects of bile salts are low; therefore the function of bile salts still needs to be probed.
2019, 35(7): 697-708
doi: 10.3866/PKU.WHXB201807071
Abstract:
With the development of synthetic chemistry, more and more efficient catalysts are exploited to activate inert chemical bonds and organic molecules. In the synthetic chemistry, catalysts play an important role, scientists are paying more and more attention to the design and synthesis of catalysts. The majority of catalysts in homogeneous catalytic systems belong to mononuclear active species. In addition to the development of catalysis science, major research is also being conducted on the development of the coordination environment for metal centers to increase their catalytic ability and thereby create enhanced catalytic processes. The catalytic activity of dinuclear catalysts varies from those of mononuclear catalysts. Due to the synergistic effect between the two metal centers, the catalytic activity of dinuclear catalytic systems exhibits particular performance characteristics. The first row of elements in group Ⅷ of the periodic table, Fe, Co, and Ni, are also known as the ferrous group. These metals have drawn attention in recent years because of their relatively low price, stable structure, commercial availability, and ability to catalyze various type of reactions. Homodinuclear ferrous group metal complexes are applied in a wide variety of reactions, including hydroboration, hydrosilylation, cross-coupling reactions, asymmetric 1, 4-addition, asymmetric Mannich reactions, CO2 activation, copolymerization, and alkyne cyclotrimerizations. Compared with mononuclear metal catalytic systems, there are currently relatively few types of homogenous catalytic systems that are catalyzed by bimetal catalysts. However, such catalytic systems possess significant advantages over mononuclear catalytic systems. For example, the catalytic activity and reaction selectivity of dinuclear metal catalytic systems are far superior, the reaction conditions milder, and the operations required simpler. However, research on the mechanisms of dinuclear metal catalytic systems is still insufficient. For example, the interaction between metals and substrates requires further investigation. This review focusses on the synthesis and characterization of homodinuclear bimetallic iron complexes. The application of homodinuclear iron, cobalt, and nickel complexes in homogeneous catalytic systems is introduced and summarized in detail. Finally, the challenges for the future development of homogeneous catalytic systems that utilize homodinuclear bimetallic iron complexes are outlined. ![]()
With the development of synthetic chemistry, more and more efficient catalysts are exploited to activate inert chemical bonds and organic molecules. In the synthetic chemistry, catalysts play an important role, scientists are paying more and more attention to the design and synthesis of catalysts. The majority of catalysts in homogeneous catalytic systems belong to mononuclear active species. In addition to the development of catalysis science, major research is also being conducted on the development of the coordination environment for metal centers to increase their catalytic ability and thereby create enhanced catalytic processes. The catalytic activity of dinuclear catalysts varies from those of mononuclear catalysts. Due to the synergistic effect between the two metal centers, the catalytic activity of dinuclear catalytic systems exhibits particular performance characteristics. The first row of elements in group Ⅷ of the periodic table, Fe, Co, and Ni, are also known as the ferrous group. These metals have drawn attention in recent years because of their relatively low price, stable structure, commercial availability, and ability to catalyze various type of reactions. Homodinuclear ferrous group metal complexes are applied in a wide variety of reactions, including hydroboration, hydrosilylation, cross-coupling reactions, asymmetric 1, 4-addition, asymmetric Mannich reactions, CO2 activation, copolymerization, and alkyne cyclotrimerizations. Compared with mononuclear metal catalytic systems, there are currently relatively few types of homogenous catalytic systems that are catalyzed by bimetal catalysts. However, such catalytic systems possess significant advantages over mononuclear catalytic systems. For example, the catalytic activity and reaction selectivity of dinuclear metal catalytic systems are far superior, the reaction conditions milder, and the operations required simpler. However, research on the mechanisms of dinuclear metal catalytic systems is still insufficient. For example, the interaction between metals and substrates requires further investigation. This review focusses on the synthesis and characterization of homodinuclear bimetallic iron complexes. The application of homodinuclear iron, cobalt, and nickel complexes in homogeneous catalytic systems is introduced and summarized in detail. Finally, the challenges for the future development of homogeneous catalytic systems that utilize homodinuclear bimetallic iron complexes are outlined.
