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2023 Volume 39 Issue 1
2023, 39(1): 201203
doi: 10.3866/PKU.WHXB202012030
Abstract:
2023, 39(1): 201203
doi: 10.3866/PKU.WHXB202012031
Abstract:
2023, 39(1): 201207
doi: 10.3866/PKU.WHXB202012072
Abstract:
2023, 39(1): 210902
doi: 10.3866/PKU.WHXB202109022
Abstract:
2023, 39(1): 220702
doi: 10.3866/PKU.WHXB202207025
Abstract:
2023, 39(1): 210701
doi: 10.3866/PKU.WHXB202107017
Abstract:
In recent years, flexible and wearable electronic devices have attracted increasing research, industrial, and consumer attention. In particular, flexible zinc-air batteries (ZABs) are expected to become a promising power supply source for next-generation electronic products, especially the flexible and wearable ones, because of their high theoretical energy density, high specific capacity, high safety, and adaptability to uneven surfaces like human body. In the research field of flexible ZABs, a steady progress has been observed, and various ZAB preparation methods have been recently proposed. In this review, the main achievements and limitations of the recent research related to flexible ZABs are described. Firstly, the importance and applications of ZABs are discussed, followed by the working principle and configuration of typical ZABs. In the main text, the recent development of gel electrolytes, anodes, and cathodes is reviewed in detail. Currently, one of the most important limitations in the preparation of high-performance ZABs is the selection or preparation of a suitable gel electrolyte. A good gel electrolyte should have the ability of high-water holding capacity, high and low temperature resistance, high CO2-tolerance, excellent ionic conductivity, and good mechanical ductility. Several gel electrolytes with various functions have been developed. However, novel gel electrolytes with multifunctional properties have not been developed. In addition, interfaces between the gel electrolyte and air cathode and those between the gel electrolyte and metal anode must be investigated in detail for ZAB performance improvement. Till now, only the effects of physical compression on the electrolyte-air cathode and electrolyte-metal anode interfaces have been adopted and investigated. Moreover, the air cathode and metal anode must exhibit high flexibility to expand the application scope of ZABs as flexible power supplies. Carbon cloth has been typically used as the substrate of the air cathode; however, carbon corrosion occurs under high potential, which needs to be overcome. Meanwhile, the use of nickel mesh or copper foam as the substrate for the cathode will make the flexible ZABs too rigid and not bendable. For the metal anode, mostly zinc sheet or zinc spring have been used to meet the demand of flexibility. However, if novel strategies for the development of doped zinc anodes are investigated, such as those based on the utilization of zinc powder-metal combination, ZAB performance will be significantly improved. If the above-mentioned limitations are overcome, flexible ZABs will not be limited to laboratory use, and can be widely applied in commercial wearable electronic products. Furthermore, the challenges and future perspectives of ZABs are discussed in this review.![]()
In recent years, flexible and wearable electronic devices have attracted increasing research, industrial, and consumer attention. In particular, flexible zinc-air batteries (ZABs) are expected to become a promising power supply source for next-generation electronic products, especially the flexible and wearable ones, because of their high theoretical energy density, high specific capacity, high safety, and adaptability to uneven surfaces like human body. In the research field of flexible ZABs, a steady progress has been observed, and various ZAB preparation methods have been recently proposed. In this review, the main achievements and limitations of the recent research related to flexible ZABs are described. Firstly, the importance and applications of ZABs are discussed, followed by the working principle and configuration of typical ZABs. In the main text, the recent development of gel electrolytes, anodes, and cathodes is reviewed in detail. Currently, one of the most important limitations in the preparation of high-performance ZABs is the selection or preparation of a suitable gel electrolyte. A good gel electrolyte should have the ability of high-water holding capacity, high and low temperature resistance, high CO2-tolerance, excellent ionic conductivity, and good mechanical ductility. Several gel electrolytes with various functions have been developed. However, novel gel electrolytes with multifunctional properties have not been developed. In addition, interfaces between the gel electrolyte and air cathode and those between the gel electrolyte and metal anode must be investigated in detail for ZAB performance improvement. Till now, only the effects of physical compression on the electrolyte-air cathode and electrolyte-metal anode interfaces have been adopted and investigated. Moreover, the air cathode and metal anode must exhibit high flexibility to expand the application scope of ZABs as flexible power supplies. Carbon cloth has been typically used as the substrate of the air cathode; however, carbon corrosion occurs under high potential, which needs to be overcome. Meanwhile, the use of nickel mesh or copper foam as the substrate for the cathode will make the flexible ZABs too rigid and not bendable. For the metal anode, mostly zinc sheet or zinc spring have been used to meet the demand of flexibility. However, if novel strategies for the development of doped zinc anodes are investigated, such as those based on the utilization of zinc powder-metal combination, ZAB performance will be significantly improved. If the above-mentioned limitations are overcome, flexible ZABs will not be limited to laboratory use, and can be widely applied in commercial wearable electronic products. Furthermore, the challenges and future perspectives of ZABs are discussed in this review.
