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2020 Volume 78 Issue 12
2020, 78(12): 1287-1296
doi: 10.6023/A20080342
Abstract:
Doping is an effective method to improve the carrier densities and charge transport capabilities of organic semiconductors. In recent years, n-doping of organic semiconductors via Lewis base anions has attracted much attentions of researchers, which takes place under mild condition and controllable fashion, hence exhibiting broad applications in optoelectronics. This perspective focuses on discussing the mechanism of anion-induced electron transfer to semiconductors, summarizing its recent progresses in interfacial materials and doped active layers for optoelectronic devices, as well as analyzing the future development of this field.
Doping is an effective method to improve the carrier densities and charge transport capabilities of organic semiconductors. In recent years, n-doping of organic semiconductors via Lewis base anions has attracted much attentions of researchers, which takes place under mild condition and controllable fashion, hence exhibiting broad applications in optoelectronics. This perspective focuses on discussing the mechanism of anion-induced electron transfer to semiconductors, summarizing its recent progresses in interfacial materials and doped active layers for optoelectronic devices, as well as analyzing the future development of this field.
2020, 78(12): 1297-1308
doi: 10.6023/A20070294
Abstract:
Organoboronic acids and esters are highly valuable building blocks in cross-coupling reactions and practical intermediates of various functional group transformations. Additionally, organoboronic acids can be utilized directly as small molecule drugs. Therefore, development of efficient methods to synthesize organoboronic compounds is of significant importance. Traditional pathways to synthesize organoboronic compounds mainly rely on electrophilic borylation of organometallic reagent and transition-metal-catalyzed borylation. Radical intermediates have unique chemical properties which are quite different from those of polar intermediates resulted from the heterolysis of chemical bonds and those of the organometallic compounds during transition metal catalysis. As such, borylation based on radical mechanism possesses distinctive reaction process, substrate scope, reaction selectivity, etc., and have great potential in synthesis of organoboronic compounds. In 2010, the Wang's group first reported borylation via a radical mechanism. This method realized an efficient direct conversion of anilines into aryl organoboronic esters. Inspired by this innovative work, more and more borylation methods via radical intermediates have been reported and developed as new avenues for C-B bond formation in the past decade. A series of studies show that organoboronic acids and esters could be efficiently constructed by the reaction of aryl/alkyl radicals with diboron compounds. In this paper, we summarize the recent development of borylation reactions via radical mechanisms, including aryl and alkyl radical borylation. As for aryl radical borylation, the activation of substrates containing C-N, C-O, C-S, C-X (X=halogen) bonds and carboxylic acids to C-B bond is summarized respectively. As for alkyl radical borylation, the activation of substrates containing C-N, C-O, C-X (X=halogen), C-C bonds and carboxylic acids to C-B bond is summarized respectively. Finally, we provide a perspective on the future development direction of this research area.
Organoboronic acids and esters are highly valuable building blocks in cross-coupling reactions and practical intermediates of various functional group transformations. Additionally, organoboronic acids can be utilized directly as small molecule drugs. Therefore, development of efficient methods to synthesize organoboronic compounds is of significant importance. Traditional pathways to synthesize organoboronic compounds mainly rely on electrophilic borylation of organometallic reagent and transition-metal-catalyzed borylation. Radical intermediates have unique chemical properties which are quite different from those of polar intermediates resulted from the heterolysis of chemical bonds and those of the organometallic compounds during transition metal catalysis. As such, borylation based on radical mechanism possesses distinctive reaction process, substrate scope, reaction selectivity, etc., and have great potential in synthesis of organoboronic compounds. In 2010, the Wang's group first reported borylation via a radical mechanism. This method realized an efficient direct conversion of anilines into aryl organoboronic esters. Inspired by this innovative work, more and more borylation methods via radical intermediates have been reported and developed as new avenues for C-B bond formation in the past decade. A series of studies show that organoboronic acids and esters could be efficiently constructed by the reaction of aryl/alkyl radicals with diboron compounds. In this paper, we summarize the recent development of borylation reactions via radical mechanisms, including aryl and alkyl radical borylation. As for aryl radical borylation, the activation of substrates containing C-N, C-O, C-S, C-X (X=halogen) bonds and carboxylic acids to C-B bond is summarized respectively. As for alkyl radical borylation, the activation of substrates containing C-N, C-O, C-X (X=halogen), C-C bonds and carboxylic acids to C-B bond is summarized respectively. Finally, we provide a perspective on the future development direction of this research area.
2020, 78(12): 1309-1335
doi: 10.6023/A20080359
Abstract:
Hydrogen-bonded organic frameworks (HOFs), usually self-assembled by organic or metal-organic building blocks via intermolecular H-bonding interactions, have become a unique type of crystalline porous material. Although the weak and flexible nature of hydrogen bonds makes most HOFs fragile, the high stability and permanent porosity could be realized by the judicious selection of rigid building blocks with special spatial configuration as well as the introduction of framework interpenetration and/or other intermolecular interactions like π-π stacking and electrostatic interactions, etc. Compared with other crystalline porous materials like metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), HOFs feature mild preparation condition, high crystallinity, permissible solution processability, easy healing and regeneration, etc. These distinguishing merits make HOFs capable to be used as unique multifunctional porous materials. Herein, we first review the basic rules to design and synthesize stable and porous HOFs, and then systematically summarize the representative supramolecular synthons and backbones that have been used to build stable and porous HOFs. Emphasis is put on the potential applications of HOFs in gas adsorption and separation, proton conduction, heterogeneous catalysis, luminescence and sensing, biological applications, enantiomeric resolution and aromatic compounds separation, pollutants removal, and structure determination, etc.
Hydrogen-bonded organic frameworks (HOFs), usually self-assembled by organic or metal-organic building blocks via intermolecular H-bonding interactions, have become a unique type of crystalline porous material. Although the weak and flexible nature of hydrogen bonds makes most HOFs fragile, the high stability and permanent porosity could be realized by the judicious selection of rigid building blocks with special spatial configuration as well as the introduction of framework interpenetration and/or other intermolecular interactions like π-π stacking and electrostatic interactions, etc. Compared with other crystalline porous materials like metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), HOFs feature mild preparation condition, high crystallinity, permissible solution processability, easy healing and regeneration, etc. These distinguishing merits make HOFs capable to be used as unique multifunctional porous materials. Herein, we first review the basic rules to design and synthesize stable and porous HOFs, and then systematically summarize the representative supramolecular synthons and backbones that have been used to build stable and porous HOFs. Emphasis is put on the potential applications of HOFs in gas adsorption and separation, proton conduction, heterogeneous catalysis, luminescence and sensing, biological applications, enantiomeric resolution and aromatic compounds separation, pollutants removal, and structure determination, etc.
