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2025 Volume 41 Issue 3
2025, 41(3): 230805
doi: 10.3866/PKU.WHXB202308052
Abstract:
Photo-/electrocatalytic reduction of carbon dioxide (CO2) to carbon-based fuel molecules driven by renewable energy is an attractive strategy for resource regeneration and energy storage, especially for achieving carbon peak and carbon-neutral goals. However, the high thermodynamic stability and chemical inertness of CO2 molecules make the conversion efficiency and selectivity of reduction products very low, which further hinders its application. In addition, different CO2 reduction products have similar reduction potential and usually face severe hydrogen evolution competition under aqueous system conditions, which makes the selectivity of specific reduction products unable to be effectively controlled. To overcome these bottlenecks, researchers have been working for many years to develop efficient photo/electrocatalysts to enhance the activity and product selectivity of CO2 reduction. Thanks to the ultrathin thickness and large specific surface area, ultrathin two-dimensional materials possess highly active sites with high density and high uniformity, which can effectively regulate the key thermodynamic and kinetic factors of CO2 photo-/electroreduction reactions. As a typical two-dimensional material, the defective ultrathin two-dimensional materials can provide a large number of electron-rich catalytic sites to efficiently adsorb and highly activate CO2 molecules, which can effectively reduce the reaction barrier, thus accelerating CO2 reduction and enhancing product selectivity. Moreover, the local atomic and electronic structure of the defects can effectively stabilize the intermediate of CO2 reduction reactions, thus further optimizing the kinetics of CO2 reduction reactions. Furthermore, the surface defects are beneficial to the mass and electron transfer in the catalytic process, thus further improving the catalytic activity of the catalysts. In this review, we overview the latest research progress in CO2 photo-/electrocatalytic reduction using defective ultrathin two-dimensional materials, including the controllable synthesis and fine structure characterization of defective ultrathin two-dimensional materials; the modulation effect of defect structure on the local atomic and electronic structure; the advantages of defective ultrathin two-dimensional materials for CO2 reduction. We also discuss the challenges and opportunities of defective ultrathin two-dimensional materials for future development of CO2 photo-/electrocatalytic reduction. It is expected that this review will provide a guide for designing highly efficient CO2 reduction systems. ![]()
Photo-/electrocatalytic reduction of carbon dioxide (CO2) to carbon-based fuel molecules driven by renewable energy is an attractive strategy for resource regeneration and energy storage, especially for achieving carbon peak and carbon-neutral goals. However, the high thermodynamic stability and chemical inertness of CO2 molecules make the conversion efficiency and selectivity of reduction products very low, which further hinders its application. In addition, different CO2 reduction products have similar reduction potential and usually face severe hydrogen evolution competition under aqueous system conditions, which makes the selectivity of specific reduction products unable to be effectively controlled. To overcome these bottlenecks, researchers have been working for many years to develop efficient photo/electrocatalysts to enhance the activity and product selectivity of CO2 reduction. Thanks to the ultrathin thickness and large specific surface area, ultrathin two-dimensional materials possess highly active sites with high density and high uniformity, which can effectively regulate the key thermodynamic and kinetic factors of CO2 photo-/electroreduction reactions. As a typical two-dimensional material, the defective ultrathin two-dimensional materials can provide a large number of electron-rich catalytic sites to efficiently adsorb and highly activate CO2 molecules, which can effectively reduce the reaction barrier, thus accelerating CO2 reduction and enhancing product selectivity. Moreover, the local atomic and electronic structure of the defects can effectively stabilize the intermediate of CO2 reduction reactions, thus further optimizing the kinetics of CO2 reduction reactions. Furthermore, the surface defects are beneficial to the mass and electron transfer in the catalytic process, thus further improving the catalytic activity of the catalysts. In this review, we overview the latest research progress in CO2 photo-/electrocatalytic reduction using defective ultrathin two-dimensional materials, including the controllable synthesis and fine structure characterization of defective ultrathin two-dimensional materials; the modulation effect of defect structure on the local atomic and electronic structure; the advantages of defective ultrathin two-dimensional materials for CO2 reduction. We also discuss the challenges and opportunities of defective ultrathin two-dimensional materials for future development of CO2 photo-/electrocatalytic reduction. It is expected that this review will provide a guide for designing highly efficient CO2 reduction systems.