2019, 35(7): 709-724
doi: 10.3866/PKU.WHXB201807051
Abstract:
It is a widespread concern that the extensive use of antibiotics has caused not only harm to the human body but also heavy environmental pollution. Because of its high efficiency and universal applicability, adsorption technology has significant application potential for the removal of antibiotics. The development of new adsorbents is critical for high-efficiency adsorption treatment. In recent years, the excellent physical, chemical, and adsorption properties of graphene have made it an important antibiotic adsorbent. The high specific surface area and large number of pores of graphene provide many adsorption sites for antibiotics. In addition, the conjugated structure makes graphene relatively electronegative, which also affects adsorption. Due to the limitations of graphene and the increasing requirements for efficiency and stability of graphene adsorbents, a variety of graphene-based adsorbents have been developed to solve the issues of graphene agglomeration in aqueous solutions, poor graphene dispersibility, and poor adsorption performance. Thus far, there has not been a systematic review on the design, synthesis, and adsorption mechanism of graphene-based composites for the removal of antibiotics in aqueous solutions. The design and preparation methods for magnetic graphene adsorbents, polymer/graphene adsorbents, three-dimensional graphene gels, graphene/biochar adsorbents, and graphene-based adsorbents for catalytic degradation of antibiotics are also reviewed. We show the synthesis and design concepts of various graphene-based adsorbents, as well as their different physical and chemical properties and adsorption performance, so that we can distinguish and select different graphene-based adsorbents. We also discuss the design of adsorbents for different kinds of antibiotic contaminants to provide guidance to future researchers for choosing the appropriate design methods based on the antibiotic type. These graphene-based adsorbents can also be extended to the adsorption of various pollutants, which is of great significance for environmental protection. The main adsorption mechanism of antibiotics on graphene-based adsorbents in aqueous solutions is expounded. The cyclic structure of graphene determines the interaction between graphene and antibiotics, such as π–π and cation–π interactions. The numerous oxygen-containing functional groups on the surface of graphene oxide (GO) provide more possibilities for the design of graphene composites. Finally, the future development of graphene-based adsorbents for the removal of antibiotics in aqueous solutions is discussed. We recommend the design of highly-efficient, broad-spectrum, and selective adsorbents for high adsorption performance for multiple antibiotic contaminants in the environment. We also address the regeneration and disposal of graphene-based sorbents and promote green, harmless, and resource-based disposal. ![]()
It is a widespread concern that the extensive use of antibiotics has caused not only harm to the human body but also heavy environmental pollution. Because of its high efficiency and universal applicability, adsorption technology has significant application potential for the removal of antibiotics. The development of new adsorbents is critical for high-efficiency adsorption treatment. In recent years, the excellent physical, chemical, and adsorption properties of graphene have made it an important antibiotic adsorbent. The high specific surface area and large number of pores of graphene provide many adsorption sites for antibiotics. In addition, the conjugated structure makes graphene relatively electronegative, which also affects adsorption. Due to the limitations of graphene and the increasing requirements for efficiency and stability of graphene adsorbents, a variety of graphene-based adsorbents have been developed to solve the issues of graphene agglomeration in aqueous solutions, poor graphene dispersibility, and poor adsorption performance. Thus far, there has not been a systematic review on the design, synthesis, and adsorption mechanism of graphene-based composites for the removal of antibiotics in aqueous solutions. The design and preparation methods for magnetic graphene adsorbents, polymer/graphene adsorbents, three-dimensional graphene gels, graphene/biochar adsorbents, and graphene-based adsorbents for catalytic degradation of antibiotics are also reviewed. We show the synthesis and design concepts of various graphene-based adsorbents, as well as their different physical and chemical properties and adsorption performance, so that we can distinguish and select different graphene-based adsorbents. We also discuss the design of adsorbents for different kinds of antibiotic contaminants to provide guidance to future researchers for choosing the appropriate design methods based on the antibiotic type. These graphene-based adsorbents can also be extended to the adsorption of various pollutants, which is of great significance for environmental protection. The main adsorption mechanism of antibiotics on graphene-based adsorbents in aqueous solutions is expounded. The cyclic structure of graphene determines the interaction between graphene and antibiotics, such as π–π and cation–π interactions. The numerous oxygen-containing functional groups on the surface of graphene oxide (GO) provide more possibilities for the design of graphene composites. Finally, the future development of graphene-based adsorbents for the removal of antibiotics in aqueous solutions is discussed. We recommend the design of highly-efficient, broad-spectrum, and selective adsorbents for high adsorption performance for multiple antibiotic contaminants in the environment. We also address the regeneration and disposal of graphene-based sorbents and promote green, harmless, and resource-based disposal.
2019, 35(7): 725-733
doi: 10.3866/PKU.WHXB201810019
Abstract:
Morin is a natural flavonoid compound extracted from the bark of mulberry, orange, and other fruit trees. Serum albumin (SA) is the most abundant carrier protein in animal plasma, as well as the most common soluble protein in the circulatory system. The study of the binding behavior of Morin and the characteristics of the binding of Morin to SA would help in further elucidating its transport process and mechanism of action in vivo at the molecular level. Herein, the thermodynamics of the interaction between bovine serum albumin (BSA) and Morin was investigated by fluorescence, UV-Vis absorbance, CD, and molecular modeling under physiological conditions. The quenching constants (KSV) decreased as the temperature increased, indicating that the fluorescence quenching of BSA by Morin was a static process. The static quenching mechanism was further supported by the measurement of the UV-vis spectra of the BSA-Morin system. Based on the van't Hoff equation, the ΔHƟ, ΔSƟ, and ΔGƟ were calculated to be around −81.20 kJ·mol−1, −181.01 J·mol−1·K−1, and −27.19 kJ·mol−1, respectively. The negative ΔGƟ value indicated that the interaction between Morin and BSA was a spontaneous process. The hydrogen bonds and van der Waals force played a predominant role in the binding process. Our data indicate that Morin binds solely with the BSA molecule. The