Methane’s complete catalytic oxidation process has been widely studied,but efficient catalytic oxidation of low-concentration methane(≤0.75%)remains a crucial problem in the coal chemical industry.How to prevent the...Methane’s complete catalytic oxidation process has been widely studied,but efficient catalytic oxidation of low-concentration methane(≤0.75%)remains a crucial problem in the coal chemical industry.How to prevent the sintering deactivation of the active component in Pd-based catalysts and achieve efficient and stable operation of sub-nanometer catalysts remains challenging.Here,we utilize the interaction between amine ligands and Pd nanoparticles to stabilize and encapsulate the Pd particles within the pores of a molecular sieve carrier,effectively promoting the high dispersion of Pd particles.By leveraging the low acidity,high hydrophobicity,and high hydrothermal stability of the zeolite carrier,the Pd@S-1 catalyst exhibits excellent activity and stability in the catalytic oxidation of methane at lowconcentrations.Finally,density functional theory is employed to investigate the reaction mechanism of low-concentration methane during the catalytic process.Encapsulating the active metal component in zeolite to improve catalytic activity and stability provides a theoretical basis and direction for preparing complete oxidation catalysts for low-concentration methane.展开更多
Silicon/carbon composites are promising alternatives to current graphite anodes in commercial lithiumion batteries(LIBs)because of their high capacity and excellent safety.Nevertheless,the unsatisfactory fastcharging ...Silicon/carbon composites are promising alternatives to current graphite anodes in commercial lithiumion batteries(LIBs)because of their high capacity and excellent safety.Nevertheless,the unsatisfactory fastcharging capability and cycle stability of Si/C composites caused by slow charge transport capability and huge volume change under industrial electrode conditions severely hamper their development.Here,a novel Si/C anode was fabricated by homogeneously depositing amorphous C-Si nanolayers on graphite(C-Si@graphite).C-Si nanolayers with uniformly dispersed sub-nanometer Si particles in 3D carbon skeleton significantly boost electron and Li-ion transport and efficiently relieve Si's agglomeration and volume change.As a result,the tailored C-Si@graphite electrodes show an excellent rate capacity(760.3 mAh·g^(-1)at 5.0C)and long cycle life of over 1000 cycles at 1.0C and800 cycles at 2.0C under industrial electrode conditions.In addition,the assembled full cells(C-Si@graphite,anode;Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2),cathode)present superior fastcharging capability(240.4 Wh·kg^(-1),charging for16.2 min,3.0C)and long cycle life(80.7%capacity retention after 500 cycles at 1.0C),demonstrating the massive potential of C-Si@graphite for practical application.展开更多
Preparing carbon nanosheets with precise control of open porous morphology via universal process and understanding the relationship between structure and capacitive performance are very urgent for achieving advanced s...Preparing carbon nanosheets with precise control of open porous morphology via universal process and understanding the relationship between structure and capacitive performance are very urgent for achieving advanced supercapacitors.Herein,we propose a simple yet effective additive-free method to transform a bulk layered potassium phthalimide salt to novel nitrogen-doped twodimensional carbon sheets by self-activation during calcination.The obtained samples showed large-sized and flat structure with lateral size around 10μm,uniform sub-nanometer micropore size distribution of about 0.65 nm dimension,large specific surface area up to 2276.7 m^(2)g^(-1),and suitable nitrogen doping.Benefited from these merits,the optimized sample delivers a high specific capacitance of 345 F g^(-1)at 1 A g^(-1)and retains 270 F g^(-1)even at 50 A g^(-1)in6.0 M KOH electrolyte.Remarkably,the symmetric supercapacitor shows maximum energy densities of 16.43 Wh kg^(-1)and 23.6 Wh kg^(-1)in 6.0 M KOH and 1.0 M Na_(2)SO_(4)electrolytes,respectively.Importantly,on account the universality and simplicity of this method,the undoped as-prepared carbon sheet with uniform sub-nanometer micropore distribution can be synthesized from different potassium-containing salts with layered structure,which can be employed as a model for a deep understanding the effect of sub-nanometer micropores on capacitive performances.We find the number of micropores centered at 0.65 nm can be applied as one indicator to clarify the correlation between capacitance and critical pore size below 1 nm.展开更多