2025, 41(3): 231100
doi: 10.3866/PKU.WHXB202311005
Abstract:
The rapid advancement of scientific technology leads to a growing need for energy storage equipment in modern society. Lithium-ion batteries (LIBs) are extensively utilized in portable electronics, handy electric tools, medical electronics, and other industries due to their exceptional features such as high energy density, high power density, long lifespan, low self-discharge rate, wide operating temperature range and environmentally-friendly nature. However, the recent rapid development of mobile electronics and electric vehicles requires energy storage devices with even higher energy and power densities. To achieve this goal, it is essential to develop advanced electrode materials featuring high capacity, high rate capability, and long cycle life. The design of high-performance anode materials is an important aspect of constructing the ideal LIB devices. Besides the commercialized graphite, many metal oxides can also act as anode in the LIBs. In detail, the oxides that served as LIB anodes can be classified into intercalation-type, conversion-type and conversion-alloying-type anodes based on their Li+ storage mechanisms. Due to their robust metal-oxygen bonds, intercalation-type anodes, such as d0 metal oxides, exhibit stable cycling performance and high-rate capability. However, the limited valence change of intercalation-type metal ions often results in low theoretical capacities. In comparison, conversion-alloying type anodes, exemplified by p-block metal oxides, offer high theoretical capacities and low Li+ extraction potential, making them suitable for high-energy-density LIBs. Nevertheless, the Li+ intercalation process induces severe phase agglomeration and volume expansion, leading to rapid capacity decay and poor rate capability. Therefore, these drawbacks severely limit the wild utilization s of metal oxide anodes in commercialized LIBs. Recently, substantial efforts have been made to design novel bimetallic oxide anodes. Among these anodes, the incorporation of intercalation-type or conversion-type motifs into conversion-alloying-type metal oxides enables the creation of bimetallic oxide anodes with optimized electronic and ionic conductivities. This approach has the potential to combine the advantages of high capacity, high-rate capability, and long cycle life in a single system. To uncover the underlying Li+ storage mechanisms, this review analyzes the bond situations and electronic structures of various metal oxides. Additionally, it introduces a new graphic representation of the Li+-ion charge/discharge process using density-of-states (DOS) graphs. The multi-step lithium storage mechanisms in bimetallic oxide anodes are also discussed. Drawing on recent progress in the field, this review provides fundamental academic insights and practical perspectives for the development of high-capacity, high-rate, and robust bimetallic compound anodes. ![]()
The rapid advancement of scientific technology leads to a growing need for energy storage equipment in modern society. Lithium-ion batteries (LIBs) are extensively utilized in portable electronics, handy electric tools, medical electronics, and other industries due to their exceptional features such as high energy density, high power density, long lifespan, low self-discharge rate, wide operating temperature range and environmentally-friendly nature. However, the recent rapid development of mobile electronics and electric vehicles requires energy storage devices with even higher energy and power densities. To achieve this goal, it is essential to develop advanced electrode materials featuring high capacity, high rate capability, and long cycle life. The design of high-performance anode materials is an important aspect of constructing the ideal LIB devices. Besides the commercialized graphite, many metal oxides can also act as anode in the LIBs. In detail, the oxides that served as LIB anodes can be classified into intercalation-type, conversion-type and conversion-alloying-type anodes based on their Li+ storage mechanisms. Due to their robust metal-oxygen bonds, intercalation-type anodes, such as d0 metal oxides, exhibit stable cycling performance and high-rate capability. However, the limited valence change of intercalation-type metal ions often results in low theoretical capacities. In comparison, conversion-alloying type anodes, exemplified by p-block metal oxides, offer high theoretical capacities and low Li+ extraction potential, making them suitable for high-energy-density LIBs. Nevertheless, the Li+ intercalation process induces severe phase agglomeration and volume expansion, leading to rapid capacity decay and poor rate capability. Therefore, these drawbacks severely limit the wild utilization s of metal oxide anodes in commercialized LIBs. Recently, substantial efforts have been made to design novel bimetallic oxide anodes. Among these anodes, the incorporation of intercalation-type or conversion-type motifs into conversion-alloying-type metal oxides enables the creation of bimetallic oxide anodes with optimized electronic and ionic conductivities. This approach has the potential to combine the advantages of high capacity, high-rate capability, and long cycle life in a single system. To uncover the underlying Li+ storage mechanisms, this review analyzes the bond situations and electronic structures of various metal oxides. Additionally, it introduces a new graphic representation of the Li+-ion charge/discharge process using density-of-states (DOS) graphs. The multi-step lithium storage mechanisms in bimetallic oxide anodes are also discussed. Drawing on recent progress in the field, this review provides fundamental academic insights and practical perspectives for the development of high-capacity, high-rate, and robust bimetallic compound anodes.
2025, 41(3): 231101
doi: 10.3866/PKU.WHXB202311015
Abstract:
Sodium ion batteries (SIBs), characterized by high energy density, prolonged cycle life, and cost-effectiveness, have garnered substantial attention as scalable energy storage devices. However, the primary challenge facing SIBs is the identification of suitable electrode materials capable of accommodating sodium ions reversibly and sustainably. To transition SIBs from the experimental stage to practical applications, the identification of electrode materials exhibiting satisfactory electrochemical performance is imperative. Iron (Fe), as a widely utilized metal element, exhibits considerable potential for application as anode materials in SIBs due to its abundance, cost-effectiveness, and high specific capacity. Nonetheless, Fe-based electrode materials suffer from low conductivity and significant volume changes during charge and discharge processes, leading to poor rate performance and cyclic stability, thereby restricting their widespread application in SIBs. Various modification strategies, such as nanosizing electrode materials, heteroatom doping, heterostructure construction, and combination with fast ion conductors, have been reported to address these challenges. Importantly, engineering Fe-based electrode materials with heterogeneous structures, integrating two or more components via van der Waals forces or chemical bonds, is crucial for creating intricate heterogeneous interfaces. These interfaces generate self-built electric fields that expedite ion transport, enhance reaction kinetics, and mitigate structural damage due to volume changes during cycling, thereby significantly improving the overall electrochemical performance of Fe-based materials in SIBs. Given the rapid advancements in the utilization of Fe-based materials in SIBs, a comprehensive review is necessary to not only summarize recent progress but also provide insight and guidance on their application in SIBs. This review offers a detailed overview of the research progress on Fe-based anode materials with heterostructure in SIBs. Emphasis is placed on synthesis methods, characterization techniques, and energy storage mechanisms of heterostructure Fe-based electrode materials. Additionally, the sodium ion storage characteristics, modification strategies, and strengthening mechanisms of Fe-based materials, including Fe-based oxides, sulfides, phosphides, selenides, as well as dual-anion Fe-based anode materials, are summarized. Finally, the remaining challenges and future development prospects of Fe-based heterostructure anode materials are discussed, aiming to promote the rapid development and practical application of these materials for SIBs. ![]()
Sodium ion batteries (SIBs), characterized by high energy density, prolonged cycle life, and cost-effectiveness, have garnered substantial attention as scalable energy storage devices. However, the primary challenge facing SIBs is the identification of suitable electrode materials capable of accommodating sodium ions reversibly and sustainably. To transition SIBs from the experimental stage to practical applications, the identification of electrode materials exhibiting satisfactory electrochemical performance is imperative. Iron (Fe), as a widely utilized metal element, exhibits considerable potential for application as anode materials in SIBs due to its abundance, cost-effectiveness, and high specific capacity. Nonetheless, Fe-based electrode materials suffer from low conductivity and significant volume changes during charge and discharge processes, leading to poor rate performance and cyclic stability, thereby restricting their widespread application in SIBs. Various modification strategies, such as nanosizing electrode materials, heteroatom doping, heterostructure construction, and combination with fast ion conductors, have been reported to address these challenges. Importantly, engineering Fe-based electrode materials with heterogeneous structures, integrating two or more components via van der Waals forces or chemical bonds, is crucial for creating intricate heterogeneous interfaces. These interfaces generate self-built electric fields that expedite ion transport, enhance reaction kinetics, and mitigate structural damage due to volume changes during cycling, thereby significantly improving the overall electrochemical performance of Fe-based materials in SIBs. Given the rapid advancements in the utilization of Fe-based materials in SIBs, a comprehensive review is necessary to not only summarize recent progress but also provide insight and guidance on their application in SIBs. This review offers a detailed overview of the research progress on Fe-based anode materials with heterostructure in SIBs. Emphasis is placed on synthesis methods, characterization techniques, and energy storage mechanisms of heterostructure Fe-based electrode materials. Additionally, the sodium ion storage characteristics, modification strategies, and strengthening mechanisms of Fe-based materials, including Fe-based oxides, sulfides, phosphides, selenides, as well as dual-anion Fe-based anode materials, are summarized. Finally, the remaining challenges and future development prospects of Fe-based heterostructure anode materials are discussed, aiming to promote the rapid development and practical application of these materials for SIBs.