apparent binding constant of the Morin-BSA system reached the order of 104, which further confirmed the strong binding between Morin and BSA. This indicates that serum albumin can store and transport Morin molecules in the body, enabling them to reach the action site through blood circulation; thus, they can exert their physiological and biochemical effects. By using the fluorescence resonance energy transfer theory and the molecular simulation method, we found that Morin bound at Site Ⅱ in the hydrophobic cavity of the substructure domain IIIA of BSA, and the average distance between the two tryptophan residues and Morin was 3.09 nm. The synchronous fluorescence spectrum also revealed that Morin was far away from the two tryptophans of BSA, and therefore, cannot change the spatial structure near tryptophan. The CD spectra demonstrated that the α-helix content of BSA decreased from 59.5% to 53.9% after its interaction with Morin, while the disordered structure increased from 20.6% to 23.7%. The best-fitted docking poses reveal that Morin mainly contacted with the side-chains of surrounding hydrophobic amino acid residues. In addition, the generation of hydrogen bonds between hydroxyl groups on Morin molecules and the side-chains of R413 and K437 can be observed. These results provide basic knowledge for understanding the pharmacology of Morin, and useful guidance for designing, modifying, and screening flavonoid drug molecules. ![]()
Morin is a natural flavonoid compound extracted from the bark of mulberry, orange, and other fruit trees. Serum albumin (SA) is the most abundant carrier protein in animal plasma, as well as the most common soluble protein in the circulatory system. The study of the binding behavior of Morin and the characteristics of the binding of Morin to SA would help in further elucidating its transport process and mechanism of action in vivo at the molecular level. Herein, the thermodynamics of the interaction between bovine serum albumin (BSA) and Morin was investigated by fluorescence, UV-Vis absorbance, CD, and molecular modeling under physiological conditions. The quenching constants (KSV) decreased as the temperature increased, indicating that the fluorescence quenching of BSA by Morin was a static process. The static quenching mechanism was further supported by the measurement of the UV-vis spectra of the BSA-Morin system. Based on the van't Hoff equation, the ΔHƟ, ΔSƟ, and ΔGƟ were calculated to be around −81.20 kJ·mol−1, −181.01 J·mol−1·K−1, and −27.19 kJ·mol−1, respectively. The negative ΔGƟ value indicated that the interaction between Morin and BSA was a spontaneous process. The hydrogen bonds and van der Waals force played a predominant role in the binding process. Our data indicate that Morin binds solely with the BSA molecule. The apparent binding constant of the Morin-BSA system reached the order of 104, which further confirmed the strong binding between Morin and BSA. This indicates that serum albumin can store and transport Morin molecules in the body, enabling them to reach the action site through blood circulation; thus, they can exert their physiological and biochemical effects. By using the fluorescence resonance energy transfer theory and the molecular simulation method, we found that Morin bound at Site Ⅱ in the hydrophobic cavity of the substructure domain IIIA of BSA, and the average distance between the two tryptophan residues and Morin was 3.09 nm. The synchronous fluorescence spectrum also revealed that Morin was far away from the two tryptophans of BSA, and therefore, cannot change the spatial structure near tryptophan. The CD spectra demonstrated that the α-helix content of BSA decreased from 59.5% to 53.9% after its interaction with Morin, while the disordered structure increased from 20.6% to 23.7%. The best-fitted docking poses reveal that Morin mainly contacted with the side-chains of surrounding hydrophobic amino acid residues. In addition, the generation of hydrogen bonds between hydroxyl groups on Morin molecules and the side-chains of R413 and K437 can be observed. These results provide basic knowledge for understanding the pharmacology of Morin, and useful guidance for designing, modifying, and screening flavonoid drug molecules.
2019, 35(7): 734-739
doi: 10.3866/PKU.WHXB201806063
Abstract:
Li-S batteries are considered promising next-generation energy storage systems because they offer high theoretical specific capacity (1675 mAh∙g−1), high energy density (2600 Wh∙kg−1), environmental friendliness, and low cost. However, large-scale commercial applications are hindered by the low electrical conductivity of S, high volume expansion ratio, and high solubility of intermediate polysulfides in organic electrolytes. Li-Se batteries using Se as the cathode material have high discharge rates, good cyclic performance, high electrical conductivities, high output voltages, and high volumetric capacity densities, and therefore, they are potential alternatives to Li-S systems. Recently, covalent organic frameworks (COFs) have emerged as new porous crystalline materials with large specific surface areas, high porosities, low densities, good thermal stabilities, and controllable structures. Therefore, COFs have wide potential applicability in the fields of gas adsorption, heterogeneous catalysis, energy storage, and drug delivery. Based on the above analysis, a simple core-shell multiwalled carbon nanotube (MWCNT)/1, 3, 5-triformylphloroglucinol (Tp)-phenylenediamine (Pa) COF nanocomposite (MWCNT@TpPa-COF) was prepared by growing a TpPa-COF on MWCNTs through a simple solvothermal reaction. The MWCNT@TpPa-COF high-performance cathode material realizes the first application of a COF in Li-Se batteries. The MWCNTs can encapsulate Se, limit the diffusion of polyselenides (Li2Sen, 3 ≤ n ≤ 8), and provide rapid electron conduction and ion transmission. In addition, the π-π interaction between MWCNTs and COFs promotes COF growth and distribution on the MWCNTs, thereby forming core-shell MWCNT@TpPa-COF nanocomposites, which can further increase the loading of Se. Measurements via field-emission scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy confirmed the successful combination of MWCNTs and COFs. The rich micro- and mesoporous hierarchical structure provides the MWCNT@TpPa-COF nanocomposites with initial specific discharge capacities reaching 463.5 mAh∙g−1 at the current density of 3C (1C = 675 mA∙g−1). Cells utilizing the nanocomposite electrodes maintained 99% Coulombic efficiency, with the average cyclic capacitive loss of 0.14% after 500 cycles. In addition, electrochemical impedance spectroscopy, cyclic voltammetry, and multiple-rate cycling analyses support the excellent electrochemical performance of the proposed cathode material. This work provides a promising new prospect for the future development of rechargeable Li-Se batteries utilizing new COF-based cathode materials. ![]()