We established a complete model and relationship between laser source characteristics and measurement accuracy of high precision fiber microprobe sensor(FMS)based on phase generated carrier demodulation.The laser carr...We established a complete model and relationship between laser source characteristics and measurement accuracy of high precision fiber microprobe sensor(FMS)based on phase generated carrier demodulation.The laser carried out high-bandwidth frequency modulation to improve the measurement speed.Meanwhile,the laser also carried out large-amplitude frequency modulation to eliminate tens of nanometers of nonlinear error,thus improving the measurement accuracy.Further,the laser center wavelength is required to be stabilized under the above modulation to achieve a high measurement stability.The conflict between laser frequency modulation and central stability is revealed and analyzed alongside the distortion of measurement accuracy.A modified frequency stabilization method for laser source under high-bandwidth and large-amplitude modulation is proposed for improving measurement accuracy to realize sub-nanometer precision.The experimental results showed that when the modulation bandwidth was 1 MHz and maximum modulation amplitude was 2.61 GHz,the distributed feedback laser central wavelength stability was 2.9×10^(−10)(τ=1s)according to Allan variance.Additionally,the relative expanded uncertainty of the laser wavelength was demonstrated to be superior to 5×10^(−8)(k=2)within 3 hr,which was at least one order of magnitude higher than that of the traditional method.The resolution and stability of FMS is better than 0.4 nm,and the nonlinear error is reduced from tens of nm to 0.8 nm,which meets the requirements of sub-nanometer measurements.展开更多
Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed du...Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.展开更多
Surface segregation is ubiquitous in multi-component materials and is of great important for catalysis but little is known on the surface structure under graphene encapsulation.Here,we show that the graphene encapsula...Surface segregation is ubiquitous in multi-component materials and is of great important for catalysis but little is known on the surface structure under graphene encapsulation.Here,we show that the graphene encapsulated CoCu performs well for the electrocatalytic oxidation of 5-hydroxymethylfurfural(HMF)to2,5-furandicarboxylic acid(FDCA)with the onset potential before 1.23 VRHEand a nearly 100%selectivity of FDCA under 1.4 VRHE.From the experimental results,the unprecedented catalytic performance was attributed to local structural distortion and sub-nanometer lattice composition of the CoCu surface.We accurately show the dispersed Cu doped Co_(3)O_(4) nano-islands with a lot of edge sites on the bimetallic Co-Cu surface.While,the gradient components effectively facilitate the establishment of built-in electric field and accelerate the charge transfer.Theoretical and experimental results reveal that the surface Co and neighbouring Cu atoms in sub-nanometer lattice synergistically promote the catalysis of HMF.This work offers new insights into surface segregation in tuning the element spatial distribution for catalysis.展开更多
Quantitative optical measurements of deep subwavelength,three-dimensional(3D),nanometric structures with sensitivity to sub-nanometer details address a ubiquitous measurement challenge.A Fourier domain normalization a...Quantitative optical measurements of deep subwavelength,three-dimensional(3D),nanometric structures with sensitivity to sub-nanometer details address a ubiquitous measurement challenge.A Fourier domain normalization approach is used in the Fourier optical imaging code to simulate the full 3D scattered light field of nominally 15 nm-sized structures,accurately replicating the light field as a function of the focus position.Using the full 3D light field,nanometer scale details such as a 2 nm thin conformal oxide and nanometer topography are rigorously fitted for features less than one-thirtieth of the wavelength in size.The densely packed structures are positioned nearly an order of magnitude closer than the conventional Rayleigh resolution limit and can be measured with sub-nanometer parametric uncertainties.This approach enables a practical measurement sensitivity to size variations of only a few atoms in size using a high-throughput optical configuration with broad application in measuring nanometric structures and nanoelectronic devices.展开更多
基金supported by the National Natural Science Foundation of China(No.52270114)the State key laboratory of coal mine disaster dynamics and control(No.2011DA105827-FW202210).