2025, 41(3): 231000
doi: 10.3866/PKU.WHXB202310004
Abstract:
In recent years, there has been a growing interest in self-powered photodetectors, which can detect light without needing an external power supply. This unique feature makes them highly attractive for addressing the current energy shortage and the future demand for miniaturized devices. Among various design approaches for self-powered photodetectors, the use of low-dimensional materials holds great promise. Low-dimensional nanomaterials offer several advantages for self-powered photodetectors. They can be assembled into large area ordered structures such as ultra-thin layers, nanowire arrays, and quantum dot superlattices. Additionally, their atomic-level thickness provides a large specific surface area and facilitates integration with other materials. By combining different low-dimensional materials with complementary enhancements in bandgap, carrier transport rate, and light collection efficiency, the performance of self-powered photodetectors can be significantly improved. These devices can be scaled down to micro-nano levels while taking advantage of the adjustable bandgap, wide spectral response, high carrier migration rate, and high light absorption efficiency offered by low-dimensional materials. This article introduces the performance metrics of photodetectors, including photoresponsivity, noise equivalent power, detectivity, and response time. It then discusses the latest advancements in self-powered photodetectors based on 0D, 1D, and 2D materials. In the section on 0D material self-powered photodetectors, the device structure design using 0D materials as heterojunction components and doping materials is presented, highlighting their respective advantages. The section on 1D material self-powered photodetectors summarizes three main device structure types: planar, vertical, and core-shell, along with their individual advantages. The focus is placed on the content related to 2D material self-powered photodetectors. Graphene, transition metal dichalcogenides (TMDs), and black phosphorus are the most widely used 2D materials, and their preparation methods and the latest advancements in self-powered photodetectors are discussed. The controllable diversity in electrical properties resulting from interlayer interactions in two-dimensional materials offers great potential for new principles and multifunctional electronic devices. Finally, the article summarizes and discusses the key challenges and future development directions for self-powered photodetectors based on low-dimensional materials. In summary, the utilization of low-dimensional materials in self-powered photodetectors presents a promising direction for the development of advanced optoelectronic devices. By utilizing the unique properties of these materials, such as their atomic-level thickness, large specific surface area, and controllable electrical properties, significant advancements can be made in the field of self-powered photodetectors. The challenges associated with these materials, such as their complex fabrication processes, will need to be addressed to fully realize their potential in practical applications. ![]()
In recent years, there has been a growing interest in self-powered photodetectors, which can detect light without needing an external power supply. This unique feature makes them highly attractive for addressing the current energy shortage and the future demand for miniaturized devices. Among various design approaches for self-powered photodetectors, the use of low-dimensional materials holds great promise. Low-dimensional nanomaterials offer several advantages for self-powered photodetectors. They can be assembled into large area ordered structures such as ultra-thin layers, nanowire arrays, and quantum dot superlattices. Additionally, their atomic-level thickness provides a large specific surface area and facilitates integration with other materials. By combining different low-dimensional materials with complementary enhancements in bandgap, carrier transport rate, and light collection efficiency, the performance of self-powered photodetectors can be significantly improved. These devices can be scaled down to micro-nano levels while taking advantage of the adjustable bandgap, wide spectral response, high carrier migration rate, and high light absorption efficiency offered by low-dimensional materials. This article introduces the performance metrics of photodetectors, including photoresponsivity, noise equivalent power, detectivity, and response time. It then discusses the latest advancements in self-powered photodetectors based on 0D, 1D, and 2D materials. In the section on 0D material self-powered photodetectors, the device structure design using 0D materials as heterojunction components and doping materials is presented, highlighting their respective advantages. The section on 1D material self-powered photodetectors summarizes three main device structure types: planar, vertical, and core-shell, along with their individual advantages. The focus is placed on the content related to 2D material self-powered photodetectors. Graphene, transition metal dichalcogenides (TMDs), and black phosphorus are the most widely used 2D materials, and their preparation methods and the latest advancements in self-powered photodetectors are discussed. The controllable diversity in electrical properties resulting from interlayer interactions in two-dimensional materials offers great potential for new principles and multifunctional electronic devices. Finally, the article summarizes and discusses the key challenges and future development directions for self-powered photodetectors based on low-dimensional materials. In summary, the utilization of low-dimensional materials in self-powered photodetectors presents a promising direction for the development of advanced optoelectronic devices. By utilizing the unique properties of these materials, such as their atomic-level thickness, large specific surface area, and controllable electrical properties, significant advancements can be made in the field of self-powered photodetectors. The challenges associated with these materials, such as their complex fabrication processes, will need to be addressed to fully realize their potential in practical applications.