Li-S batteries are considered promising next-generation energy storage systems because they offer high theoretical specific capacity (1675 mAh∙g−1), high energy density (2600 Wh∙kg−1), environmental friendliness, and low cost. However, large-scale commercial applications are hindered by the low electrical conductivity of S, high volume expansion ratio, and high solubility of intermediate polysulfides in organic electrolytes. Li-Se batteries using Se as the cathode material have high discharge rates, good cyclic performance, high electrical conductivities, high output voltages, and high volumetric capacity densities, and therefore, they are potential alternatives to Li-S systems. Recently, covalent organic frameworks (COFs) have emerged as new porous crystalline materials with large specific surface areas, high porosities, low densities, good thermal stabilities, and controllable structures. Therefore, COFs have wide potential applicability in the fields of gas adsorption, heterogeneous catalysis, energy storage, and drug delivery. Based on the above analysis, a simple core-shell multiwalled carbon nanotube (MWCNT)/1, 3, 5-triformylphloroglucinol (Tp)-phenylenediamine (Pa) COF nanocomposite (MWCNT@TpPa-COF) was prepared by growing a TpPa-COF on MWCNTs through a simple solvothermal reaction. The MWCNT@TpPa-COF high-performance cathode material realizes the first application of a COF in Li-Se batteries. The MWCNTs can encapsulate Se, limit the diffusion of polyselenides (Li2Sen, 3 ≤ n ≤ 8), and provide rapid electron conduction and ion transmission. In addition, the π-π interaction between MWCNTs and COFs promotes COF growth and distribution on the MWCNTs, thereby forming core-shell MWCNT@TpPa-COF nanocomposites, which can further increase the loading of Se. Measurements via field-emission scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy confirmed the successful combination of MWCNTs and COFs. The rich micro- and mesoporous hierarchical structure provides the MWCNT@TpPa-COF nanocomposites with initial specific discharge capacities reaching 463.5 mAh∙g−1 at the current density of 3C (1C = 675 mA∙g−1). Cells utilizing the nanocomposite electrodes maintained 99% Coulombic efficiency, with the average cyclic capacitive loss of 0.14% after 500 cycles. In addition, electrochemical impedance spectroscopy, cyclic voltammetry, and multiple-rate cycling analyses support the excellent electrochemical performance of the proposed cathode material. This work provides a promising new prospect for the future development of rechargeable Li-Se batteries utilizing new COF-based cathode materials.
2019, 35(7): 749-754
doi: 10.3866/PKU.WHXB201810051
Abstract:
Direct methanol fuel cell (DMFC) is a potential clean energy facility because of abundant resources, easy storage, and high safety of methanol. However, the low activity, poor durability, and high price of the catalysts hamper the development of DMFC. High-index faceted nanocrystals usually show high catalytic activity for the electro-oxidation of small organic molecules due to high densities of low-coordinated surface sites. Surface modification is an alternative approach for improving catalyst performance via ligand effect or electronic effect. Herein, we prepared tetrahexahedral Pd nanocrystals (THH Pd NCs) enclosed by {730} high-index facets via electrochemical square-wave potential deposition, and modified the THH Pd NCs with Ru using cyclic voltammetry (CV). The coverages of Ru (θRu) were controlled by limiting the CV cycles. The electrocatalytic performance of the Ru-modified THH Pd NCs for methanol oxidation was studied using CV in an alkaline methanol solution. We found that Ru modification can greatly reduce the onset and peak potentials of methanol electro-oxidation from -0.33 to -0.39 V and from -0.16 to -0.26 V, respectively. The current densities at -0.3 V during methanol electro-oxidation increased with increasing θRu from 0 to 0.08, and decreased with increasing θRu from 0.08 to 0.27. When θRu was 0.08, the current density on the Ru-modified THH Pd NCs reached 1.5 mA∙cm-2, which was 10 times higher than that achieved for the THH Pd NCs. To detect the products at molecular level during methanol electro-oxidation, in-situ electrochemical Fourier-transform infrared (FTIR) spectroscopy was applied. The spectra of both THH Pd NCs and Ru-modified THH Pd NCs (θRu = 0.08) showed that both CO2 and formate were produced. The band intensities of CO2 and formate on Ru-modified THH Pd NCs (θRu = 0.08) were 1.6- and 1.2-times larger than those of THH Pd NCs, respectively. However, the band intensity of COad during methanol electro-oxidation was almost equal on the two catalysts, implying that the "CO poison path" is not suppressed by Ru modification. These results indicate that a small amount of Ru (θRu = 0.08) modification is beneficial for the electrocatalytic oxidation of methanol by enhancing the "formate path" at low potential. Overall, this study illustrates the influence of Ru modification of THH Pd NCs on its catalytic performance in methanol electro-oxidation, which throws light on the synthesis and application of catalysts with high activities. ![]()
Direct methanol fuel cell (DMFC) is a potential clean energy facility because of abundant resources, easy storage, and high safety of methanol. However, the low activity, poor durability, and high price of the catalysts hamper the development of DMFC. High-index faceted nanocrystals usually show high catalytic activity for the electro-oxidation of small organic molecules due to high densities of low-coordinated surface sites. Surface modification is an alternative approach for improving catalyst performance via ligand effect or electronic effect. Herein, we prepared tetrahexahedral Pd nanocrystals (THH Pd NCs) enclosed by {730} high-index facets via electrochemical square-wave potential deposition, and modified the THH Pd NCs with Ru using cyclic voltammetry (CV). The coverages of Ru (θRu) were controlled by limiting the CV cycles. The electrocatalytic performance of the Ru-modified THH Pd NCs for methanol oxidation was studied using CV in an alkaline methanol solution. We found that Ru modification can greatly reduce the onset and peak potentials of methanol electro-oxidation from -0.33 to -0.39 V and from -0.16 to -0.26 V, respectively. The current densities at -0.3 V during methanol electro-oxidation increased with increasing θRu from 0 to 0.08, and decreased with increasing θRu from 0.08 to 0.27. When θRu was 0.08, the current density on the Ru-modified THH Pd NCs reached 1.5 mA∙cm-2, which was 10 times higher than that achieved for the THH Pd NCs. To detect the products at molecular level during methanol electro-oxidation, in-situ electrochemical Fourier-transform infrared (FTIR) spectroscopy was applied. The spectra of both THH Pd NCs and Ru-modified THH Pd NCs (θRu = 0.08) showed that both CO2 and formate were produced. The band intensities of CO2 and formate on Ru-modified THH Pd NCs (θRu = 0.08) were 1.6- and 1.2-times larger than those of THH Pd NCs, respectively. However, the band intensity of COad during methanol electro-oxidation was almost equal on the two catalysts, implying that the "CO poison path" is not suppressed by Ru modification. These results indicate that a small amount of Ru (θRu = 0.08) modification is beneficial for the electrocatalytic oxidation of methanol by enhancing the "formate path" at low potential. Overall, this study illustrates the influence of Ru modification of THH Pd NCs on its catalytic performance in methanol electro-oxidation, which throws light on the synthesis and application of catalysts with high activities.
