Phonons are the primary heat carriers in non-metallic solids.In compositionally heterogeneous materials,the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder ...Phonons are the primary heat carriers in non-metallic solids.In compositionally heterogeneous materials,the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations,while the effects of compositional fluctuation induced local phonon states are usually ignored.Here,by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations,we identify the vibrational properties of ingredient-dependent interface phonon modes in Alx Ga1-x N and quantify their various contributions to the local interface thermal conductance.We demonstrate that atomic-scale compositional fluctuation has significant influence on the vibrational thermodynamic properties,highly affecting the mode ratio and vibrational amplitude of interface phonon modes and subsequently redistributing their modal contribution to the interface thermal conductance.Our work provides fundamental insights into understanding of local phonon-boundary interactions in nanoscale inhomogeneities,which reveal new opportunities for optimization of thermal properties via engineering ingredient distribution.展开更多
Co-catalysts decorations provide unique opportunity in promoting the photocatalytic water splitting performance of graphite carbon nitride(g-C_(3)N_(4))system,while mechanistic understanding of this complex catalytic ...Co-catalysts decorations provide unique opportunity in promoting the photocatalytic water splitting performance of graphite carbon nitride(g-C_(3)N_(4))system,while mechanistic understanding of this complex catalytic network remains elusive.Here,taking the single-atom-based photocatalysts(M1-g-C_(3)N_(4))as an unprecedented simplified model system,we theoretically tracked the photocatalytic kinetics for a comprehensive understanding of the photocatalytic process and afforded the descriptorαS1-T1/αT1-S0(ratio of the extent of S1-T1 and T1-S0 state mixing)andΔGH^(*)(hydrogen adsorpti on free energy)for rational screening of photocatalysts.The targeted Fe1-g-C_(3)N_(4)yields an excellent H_(2)evolution rate(ca.3.2⋅mmol⋅gcat^(-1)⋅h^(-1)under full arc),two order of magnitude improvement relative to pristine g-C_(3)N_(4)counterpart and also outperforms other representative 3d-transition-metal-based photocatalysts.This work presents a comprehensive understanding of the essential role of isolated atomic sites in the photocatalytic course and sheds light on the design of photocatalysts from both photophysical and photochemical aspects.展开更多
Transition metal dichalcogenides, featuring layered structures, have aroused enormous interest as a platform for novel physical phenomena and a wide range of potential applications. Among them, special interest has be...Transition metal dichalcogenides, featuring layered structures, have aroused enormous interest as a platform for novel physical phenomena and a wide range of potential applications. Among them, special interest has been placed upon WTe_2 and MoTe_2, which exhibit non-trivial topology both in single layer and bulk as well as pressure induced or enhanced superconductivity. We study another distorted IT material NbTe_2 through systematic electrical transport measurements. Intrinsic superconductivity with onset transition temperature(T_c^(onset)) up to 0.72 K is detected where the upper critical field(H_c) shows unconventional quasi-linear behavior,indicating spin-orbit coupling induced p-wave paring. Furthermore, a general model is proposed to fit the angledependent magnetoresistance, which reveals the Fermi surface anisotropy of NbTe_2. Finally, non-saturating linear magnetoresistance up to 50 T is observed and attributed to the quantum limit transport.展开更多
Nitrile compounds are a class of high-value chemicals and versatile intermediates which can easily be transformed into a variety of useful products bearing functional groups such as carboxyl, carbamoyl, aminomethyl, k...Nitrile compounds are a class of high-value chemicals and versatile intermediates which can easily be transformed into a variety of useful products bearing functional groups such as carboxyl, carbamoyl, aminomethyl, ketyl and heterocyclic derivatives. Various thermal catalytic cyanation procedures have been devised and scaled up industrially while developing alternative methods are actively pursued. The access to these classes of molecules electrochemically offers greener alternatives to their preparation. The development of electrochemical synthesis of cyano-containing compounds under mild conditions with low energy consumption will imminently become indispensable approaches for industrial production of nitriles. The electrochemical cyanation presents many challenges from the toxicity of cyanide to the development of catalysts and the design of electrochemical cells. Electrochemical cyanation reaction offers promise to conveniently accessing nitriles but still requires efficient electro-catalysts, safe protocols and scale up considerations. This review discusses recent progress in the field of electrochemical synthesis of nitrile compounds placing emphasis on electro-synthetic and electro-catalytic mechanism aspects while making reference to original works to highlight the progress in this area.展开更多