2020, 78(12): 1336-1348
doi: 10.6023/A20090439
Abstract:
Chiral metal-organic frameworks have shown important applications in the identification and separation of enantiomers and asymmetric heterogeneous catalysis, owing to their structural diversities and multifunctionalities. Recently, the applications of chiral metal-organic frameworks have been expanded to other research fields, such as circularly polarized luminescence and chiral ferroelectrics. Compared with achiral metal-organic frameworks, it is highly challenging to synthesize chiral metal-organic frameworks, because the chirality introduction usually results in the difficulty of the crystallization and purification process for the design of chiral metal-organic frameworks. In this review, we discussed three main strategies that have been utilized to construct chiral metal-organic frameworks, including direct synthesis by chiral ligands, spontaneous resolution with achiral ligands or in the presence of chiral-template, and post-synthetic modification of achiral metal-organic frameworks. Moreover, the recent research progresses of chiral metal-organic frameworks in chiral molecular recognition, enantiomer separation, asymmetric catalysis, circularly polarized luminescence, and chiral ferroelectrics are discussed.
Chiral metal-organic frameworks have shown important applications in the identification and separation of enantiomers and asymmetric heterogeneous catalysis, owing to their structural diversities and multifunctionalities. Recently, the applications of chiral metal-organic frameworks have been expanded to other research fields, such as circularly polarized luminescence and chiral ferroelectrics. Compared with achiral metal-organic frameworks, it is highly challenging to synthesize chiral metal-organic frameworks, because the chirality introduction usually results in the difficulty of the crystallization and purification process for the design of chiral metal-organic frameworks. In this review, we discussed three main strategies that have been utilized to construct chiral metal-organic frameworks, including direct synthesis by chiral ligands, spontaneous resolution with achiral ligands or in the presence of chiral-template, and post-synthetic modification of achiral metal-organic frameworks. Moreover, the recent research progresses of chiral metal-organic frameworks in chiral molecular recognition, enantiomer separation, asymmetric catalysis, circularly polarized luminescence, and chiral ferroelectrics are discussed.
2020, 78(12): 1349-1365
doi: 10.6023/A20060274
Abstract:
Carbon dots (CDots) not only possess the characteristics of strong luminescence and small size similar to traditional quantum dots, but also show the advantages of good water dispersibility and biocompatibility beyond traditional quantum dots. As an emerging branch of the quantum dots family, the structure, synthetic chemistry and photoelectric properties of CDots are quite different from those of traditional quantum dots, which also provide new opportunities and challenges for the development of quantum dots. With the rapid development and deepening of the field of CDots, it is more and more necessary to compare them with traditional quantum dots on some basic concepts, and to clarify the unique characteristics and key challenges of CDots from the view of traditional quantum dots. In this review, we focus on the aspects of basic structure, synthetic chemistry, optical properties and application research, in an effort to reexamine the research progress and challenges in CDots from the view of fundamental concepts of traditional quantum dots.
Carbon dots (CDots) not only possess the characteristics of strong luminescence and small size similar to traditional quantum dots, but also show the advantages of good water dispersibility and biocompatibility beyond traditional quantum dots. As an emerging branch of the quantum dots family, the structure, synthetic chemistry and photoelectric properties of CDots are quite different from those of traditional quantum dots, which also provide new opportunities and challenges for the development of quantum dots. With the rapid development and deepening of the field of CDots, it is more and more necessary to compare them with traditional quantum dots on some basic concepts, and to clarify the unique characteristics and key challenges of CDots from the view of traditional quantum dots. In this review, we focus on the aspects of basic structure, synthetic chemistry, optical properties and application research, in an effort to reexamine the research progress and challenges in CDots from the view of fundamental concepts of traditional quantum dots.
2020, 78(12): 1366-1382
doi: 10.6023/A20070306
Abstract:
Artificial intelligence (AI), especially the machine learning, is playing an increasingly important role in contemporary scientific research. Unlike the traditional computer program, machine learning can analyze a large number of data repeatedly and optimize its own model, a process which is called a "learning process". So that the AI can find the relationship underling the experiments from a large number of data, form a new model with better prediction and decisionmaking ability, and make an optimized strategy. The characteristics of chemical research just hit the strengths of machine learning. Chemical research often faces very complex material system and experimental process, so it is difficult to accurately analyze and making judgment through physical chemistry principles. Artificial intelligence can mine the correlation of massive experimental data generated in chemical experiments, help chemists make reasonable analysis and prediction, and therefore greatly accelerate the process of chemical research. This review presents the modern artificial intelligence method and its basic principles on solving chemical problems, by representative examples with specific machine learning algorithm. The application of artificial intelligence in chemical science is in a period of vigorous rise. Artificial intelligence has initially shown a powerful assist to chemical research. We hope this review can help more domestic chemical workers understand and use this powerful tool.
Artificial intelligence (AI), especially the machine learning, is playing an increasingly important role in contemporary scientific research. Unlike the traditional computer program, machine learning can analyze a large number of data repeatedly and optimize its own model, a process which is called a "learning process". So that the AI can find the relationship underling the experiments from a large number of data, form a new model with better prediction and decisionmaking ability, and make an optimized strategy. The characteristics of chemical research just hit the strengths of machine learning. Chemical research often faces very complex material system and experimental process, so it is difficult to accurately analyze and making judgment through physical chemistry principles. Artificial intelligence can mine the correlation of massive experimental data generated in chemical experiments, help chemists make reasonable analysis and prediction, and therefore greatly accelerate the process of chemical research. This review presents the modern artificial intelligence method and its basic principles on solving chemical problems, by representative examples with specific machine learning algorithm. The application of artificial intelligence in chemical science is in a period of vigorous rise. Artificial intelligence has initially shown a powerful assist to chemical research. We hope this review can help more domestic chemical workers understand and use this powerful tool.
2020, 78(12): 1383-1398
doi: 10.6023/A20070299
Abstract:
Type-Ⅱ fatty acid biosynthesis pathway (FAS-Ⅱ) is the only essential biosynthesis pathway that producing saturated and unsaturated fatty acids for bacteria and plant cell assembly and cellular metabolism. It utilizes a series of individual enzymes encoded by discrete genes to stepwisely catalyze lipid chain growing carried by the substrate carrier protein-acyl carrier protein (ACP). Due to its indispensable biological role in bacteria growth, as well as the distinct biological regulation mechanisms from mammalian fatty acid biosynthesis (FAS-Ⅰ), the enzymes involved in FAS-Ⅱ have been considered as important anti-pathogenic drug targets for a long time. Hence, investigating the catalysis and dynamic regulation mechanisms of FAS-Ⅱ, developing novel anti-pathogenic drugs against the enzymes involved in FAS-Ⅱ is critical to the field. We here summarize the catalytic mechanism studies and inhibitor discovery work involved in FAS-Ⅱ so far, which may potentially facilitate further understanding of FAS-Ⅱ biological functions as well as antibacterial drug discovery for infectious diseases.