2025, 41(3): 231103
doi: 10.3866/PKU.WHXB202311032
Abstract:
With the growth of batteries, electroplating, and mining industries, heavy metal ions such as cadmium (Cd2+) are being discharged on a massive scale, thus posing a severe threat to the environment. Conventional techniques for removing Cd2+ from wastewater with low concentrations still suffer from slow kinetics and secondary pollution. A carbon-based capacitive deionization (CDI) system is highly desired but encounters a severe co-ion expulsion effect. Herein, we developed CDI systems based on surface charge-modulated porous carbon and an asymmetric configuration. This was achieved by first preparing porous carbons through facile microwave pyrolysis of lotus leaf followed by KOH activation. The morphology, pore structure, heteroatom content, surface charge, and electrochemical behavior of porous carbons were investigated by adjusting the mass ratio of KOH to carbon. The lotus leaf-derived carbons show a morphology of nanosheet-like thin carbon (NSTC), with their specific surface areas increasing with the amount of KOH used for activation. In contrast, the heteroatom (i.e., nitrogen and oxygen) contents decrease with the increase in the mass ratio of KOH to carbon, resulting in a more positive surface charge. Notably, the NSTC with a mass ratio of 3 for KOH/carbon (NSTC-3) displays an ultrahigh specific surface area of 3705.0 m2∙g-1, and a specific capacitance of 92.5 F∙g-1 at a current density of 0.5 A∙g-1 when coupled with a commercial activated carbon in an asymmetric YP-50F//NSTC-3 supercapacitor. Consequently, the CDI cell equipped with a YP-50F as the anode and a NSTC-3 as the cathode exhibits a high specific adsorption capacity of 88.6 mgCd·gcathode-1 at 1.2 V in a 100 mg∙L-1 Cd2+ solution, which is about 36.3% higher than that of the symmetrical configuration NSTC-3//NSTC-3. Furthermore, 71% of the initial removal capacity of the YP-50F//NSTC-3 system is retained after 7 cycles of charging and discharging. Characterizations of the cathode after the adsorption process indicate that the Cd2+ is captured by both electrical-double-layer and pseudocapacitive mechanisms. Additionally, CdCO3 precipitate is also responsible for Cd2+ removal, which might be ascribed to the reaction of dissolved CO2 in aqueous media with Cd2+ under the electrified action. The high removal performance and excellent cycling stability are attributed to the tunability of the surface charge properties and the asymmetric configuration, which minimizes the co-ion expulsion and modulates potential distribution. This study provides a novel avenue to design biochar-based configurations for electrified water treatment. ![]()
With the growth of batteries, electroplating, and mining industries, heavy metal ions such as cadmium (Cd2+) are being discharged on a massive scale, thus posing a severe threat to the environment. Conventional techniques for removing Cd2+ from wastewater with low concentrations still suffer from slow kinetics and secondary pollution. A carbon-based capacitive deionization (CDI) system is highly desired but encounters a severe co-ion expulsion effect. Herein, we developed CDI systems based on surface charge-modulated porous carbon and an asymmetric configuration. This was achieved by first preparing porous carbons through facile microwave pyrolysis of lotus leaf followed by KOH activation. The morphology, pore structure, heteroatom content, surface charge, and electrochemical behavior of porous carbons were investigated by adjusting the mass ratio of KOH to carbon. The lotus leaf-derived carbons show a morphology of nanosheet-like thin carbon (NSTC), with their specific surface areas increasing with the amount of KOH used for activation. In contrast, the heteroatom (i.e., nitrogen and oxygen) contents decrease with the increase in the mass ratio of KOH to carbon, resulting in a more positive surface charge. Notably, the NSTC with a mass ratio of 3 for KOH/carbon (NSTC-3) displays an ultrahigh specific surface area of 3705.0 m2∙g-1, and a specific capacitance of 92.5 F∙g-1 at a current density of 0.5 A∙g-1 when coupled with a commercial activated carbon in an asymmetric YP-50F//NSTC-3 supercapacitor. Consequently, the CDI cell equipped with a YP-50F as the anode and a NSTC-3 as the cathode exhibits a high specific adsorption capacity of 88.6 mgCd·gcathode-1 at 1.2 V in a 100 mg∙L-1 Cd2+ solution, which is about 36.3% higher than that of the symmetrical configuration NSTC-3//NSTC-3. Furthermore, 71% of the initial removal capacity of the YP-50F//NSTC-3 system is retained after 7 cycles of charging and discharging. Characterizations of the cathode after the adsorption process indicate that the Cd2+ is captured by both electrical-double-layer and pseudocapacitive mechanisms. Additionally, CdCO3 precipitate is also responsible for Cd2+ removal, which might be ascribed to the reaction of dissolved CO2 in aqueous media with Cd2+ under the electrified action. The high removal performance and excellent cycling stability are attributed to the tunability of the surface charge properties and the asymmetric configuration, which minimizes the co-ion expulsion and modulates potential distribution. This study provides a novel avenue to design biochar-based configurations for electrified water treatment.