2019, 35(7): 755-765
doi: 10.3866/PKU.WHXB201810009
Abstract:
Supercapacitors, advanced electrochemical devices, have attracted great interest due to their extraordinary properties, such as high power density, fast charging or discharging rate, and ultra-long cycle life. Currently, great efforts have been devoted to increasing their moderate energy density (typically < 5 Wh·kg-1). Especially, room temperature ionic liquids (RTILs) have been considered as a promising electrolyte for further improving supercapacitor's performances owing to their large voltage window, high thermal stability, and wide working temperature range. However, RTILs suffer from the high viscosity and poor conductivity stemming from their strong cation–anion interactions. In this work, we investigate the influences of solvent on the capacitive performance within RTIL-based supercapacitors. Activated graphene powders are employed as the electrode active materials, and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4) is chosen as the electrolyte because of the wide applications in electrochemical energy storage. The mole fraction of BMIMBF4 (ρIL) in electrolytes can be regulated with adjusting the ratio of acetonitrile solvents (AN). Electrochemical measurements suggest that the solvent effects on the charge storage capability of supercapacitors depend strongly on the applied scan rate or current density. Specifically, at a lower scan rate of 10 mV·s-1, solvent exhibits a negligible influence on the electrochemical performance; however, at an elevated scan rate of 200 mV·s-1, solvent addition could prominently enhance the capacitance by ~2 folds. These results can resolve the controversial solvent effects reported in previous simulation and experimental studies. To interpret the as-obtained results, we further explore the solvent effects on the dynamic properties of electrolytes. It is found that solvent can effectively reduce the strong ion–ion interactions within pristine RTILs, thus decreasing the viscosity by ~29 times. Further electrical impedance spectroscopy tests suggest that the addition of solvent is able to significantly suppress the series resistance (by ~5.5 times) and dielectric relaxation time (by ~6.3 times), which thereby improves the rate capability of supercapacitors. We demonstrate that the maximum specific energy and power density of supercapacitor (ρIL = 0.25) are calculated to be 65.2 Wh·kg-1 at 1 A·g-1 and 18066.6 W·kg-1 at 20 A·g-1, respectively, among the best performances in the state-of-art literatures. More importantly, under an elevated working temperature of 50, its energy density can reach up to 85.5 Wh·kg-1 at 1 A·g-1, which is much higher than that of aqueous or organic solution based supercapacitors (< 10 Wh·kg-1) and lead-acid battery (20–35 Wh·kg-1), comparable to that of Ni metal hydride (40–100 Wh·kg-1) and lithium-ion battery (80–150 Wh·kg-1). ![]()
Supercapacitors, advanced electrochemical devices, have attracted great interest due to their extraordinary properties, such as high power density, fast charging or discharging rate, and ultra-long cycle life. Currently, great efforts have been devoted to increasing their moderate energy density (typically < 5 Wh·kg-1). Especially, room temperature ionic liquids (RTILs) have been considered as a promising electrolyte for further improving supercapacitor's performances owing to their large voltage window, high thermal stability, and wide working temperature range. However, RTILs suffer from the high viscosity and poor conductivity stemming from their strong cation–anion interactions. In this work, we investigate the influences of solvent on the capacitive performance within RTIL-based supercapacitors. Activated graphene powders are employed as the electrode active materials, and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4) is chosen as the electrolyte because of the wide applications in electrochemical energy storage. The mole fraction of BMIMBF4 (ρIL) in electrolytes can be regulated with adjusting the ratio of acetonitrile solvents (AN). Electrochemical measurements suggest that the solvent effects on the charge storage capability of supercapacitors depend strongly on the applied scan rate or current density. Specifically, at a lower scan rate of 10 mV·s-1, solvent exhibits a negligible influence on the electrochemical performance; however, at an elevated scan rate of 200 mV·s-1, solvent addition could prominently enhance the capacitance by ~2 folds. These results can resolve the controversial solvent effects reported in previous simulation and experimental studies. To interpret the as-obtained results, we further explore the solvent effects on the dynamic properties of electrolytes. It is found that solvent can effectively reduce the strong ion–ion interactions within pristine RTILs, thus decreasing the viscosity by ~29 times. Further electrical impedance spectroscopy tests suggest that the addition of solvent is able to significantly suppress the series resistance (by ~5.5 times) and dielectric relaxation time (by ~6.3 times), which thereby improves the rate capability of supercapacitors. We demonstrate that the maximum specific energy and power density of supercapacitor (ρIL = 0.25) are calculated to be 65.2 Wh·kg-1 at 1 A·g-1 and 18066.6 W·kg-1 at 20 A·g-1, respectively, among the best performances in the state-of-art literatures. More importantly, under an elevated working temperature of 50, its energy density can reach up to 85.5 Wh·kg-1 at 1 A·g-1, which is much higher than that of aqueous or organic solution based supercapacitors (< 10 Wh·kg-1) and lead-acid battery (20–35 Wh·kg-1), comparable to that of Ni metal hydride (40–100 Wh·kg-1) and lithium-ion battery (80–150 Wh·kg-1).