Type-Ⅱ fatty acid biosynthesis pathway (FAS-Ⅱ) is the only essential biosynthesis pathway that producing saturated and unsaturated fatty acids for bacteria and plant cell assembly and cellular metabolism. It utilizes a series of individual enzymes encoded by discrete genes to stepwisely catalyze lipid chain growing carried by the substrate carrier protein-acyl carrier protein (ACP). Due to its indispensable biological role in bacteria growth, as well as the distinct biological regulation mechanisms from mammalian fatty acid biosynthesis (FAS-Ⅰ), the enzymes involved in FAS-Ⅱ have been considered as important anti-pathogenic drug targets for a long time. Hence, investigating the catalysis and dynamic regulation mechanisms of FAS-Ⅱ, developing novel anti-pathogenic drugs against the enzymes involved in FAS-Ⅱ is critical to the field. We here summarize the catalytic mechanism studies and inhibitor discovery work involved in FAS-Ⅱ so far, which may potentially facilitate further understanding of FAS-Ⅱ biological functions as well as antibacterial drug discovery for infectious diseases.
2020, 78(12): 1399-1403
doi: 10.6023/A20100470
Abstract:
α-zirconium phosphate (α-ZrP) crystals with high-crystallinity were synthesized via hydrothermal method and exfoliated with tetrabutylammonium hydroxide (TBAOH) in aqueous dispersion maintained at 0℃ in an ice bath. The exfoliated α-ZrP nano-sheets were then transferred into selected organic solvents, such as acetone, via centrifugal precipitation and re-dispersion process. This process was repeated 3 to 5 times to replace the water with the desired organic solvents. During the solvent-replacing process, most of the free TBAOH in α-ZrP/H2O dispersion was also removed, which was confirmed by characterizing the organic contents via thermo-gravimetric analysis for the solids obtained from both the water dispersion and the resulted acetone dispersion. Serendipitously, the dispersions of α-ZrP/organic solvent with structural colors could be easily obtained using this solvent-replacement method. After the solvent-replacing process was repeated for 5 times, the resulted α-ZrP/acetone dispersions could reflect visible light in the range of 426 nm to 635 nm when the mass fraction of α-ZrP was between 0.76% and 1.86%, thus showing the corresponding structural colors. Increasing the concentration of TBA+ ions in α-ZrP/acetone dispersion (α-ZrP mass fraction 0.87%), its UV-Vis reflection spectrum showed a blue-shift, indicating that the formation of periodic structures mainly depended on the electrostatic repulsion between α-ZrP nano-sheets. The formation of structural color also showed a size-dependence on the exfoliated α-ZrP nano-sheets. The nano-sheets with large-size was more likely to form the long-range ordered structure showing structural color compared with the relatively small ones (1.10 μm vs. 0.48 μm). The dispersions with acetonitrile or butyronitrile as solvent, which exhibited obvious structural colors, could also be obtained using this solvent-replacement method. At present, many plate-like inorganic particles used in the research have intrinsic charges on their gallery faces that similar to the microstructure of α-ZrP crystals, so the method reported here can give general guidance for the preparation of the dispersions with long-range periodic structures for these particles.
α-zirconium phosphate (α-ZrP) crystals with high-crystallinity were synthesized via hydrothermal method and exfoliated with tetrabutylammonium hydroxide (TBAOH) in aqueous dispersion maintained at 0℃ in an ice bath. The exfoliated α-ZrP nano-sheets were then transferred into selected organic solvents, such as acetone, via centrifugal precipitation and re-dispersion process. This process was repeated 3 to 5 times to replace the water with the desired organic solvents. During the solvent-replacing process, most of the free TBAOH in α-ZrP/H2O dispersion was also removed, which was confirmed by characterizing the organic contents via thermo-gravimetric analysis for the solids obtained from both the water dispersion and the resulted acetone dispersion. Serendipitously, the dispersions of α-ZrP/organic solvent with structural colors could be easily obtained using this solvent-replacement method. After the solvent-replacing process was repeated for 5 times, the resulted α-ZrP/acetone dispersions could reflect visible light in the range of 426 nm to 635 nm when the mass fraction of α-ZrP was between 0.76% and 1.86%, thus showing the corresponding structural colors. Increasing the concentration of TBA+ ions in α-ZrP/acetone dispersion (α-ZrP mass fraction 0.87%), its UV-Vis reflection spectrum showed a blue-shift, indicating that the formation of periodic structures mainly depended on the electrostatic repulsion between α-ZrP nano-sheets. The formation of structural color also showed a size-dependence on the exfoliated α-ZrP nano-sheets. The nano-sheets with large-size was more likely to form the long-range ordered structure showing structural color compared with the relatively small ones (1.10 μm vs. 0.48 μm). The dispersions with acetonitrile or butyronitrile as solvent, which exhibited obvious structural colors, could also be obtained using this solvent-replacement method. At present, many plate-like inorganic particles used in the research have intrinsic charges on their gallery faces that similar to the microstructure of α-ZrP crystals, so the method reported here can give general guidance for the preparation of the dispersions with long-range periodic structures for these particles.