2025, 41(3): 240401
doi: 10.3866/PKU.WHXB202404012
Abstract:
Copper-based electrocatalysts have great potential to produce high-value products in CO2 reduction reaction (CO2RR), offering a promising way to achieve negative carbon emissions. Additionally, achieving ampere-level currents is crucial for realizing the industrialization of multi-carbon (C2+) products. However, the C2+ selectivity at industrial current densities remains unsatisfactory due to complex electron transport processes and inevitable side reactions. Herein, we developed a carbon-modification strategy aimed at optimizing the local environment and regulating the adsorption of intermediates at Cu active sites. Our findings demonstrated the effectiveness of Cu-Cx catalysts (where 'x' denoted the atomic percentage of C in the catalysts) in facilitating CO2RR for producing C2+ products. Especially, over Cu-C6%, the current density could reach to 1.25 A∙cm-2 at -0.72 V vs. RHE (versus reversible hydrogen electrode) in a flow cell, and the Faradaic efficiency (FE) of C2H4 and C2+ products could reach to 54.4% and 80.2%, respectively. In situ spectral analysis and density functional theory (DFT) calculations showed that the presence of C regulated the adsorption of *CO on Cu surface, reduced the energy barrier of C—C coupling, thus promoting the production of C2+ products. ![]()
Copper-based electrocatalysts have great potential to produce high-value products in CO2 reduction reaction (CO2RR), offering a promising way to achieve negative carbon emissions. Additionally, achieving ampere-level currents is crucial for realizing the industrialization of multi-carbon (C2+) products. However, the C2+ selectivity at industrial current densities remains unsatisfactory due to complex electron transport processes and inevitable side reactions. Herein, we developed a carbon-modification strategy aimed at optimizing the local environment and regulating the adsorption of intermediates at Cu active sites. Our findings demonstrated the effectiveness of Cu-Cx catalysts (where 'x' denoted the atomic percentage of C in the catalysts) in facilitating CO2RR for producing C2+ products. Especially, over Cu-C6%, the current density could reach to 1.25 A∙cm-2 at -0.72 V vs. RHE (versus reversible hydrogen electrode) in a flow cell, and the Faradaic efficiency (FE) of C2H4 and C2+ products could reach to 54.4% and 80.2%, respectively. In situ spectral analysis and density functional theory (DFT) calculations showed that the presence of C regulated the adsorption of *CO on Cu surface, reduced the energy barrier of C—C coupling, thus promoting the production of C2+ products.
2025, 41(3): 240402
doi: 10.3866/PKU.WHXB202404024
Abstract:
The rapid advancement in the integration density of electronic components has led to a pressing need for effective thermal management solutions. Among the promising materials in this regard, graphene stands out due to its exceptional thermal conductivity properties. Currently, the production of ultra-high thermally conductive thick graphene sheets primarily involves the reduction of graphene oxide. However, despite significant progress, the impact of defects on thermal properties remains inadequately understood, limiting the achievement of thermal conductivity exceeding 1500 W·m-1·K-1. During the preparation process of reduced graphene oxide-based graphene sheets, hole structures are inevitably formed, reducing the overall density and thus decreasing thermal conductivity. However, the influencing factors on thermal diffusivity, one of the determining factors of thermal conductivity, have not been reported. Thus, we defined the intrinsic thermal diffusivity specific to materials with internal holes and further investigated the correlation between the intrinsic thermal diffusivity of thick graphene sheets and microstructure through various electron microscopy characterization, thermal diffusivity measurements, and simulations. We aim to elucidate the factors and mechanisms affecting the thermal diffusivity and hence thermal conductivity. Our research reveals subtle insights, particularly regarding the impact of holes of different sizes and quantities on thermal diffusivity. Notably, our simulation results show that a real dense-small-holes structure in graphene sheets can reduce thermal diffusivity by 39.4%, more than twice the reduction caused by a single-large-hole structure (16.1%). Statistical conclusions obtained through three-dimensional reconstruction also perfectly match these computational results. We emphasize that the presence of dense-small-holes structures disrupt the original high-speed heat transfer paths more severely, while the effect of single-large-hole structures are relatively weaker, primarily reducing overall density and thus thermal conductivity. Additionally, we found that the out-of-plane crystallinity has a significant impact on thermal diffusivity, further enhancing our understanding of microstructural factors affecting thermal diffusivity. By elucidating these mechanisms, our findings make significant contributions to the technological advancement of producing ultra-high thermally conductive thick graphene sheets. A deeper understanding of the interaction between microstructure and thermal performance brings hope for the development of next-generation electronic device thermal management solutions. Through continued research in this field, we anticipate further improvements in the performance and efficiency of graphene thermal management systems, ultimately driving innovation in electronic device design and manufacturing. ![]()
The rapid advancement in the integration density of electronic components has led to a pressing need for effective thermal management solutions. Among the promising materials in this regard, graphene stands out due to its exceptional thermal conductivity properties. Currently, the production of ultra-high thermally conductive thick graphene sheets primarily involves the reduction of graphene oxide. However, despite significant progress, the impact of defects on thermal properties remains inadequately understood, limiting the achievement of thermal conductivity exceeding 1500 W·m-1·K-1. During the preparation process of reduced graphene oxide-based graphene sheets, hole structures are inevitably formed, reducing the overall density and thus decreasing thermal conductivity. However, the influencing factors on thermal diffusivity, one of the determining factors of thermal conductivity, have not been reported. Thus, we defined the intrinsic thermal diffusivity specific to materials with internal holes and further investigated the correlation between the intrinsic thermal diffusivity of thick graphene sheets and microstructure through various electron microscopy characterization, thermal diffusivity measurements, and simulations. We aim to elucidate the factors and mechanisms affecting the thermal diffusivity and hence thermal conductivity. Our research reveals subtle insights, particularly regarding the impact of holes of different sizes and quantities on thermal diffusivity. Notably, our simulation results show that a real dense-small-holes structure in graphene sheets can reduce thermal diffusivity by 39.4%, more than twice the reduction caused by a single-large-hole structure (16.1%). Statistical conclusions obtained through three-dimensional reconstruction also perfectly match these computational results. We emphasize that the presence of dense-small-holes structures disrupt the original high-speed heat transfer paths more severely, while the effect of single-large-hole structures are relatively weaker, primarily reducing overall density and thus thermal conductivity. Additionally, we found that the out-of-plane crystallinity has a significant impact on thermal diffusivity, further enhancing our understanding of microstructural factors affecting thermal diffusivity. By elucidating these mechanisms, our findings make significant contributions to the technological advancement of producing ultra-high thermally conductive thick graphene sheets. A deeper understanding of the interaction between microstructure and thermal performance brings hope for the development of next-generation electronic device thermal management solutions. Through continued research in this field, we anticipate further improvements in the performance and efficiency of graphene thermal management systems, ultimately driving innovation in electronic device design and manufacturing.