2019, 35(7): 766-774
doi: 10.3866/PKU.WHXB201809038
Abstract:
Interactions between surfactants and small organic molecules not only enhance the surface activity of the surfactants and induce aggregate transitions in them, but also improve the solubility and stability of the organic molecules. Understanding the interaction between surfactants and small molecules will help in widening the scope of application of surfactants. Folic acid, a member of the vitamin B family, has a pteridine ring, para-aminobenzoic acid, and glutamic acid, and is crucial for many reactions inside the human body. The unique structure of folic acid also facilitates the preparation of functional materials such as liquid crystals and gels. However, the poor solubility and precipitation of folic acid limit its applications. Therefore, it is essential to improve the solubility and stability of folic acid. Surfactants are efficient in solubilizing and stabilizing small molecules. The interactions of folic acid with four types of surfactants, namely, an anionic surfactant, sodium dodecyl sulfate (SDS); a cationic surfactant, dodecyl trimethylammonium bromide (DTAB); a cationic ammonium gemini surfactant, 12-6-12; and a cationic ammonium trimeric surfactant, 12-3-12-3-12; have been investigated at pH 7.0 by surface tension measurements, ultraviolet-visible (UV) absorption spectroscopy, dynamic light scattering, isothermal titration calorimetry, and nuclear magnetic resonance spectroscopy. At pH 7.0, the carboxylic acid groups of folic acid are deprotonated, so each folic acid molecule carries two negative charges. The addition of a small amount of folic acid sharply reduces the critical micelle concentration (CMC) of cationic surfactants and their surface tension at the CMC. However, the surface activity and aggregation of SDS show only minimal changes with the introduction of folic acid. In addition, the photodegradation of folic acid in the presence of different surfactants is studied by fluorescence and UV absorption spectroscopy. When irradiated with UV light, folic acid undergoes rapid degradation in aqueous solution, in the absence of any surfactants. In contrast, the degradation is greatly suppressed in the presence of surfactants. The extent of suppression by cationic surfactants is more significant than that by the anionic surfactant. The residual folic acid concentration increases from nearly 0 in the absence of any surfactant to 43%, 89%, 96%, and 96% in the presence of SDS, DTAB, 12-6-12, and 12-3-12-3-12, respectively, in the concentration range studied. The amount of surfactant required to prevent the degradation decreases with an increase in the degree of oligomerization of the cationic surfactants. The greater number of binding sites and hydrophobic tails in the gemini and oligomeric surfactants result in much stronger electrostatic and hydrophobic interactions with folic acid. In addition, the close and compact packing in these surfactant molecules prevents folic acid from coming in contact with oxygen, thereby retaining its stability and preserving its properties. This work provides a new methodology for regulating the surface activity of the surfactants and their aggregation in the presence of small functional molecules, which in turn improves the stability of the small molecules that are otherwise unstable. ![]()
Interactions between surfactants and small organic molecules not only enhance the surface activity of the surfactants and induce aggregate transitions in them, but also improve the solubility and stability of the organic molecules. Understanding the interaction between surfactants and small molecules will help in widening the scope of application of surfactants. Folic acid, a member of the vitamin B family, has a pteridine ring, para-aminobenzoic acid, and glutamic acid, and is crucial for many reactions inside the human body. The unique structure of folic acid also facilitates the preparation of functional materials such as liquid crystals and gels. However, the poor solubility and precipitation of folic acid limit its applications. Therefore, it is essential to improve the solubility and stability of folic acid. Surfactants are efficient in solubilizing and stabilizing small molecules. The interactions of folic acid with four types of surfactants, namely, an anionic surfactant, sodium dodecyl sulfate (SDS); a cationic surfactant, dodecyl trimethylammonium bromide (DTAB); a cationic ammonium gemini surfactant, 12-6-12; and a cationic ammonium trimeric surfactant, 12-3-12-3-12; have been investigated at pH 7.0 by surface tension measurements, ultraviolet-visible (UV) absorption spectroscopy, dynamic light scattering, isothermal titration calorimetry, and nuclear magnetic resonance spectroscopy. At pH 7.0, the carboxylic acid groups of folic acid are deprotonated, so each folic acid molecule carries two negative charges. The addition of a small amount of folic acid sharply reduces the critical micelle concentration (CMC) of cationic surfactants and their surface tension at the CMC. However, the surface activity and aggregation of SDS show only minimal changes with the introduction of folic acid. In addition, the photodegradation of folic acid in the presence of different surfactants is studied by fluorescence and UV absorption spectroscopy. When irradiated with UV light, folic acid undergoes rapid degradation in aqueous solution, in the absence of any surfactants. In contrast, the degradation is greatly suppressed in the presence of surfactants. The extent of suppression by cationic surfactants is more significant than that by the anionic surfactant. The residual folic acid concentration increases from nearly 0 in the absence of any surfactant to 43%, 89%, 96%, and 96% in the presence of SDS, DTAB, 12-6-12, and 12-3-12-3-12, respectively, in the concentration range studied. The amount of surfactant required to prevent the degradation decreases with an increase in the degree of oligomerization of the cationic surfactants. The greater number of binding sites and hydrophobic tails in the gemini and oligomeric surfactants result in much stronger electrostatic and hydrophobic interactions with folic acid. In addition, the close and compact packing in these surfactant molecules prevents folic acid from coming in contact with oxygen, thereby retaining its stability and preserving its properties. This work provides a new methodology for regulating the surface activity of the surfactants and their aggregation in the presence of small functional molecules, which in turn improves the stability of the small molecules that are otherwise unstable.