Atomic transition metal–nitrogen–carbon electrocatalysts exhibit outstanding activity in various electrocatalytic reactions.The challenge lies in predicting the structure of the active center,which may undergo chang...Atomic transition metal–nitrogen–carbon electrocatalysts exhibit outstanding activity in various electrocatalytic reactions.The challenge lies in predicting the structure of the active center,which may undergo changes under applied potential and interact with reactants or intermediates.Advanced characterization techniques,particularly in-situ X-ray absorption spectroscopy(XAS),provide crucial insights into the structural evolution of the metal active center during the reaction.In this study,nitrate reduction to ammonia(NO_(3)RR)was selected as a model reaction,and we introduced in-situ XAS to reveal the structural evolution during the catalytic process.A novel single atom catalyst of iron loaded on three-dimensional nitrogen–carbon nanonetwork(designated as Fe SAC/NC)was successfully synthesized.We unraveled the structural transformations occurring as pyrrole-N_(4)-Fe transitions to pyrrole-N_(3)-Fe throughout the NO_(3)RR process.Notably,the Fe SAC/NC catalyst exhibited excellent catalytic activity,achieving a Faradaic efficiency of 98.2% and an ammonia generation rate of 22,515μg·h^(−1)·mgcat−1 at−0.8 V versus reversible hydrogen electrode.Theoretical calculations combined with in-situ spectroscopic characterization showed that pyrrole-N_(3)-Fe reduced the energy barrier from *NO to*NHO and improved the selectivity of ammonia.This provides a robust reference for the design of efficient nitrate-to-ammonia synthesis catalysts.展开更多
Here,by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy,we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window ...Here,by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy,we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0-4.8 V).We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases.These Li-deficient phases exhibit structure distortion with superstructure stripes,likely caused by the migration of the vanadium,which can slow down the lithium ion diffusion or even block the diffusion channels.Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss.Thus,the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling.After 500 cycles,the thickness of active LVP layer decreases to be - 5-20 nm.Moreover,the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated,indicating the thick SEI film also contributes to the capacity loss.The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale,which is essential to understand the voltage fading and capacity decaying of LVP cathode.展开更多
We report the highly efficient conversion of readily available biomass-derived polyols with amines to valuable furfurylamines orβ-amino alcohols compounds using ruthenium catalysis.The reaction outcome is readily tun...We report the highly efficient conversion of readily available biomass-derived polyols with amines to valuable furfurylamines orβ-amino alcohols compounds using ruthenium catalysis.The reaction outcome is readily tuned by the simple addition of 4Åmolecular sieves(furfurylamines vs.β-amino alcohols)with high chemo-selectivity.The proposed reaction mechanism involves ruthenium-catalyzed hydrogen borrowing for the reduction of the imine intermediate and C–C bond cleavage of polyols via a retro-aldol process.A series of arylamines was suc-cessfully transformed into the desired products with moderate to good yields.展开更多
Surface phonon polaritons(SPh Ps) are potentially very attractive for subwavelength control and manipulation of light at the infrared to terahertz wavelengths. Probing their propagation behavior in nanostructures is c...Surface phonon polaritons(SPh Ps) are potentially very attractive for subwavelength control and manipulation of light at the infrared to terahertz wavelengths. Probing their propagation behavior in nanostructures is crucial to guide rational device design. Here, aided by monochromatic scanning transmission electron microscopy-electron energy loss spectroscopy technique, we measure the dispersion relation of SPh Ps in individual Si C nanorods and reveal the effects of size and shape. We find that the SPh Ps can be modulated by the geometric shape and size of Si C nanorods. The energy of SPh Ps shows redshift with decreasing radius and the surface optical phonon is mainly concentrated on the surface with large radius. Therefore, the fields can be precisely confined in specific positions by varying the size of the nanorod, allowing effective tuning at nanometer scale. The findings of this work are in agreement with dielectric response theory and numerical simulation, and provide novel strategies for manipulating light in polar dielectrics through shape and size control, enabling the design of novel nanoscale phononphotonic devices.展开更多