2025, 41(3): 240500
doi: 10.3866/PKU.WHXB202405002
Abstract:
Water scarcity has become a prominent global challenge in the twenty-first century, prompting the rapid advancement of desalination technology. Capacitive deionization (CDI) stands out as a cost-effective solution for sustainable water purification. The electrode material plays a pivotal role in capacitive deionization, impacting the salt ion removal and charge storage capacity. Carbon-based materials, characterized by high surface area and electrical conductivity, are ideal materials for capacitive deionization. However, their effectiveness in salt ion removal is hindered by unclear pore structures and poor wettability, limiting salt ion transport and storage. In this study, nitrogen-doped hierarchical porous carbon is successfully synthesized through the carbonization of MOF-5 and melamine mixtures, wherein melamine serves as both a nitrogen source and porogenic agent. Through optimization of carbonization temperature, the resulting MOF-5-derived nanoporous carbon (referred to as NPC-800) retains the cubic morphology of MOF-5, possesses a large surface area (754.34 m2∙g-1), high nitrogen content (10.13%), and favorable wettability. Electrochemical analysis reveals that the NPC-800 electrode demonstrates specific capacities of 91.8, 76.1, 66.3, 51.0, 28.0, and 15.2 mAh∙g-1 at current densities of 0.2, 0.5, 1.0, 2.0, 4.0, and 6.0 A∙g-1, respectively, outperforming NPC-700 (26.3, 19.7, 13.1, 6.90, 2.30, and 1.30 mAh∙g-1) and NPC-900 (46.0, 37.8, 30.4, 21.3, 11.7, and 7.50 mAh∙g-1). The superior electrochemical performance of NPC-800 can be attributed to its maximal specific surface area, abundant pore structure, and optimal wettability, facilitating increased active sites for salt ion adsorption and diffusion. Moreover, NPC-800 exhibits low intrinsic resistance, rapid ion transfer kinetics, and exceptional cycling stability (50000 cycles) with 100% capacity retention at 5 A∙g-1. Further investigation into the CDI performance of NPC electrodes under different applied voltages (0.8, 1.0, and 1.2 V) and initial NaCl solution concentrations (100, 300, and 500 mg∙L-1) demonstrates the superior adsorption capacity of the NPC-800 electrode compared to the other two electrodes. Specifically, at 1.2 V in a 500 mg∙L-1 salt solution, NPC-800 exhibits a faster salt adsorption rate (2.8 mg∙g-1∙min-1) and higher salt adsorption capacity (24.17 mg∙g-1) compared to NPC-700 and NPC-900. Consequently, the melamine-assisted synthesis of N-doped porous carbon material holds promise as an optimal choice for capacitive deionization. ![]()
Water scarcity has become a prominent global challenge in the twenty-first century, prompting the rapid advancement of desalination technology. Capacitive deionization (CDI) stands out as a cost-effective solution for sustainable water purification. The electrode material plays a pivotal role in capacitive deionization, impacting the salt ion removal and charge storage capacity. Carbon-based materials, characterized by high surface area and electrical conductivity, are ideal materials for capacitive deionization. However, their effectiveness in salt ion removal is hindered by unclear pore structures and poor wettability, limiting salt ion transport and storage. In this study, nitrogen-doped hierarchical porous carbon is successfully synthesized through the carbonization of MOF-5 and melamine mixtures, wherein melamine serves as both a nitrogen source and porogenic agent. Through optimization of carbonization temperature, the resulting MOF-5-derived nanoporous carbon (referred to as NPC-800) retains the cubic morphology of MOF-5, possesses a large surface area (754.34 m2∙g-1), high nitrogen content (10.13%), and favorable wettability. Electrochemical analysis reveals that the NPC-800 electrode demonstrates specific capacities of 91.8, 76.1, 66.3, 51.0, 28.0, and 15.2 mAh∙g-1 at current densities of 0.2, 0.5, 1.0, 2.0, 4.0, and 6.0 A∙g-1, respectively, outperforming NPC-700 (26.3, 19.7, 13.1, 6.90, 2.30, and 1.30 mAh∙g-1) and NPC-900 (46.0, 37.8, 30.4, 21.3, 11.7, and 7.50 mAh∙g-1). The superior electrochemical performance of NPC-800 can be attributed to its maximal specific surface area, abundant pore structure, and optimal wettability, facilitating increased active sites for salt ion adsorption and diffusion. Moreover, NPC-800 exhibits low intrinsic resistance, rapid ion transfer kinetics, and exceptional cycling stability (50000 cycles) with 100% capacity retention at 5 A∙g-1. Further investigation into the CDI performance of NPC electrodes under different applied voltages (0.8, 1.0, and 1.2 V) and initial NaCl solution concentrations (100, 300, and 500 mg∙L-1) demonstrates the superior adsorption capacity of the NPC-800 electrode compared to the other two electrodes. Specifically, at 1.2 V in a 500 mg∙L-1 salt solution, NPC-800 exhibits a faster salt adsorption rate (2.8 mg∙g-1∙min-1) and higher salt adsorption capacity (24.17 mg∙g-1) compared to NPC-700 and NPC-900. Consequently, the melamine-assisted synthesis of N-doped porous carbon material holds promise as an optimal choice for capacitive deionization.