2019, 35(7): 775-786
doi: 10.3866/PKU.WHXB201811046
Abstract:
A novel template-free oxalate route was applied to synthesize a series of MnOx catalysts with different Cu content (MnOx, Cu1-MnOx, Cu2-MnOx, Cu3-MnOx, Cu4-MnOx, Cu2-450, and Cu2-550), which were then used in 1, 2, 3, 4-tetrahydroquinoline (THQL) oxidative dehydrogenation aromatization. To obtain insight into the structure-activity relationships of the catalysts, the samples were characterized by thermogravimetry and heat flow analysis, X-ray diffraction (XRD), N2 physical adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and atomic absorption spectroscopy (AAS). The results showed that Cu2-MnOx possesses the following characteristics: amorphous nature, high specific surface area, increased mesoporous average pore diameter, lower reduction temperature, highest Mn3+ and adsorbed oxygen content, and highest Mn3+/Mn4+ ratio among the seven manganese oxide catalysts. Cu2-MnOx for the oxidative dehydrogenation aromatization of THQL showed conversion (99.1%) and selectivity (97.2%) for quinoline under mild reaction conditions, with cheap air as oxidant and no alkali additive. Cu2-MnOx was reusable and achieved 95.8% conversion even after five reuse tests. Selectivity decreased slightly with the increase in reuse time, which could be attributed to the leaching of the Cu element. Comparison of structure-activity relationships showed increased catalytic activity when Mn3+ and adsorbed oxygen content were highest among these amorphous manganese oxides. Mn4+ content was related to the formation of quinoline N-oxide by over oxidation. Despite their high Mn3+ content and Mn3+/Mn4+ ratio, Cu2-450 and Cu2-550 had reduced surface area, adsorbed oxygen content, and lattice oxygen mobility, which resulted in poor catalytic performance. Although Cu3-MnOx had the largest BET surface area, highest lattice oxygen mobility, and similar Mn3+ and adsorbed oxygen content as Cu2-MnOx, the smaller average pore diameter of Cu3-MnOx perhaps caused its conversion and selectivity to be similar to Cu2-MnOx. The amorphous nature, Mn3+ and adsorbed oxygen content, Mn3+/Mn4+ ratio, lattice oxygen mobility, and synergistic effect between CuO and MnOx were found to play key roles in catalytic performance. The absence of precious metals, the simple catalyst preparation process, the cheap air as the sole oxidant, no ligand and alkali, the mild reaction conditions, along with catalyst reusability and easy isolation of the aromatized products made our catalytic protocol both green and environmentally benign. ![]()
A novel template-free oxalate route was applied to synthesize a series of MnOx catalysts with different Cu content (MnOx, Cu1-MnOx, Cu2-MnOx, Cu3-MnOx, Cu4-MnOx, Cu2-450, and Cu2-550), which were then used in 1, 2, 3, 4-tetrahydroquinoline (THQL) oxidative dehydrogenation aromatization. To obtain insight into the structure-activity relationships of the catalysts, the samples were characterized by thermogravimetry and heat flow analysis, X-ray diffraction (XRD), N2 physical adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and atomic absorption spectroscopy (AAS). The results showed that Cu2-MnOx possesses the following characteristics: amorphous nature, high specific surface area, increased mesoporous average pore diameter, lower reduction temperature, highest Mn3+ and adsorbed oxygen content, and highest Mn3+/Mn4+ ratio among the seven manganese oxide catalysts. Cu2-MnOx for the oxidative dehydrogenation aromatization of THQL showed conversion (99.1%) and selectivity (97.2%) for quinoline under mild reaction conditions, with cheap air as oxidant and no alkali additive. Cu2-MnOx was reusable and achieved 95.8% conversion even after five reuse tests. Selectivity decreased slightly with the increase in reuse time, which could be attributed to the leaching of the Cu element. Comparison of structure-activity relationships showed increased catalytic activity when Mn3+ and adsorbed oxygen content were highest among these amorphous manganese oxides. Mn4+ content was related to the formation of quinoline N-oxide by over oxidation. Despite their high Mn3+ content and Mn3+/Mn4+ ratio, Cu2-450 and Cu2-550 had reduced surface area, adsorbed oxygen content, and lattice oxygen mobility, which resulted in poor catalytic performance. Although Cu3-MnOx had the largest BET surface area, highest lattice oxygen mobility, and similar Mn3+ and adsorbed oxygen content as Cu2-MnOx, the smaller average pore diameter of Cu3-MnOx perhaps caused its conversion and selectivity to be similar to Cu2-MnOx. The amorphous nature, Mn3+ and adsorbed oxygen content, Mn3+/Mn4+ ratio, lattice oxygen mobility, and synergistic effect between CuO and MnOx were found to play key roles in catalytic performance. The absence of precious metals, the simple catalyst preparation process, the cheap air as the sole oxidant, no ligand and alkali, the mild reaction conditions, along with catalyst reusability and easy isolation of the aromatized products made our catalytic protocol both green and environmentally benign.
