A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural featur...A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural features shows that the NCs samples are composed of few-layered graphene-like nanoflakes with controlled in situ N doping, which is attributed to the confined pyrolysis of citric acid within the interlayers of the dicyandiamide-derived g-C_3N_4 with high nitrogen contents. Evidently, the pore volumes of the NCs increased with the increasing content of dicyandiamide in the precursor. Among these samples, the NCs nanoflakes prepared with the citric acid/dicyandiamide mass ratio of 1:6, NC-6,show the highest N content of ~6.2 at%, in which pyridinic and graphitic N groups are predominant. Compared to the commercial Pt/C catalyst, the as-prepared NC-6 exhibits a small negative shift of ~66 mV at the half-wave potential, demonstrating excellent electrocatalytic activity in the oxygen reduction reaction. Moreover, NC-6 also shows better long-term stability and resistance to methanol crossover compared to Pt/C. The efficient and stable performance are attributed to the graphene-like microstructure and high content of pyridinic and graphitic doped nitrogen in the sample, which creates more active sites as well as facilitating charge transfer due to the close four-electron reaction pathway. The superior electrocatalytic activity coupled with the facile synthetic method presents a new pathway to cost-effective electrocatalysts for practical fuel cells or metal–air batteries.展开更多
Rational design of advanced cost-effective electrocatalysts is vital for the development of water electrolysis. Herein, we report a novel binder-free efficient CoS@CoOcore/shell electrocatalysts for oxygen evolution r...Rational design of advanced cost-effective electrocatalysts is vital for the development of water electrolysis. Herein, we report a novel binder-free efficient CoS@CoOcore/shell electrocatalysts for oxygen evolution reaction（OER） via a combined hydrothermal-sulfurization method. The sulfurized net-like CoSnanoflakes are strongly anchored on the CoOnanowire core forming self-supported binder-free core/shell electrocatalysts. Positive advantages including larger active surface area of CoSnanoflakes,and reinforced structural stability are achieved in the CoS@CoOcore/shell arrays. The OER performances of the CoS@CoOcore/shell arrays are thoroughly tested and enhanced electrocatalytic performance with lower over-potential(260 m V at 20 m A cm) and smaller Tafel slopes（56 mV dec-1） as well as long-term durability are demonstrated in alkaline medium. Our proposed core/shell smart design may provide a new way to construct other advanced binder-free electrocatalysts for applications in electrochemical catalysis.展开更多
We perform first-principles calculations and coherent laser-matter interaction analyses to investigate the laser-induced ultrafast spin flip on graphene nanoflakes(GNFs)with transition metal elements attached on the b...We perform first-principles calculations and coherent laser-matter interaction analyses to investigate the laser-induced ultrafast spin flip on graphene nanoflakes(GNFs)with transition metal elements attached on the boundary[TM&GNFs(TM=Fe,Co,Ni)].It is shown that the spin-flip process on TM&GNFs is highly influenced by the involved element species and the position attached to the nanoflakes.Furthermore,taking Ni&GNF as an example,the first-principles tensile test predicts that the variation of the C-Ni bond length plays an important role in the spin density distribution,especially for the low-lying magnetic states,and can therefore dominate the spin-flip processes.The fastest spin-flip scenario is achieved within 80 fs in a Ni&GNF structure under 10%tensile strain along the C-Ni bond.The local deformation modulation of spin flip provides the precursory guidance for further study of ultrafast magnetization control in GNFs,which could lead to potential applications in future integrated straintronic devices.展开更多
PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly...PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly in the ranges of 50–100 nm and 0.5–3 μm, respectively. The x-ray diffraction patterns demonstrate that the heat treatment can increase the single phase and crystallinity of the PrCo5 compound, and combined with the demagnetization curves, indicate that the single phase and crystallinity are important for preparing high-coercivity and strong-textured rare earth permanent magnetic nanoflakes. In addition, the coercivity mechanism of the as-milled PrCo5 nanoflakes is studied by the angle dependence of coercivity for an aligned sample and the field dependence of coercivity, isothermal（IRM） and dc demagnetizing（DCD）remanence curves for an unaligned sample. The results indicate that the coercivity is dominated by co-existing mechanisms of pinning and nucleation. Furthermore, exchange coupling and dipolar coupling also co-exist in the sample.展开更多