2025, 41(3): 240600
doi: 10.3866/PKU.WHXB202406007
Abstract:
Interlayer materials play a crucial role in achieving high efficiency in organic solar cells (OSCs). However, slight increases in film thickness often lead to significant charge accumulation and recombination, presenting a challenge for large-scale OSC device fabrication. Therefore, there is a pressing need for interlayer materials that are insensitive to variations in thickness. In this study, we synthesized a cost-effective cyano-modified perylene diimide (PDI) derivative, PDINBrCN, as an interlayer material. Compared to the analogous PDINBr, the introduction of cyano groups lowers the lowest unoccupied molecular orbital (LUMO) energy level of the molecule, enhancing electron injection and charge transport efficiency. Additionally, PDINBrCN demonstrates excellent solubility in 2, 2, 2-trifluoroethanol (TFE) and effectively modifies the electrode work function, facilitating device fabrication through orthogonal solvent processing. When utilized as the cathode interlayer in D18:L8-BO devices, PDINBrCN achieved a high power conversion efficiency (PCE) of 18.83% with a film thickness of 10 nm. Importantly, PDINBrCN maintained a PCE of 17.90% even when the film thickness was increased to 50 nm. In contrast, the analogous PDI derivatives PDINBr and the star cathode interlayer material anthra[2, 1, 9-def: 6, 5, 10-d'e'f']diisoquinoline-1, 3, 8, 10(2H, 9H)-tetrone (PDINN) achieved PCEs of 17.17% and 17.06%, respectively, at the same film thickness. Notably, PDINBrCN maintained a PCE of over 16% even with an interlayer thickness of 80 nm, marking one of the best results for small molecule PDI derivatives as cathode interlayer materials at this thickness. Our findings demonstrate that PDINBrCN exhibits excellent processability, electrode work function adjustment capability, and crucially, thickness-insensitive properties. Therefore, PDINBrCN holds promise as an efficient and cost-effective cathode interlayer material, with potential for future commercial applications in OSCs. ![]()
Interlayer materials play a crucial role in achieving high efficiency in organic solar cells (OSCs). However, slight increases in film thickness often lead to significant charge accumulation and recombination, presenting a challenge for large-scale OSC device fabrication. Therefore, there is a pressing need for interlayer materials that are insensitive to variations in thickness. In this study, we synthesized a cost-effective cyano-modified perylene diimide (PDI) derivative, PDINBrCN, as an interlayer material. Compared to the analogous PDINBr, the introduction of cyano groups lowers the lowest unoccupied molecular orbital (LUMO) energy level of the molecule, enhancing electron injection and charge transport efficiency. Additionally, PDINBrCN demonstrates excellent solubility in 2, 2, 2-trifluoroethanol (TFE) and effectively modifies the electrode work function, facilitating device fabrication through orthogonal solvent processing. When utilized as the cathode interlayer in D18:L8-BO devices, PDINBrCN achieved a high power conversion efficiency (PCE) of 18.83% with a film thickness of 10 nm. Importantly, PDINBrCN maintained a PCE of 17.90% even when the film thickness was increased to 50 nm. In contrast, the analogous PDI derivatives PDINBr and the star cathode interlayer material anthra[2, 1, 9-def: 6, 5, 10-d'e'f']diisoquinoline-1, 3, 8, 10(2H, 9H)-tetrone (PDINN) achieved PCEs of 17.17% and 17.06%, respectively, at the same film thickness. Notably, PDINBrCN maintained a PCE of over 16% even with an interlayer thickness of 80 nm, marking one of the best results for small molecule PDI derivatives as cathode interlayer materials at this thickness. Our findings demonstrate that PDINBrCN exhibits excellent processability, electrode work function adjustment capability, and crucially, thickness-insensitive properties. Therefore, PDINBrCN holds promise as an efficient and cost-effective cathode interlayer material, with potential for future commercial applications in OSCs.