2020, 78(12): 1404-1410
doi: 10.6023/A20080346
Abstract:
A series of Mo/beta zeolite samples with different Mo loadings were prepared via a two-step post-synthesis strategy using dealuminated Si-beta and bis(cyclopentadienyl) molybdenum dichloride (Cp2MoCl2) as precursors. The as-prepared samples were thoroughly characterized by a series of techniques including X-ray diffraction (XRD), the diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), temperature-programmed reduction by hydrogen (H2-TPR), high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM), Mo the K-edge X-ray absorption near edge structure (XANES), the extended X-ray absorption fine structure (EXAFS) and Raman spectroscopy. Dioxo (Si-O)2Mo(=O)2 species were determined to be the dominant Mo species confined and stabilized in structure of beta zeolite. The as-prepared Mo/beta samples were applied as potential catalysts in the reaction of oxidative desulfurization (ODS) from model fuel. The effects of catalyst supports, molybdenum loadings, reaction temperature, and sulfur substrates on the ODS performance were investigated in detail, and typical kinetic analyses of dibenzothiophene (DBT) oxidation were conducted, giving an apparent activation energy value of 50.2 kJ/mol. Owing to the structure confinement, Mo species can be well stabilized within the pores and cages of beta zeolite, and the distribution of which can be regulated by controlling the anchoring sites in the zeolite support to derive well-defined isolated dioxo Mo species. 1% Mo/beta exhibited remarkable oxidative desulfurization efficiency in the removal of heterocyclic sulfur compounds like DBT from the model fuel among all the catalysts tested. Typically, 99.3% of DBT could be oxidized to the corresponding sulfone within 120 min at 333 K. Moreover, 1% Mo/beta showed good recyclability and no obvious activity loss could be observed in five recycles, in significant contrast to poor cyclic stability of traditional Mo/SiO2 catalyst caused by the significant loss of Mo species during desulfurization reaction. Therefore, Mo/beta might be developed as efficient and stable ODS catalysts for future applications under mild reaction conditions.
A series of Mo/beta zeolite samples with different Mo loadings were prepared via a two-step post-synthesis strategy using dealuminated Si-beta and bis(cyclopentadienyl) molybdenum dichloride (Cp2MoCl2) as precursors. The as-prepared samples were thoroughly characterized by a series of techniques including X-ray diffraction (XRD), the diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), temperature-programmed reduction by hydrogen (H2-TPR), high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM), Mo the K-edge X-ray absorption near edge structure (XANES), the extended X-ray absorption fine structure (EXAFS) and Raman spectroscopy. Dioxo (Si-O)2Mo(=O)2 species were determined to be the dominant Mo species confined and stabilized in structure of beta zeolite. The as-prepared Mo/beta samples were applied as potential catalysts in the reaction of oxidative desulfurization (ODS) from model fuel. The effects of catalyst supports, molybdenum loadings, reaction temperature, and sulfur substrates on the ODS performance were investigated in detail, and typical kinetic analyses of dibenzothiophene (DBT) oxidation were conducted, giving an apparent activation energy value of 50.2 kJ/mol. Owing to the structure confinement, Mo species can be well stabilized within the pores and cages of beta zeolite, and the distribution of which can be regulated by controlling the anchoring sites in the zeolite support to derive well-defined isolated dioxo Mo species. 1% Mo/beta exhibited remarkable oxidative desulfurization efficiency in the removal of heterocyclic sulfur compounds like DBT from the model fuel among all the catalysts tested. Typically, 99.3% of DBT could be oxidized to the corresponding sulfone within 120 min at 333 K. Moreover, 1% Mo/beta showed good recyclability and no obvious activity loss could be observed in five recycles, in significant contrast to poor cyclic stability of traditional Mo/SiO2 catalyst caused by the significant loss of Mo species during desulfurization reaction. Therefore, Mo/beta might be developed as efficient and stable ODS catalysts for future applications under mild reaction conditions.
2020, 78(12): 1411-1417
doi: 10.6023/A20070337
Abstract:
Metal-organic cages (MOCs) as a new type of molecular containers have attracted great interest because of their special cavities and wide applications in molecule recognition and separation, drug delivery and catalysis, etc. However, in the past decades, most researchers just devote to constructing discrete MOCs with special functions. Since many cage compounds are not soluble and stable in the solvent, the further assembly of cages into advanced materials is relatively less developed. In our previous study, we reported a water-soluble and ultrastable Ti4L6 (L=embonate) tetrahedron with coordination assembly function, which has been applied as the starting material to realize coordination assembly with different metal ions through two-step reaction. In this work, by employing the Ti4L6 cages to assemble with Mn2+, Nd3+, Ba2+ and Ca2+ ions, respectively, a series of Ti4L6-based complexes have been synthesized under different solvothermal reaction conditions, namely, (Me2NH2)9(Me4N)[Mn3(Ti4L6)2(H2O)9(DMF)6]·Guests (PTC-241, DMF=N, N-dimethylformamide); (Me2NH2)5- [Nd(Ti4L6)(H2O)2(DMF)5]·Guests (PTC-242); (Me2NH2)2[Ba4(Ti4L6)(OH)2(H2O)8(TEA)5]·Guests (PTC-243, TEA=Triethanolamine); (Me2NH2)2[Ca3(Ti4L6)(H2O)8(DEA)2]·Guests (PTC-242, DEA=Diethanolamine); (Me2NH2)2[Ca3(Ti4L6)-(H2O)15]·Guests (PTC-245). Their structures were characterized by X-ray single crystal diffraction, thermo gravimetric analyzer (TGA), infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Single-crystal analysis reveals that PTC-241 is a supramolecular homochiral architecture formed by the staggered accumulation of ΔΔΔΔ-[Ti4L6] and ΔΔΔΔ-[Ti4L6]-Mn3 cages by weak interactions (such as hydrogen bonding and π-π stacking). PTC-242 is also a supramolecular structure, in which the Ti4L6-Nd cages are linked by (Me2NH2)+ cations and ethanediamine (en) molecules via the weak N-H…O hydrogen bonding force, giving rise to a 3D H-bonding framework with a honeycomb lattice of hexagonal channels along the b axis. PTC-243 is a linear Ti4L6-Ba4 chain structure. Both PTC-242 and PTC-245 are two-dimensional (2D) Ti4L6-Ca3 layers with honeycomb-like structures. In addition, we also investigated the fluorescent properties of PTC-242 and PTC-245 in the solid state, and the results show that both of them display strong emitting bands in the visible region.