Gaseous-Promotor-Assisted Direct Growth of Graphene on Insulating Substrates: Progress and Prospects
2023, 39(1): 211101
doi: 10.3866/PKU.WHXB202111011
Abstract:
Utilizing a direct chemical vapor deposition approach to synthesize graphene on insulating substrates has received enormous attention to date in both scientific and technological realms. In contrast to the graphene growth on metal substrates, the catalytic inertness of insulators toward feedstock decomposition and the high energy barrier for carbon fragment migration on the insulating surface result in not only high density of grain boundaries but also a low growth rate. Thus-obtained graphene film is usually accompanied by massive defects and limited crystal quality, which adversely affect the physical integrity and electrical performance of the fabricated graphene-based device. In this respect, various strategies have been adopted to modify the direct growth processes of graphene, e.g., sacrificial metal catalysis approach, self-terminating confinement approach and near-equilibrium growth approach. Among these mentioned above, the gaseous-promotor-assisted growth methodology has proven to be a beneficial way in enhancing crystal quality and augmenting the growth rate of graphene. For the gaseous-promotor-assisted chemical vapor deposition route, the gaseous promotor can not only regulate the composition/content of active carbon species in the gas-phase reaction process but also promote the surface migration and growth reactions. In this contribution, we review the recent advances in gaseous-promotor-assisted direct growth of graphene with high crystallinity, optimized uniformity, and enhanced growth rate on insulating substrates. First of all, we provide a systematic description of the growth behavior of graphene on insulators, including both the surface and gas-phase reactions combined with elementary steps during the growth process. We then summarize developed strategies aiming to achieve the direct growth of high-quality graphene via the assistance of gaseous promotors, with special emphasis on the effects and mechanisms of the growth process. The types of promotors commonly used in the gaseous-promotor-assisted strategy can be divided into metallic and non-metallic vapor species. These gaseous promotors can play influence on the feedstock decomposition, graphene nucleation, and enhance the enlargement and merging of individual domains. The corresponding mechanisms of the strategy can be classified into three parts: (1) The existence of highly concentrated metallic vapor species can promote thermal decomposition of carbon feedstock, which is the key to the growth of high-quality graphene; (2) The introduction of oxygen-containing species can effectively reduce the nucleation density, etch the amorphous carbon, leading to a high-quality, uniform growth of graphene film. In addition, hydroxylation of substrate through oxygen-containing species weakens the binding energy between the graphene edge and surface of the substrate, facilitating carbon fragment migration to evolve uniform monolayer graphene film; (3) The appearance of silicon and fluorine species reduces the growth kinetic barrier for carbon feedstock migrating onto the graphene edge to form the honeycomb lattice, which ensures the ultrafast growth of graphene on insulating substrates. Finally, we describe existed challenges and present future perspectives on the direct growth of high-quality graphene on insulating substrates to stimulate more efforts devoted to direct graphene growth and ultimate applications. We hope this review can propel in-depth comprehension of the direct growth of graphene on insulators by gaseous-promotor-assisted strategy, and pave the way for the development and applications of graphene materials.![]()
Utilizing a direct chemical vapor deposition approach to synthesize graphene on insulating substrates has received enormous attention to date in both scientific and technological realms. In contrast to the graphene growth on metal substrates, the catalytic inertness of insulators toward feedstock decomposition and the high energy barrier for carbon fragment migration on the insulating surface result in not only high density of grain boundaries but also a low growth rate. Thus-obtained graphene film is usually accompanied by massive defects and limited crystal quality, which adversely affect the physical integrity and electrical performance of the fabricated graphene-based device. In this respect, various strategies have been adopted to modify the direct growth processes of graphene, e.g., sacrificial metal catalysis approach, self-terminating confinement