2025, 41(3): 240600
doi: 10.3866/PKU.WHXB202406009
Abstract:
Activated carbons are widely used as the electrode material for supercapacitors owing to their large surface area, moderate conductivity, and outstanding electrochemical stability. However, large-surface-area activated carbons usually show low density and poor volumetric energy storage performance, which is difficult to meet the development of devices miniaturization. Mechanical compression is a simple and effective method to improve the density of the activated carbons. However, most of the studies focus on mechanical compression of the as-prepared porous carbon materials. Preparation of high-density activated carbons by mechanical compression of the carbon precursors has been proposed. But the surface area and porous structure evolution, and the possible mechanism have rarely investigated. Herein, we propose a universal method to improve the density of the activated carbons by mechanical compression of the precursors before activation. The influence of mechanical compression on the surface area, porous structure, and capacitive energy storage performance of the activated carbons prepared by two typical methods, outside-in activation (carbon powder/KOH mixture) and homogeneous ion activation (pyrolysis of potassium-containing salts), are studied. Mechanical compression of the precursors can generally improve the activation reaction efficiency, as well as the density and volumetric capacitive performance of the activated carbons. However, the surface area and porous structure evolution mainly depend on the carbon precursor and pore-forming process. For outside-in activation, the surface area and porosity of the activated carbons show a first increasing and then decreasing trend with the increase of mechanical pressure. This is because mechanical compression enhances the contact between the carbon precursors and activator through eliminating the voids between particles, significantly improves the activation efficiency. For homogeneous ion activation, the surface area and porosity of activated carbons show a trend of decreasing first and then increasing. The reason is deduced as compressed precursors inhibit the rapid release of active gas molecules (H2O, CO2 etc.) produced during pyrolysis. These gas molecules further participate in the activation etching reaction and promote the activation efficiency. The optimized sample shows high gravimetric and volumetric capacitances of 316 F·g-1/291 F·cm-3 and 131 F·g-1/92 F·cm-3 at 1 A·g-1 in aqueous and organic electrolytes, respectively. This work provides a simple way for design and preparation of activated carbons with large surface area and high density. ![]()
Activated carbons are widely used as the electrode material for supercapacitors owing to their large surface area, moderate conductivity, and outstanding electrochemical stability. However, large-surface-area activated carbons usually show low density and poor volumetric energy storage performance, which is difficult to meet the development of devices miniaturization. Mechanical compression is a simple and effective method to improve the density of the activated carbons. However, most of the studies focus on mechanical compression of the as-prepared porous carbon materials. Preparation of high-density activated carbons by mechanical compression of the carbon precursors has been proposed. But the surface area and porous structure evolution, and the possible mechanism have rarely investigated. Herein, we propose a universal method to improve the density of the activated carbons by mechanical compression of the precursors before activation. The influence of mechanical compression on the surface area, porous structure, and capacitive energy storage performance of the activated carbons prepared by two typical methods, outside-in activation (carbon powder/KOH mixture) and homogeneous ion activation (pyrolysis of potassium-containing salts), are studied. Mechanical compression of the precursors can generally improve the activation reaction efficiency, as well as the density and volumetric capacitive performance of the activated carbons. However, the surface area and porous structure evolution mainly depend on the carbon precursor and pore-forming process. For outside-in activation, the surface area and porosity of the activated carbons show a first increasing and then decreasing trend with the increase of mechanical pressure. This is because mechanical compression enhances the contact between the carbon precursors and activator through eliminating the voids between particles, significantly improves the activation efficiency. For homogeneous ion activation, the surface area and porosity of activated carbons show a trend of decreasing first and then increasing. The reason is deduced as compressed precursors inhibit the rapid release of active gas molecules (H2O, CO2 etc.) produced during pyrolysis. These gas molecules further participate in the activation etching reaction and promote the activation efficiency. The optimized sample shows high gravimetric and volumetric capacitances of 316 F·g-1/291 F·cm-3 and 131 F·g-1/92 F·cm-3 at 1 A·g-1 in aqueous and organic electrolytes, respectively. This work provides a simple way for design and preparation of activated carbons with large surface area and high density.
2025, 41(3): 240702
doi: 10.3866/PKU.WHXB202407025
Abstract:
Organic-inorganic metal halide perovskite solar cells (PSCs) are favorable candidates for next-generation solar cells, due to their excellent photovoltaic performance and promising low-cost fabrication process. Particularly, tin oxide (SnO2), with excellent charge mobility and extraction efficiency, is widely used as electron transport layers (ETLs), and the efficiency of the corresponding n-i-p-type perovskites has been certified as high as 26.21% in single-junction devices. The SnO2 layer serves as the substrate for the growth of perovskite films, determining the crystalline quality and the buried interface of perovskite films. However, due to the different thermal expansion coefficient of SnO2 and perovskite, the subsequent perovskite annealing process leads to the residual stress at the buried interfaces and lattice distortion in the perovskite films, which seriously affects their optoelectronic performance and stability. To release this interfacial stress, researchers have made some progress by applying different polymers and small molecules to the SnO2/perovskite interface as a buffer layer. Among these, two-dimensional (2D) nanosheets with high carrier mobility, a wide bandgap range, and excellent optical absorption properties are promising, especially 2D NbSe2 nanosheets showing the advantages of solution-processability, high intrinsic conductivity and clean smooth surface, namely without dangling bonded atoms. Herein, 2D NbSe2 nanosheets have been introduced at the SnO2/perovskite interface to release the undesired residual tensile strain in perovskite films and to form a more matched interfacial energy level alignment. As a result, we have obtained a high-quality perovskite film and further an improved photovoltaic performance. The PCE has been increased from 21.81% to 24.05%. The unencapsulated cell maintained 91% of the initial efficiency after aging over 1000 h under atmospheric condition. ![]()
Organic-inorganic metal halide perovskite solar cells (PSCs) are favorable candidates for next-generation solar cells, due to their excellent photovoltaic performance and promising low-cost fabrication process. Particularly, tin oxide (SnO2), with excellent charge mobility and extraction efficiency, is widely used as electron transport layers (ETLs), and the efficiency of the corresponding n-i-p-type perovskites has been certified as high as 26.21% in single-junction devices. The SnO2 layer serves as the substrate for the growth of perovskite films, determining the crystalline quality and the buried interface of perovskite films. However, due to the different thermal expansion coefficient of SnO2 and perovskite, the subsequent perovskite annealing process leads to the residual stress at the buried interfaces and lattice distortion in the perovskite films, which seriously affects their optoelectronic performance and stability. To release this interfacial stress, researchers have made some progress by applying different polymers and small molecules to the SnO2/perovskite interface as a buffer layer. Among these, two-dimensional (2D) nanosheets with high carrier mobility, a wide bandgap range, and excellent optical absorption properties are promising, especially 2D NbSe2 nanosheets showing the advantages of solution-processability, high intrinsic conductivity and clean smooth surface, namely without dangling bonded atoms. Herein, 2D NbSe2 nanosheets have been introduced at the SnO2/perovskite interface to release the undesired residual tensile strain in perovskite films and to form a more matched interfacial energy level alignment. As a result, we have obtained a high-quality perovskite film and further an improved photovoltaic performance. The PCE has been increased from 21.81% to 24.05%. The unencapsulated cell maintained 91% of the initial efficiency after aging over 1000 h under atmospheric condition.