α,β-Unsaturated primary amides are important intermediates and building blocks in organic synthesis.Herein,we report a ligand-free iron-catalyzed hydroaminocarbonylation of alkynes using NH_(4)HCO_(3)as the ammonia ...α,β-Unsaturated primary amides are important intermediates and building blocks in organic synthesis.Herein,we report a ligand-free iron-catalyzed hydroaminocarbonylation of alkynes using NH_(4)HCO_(3)as the ammonia source,enabling the highly efficient and regioselective synthesis of linearα,β-unsaturated primary amides.Various aromatic and aliphatic alkynes are transformed into the desired linearα,β-unsaturated primary amides in good to excellent yields.Further studies show that using NH_(4)HCO_(3)as the ammonia source is key to obtain good yields and selectivity.The utility of this route is demonstrated with the synthesis of linearα,β-unsaturated amides including vanilloid receptor-1 antagonist TRPV-1.展开更多
Epoxidation is an important chemical process for the production of epoxides,key building blocks in chemical industry.Despite great efforts being made to facilitate this process,it remains a significant challenge to de...Epoxidation is an important chemical process for the production of epoxides,key building blocks in chemical industry.Despite great efforts being made to facilitate this process,it remains a significant challenge to develop cost-effective,environmental-friendly,and selective catalysts.Herein,we reported a highly dispersed Mn supported by g-C_(3)N_(4)(Mn/g-C_(3)N_(4))with Mn loading up to 2.56 wt%.The Mn/g-CN_(4)exhibited satisfied catalytic performance for olefin epoxidation with excellent conversion(91%),high selectivity(93%)as well as outstanding recycling stability.Further analysis revealed the importance of Mn-N structure for the generation of active oxo-containing species and subsequent oxygen atom transfer.Besides,an efficient synthesis of cyclic carbonates from styrene epoxide and CO_(2)has been achieved(88%conversion,89%selectivity)based on the polar Mn-N coordinated characteristics of Mn/g-C_(3)N_(4)catalyst.展开更多
基金the National Key R&D Program of China(Grant No.2019YFA0708200)the National Natural Science Foundation of China(Grant Nos.52125307,11974023,12104017,and 52021006)+1 种基金the“2011 Program”from the Peking-Tsinghua-IOP Collaborative Innovation Center of Quantum MatterYouth Innovation Promotion Association,CAS。
文摘Phonons are the primary heat carriers in non-metallic solids.In compositionally heterogeneous materials,the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations,while the effects of compositional fluctuation induced local phonon states are usually ignored.Here,by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations,we identify the vibrational properties of ingredient-dependent interface phonon modes in Alx Ga1-x N and quantify their various contributions to the local interface thermal conductance.We demonstrate that atomic-scale compositional fluctuation has significant influence on the vibrational thermodynamic properties,highly affecting the mode ratio and vibrational amplitude of interface phonon modes and subsequently redistributing their modal contribution to the interface thermal conductance.Our work provides fundamental insights into understanding of local phonon-boundary interactions in nanoscale inhomogeneities,which reveal new opportunities for optimization of thermal properties via engineering ingredient distribution.
基金supported by the National Natural Science Foundation of China(Grant Nos.51773025 and 22002013)the Fundamental Research Funds for the Central Universities(DUT20RC(3)021)+1 种基金the Natural Foundation of Liaoning Province(Materials Joint Foundation,Grant No.20180510027)The authors thank NSRL(BL12Ba),BSRF(1W1B),and SSRF(BL11B)for the synchrotron radiation beam time.
文摘Co-catalysts decorations provide unique opportunity in promoting the photocatalytic water splitting performance of graphite carbon nitride(g-C_(3)N_(4))system,while mechanistic understanding of this complex catalytic network remains elusive.Here,taking the single-atom-based photocatalysts(M1-g-C_(3)N_(4))as an unprecedented simplified model system,we theoretically tracked the photocatalytic kinetics for a comprehensive understanding of the photocatalytic process and afforded the descriptorαS1-T1/αT1-S0(ratio of the extent of S1-T1 and T1-S0 state mixing)andΔGH^(*)(hydrogen adsorpti on free energy)for rational screening of photocatalysts.The targeted Fe1-g-C_(3)N_(4)yields an excellent H_(2)evolution rate(ca.3.2⋅mmol⋅gcat^(-1)⋅h^(-1)under full arc),two order of magnitude improvement relative to pristine g-C_(3)N_(4)counterpart and also outperforms other representative 3d-transition-metal-based photocatalysts.This work presents a comprehensive understanding of the essential role of isolated atomic sites in the photocatalytic course and sheds light on the design of photocatalysts from both photophysical and photochemical aspects.