approach and near-equilibrium growth approach. Among these mentioned above, the gaseous-promotor-assisted growth methodology has proven to be a beneficial way in enhancing crystal quality and augmenting the growth rate of graphene. For the gaseous-promotor-assisted chemical vapor deposition route, the gaseous promotor can not only regulate the composition/content of active carbon species in the gas-phase reaction process but also promote the surface migration and growth reactions. In this contribution, we review the recent advances in gaseous-promotor-assisted direct growth of graphene with high crystallinity, optimized uniformity, and enhanced growth rate on insulating substrates. First of all, we provide a systematic description of the growth behavior of graphene on insulators, including both the surface and gas-phase reactions combined with elementary steps during the growth process. We then summarize developed strategies aiming to achieve the direct growth of high-quality graphene via the assistance of gaseous promotors, with special emphasis on the effects and mechanisms of the growth process. The types of promotors commonly used in the gaseous-promotor-assisted strategy can be divided into metallic and non-metallic vapor species. These gaseous promotors can play influence on the feedstock decomposition, graphene nucleation, and enhance the enlargement and merging of individual domains. The corresponding mechanisms of the strategy can be classified into three parts: (1) The existence of highly concentrated metallic vapor species can promote thermal decomposition of carbon feedstock, which is the key to the growth of high-quality graphene; (2) The introduction of oxygen-containing species can effectively reduce the nucleation density, etch the amorphous carbon, leading to a high-quality, uniform growth of graphene film. In addition, hydroxylation of substrate through oxygen-containing species weakens the binding energy between the graphene edge and surface of the substrate, facilitating carbon fragment migration to evolve uniform monolayer graphene film; (3) The appearance of silicon and fluorine species reduces the growth kinetic barrier for carbon feedstock migrating onto the graphene edge to form the honeycomb lattice, which ensures the ultrafast growth of graphene on insulating substrates. Finally, we describe existed challenges and present future perspectives on the direct growth of high-quality graphene on insulating substrates to stimulate more efforts devoted to direct graphene growth and ultimate applications. We hope this review can propel in-depth comprehension of the direct growth of graphene on insulators by gaseous-promotor-assisted strategy, and pave the way for the development and applications of graphene materials.
2023, 39(1): 220602
doi: 10.3866/PKU.WHXB202206029
Abstract:
Graphdiyne (GDY) bearing sp- and sp2-hybridized carbon networks, which is usually artificially synthesized via the in situ homocoupling reaction of hexaethylbenzene on copper foil, is an emerging two-dimensional (2D) carbon allotrope. During preparation, well-defined GDY structures including nanowires, nanowalls, and nanotubes are obtained. Such materials with varying morphologies have been shown to possess promising electronic, chemical, magnetic, and mechanical properties, rendering them applicable in various domains including energy storage, catalysis, and field emission. In addition, replacing hexaethylbenzene with other aryne derivatives under similar synthesis conditions has resulted in the generation of various GDY derivatives. Thus, a series of GDY derivatives with specific structures and controllable sizes have been readily prepared in recent years. Aryne precursors typically contain polycyclic aromatic carbocycles, heteroarenes (e.g., N, B, S, P, Si, Ge, and Ga). The intrinsic GDY has also been doped with metal elements (e.g., Hg, Ag, and Au). Chemical synthetic strategies such as Glaser coupling, Glaser-Hay coupling, and Eglinton coupling are also described. The structural design of various precursors has been effectively tailored to the constitution of the local carbon framework of GDY-based materials, which has enabled the realization of the targeted performance in terms of the electronic conductivity, band gap, mobility, cavity size, and charge separation. For example, three-dimensional (3D) carbyne riched nanospheres formed by the extended coupling of spatially rigid-structured spirobifluorene have provided abundant storage spaces and convenient multi-directional transmission paths for metal ions. The use of hetero-doped GDY has enabled the effective optimization of the thermal stability and