A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes(GNFs),including sum-and difference-frequency generation,as well as four-wave mixing.Our analysis s...A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes(GNFs),including sum-and difference-frequency generation,as well as four-wave mixing.Our analysis shows that molecular-scale GNFs support quantum plasmons in the visible spectrum region,and significant enhancement of nonlinear optical wave mixing is achieved.Specifically,the second-and third-order wave-mixing polarizabilities of GNFs are dramatically enhanced,provided that one(or more) of the input or output frequencies coincide with a quantum plasmon resonance.Moreover,by embedding a cavity into hexagonal GNFs,we show that one can break the structural inversion symmetry and enable otherwise forbidden second-order wave mixing,which is found to be enhanced by the quantum plasmon resonance too.This study reveals that the molecular-sized graphene could be used in the quantum regime for nanoscale nonlinear optical devices and ultrasensitive molecular sensors.展开更多
Adsorption of 1,3,5-triphenylbenzene （TPB） molecules on Cu（100） surface is studied using ultraviolet photo- electron spectroscopy （UPS） and density functional theory （DFT） calculations. Researches on the botto...Adsorption of 1,3,5-triphenylbenzene （TPB） molecules on Cu（100） surface is studied using ultraviolet photo- electron spectroscopy （UPS） and density functional theory （DFT） calculations. Researches on the bottom-up fabrication of graphene nanoflakes （GNFs） with TPB as a precursor on the Cu（100） surface are carried out based on UPS and DFT calculations. Three emission features d, e and f originating from the TPB molecules are located at 3.095, 7.326 and 9.349 eV below the Fermi level, respectively. With the increase of TPB coverage on the Cu（100） substrate, the work function decreases due to the formation of interfacial dipoles and charge （electron） rearrangement at the TPB/Cu（100） interface. Upon the formation of GNFs, five emission characteristic peaks of g, h, i, j and k originating from the GNFs are located at 1.100, 3.529, 6.984, 8.465 and 9.606eV below the Fermi level, respectively. Angle resolved ultraviolet photoelectron spectroscopy （ARUPS） and DFT calculations indicate that TPB molecules adopt a lying-down configuration with their molecular plane nearly parallel to the Cu（100） substrate at the monolayer stage. At the same time, the lying-down configuration for the GNFs on the Cu（100） surface is also unveiled by ARUPS and DFT calculations.展开更多
Oxygen vacancy plays vital roles in regulating the electronic and charge distribution of the oxygen deficient materials.Herein,abundant oxygen vacancies are created during assembling the two-dimensional(2D)ultra-thin ...Oxygen vacancy plays vital roles in regulating the electronic and charge distribution of the oxygen deficient materials.Herein,abundant oxygen vacancies are created during assembling the two-dimensional(2D)ultra-thin Bi_(2)MoO_(6) nanoflakes into three dimensional(3D)Bi_(2)MoO_(6) nanospheres,resulting in significantly improved performance for photocatalytical conversion of CO_(2) into liquid hydrocarbons.The increased performance is contributed by two primary sites,namely the abundant oxygen vacancy and the exposed molybdenum(Mo)atom induced by oxygen-migration,as revealed by the theoretical calculation.The oxygen vacancy(Ov)and uncovered Mo atom serving as dual binding sites for trapping CO_(2) molecules render the synchronous fixation-reduction process,resulting in the decline of activation energy for CO_(2) reduction from 2.15 eV on bulk Bi_(2)MoO_(6) to 1.42 eV on Ov-rich Bi_(2)MoO_(6).Such a striking decrease in the activation energy induces the efficient selective generation of liquid hydrocarbons,especially the methanol(C_(2)H_(5) OH)and ethanol(CH_(3) OH).The yields of CH_(3) OH and C_(2)H_(5) OH over the optimal Ov-Bi_(2)MoO_(6) is high up to 106.5 and 10.3μmol g^(-1) respectively,greatly outperforming that on the Bulk-Bi_(2)MoO_(6).展开更多
