Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and ...Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.展开更多
Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications,such as imaging,information encryption,and all-optical cohere...Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications,such as imaging,information encryption,and all-optical coherent control of terahertz nonlinear phenomena.Topological insulators featuring unique spinmomentum-locked surface state have already exhibited very promising prospects in terahertz emission,detection,and modulation,which may lay a foundation for future on-chip topological insulator-based terahertz systems.However,polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored.We systematically investigated the terahertz radiation from topological insulator Bi2Te3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality,ellipticity,and principal axis.The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect(PGE)-induced photocurrent,while the linearly polarized terahertz waves originated from linear PGE-induced shift currents.Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.展开更多
Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance m...Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance materials in renewable,green energy conversions,devices for energy storage,and as biosensors for environmental pollutants.However,several strategies used in fabricating these materials still impose enormous challenges,arising from lack of even size distribution,shape uniformity,and controlled composition,which are critical in determining their specific activities and efficiencies.Herein,we report a facile approach for preparing sub-nano-thick palladium nanobelt-based(PdNB)materials.Then we rationalized the formation mechanism of such highly anisotropic structures by morphology-related thermodynamic and kinetic analysis.Moreover,we investigated if electrocatalysis performance of these NB-basedmaterialswere enhanced.Thepalladium(Pd)NBs featured a thickness of∼0.9-1.2 nm and width of 5-18nmwith length extending to severalmicrometers[denoted as Pd(0.9)],or a thickness of∼0.7-0.9 nm and width of 2.5-6 nmwith length of several hundreds of nanometers[denoted as Pd(0.7)].According to our theoretical analysis,one-dimensional(1D)growth encountered almost no energy barrier at optimal reaction conditions,whereas the growth of Pd nanostructures with other dimensions confronted high barriers,indicating that it was plausible to prepare 1D structures with sizes close to single-unit cells.Also,platinum(Pt)could be successfully doped into the Pd(0.9)NBs through a galvanic epitaxial growth,forming edge-Pt-enriched Pd NBs(eePtPd NBs).Further,electron transfer from Pd to Pt imparted the eePtPd NBs with high hydrogen evolution reaction(HER)activity.The eePtPd NBs showed a 3.5 and 1.8 times higher in exchange current density and mass activity(at−0.1 V),respectively,compared to those of Pt catalysts in perchloric acid(HClO_(4))solutions.Finally,the NBs all showed high activity toward ethanol and formic acid oxidation reactions.Our current work aids in gaining insights into tailoring Pd nanostructures at an atomic level and provides Pd sub-nanometric 1D structures for further research.Moreover,our morphology-related thermodynamic and kinetic analysis extend our understanding of the control of nanostructure morphology and might shed light on the precision of designing specific morphologies of noble metal nanocrystal structures.展开更多
We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources,...We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources,which is difficult to be resolved in conventional terahertz imaging systems.To verify the method,we intentionally fabricate tiny variations of the terahertz beam through tuning the iris for the infrared pumping beam before the tilted-pulse-front pumping setups.The phenomena can be well explained by the theory based on the tilted-pulse-front technique and terahertz diffraction.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.22278123).
文摘Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.
基金This work was supported by Beijing Natural Science Foundation(Grant No.4194083)the National Natural Science Foundation of China(Grant Nos.61905007,61774013,11827807,and 61731001)+3 种基金the National Key R&D Program of China(Grant Nos.2019YFB2203102 and 2018YFB0407602)the International Collaboration Project(Grant No.B16001)the National Key Technology Program of China(Grant No.2017ZX01032101)the Open Project Program of Wuhan National Laboratory for Optoelectronics(Grant No.2018WNLOKF001).
文摘Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications,such as imaging,information encryption,and all-optical coherent control of terahertz nonlinear phenomena.Topological insulators featuring unique spinmomentum-locked surface state have already exhibited very promising prospects in terahertz emission,detection,and modulation,which may lay a foundation for future on-chip topological insulator-based terahertz systems.However,polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored.We systematically investigated the terahertz radiation from topological insulator Bi2Te3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality,ellipticity,and principal axis.The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect(PGE)-induced photocurrent,while the linearly polarized terahertz waves originated from linear PGE-induced shift currents.Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.
基金This work was supported by the National Key R&D Program of China(2017YFA0700101 and 2016YFA0202801)NSFC(21431003 and 21521091).
文摘Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance materials in renewable,green energy conversions,devices for energy storage,and as biosensors for environmental pollutants.However,several strategies used in fabricating these materials still impose enormous challenges,arising from lack of even size distribution,shape uniformity,and controlled composition,which are critical in determining their specific activities and efficiencies.Herein,we report a facile approach for preparing sub-nano-thick palladium nanobelt-based(PdNB)materials.Then we rationalized the formation mechanism of such highly anisotropic structures by morphology-related thermodynamic and kinetic analysis.Moreover,we investigated if electrocatalysis performance of these NB-basedmaterialswere enhanced.Thepalladium(Pd)NBs featured a thickness of∼0.9-1.2 nm and width of 5-18nmwith length extending to severalmicrometers[denoted as Pd(0.9)],or a thickness of∼0.7-0.9 nm and width of 2.5-6 nmwith length of several hundreds of nanometers[denoted as Pd(0.7)].According to our theoretical analysis,one-dimensional(1D)growth encountered almost no energy barrier at optimal reaction conditions,whereas the growth of Pd nanostructures with other dimensions confronted high barriers,indicating that it was plausible to prepare 1D structures with sizes close to single-unit cells.Also,platinum(Pt)could be successfully doped into the Pd(0.9)NBs through a galvanic epitaxial growth,forming edge-Pt-enriched Pd NBs(eePtPd NBs).Further,electron transfer from Pd to Pt imparted the eePtPd NBs with high hydrogen evolution reaction(HER)activity.The eePtPd NBs showed a 3.5 and 1.8 times higher in exchange current density and mass activity(at−0.1 V),respectively,compared to those of Pt catalysts in perchloric acid(HClO_(4))solutions.Finally,the NBs all showed high activity toward ethanol and formic acid oxidation reactions.Our current work aids in gaining insights into tailoring Pd nanostructures at an atomic level and provides Pd sub-nanometric 1D structures for further research.Moreover,our morphology-related thermodynamic and kinetic analysis extend our understanding of the control of nanostructure morphology and might shed light on the precision of designing specific morphologies of noble metal nanocrystal structures.
基金the Science Challenge Project(No.TZ2016005)the NationalNatural Science Foundation of China(Nos.11827807,61905007,11520101003,and 11861121001)the Strategic Priority Research Programof the Chinese Academy of Sciences(No.XDB16010200)。
文摘We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources,which is difficult to be resolved in conventional terahertz imaging systems.To verify the method,we intentionally fabricate tiny variations of the terahertz beam through tuning the iris for the infrared pumping beam before the tilted-pulse-front pumping setups.The phenomena can be well explained by the theory based on the tilted-pulse-front technique and terahertz diffraction.