Metal-organic cages (MOCs) as a new type of molecular containers have attracted great interest because of their special cavities and wide applications in molecule recognition and separation, drug delivery and catalysis, etc. However, in the past decades, most researchers just devote to constructing discrete MOCs with special functions. Since many cage compounds are not soluble and stable in the solvent, the further assembly of cages into advanced materials is relatively less developed. In our previous study, we reported a water-soluble and ultrastable Ti4L6 (L=embonate) tetrahedron with coordination assembly function, which has been applied as the starting material to realize coordination assembly with different metal ions through two-step reaction. In this work, by employing the Ti4L6 cages to assemble with Mn2+, Nd3+, Ba2+ and Ca2+ ions, respectively, a series of Ti4L6-based complexes have been synthesized under different solvothermal reaction conditions, namely, (Me2NH2)9(Me4N)[Mn3(Ti4L6)2(H2O)9(DMF)6]·Guests (PTC-241, DMF=N, N-dimethylformamide); (Me2NH2)5- [Nd(Ti4L6)(H2O)2(DMF)5]·Guests (PTC-242); (Me2NH2)2[Ba4(Ti4L6)(OH)2(H2O)8(TEA)5]·Guests (PTC-243, TEA=Triethanolamine); (Me2NH2)2[Ca3(Ti4L6)(H2O)8(DEA)2]·Guests (PTC-242, DEA=Diethanolamine); (Me2NH2)2[Ca3(Ti4L6)-(H2O)15]·Guests (PTC-245). Their structures were characterized by X-ray single crystal diffraction, thermo gravimetric analyzer (TGA), infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Single-crystal analysis reveals that PTC-241 is a supramolecular homochiral architecture formed by the staggered accumulation of ΔΔΔΔ-[Ti4L6] and ΔΔΔΔ-[Ti4L6]-Mn3 cages by weak interactions (such as hydrogen bonding and π-π stacking). PTC-242 is also a supramolecular structure, in which the Ti4L6-Nd cages are linked by (Me2NH2)+ cations and ethanediamine (en) molecules via the weak N-H…O hydrogen bonding force, giving rise to a 3D H-bonding framework with a honeycomb lattice of hexagonal channels along the b axis. PTC-243 is a linear Ti4L6-Ba4 chain structure. Both PTC-242 and PTC-245 are two-dimensional (2D) Ti4L6-Ca3 layers with honeycomb-like structures. In addition, we also investigated the fluorescent properties of PTC-242 and PTC-245 in the solid state, and the results show that both of them display strong emitting bands in the visible region.
Oligomerization and Polymerization of Isoprene Catalyzed by Alkylaluminium with Different Structures
2020, 78(12): 1418-1425
doi: 10.6023/A20070336
Abstract:
Alkylaluminium (AlR3), as co-catalyst component in Ziegler-Natta catalytic system, plays important roles in the alkylation, forming and changing the structure and concentration of active centers through the reduction and reversible adsorption-desorption reactions with the metal compound of the catalyst, acting as chain transfer agent, etc. However, the alkylaluminium itself do have the catalytic effect on the conjugated diene monomers. In this article, alkylaluminium with different structures such as triethylaluminium (AlEt3), triisobutylaluminium (Al(i-Bu)3), diisobutylaluminium hydride (AlH(i-Bu)2), diethylaluminium chloride (AlEt2Cl), ethylaluminium dichloride (AlEtCl2) were used to catalyze isoprene oligomerization and polymerization. The effects of the structure and concentration of alkylaluminiums (n(Al)/n(M)=7×10-5, 35×10-5, 350×10-5, 1050×10-5) on the catalytic behaviors of isoprene were studied. The microstructure (trans-1, 4 and cis-1, 4), molecular weight and molecular weight distribution of the products were characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC) and gas chromatography-mass spectrometry (GC-MS). It was found that alkylaluminium could initiate oligomerization and cationic polymerization of isoprene under the minor incorporation of H2O, which were affected greatly by the structure and concentration of alkylaluminium. Using AlEtCl2 led to the highest catalytic activity and produced products containing more linear polymers with mixed cis-1, 4/trans-1, 4 structures when n(Al)/n(M)=1050×10-5. The Al(i-Bu)3 and AlH(i-Bu)2 didn't have basically cation initiation ability, which led to isoprene oligomerization. The alkylaluminium with n(Al)/n(M) ≤ 350×10-5 had negligible influence on the isoprene polymerization and oligomerization. And lower or higher alkylaluminium concentration were not beneficial to obtain polyisoprene with high molecular weight. The catalytic mechanism of alkylaluminium on isoprene was discussed, which provided a further understanding on the catalytic behavior of alkylaluminium components in Ziegler-Natta catalyst and the effect of alkylaluminium on polymers.
Alkylaluminium (AlR3), as co-catalyst component in Ziegler-Natta catalytic system, plays important roles in the alkylation, forming and changing the structure and concentration of active centers through the reduction and reversible adsorption-desorption reactions with the metal compound of the catalyst, acting as chain transfer agent, etc. However, the alkylaluminium itself do have the catalytic effect on the conjugated diene monomers. In this article, alkylaluminium with different structures such as triethylaluminium (AlEt3), triisobutylaluminium (Al(i-Bu)3), diisobutylaluminium hydride (AlH(i-Bu)2), diethylaluminium chloride (AlEt2Cl), ethylaluminium dichloride (AlEtCl2) were used to catalyze isoprene oligomerization and polymerization. The effects of the structure and concentration of alkylaluminiums (n(Al)/n(M)=7×10-5, 35×10-5, 350×10-5, 1050×10-5) on the catalytic behaviors of isoprene were studied. The microstructure (trans-1, 4 and cis-1, 4), molecular weight and molecular weight distribution of the products were characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC) and gas chromatography-mass spectrometry (GC-MS). It was found that alkylaluminium could initiate oligomerization and cationic polymerization of isoprene under the minor incorporation of H2O, which were affected greatly by the structure and concentration of alkylaluminium. Using AlEtCl2 led to the highest catalytic activity and produced products containing more linear polymers with mixed cis-1, 4/trans-1, 4 structures when n(Al)/n(M)=1050×10-5. The Al(i-Bu)3 and AlH(i-Bu)2 didn't have basically cation initiation ability, which led to isoprene oligomerization. The alkylaluminium with n(Al)/n(M) ≤ 350×10-5 had negligible influence on the isoprene polymerization and oligomerization. And lower or higher alkylaluminium concentration were not beneficial to obtain polyisoprene with high molecular weight. The catalytic mechanism of alkylaluminium on isoprene was discussed, which provided a further understanding on the catalytic behavior of alkylaluminium components in Ziegler-Natta catalyst and the effect of alkylaluminium on polymers.