文摘Methane’s complete catalytic oxidation process has been widely studied,but efficient catalytic oxidation of low-concentration methane(≤0.75%)remains a crucial problem in the coal chemical industry.How to prevent the sintering deactivation of the active component in Pd-based catalysts and achieve efficient and stable operation of sub-nanometer catalysts remains challenging.Here,we utilize the interaction between amine ligands and Pd nanoparticles to stabilize and encapsulate the Pd particles within the pores of a molecular sieve carrier,effectively promoting the high dispersion of Pd particles.By leveraging the low acidity,high hydrophobicity,and high hydrothermal stability of the zeolite carrier,the Pd@S-1 catalyst exhibits excellent activity and stability in the catalytic oxidation of methane at lowconcentrations.Finally,density functional theory is employed to investigate the reaction mechanism of low-concentration methane during the catalytic process.Encapsulating the active metal component in zeolite to improve catalytic activity and stability provides a theoretical basis and direction for preparing complete oxidation catalysts for low-concentration methane.
基金financially supported by Guangdong Basic and Applied Basic Research Foundation (No.2020A1515110762)。
文摘Silicon/carbon composites are promising alternatives to current graphite anodes in commercial lithiumion batteries(LIBs)because of their high capacity and excellent safety.Nevertheless,the unsatisfactory fastcharging capability and cycle stability of Si/C composites caused by slow charge transport capability and huge volume change under industrial electrode conditions severely hamper their development.Here,a novel Si/C anode was fabricated by homogeneously depositing amorphous C-Si nanolayers on graphite(C-Si@graphite).C-Si nanolayers with uniformly dispersed sub-nanometer Si particles in 3D carbon skeleton significantly boost electron and Li-ion transport and efficiently relieve Si's agglomeration and volume change.As a result,the tailored C-Si@graphite electrodes show an excellent rate capacity(760.3 mAh·g^(-1)at 5.0C)and long cycle life of over 1000 cycles at 1.0C and800 cycles at 2.0C under industrial electrode conditions.In addition,the assembled full cells(C-Si@graphite,anode;Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2),cathode)present superior fastcharging capability(240.4 Wh·kg^(-1),charging for16.2 min,3.0C)and long cycle life(80.7%capacity retention after 500 cycles at 1.0C),demonstrating the massive potential of C-Si@graphite for practical application.
基金support from the National Natural Science Foundation of China(Grant No.21905220,51772240,21503158 and Distinguished Youth Scientist Program of 51425301)the Key Research and Development Plan of Shanxi Province(China,Grant No.2018ZDXM-GY-135)+3 种基金the Fundamental Research Funds for“Young Talent Support Plan”of Xi’an Jiaotong University(HG6J003)“1000-Plan program”of Shanxi ProvinceSanyo Chem.Co.Ltdthe grant from Shaanxi Joint Laboratory of Graphene(NPU)
文摘Preparing carbon nanosheets with precise control of open porous morphology via universal process and understanding the relationship between structure and capacitive performance are very urgent for achieving advanced supercapacitors.Herein,we propose a simple yet effective additive-free method to transform a bulk layered potassium phthalimide salt to novel nitrogen-doped twodimensional carbon sheets by self-activation during calcination.The obtained samples showed large-sized and flat structure with lateral size around 10μm,uniform sub-nanometer micropore size distribution of about 0.65 nm dimension,large specific surface area up to 2276.7 m^(2)g^(-1),and suitable nitrogen doping.Benefited from these merits,the optimized sample delivers a high specific capacitance of 345 F g^(-1)at 1 A g^(-1)and retains 270 F g^(-1)even at 50 A g^(-1)in6.0 M KOH electrolyte.Remarkably,the symmetric supercapacitor shows maximum energy densities of 16.43 Wh kg^(-1)and 23.6 Wh kg^(-1)in 6.0 M KOH and 1.0 M Na_(2)SO_(4)electrolytes,respectively.Importantly,on account the universality and simplicity of this method,the undoped as-prepared carbon sheet with uniform sub-nanometer micropore distribution can be synthesized from different potassium-containing salts with layered structure,which can be employed as a model for a deep understanding the effect of sub-nanometer micropores on capacitive performances.We find the number of micropores centered at 0.65 nm can be applied as one indicator to clarify the correlation between capacitance and critical pore size below 1 nm.