基金Supported by the National Basic Research Program of China under Grant Nos 2018YFA0305600 and 2017YFA0303302the National Natural Science Foundation of China under Grant Nos 11888101,11774008,11704414 and 11427805+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB28000000Beijing Natural Science Foundation(Z180010)
文摘Transition metal dichalcogenides, featuring layered structures, have aroused enormous interest as a platform for novel physical phenomena and a wide range of potential applications. Among them, special interest has been placed upon WTe_2 and MoTe_2, which exhibit non-trivial topology both in single layer and bulk as well as pressure induced or enhanced superconductivity. We study another distorted IT material NbTe_2 through systematic electrical transport measurements. Intrinsic superconductivity with onset transition temperature(T_c^(onset)) up to 0.72 K is detected where the upper critical field(H_c) shows unconventional quasi-linear behavior,indicating spin-orbit coupling induced p-wave paring. Furthermore, a general model is proposed to fit the angledependent magnetoresistance, which reveals the Fermi surface anisotropy of NbTe_2. Finally, non-saturating linear magnetoresistance up to 50 T is observed and attributed to the quantum limit transport.
基金supports from the National Natural Science Foundation of China(22022204,21633013)the Natural Science Foundation of Jiangsu Province(BK20180248).
文摘Nitrile compounds are a class of high-value chemicals and versatile intermediates which can easily be transformed into a variety of useful products bearing functional groups such as carboxyl, carbamoyl, aminomethyl, ketyl and heterocyclic derivatives. Various thermal catalytic cyanation procedures have been devised and scaled up industrially while developing alternative methods are actively pursued. The access to these classes of molecules electrochemically offers greener alternatives to their preparation. The development of electrochemical synthesis of cyano-containing compounds under mild conditions with low energy consumption will imminently become indispensable approaches for industrial production of nitriles. The electrochemical cyanation presents many challenges from the toxicity of cyanide to the development of catalysts and the design of electrochemical cells. Electrochemical cyanation reaction offers promise to conveniently accessing nitriles but still requires efficient electro-catalysts, safe protocols and scale up considerations. This review discusses recent progress in the field of electrochemical synthesis of nitrile compounds placing emphasis on electro-synthetic and electro-catalytic mechanism aspects while making reference to original works to highlight the progress in this area.
基金supported by the National Natural Science Foundation of China(Nos.22002013 and 52272193)the Fundamental Research Funds for the Central Universities(Nos.DUT22LAB602 and DUT20RC(3)021)+1 种基金Liaoning Revitalization Talents Program(No.XLYC2008032)China Postdoctoral Science Foundation(No.2023M740496)。
文摘Atomic transition metal–nitrogen–carbon electrocatalysts exhibit outstanding activity in various electrocatalytic reactions.The challenge lies in predicting the structure of the active center,which may undergo changes under applied potential and interact with reactants or intermediates.Advanced characterization techniques,particularly in-situ X-ray absorption spectroscopy(XAS),provide crucial insights into the structural evolution of the metal active center during the reaction.In this study,nitrate reduction to ammonia(NO_(3)RR)was selected as a model reaction,and we introduced in-situ XAS to reveal the structural evolution during the catalytic process.A novel single atom catalyst of iron loaded on three-dimensional nitrogen–carbon nanonetwork(designated as Fe SAC/NC)was successfully synthesized.We unraveled the structural transformations occurring as pyrrole-N_(4)-Fe transitions to pyrrole-N_(3)-Fe throughout the NO_(3)RR process.Notably,the Fe SAC/NC catalyst exhibited excellent catalytic activity,achieving a Faradaic efficiency of 98.2% and an ammonia generation rate of 22,515μg·h^(−1)·mgcat−1 at−0.8 V versus reversible hydrogen electrode.Theoretical calculations combined with in-situ spectroscopic characterization showed that pyrrole-N_(3)-Fe reduced the energy barrier from *NO to*NHO and improved the selectivity of ammonia.This provides a robust reference for the design of efficient nitrate-to-ammonia synthesis catalysts.
基金supported by the National Natural Science Foundation of China (Nos.51502032,51575135,U1537206,51502007,and 51672007)the National Basic Research Program of China (Nos.2016YFA0300804 and 2016YFA0300903]"2011 Program" Peking-Tsinghua-IOP Collaborative Innovation Center of Quantum Matter.