2020, 78(12): 1426-1433
doi: 10.6023/A20070330
Abstract:
Lithium-rich manganese-based oxides (LRMO) are promising cathode materials to build next generation lithium-ion batteries because of high capacity and low cost. However, the severe capacity fade and voltage decay, which originate from surface oxygen loss, side reactions and irreversible phase transformation, restrict their practical application. Proposed approaches to address these issues include electrolyte modification, synthesis condition optimization, tuning elemental composition, bulk doping and surface coating. Surface coating has been proved to be an effective method to stabilize the interface between LRMO and electrolyte. Herein, we report a facile approach to synthesize Li3PO4-coated LRMO (LRMO@LPO) by in-situ carbonate-phosphate precipitate conversion reaction. The formation of Li3PO4 layer and its contribution to enhanced electrochemical performance are investigated in detail. Transmission electron microscopy (TEM) reveals that the surface of carbonate precursor converts to Ni3(PO4)2 after reacting with Na2HPO4 solution, which finally transforms to Li3PO4 coating layer with thickness below 30 nm during calcination process. Quinoline phosphomolybdate gravimetric method gives the optimal Li3PO4 coating content of 0.56%. The modified LRMO@LPO sample exhibits improved cycling stability (191.1 mAh·g-1 after 175 cycles at 0.5C between 2.0~4.8 V and 81.8% capacity retention) and suppressed voltage decay (1.09 mV per cycle), compared with bare LRMO material (72.9% capacity retention, 1.78 mV per cycle). The electrodes are studied by galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, TEM and inductively coupled plasma atomic emission spectrometry. The results suggest efficient mitigation of phase transformation and dissolution of transition metal in LRMO@LPO. As a coating material with lithium-ion conductivity, Li3PO4 not only acts as a physical barrier to inhibit side reaction between the electrolyte and LRMO, but also promotes lithium ion transport at the surface region of cathode. The in-situ surface modification approach simplifies the traditional post coating process, and may provide new insight to build stable and low cost Li-rich cathode for lithium-ion batteries.
Lithium-rich manganese-based oxides (LRMO) are promising cathode materials to build next generation lithium-ion batteries because of high capacity and low cost. However, the severe capacity fade and voltage decay, which originate from surface oxygen loss, side reactions and irreversible phase transformation, restrict their practical application. Proposed approaches to address these issues include electrolyte modification, synthesis condition optimization, tuning elemental composition, bulk doping and surface coating. Surface coating has been proved to be an effective method to stabilize the interface between LRMO and electrolyte. Herein, we report a facile approach to synthesize Li3PO4-coated LRMO (LRMO@LPO) by in-situ carbonate-phosphate precipitate conversion reaction. The formation of Li3PO4 layer and its contribution to enhanced electrochemical performance are investigated in detail. Transmission electron microscopy (TEM) reveals that the surface of carbonate precursor converts to Ni3(PO4)2 after reacting with Na2HPO4 solution, which finally transforms to Li3PO4 coating layer with thickness below 30 nm during calcination process. Quinoline phosphomolybdate gravimetric method gives the optimal Li3PO4 coating content of 0.56%. The modified LRMO@LPO sample exhibits improved cycling stability (191.1 mAh·g-1 after 175 cycles at 0.5C between 2.0~4.8 V and 81.8% capacity retention) and suppressed voltage decay (1.09 mV per cycle), compared with bare LRMO material (72.9% capacity retention, 1.78 mV per cycle). The electrodes are studied by galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, TEM and inductively coupled plasma atomic emission spectrometry. The results suggest efficient mitigation of phase transformation and dissolution of transition metal in LRMO@LPO. As a coating material with lithium-ion conductivity, Li3PO4 not only acts as a physical barrier to inhibit side reaction between the electrolyte and LRMO, but also promotes lithium ion transport at the surface region of cathode. The in-situ surface modification approach simplifies the traditional post coating process, and may provide new insight to build stable and low cost Li-rich cathode for lithium-ion batteries.
2020, 78(12): 1434-1440
doi: 10.6023/A20070290
Abstract:
Among the numerous successors of Li-ion batteries, Li-O2 cells become promising candidates because of their higher theoretical energy density (3500 Wh·kg-1). However, the uncontrolled dendrite growth and serious corrosion issues of lithium metal anode are major bottlenecks for practical application of Li-O2 batteries. To solve the above challenges, herein, we prepared metal-organic frameworks materials (MOF-801) with high specific surface area and abundant pores as a protection layer on lithium metal anode in Li-O2 batteries. In this manuscript, pure and cubic-shaped MOF-801 materials are successfully synthesized and the high specific surface area (762.9 m2·g-1) is confirmed. And MOF-801 is verified stable enough as a protection layer towards lithium metal anode and tetraethylene glycol dimethyl ether (TEGDME) 1 mol·L-1 LiCF3SO3 electrolyte system. Due to the rich pore structures and high specific surface area, MOF-801 can assist to form uniform Li+ flux and dendrite-free lithium deposition morphology can be confirmed in the scanning electron microscope images, which can avoid the short circuit even fire disaster from the uncontrollable dendrite growth. Besides, the shield effect as well as the water capture function of MOF-801 protection layer can also effectively prevent serious side reactions from the shuttle effect of the contaminants (H2O, O2 and strong oxidizing species). Consequently, this strategy enables stable electrode/electrolyte interface and achieves 800 h plating/stripping cycles under a low overpotential of 0.023 V. In contrast, the batteries without protection can only run for 254 h with the overpotential as high as 5 V at last. The electrochemical impedance spectroscopy results also verify that the much lower impedance of the lithium metal anode after protection. When applied in practical Li-O2 batteries with a fixed capacity of 1000 mAh·g-1 at a current density of 500 mA·g-1, stable and long-life cycle performance(170 cycles) has been realized in the Li-O2 batteries with MOF-801 protection layer, which is 2.88 times longer than those without protection. The batteries with MOF-801 protection layer also deliver a high discharge specific capacity of 8935 mAh·g-1. This unique protection layer design strategy illustrates fresh insight towards protection strategy in alkali metal anode batteries.
Among the numerous successors of Li-ion batteries, Li-O2 cells become promising candidates because of their higher theoretical energy density (3500 Wh·kg-1). However, the uncontrolled dendrite growth and serious corrosion issues of lithium metal anode are major bottlenecks for practical application of Li-O2 batteries. To solve the above challenges, herein, we prepared metal-organic frameworks materials (MOF-801) with high specific surface area and abundant pores as a protection layer on lithium metal anode in Li-O2 batteries. In this manuscript, pure and cubic-shaped MOF-801 materials are successfully synthesized and the high specific surface area (762.9 m2·g-1) is confirmed. And MOF-801 is verified stable enough as a protection layer towards lithium metal anode and tetraethylene glycol dimethyl ether (TEGDME) 1 mol·L-1 LiCF3SO3 electrolyte system. Due to the rich pore structures and high specific surface area, MOF-801 can assist to form uniform Li+ flux and dendrite-free lithium deposition morphology can be confirmed in the scanning electron microscope images, which can avoid the short circuit even fire disaster from the uncontrollable dendrite growth. Besides, the shield effect as well as the water capture function of MOF-801 protection layer can also effectively prevent serious side reactions from the shuttle effect of the contaminants (H2O, O2 and strong oxidizing species). Consequently, this strategy enables stable electrode/electrolyte interface and achieves 800 h plating/stripping cycles under a low overpotential of 0.023 V. In contrast, the batteries without protection can only run for 254 h with the overpotential as high as 5 V at last. The electrochemical impedance spectroscopy results also verify that the much lower impedance of the lithium metal anode after protection. When applied in practical Li-O2 batteries with a fixed capacity of 1000 mAh·g-1 at a current density of 500 mA·g-1, stable and long-life cycle performance(170 cycles) has been realized in the Li-O2 batteries with MOF-801 protection layer, which is 2.88 times longer than those without protection. The batteries with MOF-801 protection layer also deliver a high discharge specific capacity of 8935 mAh·g-1. This unique protection layer design strategy illustrates fresh insight towards protection strategy in alkali metal anode batteries.