基金supported by the National Key Research and Development Projects of China(No.2022YFF0705802)National Natural Science Foundation of China(62305090)+1 种基金China Postdoctoral Science Foundation(2023M730883)Fellowship of China National Postdoctoral Program for Innovative Talents(BX20230478).
文摘We established a complete model and relationship between laser source characteristics and measurement accuracy of high precision fiber microprobe sensor(FMS)based on phase generated carrier demodulation.The laser carried out high-bandwidth frequency modulation to improve the measurement speed.Meanwhile,the laser also carried out large-amplitude frequency modulation to eliminate tens of nanometers of nonlinear error,thus improving the measurement accuracy.Further,the laser center wavelength is required to be stabilized under the above modulation to achieve a high measurement stability.The conflict between laser frequency modulation and central stability is revealed and analyzed alongside the distortion of measurement accuracy.A modified frequency stabilization method for laser source under high-bandwidth and large-amplitude modulation is proposed for improving measurement accuracy to realize sub-nanometer precision.The experimental results showed that when the modulation bandwidth was 1 MHz and maximum modulation amplitude was 2.61 GHz,the distributed feedback laser central wavelength stability was 2.9×10^(−10)(τ=1s)according to Allan variance.Additionally,the relative expanded uncertainty of the laser wavelength was demonstrated to be superior to 5×10^(−8)(k=2)within 3 hr,which was at least one order of magnitude higher than that of the traditional method.The resolution and stability of FMS is better than 0.4 nm,and the nonlinear error is reduced from tens of nm to 0.8 nm,which meets the requirements of sub-nanometer measurements.
基金supported by the National Natural Science Foundation of China(21722305,21673195,21973079,and 21703188)the National Key R&D Program of China(2017YFA0204902)the Guangdong Basic and Applied Basic Research Foundation(2020A151511106).
文摘Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.
基金supported by the National Key R&D Program of China(2020YFA0710000)the National Natural Science Foundation of China(Grant No.:22122901,21902047)the Provincial Natural Science Foundation of Hunan(2020JJ5045,2021JJ20024,2021RC3054)。
文摘Surface segregation is ubiquitous in multi-component materials and is of great important for catalysis but little is known on the surface structure under graphene encapsulation.Here,we show that the graphene encapsulated CoCu performs well for the electrocatalytic oxidation of 5-hydroxymethylfurfural(HMF)to2,5-furandicarboxylic acid(FDCA)with the onset potential before 1.23 VRHEand a nearly 100%selectivity of FDCA under 1.4 VRHE.From the experimental results,the unprecedented catalytic performance was attributed to local structural distortion and sub-nanometer lattice composition of the CoCu surface.We accurately show the dispersed Cu doped Co_(3)O_(4) nano-islands with a lot of edge sites on the bimetallic Co-Cu surface.While,the gradient components effectively facilitate the establishment of built-in electric field and accelerate the charge transfer.Theoretical and experimental results reveal that the surface Co and neighbouring Cu atoms in sub-nanometer lattice synergistically promote the catalysis of HMF.This work offers new insights into surface segregation in tuning the element spatial distribution for catalysis.
文摘Quantitative optical measurements of deep subwavelength,three-dimensional(3D),nanometric structures with sensitivity to sub-nanometer details address a ubiquitous measurement challenge.A Fourier domain normalization approach is used in the Fourier optical imaging code to simulate the full 3D scattered light field of nominally 15 nm-sized structures,accurately replicating the light field as a function of the focus position.Using the full 3D light field,nanometer scale details such as a 2 nm thin conformal oxide and nanometer topography are rigorously fitted for features less than one-thirtieth of the wavelength in size.The densely packed structures are positioned nearly an order of magnitude closer than the conventional Rayleigh resolution limit and can be measured with sub-nanometer parametric uncertainties.This approach enables a practical measurement sensitivity to size variations of only a few atoms in size using a high-throughput optical configuration with broad application in measuring nanometric structures and nanoelectronic devices.