mechanical, electronic, and optical properties. Metal element-based GDY, referred to as "metalated" GDY, could serve as efficient bifunctional catalysts possessing favorable transport properties to facilitate the diffusion of small molecules. By extension, such materials can be used more broadly in electrochemical energy storage, electrocatalysis, optoelectronics, nonlinear optics, oil-water separation, and numerous other fields. In this review, we have summarized the design, synthesis, and structural characterization of various GDY derivatives through the recently demonstrated substitution of various aryne precursors for hexaethylbenzene, while examining the functional relationships between the desired optoelectronic properties of GDY derivatives and their defined nanostructures and morphologies. In addition, important prospective applications of GDY derivatives have been described. These observations may motivate the construction of novel polar and electron-rich GDY derivatives with unique properties that can address practical challenges encountered in various devices.![]()
Graphdiyne (GDY) bearing sp- and sp2-hybridized carbon networks, which is usually artificially synthesized via the in situ homocoupling reaction of hexaethylbenzene on copper foil, is an emerging two-dimensional (2D) carbon allotrope. During preparation, well-defined GDY structures including nanowires, nanowalls, and nanotubes are obtained. Such materials with varying morphologies have been shown to possess promising electronic, chemical, magnetic, and mechanical properties, rendering them applicable in various domains including energy storage, catalysis, and field emission. In addition, replacing hexaethylbenzene with other aryne derivatives under similar synthesis conditions has resulted in the generation of various GDY derivatives. Thus, a series of GDY derivatives with specific structures and controllable sizes have been readily prepared in recent years. Aryne precursors typically contain polycyclic aromatic carbocycles, heteroarenes (e.g., N, B, S, P, Si, Ge, and Ga). The intrinsic GDY has also been doped with metal elements (e.g., Hg, Ag, and Au). Chemical synthetic strategies such as Glaser coupling, Glaser-Hay coupling, and Eglinton coupling are also described. The structural design of various precursors has been effectively tailored to the constitution of the local carbon framework of GDY-based materials, which has enabled the realization of the targeted performance in terms of the electronic conductivity, band gap, mobility, cavity size, and charge separation. For example, three-dimensional (3D) carbyne riched nanospheres formed by the extended coupling of spatially rigid-structured spirobifluorene have provided abundant storage spaces and convenient multi-directional transmission paths for metal ions. The use of hetero-doped GDY has enabled the effective optimization of the thermal stability and mechanical, electronic, and optical properties. Metal element-based GDY, referred to as "metalated" GDY, could serve as efficient bifunctional catalysts possessing favorable transport properties to facilitate the diffusion of small molecules. By extension, such materials can be used more broadly in electrochemical energy storage, electrocatalysis, optoelectronics, nonlinear optics, oil-water separation, and numerous other fields. In this review, we have summarized the design, synthesis, and structural characterization of various GDY derivatives through the recently demonstrated substitution of various aryne precursors for hexaethylbenzene, while examining the functional relationships between the desired optoelectronic properties of GDY derivatives and their defined nanostructures and morphologies. In addition, important prospective applications of GDY derivatives have been described. These observations may motivate the construction of novel polar and electron-rich GDY derivatives with unique properties that can address practical challenges encountered in various devices.
2023, 39(1): 211004
doi: 10.3866/PKU.WHXB202110040
Abstract:
High-energy rechargeable lithium metal batteries (LMBs) have attracted significant attention recently. These batteries can be bulit using high areal-capacity (> 4 mAh∙cm−2) layered oxide cathodes and thin lithium (Li) metal anodes (< 50 μm in thickness), whose cycle performance are severely limited by the unregulated growth of Li particles having high surface areas, including dendrites and mossy Li. To improve the cycle performance of LMBs, many approaches have been developed in recent years to promote dendrite-free and dense Li electrodeposition, such as electrolyte engineering (for liquid cells), Li anode surface modification, three-dimensional current collector design, and using solid-state electrolytes. In addition to these heavily researched chemical-based approaches, applying external pressure to LMBs can also strongly impact the morphology of the electrochemically deposited Li particles due to the malleable nature of metallic Li and has been shown to improve the cycle performance. However, the relationship between the applied pressure, morphological evolution of the Li anode and the cycle performance has not been fully understood, especially in coin cells, which are widely used for LMB research. Here we report a custom-designed pressure applying/measurement device based on thin-film pressure sensors to realize real-time tracking of the pressure evolution in LMB coin cells. Our results show that moderate pressure is conducive to dense Li deposition and increases the cycle life, whereas excessive pressure causes Li inward-growth and the deformation of Li anode, which will impare the electrochemical performance of LMBs. Although these observations are made in coin cells, they could have important implications for pouch cells and solid-state batteries, both of which are commonly tested under pressure. The cycle performance of LMBs is significantly improved in both coin cells (under actual relevant conditions) and large pouch cells. A 5 Ah pouch-type LMB with a high energy density exceeding 380 Wh∙kg−1 could achieve stable cycling over 50 cycles under a stack pressure of ~1.2 MPa. It was also confirmed that the cell holders or clamps commonly used for coin cells can only exert a small amount of pressure, which is unlikely to exaggerate the cycle performance of the LMB coin cells. However, we do suggest that the electrochemical performance of LMBs should be reported along with the information on the applied pressure. This research practice will improve the consistency and quality of the reported data in the LMB research community and help unite the efforts to further improve the high energy density LMBs.![]()
High-energy rechargeable lithium metal batteries (LMBs) have attracted significant attention recently. These batteries can be bulit using high areal-capacity (> 4 mAh∙cm−2) layered oxide cathodes and thin lithium (Li) metal anodes (< 50 μm in thickness), whose cycle performance are severely limited by the unregulated growth of Li particles having high surface areas, including dendrites and mossy Li. To improve the cycle performance of LMBs, many approaches have been developed in recent years to promote dendrite-free and dense Li electrodeposition, such as electrolyte engineering (for liquid cells), Li anode surface modification, three-dimensional current collector design, and using solid-state electrolytes. In addition to these heavily researched chemical-based approaches, applying external pressure to LMBs can also strongly impact the morphology of the electrochemically deposited Li particles due to the malleable nature of metallic Li and has been shown to improve the cycle performance. However, the relationship between the applied pressure, morphological evolution of the Li anode and the cycle performance has not been fully understood, especially in coin cells, which are widely used for LMB research. Here we report a custom-designed pressure applying/measurement device based on thin-film pressure sensors to realize real-time tracking of the pressure evolution in LMB coin cells. Our results show that moderate pressure is conducive to dense Li deposition and increases the cycle life, whereas excessive pressure causes Li inward-growth and the deformation of Li anode, which will impare the electrochemical performance of LMBs. Although these observations are made in coin cells, they could have important implications for pouch cells and solid-state batteries, both of which are commonly tested under pressure. The cycle performance of LMBs is significantly improved in both coin cells (under actual relevant conditions) and large pouch cells. A 5 Ah pouch-type LMB with a high energy density exceeding 380 Wh∙kg−1 could achieve stable cycling over 50 cycles under a stack pressure of ~1.2 MPa. It was also confirmed that the cell holders or clamps commonly used for coin cells can only exert a small amount of pressure, which is unlikely to exaggerate the cycle performance of the LMB coin cells. However, we do suggest that the electrochemical performance of LMBs should be reported along with the information on the applied pressure. This research practice will improve the consistency and quality of the reported data in the LMB research community and help unite the efforts to further improve the high energy density LMBs.