2020, 78(12): 1441-1447
doi: 10.6023/A20080356
Abstract:
With the fast developing of new energy industry and energy storage, the safety and energy density of secondary batteries is more and more important. The commercial lithium ion batteries contain the organic liquid electrolyte, which is flammable. Therefore, the solid-state lithium metal battery with high safety and energy density attract more and more attentions. However, the low ionic conductivity and high interface resistance hinder the application of solid-state lithium metal batteries. Therefore, the developing of solid-state electrolyte with high ionic conductivity is the key to develop the solid-state lithium metal batteries. Polymer electrolyte films consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and liquid electrolyte were prepared by spay casting and examined in order to obtain the best compromise between high conductivity, homogeneity, dimensional and electrochemical stability. The PEO-PAN-PMMA gel polymer electrolyte (GPE) was got by absorbing the electrolyte for 12 h. The PEO-PAN-PMMA membrane is homogeneous and transparent. PEO-PAN-PMMA membrane is characterized by scanning electron microscope (SEM), thermogravimetric (TG) and X-ray diffraction (XRD). The PEO-PAN-PMMA membrane is stable below 380℃. Although it has two XRD peaks, the films could absorb 59% liquid electrolyte, which is significant. The high ionic conductivity of PEO-PAN-PMMA GPE is examined using electrochemical impedance spectroscopy (EIS) and attended due to the high absorption. And the highest ionic conductivity is 0.4 mS/cm at room temperature. The electrochemical window of the PEO-PAN-PMMA GPE is examined using linear sweeping voltammetry, and the films is stable at 0~4.2 V. Solid state lithium metal battery using the PEO-PAN-PMMA GPE has a charging capacity of 129.8 mAh/g at first cycle and 119.51 mAh/g at 100th cycle. The capacities of the batteries are 129.8 mAh/g, 99.5 mAh/g, 86.1 mAh/g, 64 mAh/g at 0.1 C, 0.2 C, 0.5 C, 1 C rate, respectively. This work pave the way to rechargeable Li batteries with high safety and long cycle life.
With the fast developing of new energy industry and energy storage, the safety and energy density of secondary batteries is more and more important. The commercial lithium ion batteries contain the organic liquid electrolyte, which is flammable. Therefore, the solid-state lithium metal battery with high safety and energy density attract more and more attentions. However, the low ionic conductivity and high interface resistance hinder the application of solid-state lithium metal batteries. Therefore, the developing of solid-state electrolyte with high ionic conductivity is the key to develop the solid-state lithium metal batteries. Polymer electrolyte films consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and liquid electrolyte were prepared by spay casting and examined in order to obtain the best compromise between high conductivity, homogeneity, dimensional and electrochemical stability. The PEO-PAN-PMMA gel polymer electrolyte (GPE) was got by absorbing the electrolyte for 12 h. The PEO-PAN-PMMA membrane is homogeneous and transparent. PEO-PAN-PMMA membrane is characterized by scanning electron microscope (SEM), thermogravimetric (TG) and X-ray diffraction (XRD). The PEO-PAN-PMMA membrane is stable below 380℃. Although it has two XRD peaks, the films could absorb 59% liquid electrolyte, which is significant. The high ionic conductivity of PEO-PAN-PMMA GPE is examined using electrochemical impedance spectroscopy (EIS) and attended due to the high absorption. And the highest ionic conductivity is 0.4 mS/cm at room temperature. The electrochemical window of the PEO-PAN-PMMA GPE is examined using linear sweeping voltammetry, and the films is stable at 0~4.2 V. Solid state lithium metal battery using the PEO-PAN-PMMA GPE has a charging capacity of 129.8 mAh/g at first cycle and 119.51 mAh/g at 100th cycle. The capacities of the batteries are 129.8 mAh/g, 99.5 mAh/g, 86.1 mAh/g, 64 mAh/g at 0.1 C, 0.2 C, 0.5 C, 1 C rate, respectively. This work pave the way to rechargeable Li batteries with high safety and long cycle life.
2020, 78(12): 1448-1454
doi: 10.6023/A20070322
Abstract:
In order to improve light absorption range of TiO2 and utilization rate of photogenerated carriers, we use B, N co-doping and In2O3 blending to modify the TiO2 photocatalyst. Sample preparation is conducted through polymer precursor method and uniform distribution of the components is ensured. Polyethylene glycol (PEG) is added at the beginning of sample preparation and removed during the annealing process at high temperatures. X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission microscope (HRTEM), specific surface area and pore structure analyzer, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible absorption spectrum and photoluminescence (PL) spectroscopy are used to characterize the products obtained. B and N elements have been detected in the lattice of TiO2. Heterojunction structure of In2O3 and TiO2 are also observed. Formation of Ti-N-B and Ti-O-B structure is exhibited in this system. Interstitial doping of N is also observed. These factors contribute to narrow the band gap from 3.09 eV of P25 to 2.71 eV of IT-500 (the modified sample annealed at 500℃). With the introduction and pyrolysis of porogen PEG, mesoporous structure is successfully constructed. Visible light absorption range has been greatly broadened in this modified TiO2 based material. Utilization rate of photogenerated carriers has also been enhanced. When the catalyst is used in the photocatalytic hydrogen production experiment, under the irradiation of visible light (>380 nm), hydrogen production rate of IT-500 reaches 5961 μmol·g-1·h-1, which is far superior to commercial TiO2 and most of the TiO2 prepared by single modification method. The hydrogen production rate is maintained in the 5-circle test after the catalyst is separated and recycled. When the B, N-In2O3/TiO2 polymer precursor is gas sprayed, which uses polyvinylpyrrolidone as spinning aid, ethanol and acetic acid as solvents, nanofiber sponge can be obtained and used for hydrogen production. Hydrogen production rate of this material reaches 1186 μmol·g-1·h-1 and keeps 97% after 5-cycle test, which shows high potential for commercial use of this material.