2019, 35(7): 740-748
doi: 10.3866/PKU.WHXB201809003
Abstract:
Environmentally friendly and renewable energy technologies, such as fuel cells and metal-air batteries, hold great promise for solving current energy and environmental challenges. The oxygen reduction reaction (ORR) plays a pivotal role in this top-drawer question. However, the sluggish kinetics of the ORR and prohibitive costs limit the global scalability of such devices. Traditionally, platinum-based electrocatalysts exhibit the best performance for ORRs in both acid and alkaline electrolytes. However, to significantly reduce the cost and realize sustainable development, utilization of Pt must be replaced or significantly reduced in the ORR cathode for fuel cell applications. Therefore, developing earth-abundant and high-performance non-precious metal catalysts (NPMCs) for ORR is of critical importance for the commercialization of fuel cells. In comparison to traditional catalysts, metal-organic frameworks (MOFs) are ideal precursors that integrate metal, nitrogen, and carbon functionalities together into one ordered 3D crystal structure. MOFs, assembled by secondary building of units comprised of metals and organic linkers with strong bonding, have received significant research attention because they possess permanent porosity, a three-dimensional (3D) structure, and can be prepared using a diversity of metals and organic linkers. High surface area, and microporous carbon materials can be easily obtained by carbonization of MOFs at high temperatures. In particular, MOF-derived carbon nanocomposites, which were prepared from transition metals, and have the form M-N-C (M = Fe or Co), have demonstrated remarkably improved catalytic activity and stability. Herein, we report an NPMC material consisting of Fe3C nanoparticles encapsulated in mesoporous N-doped carbon (Fe-N-C), synthesized by a simple strategy involving physical mixing of MIL-100(Fe) with glucose and urea, and subsequent pyrolysis under inert atmosphere. The strong interaction between metal atoms and nitrogen atoms is beneficial in generating more active sites, and sites with a higher intrinsic catalytic activity, via carbonization. The as-obtained catalysts exhibit remarkable ORR activity in alkaline media, with the best catalyst (Fe-N-C-900, which is synthesized at 900 ℃) featuring a more positive onset potential (0.96 V vs the reversible hydrogen electrode (RHE)), a more positive half-wave potential (0.83 V vs RHE), a much higher diffusion limiting current density (6.28 mA·cm-2) and a larger electron-transfer number (n), even at low overpotentials, compared with other contrast materials. Fe-N-C-900's excellent catalytic activity and stability in ORR are due to its large BET surface area, its large total pore volume, its nitrogen dopants, its active Fe3C nanoparticles and the cooperative effects among its reactive functionalities. ![]()
Environmentally friendly and renewable energy technologies, such as fuel cells and metal-air batteries, hold great promise for solving current energy and environmental challenges. The oxygen reduction reaction (ORR) plays a pivotal role in this top-drawer question. However, the sluggish kinetics of the ORR and prohibitive costs limit the global scalability of such devices. Traditionally, platinum-based electrocatalysts exhibit the best performance for ORRs in both acid and alkaline electrolytes. However, to significantly reduce the cost and realize sustainable development, utilization of Pt must be replaced or significantly reduced in the ORR cathode for fuel cell applications. Therefore, developing earth-abundant and high-performance non-precious metal catalysts (NPMCs) for ORR is of critical importance for the commercialization of fuel cells. In comparison to traditional catalysts, metal-organic frameworks (MOFs) are ideal precursors that integrate metal, nitrogen, and carbon functionalities together into one ordered 3D crystal structure. MOFs, assembled by secondary building of units comprised of metals and organic linkers with strong bonding, have received significant research attention because they possess permanent porosity, a three-dimensional (3D) structure, and can be prepared using a diversity of metals and organic linkers. High surface area, and microporous carbon materials can be easily obtained by carbonization of MOFs at high temperatures. In particular, MOF-derived carbon nanocomposites, which were prepared from transition metals, and have the form M-N-C (M = Fe or Co), have demonstrated remarkably improved catalytic activity and stability. Herein, we report an NPMC material consisting of Fe3C nanoparticles encapsulated in mesoporous N-doped carbon (Fe-N-C), synthesized by a simple strategy involving physical mixing of MIL-100(Fe) with glucose and urea, and subsequent pyrolysis under inert atmosphere. The strong interaction between metal atoms and nitrogen atoms is beneficial in generating more active sites, and sites with a higher intrinsic catalytic activity, via carbonization. The as-obtained catalysts exhibit remarkable ORR activity in alkaline media, with the best catalyst (Fe-N-C-900, which is synthesized at 900 ℃) featuring a more positive onset potential (0.96 V vs the reversible hydrogen electrode (RHE)), a more positive half-wave potential (0.83 V vs RHE), a much higher diffusion limiting current density (6.28 mA·cm-2) and a larger electron-transfer number (n), even at low overpotentials, compared with other contrast materials. Fe-N-C-900's excellent catalytic activity and stability in ORR are due to its large BET surface area, its large total pore volume, its nitrogen dopants, its active Fe3C nanoparticles and the cooperative effects among its reactive functionalities.