2023, 39(1): 220603
doi: 10.3866/PKU.WHXB202206035
Abstract:
In this study, new lanthanide complexes were synthesized via the volatilization method in solution at room temperature. The general molecular formulas for the lanthanide complexes are as follows: [Ln(2, 4-DFBA)3(phen)]2 (Ln = Sm 1, Eu 2, and Er 3; 2, 4-DFBA = 2, 4-difluorobenzoate; and phen = 1, 10-phenanthroline), as well as [Ln(2-Cl-6-FBA)2(terpy)(NO3)(H2O)]2 (Ln = Tb 4 and Dy 5; 2-Cl-6-FBA = 2-chloro-6-fluorobenzoate; and terpy = 2, 2': 6'2''-tripyridine). Based on single-crystal X-ray analysis, the five complexes exhibited a monoclinic crystal structure belonging to the space group P21/n. Even though complexes 1, 2 (I), and 3 (II) share a general molecular formula, their coordination modes were different. For example, complexes 1 and 2 formed a muffin-like structure with nine coordinated atoms, while complex 3 formed a double hat triangular geometry with eight coordinated atoms. The two-dimensional (2D) polyhedral structures of complexes 1 and 2 were formed via weak π-π stacking interactions, whereas complex 3 exhibited a 2D faceted supramolecular structure through C―H∙∙∙F hydrogen bonds. Complexes 4 and 5 were isostructural, with the presence of nitrate ions in their structure. This occurred through the C―H∙∙∙F hydrogen bonds and π-π stacking of the molecules to form a faceted supramolecular crystal structure. A series of characterizations, such as elemental analysis, infrared and Raman spectroscopy, as well as powder X-ray diffraction, were performed on the five complexes. Thermogravimetry-derivative thermogravimetry-differential scanning calorimetry were performed between 299.25 and 1073.15 K to investigate the mechanism for the thermal decomposition of complexes 1–5. The analysis of the escaping gas stacking maps of the five complexes using thermogravimetric and 3D infrared coupling techniques further confirmed the correctness of the thermal decomposition mechanism of each complex. The results obtained revealed that similar structured complexes follow a similar thermal decomposition mechanism, and the end solid products for all complexes were their corresponding metal oxides. During the irradiation of the Xe lamp, the solid fluorescence of complexes 1, 2, 4, and 5 were measured. The characteristic transition peaks were located at 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 (1); 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 (2); 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 →7F3 (4); and 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 (5). The peaks observed indicated the characteristic transitions of Ln(III). The lanthanide complexes exhibited characteristic fluorescence due to this fact, which also explained their characteristic color. Furthermore, the fluorescence lifetimes of complexes 2 and 4 were measured, and their fluorescence decay curves indicated fluorescence lifetimes of 1.288 and 0.648 ms, respectively.![]()
In this study, new lanthanide complexes were synthesized via the volatilization method in solution at room temperature. The general molecular formulas for the lanthanide complexes are as follows: [Ln(2, 4-DFBA)3(phen)]2 (Ln = Sm 1, Eu 2, and Er 3; 2, 4-DFBA = 2, 4-difluorobenzoate; and phen = 1, 10-phenanthroline), as well as [Ln(2-Cl-6-FBA)2(terpy)(NO3)(H2O)]2 (Ln = Tb 4 and Dy 5; 2-Cl-6-FBA = 2-chloro-6-fluorobenzoate; and terpy = 2, 2': 6'2''-tripyridine). Based on single-crystal X-ray analysis, the five complexes exhibited a monoclinic crystal structure belonging to the space group P21/n. Even though complexes 1, 2 (I), and 3 (II) share a general molecular formula, their coordination modes were different. For example, complexes 1 and 2 formed a muffin-like structure with nine coordinated atoms, while complex 3 formed a double hat triangular geometry with eight coordinated atoms. The two-dimensional (2D) polyhedral structures of complexes 1 and 2 were formed via weak π-π stacking interactions, whereas complex 3 exhibited a 2D faceted supramolecular structure through C―H∙∙∙F hydrogen bonds. Complexes 4 and 5 were isostructural, with the presence of nitrate ions in their structure. This occurred through the C―H∙∙∙F hydrogen bonds and π-π stacking of the molecules to form a faceted supramolecular crystal structure. A series of characterizations, such as elemental analysis, infrared and Raman spectroscopy, as well as powder X-ray diffraction, were performed on the five complexes. Thermogravimetry-derivative thermogravimetry-differential scanning calorimetry were performed between 299.25 and 1073.15 K to investigate the mechanism for the thermal decomposition of complexes 1–5. The analysis of the escaping gas stacking maps of the five complexes using thermogravimetric and 3D infrared coupling techniques further confirmed the correctness of the thermal decomposition mechanism of each complex. The results obtained revealed that similar structured complexes follow a similar thermal decomposition mechanism, and the end solid products for all complexes were their corresponding metal oxides. During the irradiation of the Xe lamp, the solid fluorescence of complexes 1, 2, 4, and 5 were measured. The characteristic transition peaks were located at 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 (1); 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 (2); 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 →7F3 (4); and 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 (5). The peaks observed indicated the characteristic transitions of Ln(III). The lanthanide complexes exhibited characteristic fluorescence due to this fact, which also explained their characteristic color. Furthermore, the fluorescence lifetimes of complexes 2 and 4 were measured, and their fluorescence decay curves indicated fluorescence lifetimes of 1.288 and 0.648 ms, respectively.