In order to improve light absorption range of TiO2 and utilization rate of photogenerated carriers, we use B, N co-doping and In2O3 blending to modify the TiO2 photocatalyst. Sample preparation is conducted through polymer precursor method and uniform distribution of the components is ensured. Polyethylene glycol (PEG) is added at the beginning of sample preparation and removed during the annealing process at high temperatures. X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission microscope (HRTEM), specific surface area and pore structure analyzer, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible absorption spectrum and photoluminescence (PL) spectroscopy are used to characterize the products obtained. B and N elements have been detected in the lattice of TiO2. Heterojunction structure of In2O3 and TiO2 are also observed. Formation of Ti-N-B and Ti-O-B structure is exhibited in this system. Interstitial doping of N is also observed. These factors contribute to narrow the band gap from 3.09 eV of P25 to 2.71 eV of IT-500 (the modified sample annealed at 500℃). With the introduction and pyrolysis of porogen PEG, mesoporous structure is successfully constructed. Visible light absorption range has been greatly broadened in this modified TiO2 based material. Utilization rate of photogenerated carriers has also been enhanced. When the catalyst is used in the photocatalytic hydrogen production experiment, under the irradiation of visible light (>380 nm), hydrogen production rate of IT-500 reaches 5961 μmol·g-1·h-1, which is far superior to commercial TiO2 and most of the TiO2 prepared by single modification method. The hydrogen production rate is maintained in the 5-circle test after the catalyst is separated and recycled. When the B, N-In2O3/TiO2 polymer precursor is gas sprayed, which uses polyvinylpyrrolidone as spinning aid, ethanol and acetic acid as solvents, nanofiber sponge can be obtained and used for hydrogen production. Hydrogen production rate of this material reaches 1186 μmol·g-1·h-1 and keeps 97% after 5-cycle test, which shows high potential for commercial use of this material.
2020, 78(12): 1455-1460
doi: 10.6023/A20070332
Abstract:
The large-scale use of coal, oil, and natural gas will cause environmental pollution and resource shortages, which is incompatible with the sustainable development. Therefore, it is essential to the development of renewable energy. H2 has a high heat of combustion, and it's combustion products do not include greenhouse gases, so it is considered as an ideal clean energy carrier. Industrial hydrogen production methods will bring CO2 inevitably. As an emerging energy conversion device, hydrogen produced by water splitting has simple equipment and little pollution, making it the first choice for clean energy in the future. Generally, the adsorption energy of hydrogen on the surface of precious metal catalysts is close to zero, and its hydrogen evolution reaction (HER) performance is the most prominent. Pt is an excellent HER catalyst. Commercial Pt/C has high alkaline HER performance, but its higher cost, material instability and resource scarcity limit its widespread applications. Therefore, this research is devoted to the development of high-activity, low-cost transition metal catalysts for HER by water splitting. Firstly, CoMoO4 nanorods were synthesized by hydrothermal method. Then, using the precursor morphology oriented strategy method, the activated Co9S8/MoS2 heterostructure catalyst was successfully prepared by sulfurating CoMoO4 into CoS2/MoS2 and further, calcining CoS2/MoS2 nanorod in hydrogen atmosphere. X-rays diffraction (XRD), transmission electron microscopy (TEM), electron spin resonance (ESR), Raman spectra, X-ray photoelectron spectra (XPS) and synchrotron-based X-ray absorption fine structure (XAFS) characterizations exhibit that the Co coordination mode change from octahedron in CoS2 to tetrahedron in Co9S8, leading to the activation of inert basal plane in MoS2. Owing to this activation, the interlayer spacing of MoS2 is reduced and thus generate abundant defects. Meanwhile, the increased electrochemical surface area (ECSA) and roughness of the catalysts are more conducive to the adsorption of H*. The test of the contact angle data show that the electrode has good hydrophilicity, which can facilitate the penetration of electrolyte and diffusion of gas molecules quickly. When the current density is at 10 mA·cm-2 in 1 mol·L-1 KOH solution, an overpotential of 84 mV and a Tafel slope of 93 mV·dec-1 can be achieved. Due to the strong interaction between different components of the heterostructures, the nanorods possess good structural stability in alkaline solutions. This work highlights the vital role of the sulfides heterostructure construction in HER, opening a new way to advanced alkaline HER catalysts.
The large-scale use of coal, oil, and natural gas will cause environmental pollution and resource shortages, which is incompatible with the sustainable development. Therefore, it is essential to the development of renewable energy. H2 has a high heat of combustion, and it's combustion products do not include greenhouse gases, so it is considered as an ideal clean energy carrier. Industrial hydrogen production methods will bring CO2 inevitably. As an emerging energy conversion device, hydrogen produced by water splitting has simple equipment and little pollution, making it the first choice for clean energy in the future. Generally, the adsorption energy of hydrogen on the surface of precious metal catalysts is close to zero, and its hydrogen evolution reaction (HER) performance is the most prominent. Pt is an excellent HER catalyst. Commercial Pt/C has high alkaline HER performance, but its higher cost, material instability and resource scarcity limit its widespread applications. Therefore, this research is devoted to the development of high-activity, low-cost transition metal catalysts for HER by water splitting. Firstly, CoMoO4 nanorods were synthesized by hydrothermal method. Then, using the precursor morphology oriented strategy method, the activated Co9S8/MoS2 heterostructure catalyst was successfully prepared by sulfurating CoMoO4 into CoS2/MoS2 and further, calcining CoS2/MoS2 nanorod in hydrogen atmosphere. X-rays diffraction (XRD), transmission electron microscopy (TEM), electron spin resonance (ESR), Raman spectra, X-ray photoelectron spectra (XPS) and synchrotron-based X-ray absorption fine structure (XAFS) characterizations exhibit that the Co coordination mode change from octahedron in CoS2 to tetrahedron in Co9S8, leading to the activation of inert basal plane in MoS2. Owing to this activation, the interlayer spacing of MoS2 is reduced and thus generate abundant defects. Meanwhile, the increased electrochemical surface area (ECSA) and roughness of the catalysts are more conducive to the adsorption of H*. The test of the contact angle data show that the electrode has good hydrophilicity, which can facilitate the penetration of electrolyte and diffusion of gas molecules quickly. When the current density is at 10 mA·cm-2 in 1 mol·L-1 KOH solution, an overpotential of 84 mV and a Tafel slope of 93 mV·dec-1 can be achieved. Due to the strong interaction between different components of the heterostructures, the nanorods possess good structural stability in alkaline solutions. This work highlights the vital role of the sulfides heterostructure construction in HER, opening a new way to advanced alkaline HER catalysts.