文摘Here,by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy,we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0-4.8 V).We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases.These Li-deficient phases exhibit structure distortion with superstructure stripes,likely caused by the migration of the vanadium,which can slow down the lithium ion diffusion or even block the diffusion channels.Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss.Thus,the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling.After 500 cycles,the thickness of active LVP layer decreases to be - 5-20 nm.Moreover,the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated,indicating the thick SEI film also contributes to the capacity loss.The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale,which is essential to understand the voltage fading and capacity decaying of LVP cathode.
基金support from the National Natural Science Foundation of China(NSFC,Nos.21633013,22022204).
文摘We report the highly efficient conversion of readily available biomass-derived polyols with amines to valuable furfurylamines orβ-amino alcohols compounds using ruthenium catalysis.The reaction outcome is readily tuned by the simple addition of 4Åmolecular sieves(furfurylamines vs.β-amino alcohols)with high chemo-selectivity.The proposed reaction mechanism involves ruthenium-catalyzed hydrogen borrowing for the reduction of the imine intermediate and C–C bond cleavage of polyols via a retro-aldol process.A series of arylamines was suc-cessfully transformed into the desired products with moderate to good yields.
基金We gratefully acknowledge the support from the“2011 Program”Peking-Tsinghua-IOP,China Collaborative Innovation Center of Quantum Matter.The authors acknowledge Electron Microscopy Laboratory of Peking University,China for the use of Cs corrected electron microscope.This work was supported by the National Natural Science Foundation of China(11974023,51672007)the National Key R&D Program of China(2016YFA0300804)+1 种基金the National Equipment Program of China(ZDYZ2015-1)the Key-Area Research and Development Program of Guangdong Provience(2018B030327001,2018B010109009).
文摘Surface phonon polaritons(SPh Ps) are potentially very attractive for subwavelength control and manipulation of light at the infrared to terahertz wavelengths. Probing their propagation behavior in nanostructures is crucial to guide rational device design. Here, aided by monochromatic scanning transmission electron microscopy-electron energy loss spectroscopy technique, we measure the dispersion relation of SPh Ps in individual Si C nanorods and reveal the effects of size and shape. We find that the SPh Ps can be modulated by the geometric shape and size of Si C nanorods. The energy of SPh Ps shows redshift with decreasing radius and the surface optical phonon is mainly concentrated on the surface with large radius. Therefore, the fields can be precisely confined in specific positions by varying the size of the nanorod, allowing effective tuning at nanometer scale. The findings of this work are in agreement with dielectric response theory and numerical simulation, and provide novel strategies for manipulating light in polar dielectrics through shape and size control, enabling the design of novel nanoscale phononphotonic devices.
基金financial supports from the National Natural Science Foundation of China(Nos.21772035,22022204,22072167,21202206)Natural Science Foundation of Hunan Province(Nos.2021JJ40147)。
文摘α,β-Unsaturated primary amides are important intermediates and building blocks in organic synthesis.Herein,we report a ligand-free iron-catalyzed hydroaminocarbonylation of alkynes using NH_(4)HCO_(3)as the ammonia source,enabling the highly efficient and regioselective synthesis of linearα,β-unsaturated primary amides.Various aromatic and aliphatic alkynes are transformed into the desired linearα,β-unsaturated primary amides in good to excellent yields.Further studies show that using NH_(4)HCO_(3)as the ammonia source is key to obtain good yields and selectivity.The utility of this route is demonstrated with the synthesis of linearα,β-unsaturated amides including vanilloid receptor-1 antagonist TRPV-1.
基金financial supports from the National Natural Science Foundation of China(Nos.216330133and 22102197)Jiangsu Province Natural Science Foundation(No.BK20211096)the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing(Yantai,No.AMGM2021F07).
文摘Epoxidation is an important chemical process for the production of epoxides,key building blocks in chemical industry.Despite great efforts being made to facilitate this process,it remains a significant challenge to develop cost-effective,environmental-friendly,and selective catalysts.Herein,we reported a highly dispersed Mn supported by g-C_(3)N_(4)(Mn/g-C_(3)N_(4))with Mn loading up to 2.56 wt%.The Mn/g-CN_(4)exhibited satisfied catalytic performance for olefin epoxidation with excellent conversion(91%),high selectivity(93%)as well as outstanding recycling stability.Further analysis revealed the importance of Mn-N structure for the generation of active oxo-containing species and subsequent oxygen atom transfer.Besides,an efficient synthesis of cyclic carbonates from styrene epoxide and CO_(2)has been achieved(88%conversion,89%selectivity)based on the polar Mn-N coordinated characteristics of Mn/g-C_(3)N_(4)catalyst.