2023, 39(1): 220700
doi: 10.3866/PKU.WHXB202207007
Abstract:
Understanding the origin of the active site activity in the oxygen evolution reaction (OER) electrocatalysts is key for developing efficient electrocatalysts. However, crucial challenges remain due to the complexity of catalyst structure-activity relationships. Herein, various Co-N-C configurations, including single atoms, diatoms, and clusters, were designed to establish structure-activity relationships by first-principles calculations. It was revealed that the Co-N4 exhibited the best reactivity due to the high coordination number of the metal center and moderate adsorption energies for all reaction intermediates. The diatom and cluster activities originate from the highly coordinated structures formed with reaction intermediates, which serve as coordination ligands. Furthermore, other factors influencing the OER activity based on the Co-N4 configuration are discussed. For example, the weak metal-metal interaction can further optimize the adsorption of oxygen-containing intermediates by tuning antibonding energy levels of Co-O. Subsequently, an ultralow overpotential of 0.23 V for the OER in CoNi-type4 systems can be obtained by extrapolation of the volcano plot derived from the established structure-adsorption-activity relationships. This work uncovers the underlying OER activity mechanisms of Co-N-C catalysts, which helps to further understanding of high-performance of M-N-C base catalysts and will aid in the future design of high-efficiency OER catalysts.![]()
Understanding the origin of the active site activity in the oxygen evolution reaction (OER) electrocatalysts is key for developing efficient electrocatalysts. However, crucial challenges remain due to the complexity of catalyst structure-activity relationships. Herein, various Co-N-C configurations, including single atoms, diatoms, and clusters, were designed to establish structure-activity relationships by first-principles calculations. It was revealed that the Co-N4 exhibited the best reactivity due to the high coordination number of the metal center and moderate adsorption energies for all reaction intermediates. The diatom and cluster activities originate from the highly coordinated structures formed with reaction intermediates, which serve as coordination ligands. Furthermore, other factors influencing the OER activity based on the Co-N4 configuration are discussed. For example, the weak metal-metal interaction can further optimize the adsorption of oxygen-containing intermediates by tuning antibonding energy levels of Co-O. Subsequently, an ultralow overpotential of 0.23 V for the OER in CoNi-type4 systems can be obtained by extrapolation of the volcano plot derived from the established structure-adsorption-activity relationships. This work uncovers the underlying OER activity mechanisms of Co-N-C catalysts, which helps to further understanding of high-performance of M-N-C base catalysts and will aid in the future design of high-efficiency OER catalysts.
2023, 39(1): 220900
doi: 10.3866/PKU.WHXB202209007
Abstract:
Luminescent materials have attracted considerable attention because of their extensive applications, for example, in lighting, display, and imaging. As one of the emerging luminescent materials, perovskites have been widely studied and reported. Among them, Pb-based perovskites have shown great promise as their photoluminescence quantum yield (PLQY) is almost 100%. However, the high chemical toxicity and low stability of Pb-based perovskites increase their production costs and limit their practical applications. Sn-based perovskites are also widely studied and their PLQY can reach approximately 90%; however, Sn2+ easily oxidizes to Sn4+ especially upon air exposure. When compared with Pb- and Sn-based perovskites, Sb-based perovskites have the advantages of low chemical toxicity and high thermal stability. Furthermore, the optical properties of Sb-based perovskites have been improved in recent years and are expected to surpass those of Pb- and Sn-based perovskites. Herein, we report a novel series of (4-HBA)SbX5∙H2O single crystals (where 4-HBA is short for 4-hydroxybenzylamine, and X is Cl or Br). High quality single crystals of (4-HBA)SbBr5∙H2O, (4-HBA)SbBr3Cl2∙H2O, and (4-HBA)SbCl5∙H2O with Sb5+ can be prepared via the solvothermal method. The abovementioned three materials belong to the P-1 space group. The halide and hydroxyl ions surrounded by Sb5+ ions in 4-hydroxybenzylamine formed distorted octahedral structures. Based on the results of steady-state fluorescence spectroscopy, excitation spectroscopy, transient fluorescence spectroscopy, fluorescence lifetime imaging, and density functional theory, it was found that the (4-HBA)SbBr5∙H2O single crystal has a direct band gap, whereas the single crystals of (4-HBA)SbBr3Cl2∙H2O and (4-HBA)SbCl5∙H2O have an indirect band gap. When the concentration of Cl− in (4-HBA)SbX5∙H2O increased, the band gap increased from 2.99 to 3.58 eV and the photoluminescence wavelength decreased from 618 to 595 nm. The obtained results also showed that the emission of the (4-HBA)SbX5∙H2O single crystal originated from the self-trapping exciton effect. With the introduction of Cl−, the size of the [SbX5O]2− octahedron decreased, the exciton shielding reduced, and the exciton absorption was enhanced. Additionally, after replacing Br− with Cl−, the radiation recombination process of the excited electrons from the Sb5+ ions surrounding the halide ions gradually replaced the electron recombination of the hydroxyl ions, which extended the fluorescence lifetime from 12 to 22 ns and improved the PLQY by a factor of approximately 40.![]()
Luminescent materials have attracted considerable attention because of their extensive applications, for example, in lighting, display, and imaging. As one of the emerging luminescent materials, perovskites have been widely studied and reported. Among them, Pb-based perovskites have shown great promise as their photoluminescence quantum yield (PLQY) is almost 100%. However, the high chemical toxicity and low stability of Pb-based perovskites increase their production costs and limit their practical applications. Sn-based perovskites are also widely studied and their PLQY can reach approximately 90%; however, Sn2+ easily oxidizes to Sn4+ especially upon air exposure. When compared with Pb- and Sn-based perovskites, Sb-based perovskites have the advantages of low chemical toxicity and high thermal stability. Furthermore, the optical properties of Sb-based perovskites have been improved in recent years and are expected to surpass those of Pb- and Sn-based perovskites. Herein, we report a novel series of (4-HBA)SbX5∙H2O single crystals (where 4-HBA is short for 4-hydroxybenzylamine, and X is Cl or Br). High quality single crystals of (4-HBA)SbBr5∙H2O, (4-HBA)SbBr3Cl2∙H2O, and (4-HBA)SbCl5∙H2O with Sb5+ can be prepared via the solvothermal method. The abovementioned three materials belong to the P-1 space group. The halide and hydroxyl ions surrounded by Sb5+ ions in 4-hydroxybenzylamine formed distorted octahedral structures. Based on the results of steady-state fluorescence spectroscopy, excitation spectroscopy, transient fluorescence spectroscopy, fluorescence lifetime imaging, and density functional theory, it was found that the (4-HBA)SbBr5∙H2O single crystal has a direct band gap, whereas the single crystals of (4-HBA)SbBr3Cl2∙H2O and (4-HBA)SbCl5∙H2O have an indirect band gap. When the concentration of Cl− in (4-HBA)SbX5∙H2O increased, the band gap increased from 2.99 to 3.58 eV and the photoluminescence wavelength decreased from 618 to 595 nm. The obtained results also showed that the emission of the (4-HBA)SbX5∙H2O single crystal originated from the self-trapping exciton effect. With the introduction of Cl−, the size of the [SbX5O]2− octahedron decreased, the exciton shielding reduced, and the exciton absorption was enhanced. Additionally, after replacing Br− with Cl−, the radiation recombination process of the excited electrons from the Sb5+ ions surrounding the halide ions gradually replaced the electron recombination of the hydroxyl ions, which extended the fluorescence lifetime from 12 to 22 ns and improved the PLQY by a factor of approximately 40.
2023, 39(1): 211202
doi: 10.3866/PKU.WHXB202112029
Abstract:
This paper, based on the 292nd "Shuang-Qing Forum, " introduces the scientific concept of "green carbon science" and summarizes the current research progress, challenges, and future opportunities for carbon-neutral science and technology in China. Furthermore, there is scientific discussion on the path to realizing this, key scientific problems, and future research focus on carbon-neutral science and technology. It may provide a reference from which the National Science Foundation of China (NSFC) can formulate an action plan and funding scheme for basic research on carbon neutrality as a next step.
This paper, based on the 292nd "Shuang-Qing Forum, " introduces the scientific concept of "green carbon science" and summarizes the current research progress, challenges, and future opportunities for carbon-neutral science and technology in China. Furthermore, there is scientific discussion on the path to realizing this, key scientific problems, and future research focus on carbon-neutral science and technology. It may provide a reference from which the National Science Foundation of China (NSFC) can formulate an action plan and funding scheme for basic research on carbon neutrality as a next step.