Lithium-sulfur(Li-S)batteries suffer from the shuttle effect of soluble lithium polysulfides(LiPSs)and slow redox kinetics,significantly limiting their practical application.Although single-atom catalysts(SACs)offer a...Lithium-sulfur(Li-S)batteries suffer from the shuttle effect of soluble lithium polysulfides(LiPSs)and slow redox kinetics,significantly limiting their practical application.Although single-atom catalysts(SACs)offer a promising strategy to address these challenges,designing materials with optimal adsorption force and high catalytic activity remains a grand challenge.Here,we present a cobalt(Co)-based SAC with unique Co-O_(2)N_(2) coordination structures for Li-S batteries.Both experimental and theoretical studies demonstrate that O,N-coordinated Co single atoms anchored on a porous carbon framework(Co/NOC)effectively capture LiPSs and dramatically catalyze bidirectional polysulfide conversion.The expanded carbon layer spacing facilitates lithium ions diffusion and maximizes the exposure of active sites.As a result,Li-S batteries incorporating Co/NOC as separators exhibit outstanding rate performance(906.6m Ah g^(-1)at 3 C)and exceptional cycling stability,even at-10℃.Furthermore,with a high sulfur loading of 12.0 mg cm^(-2),the areal specific capacity reaches up to 12.36 mAh cm^(-2).This work provides some useful insights for the design of high-performance SACs for Li-S batteries.展开更多
Metal–organic frameworks(MOFs) are of great interest as potential electrochemically active materials.However, few studies have been conducted into understanding whether control of the shape and components of MOFs can...Metal–organic frameworks(MOFs) are of great interest as potential electrochemically active materials.However, few studies have been conducted into understanding whether control of the shape and components of MOFs can optimize their electrochemical performances due to the rational realization of their shapes. Component control of MOFs remains a significant challenge. Herein, we demonstrate a solvothermal method to realize nanostructure engineering of 2D nanoflake MOFs. The hollow structures withNi/Co-and Ni-MOF(denoted as Ni/Co-MOF nanoflakes and Ni-MOF nanoflakes) were assembled for their electrochemical performance optimizations in supercapacitors and in the oxygen reduction reaction(ORR). As a result, the Ni/CoMOF nanoflakes exhibited remarkably enhanced performance with a specific capacitance of 530.4 F g^(-1)at 0.5 A g^(-1)in1 M LiO H aqueous solution, much higher than that of NiMOF(306.8 F g^(-1)) and ZIF-67(168.3 F g^(-1)), a good rate capability, and a robust cycling performance with no capacity fading after 2000 cycles. Ni/Co-MOF nanoflakes also showed improved electrocatalytic performance for the ORR compared to Ni-MOF and ZIF-67. The present work highlights the significant role of tuning 2D nanoflake ensembles of Ni/Co-MOF in accelerating electron and charge transportation for optimizing energy storage and conversion devices.展开更多
The rational design and synthesis of two-dimensional(2D) nanoflake ensemble-based materials have garnered great attention owing to the properties of the components of these materials, such as high mechanical flexibili...The rational design and synthesis of two-dimensional(2D) nanoflake ensemble-based materials have garnered great attention owing to the properties of the components of these materials, such as high mechanical flexibility, high specific surface area, numerous active sites,chemical stability, and superior electrical and thermal conductivity. These properties render the 2D ensembles great choices as alternative electrode materials for electrochemical energy storage systems. More recently,recognition of the numerous advantages of these 2D ensemble structures has led to the realization that the performance of certain devices could be significantly enhanced by utilizing three-dimensional(3D) architectures that can furnish an increased number of active sites. The present review summarizes the recent progress in 2D ensemble-based materials for energy storage applications,including supercapacitors, lithium-ion batteries, and sodium-ion batteries. Further, perspectives relating to the challenges and opportunities in this promising research area are discussed.展开更多
Dendrite growth and thermal runaway induce serious safety hazards,impeding the practical applications of lithium metal batteries(LMBs).Although extensive advances have been attained in terms of LMB safety,most work on...Dendrite growth and thermal runaway induce serious safety hazards,impeding the practical applications of lithium metal batteries(LMBs).Although extensive advances have been attained in terms of LMB safety,most work only focus on a single aspect at a time.This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability,ionic conductivity,Li+ transference number,puncture strength,thermal stability and flame retardance.When used in LMBs,the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing,which makes it homogeneous to deposit lithium,realizing effective dendrite suppression and less volume expansion.Meanwhile,Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 ℃.A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles,not only reducing the risk of separator damage and consequent short circuit,but also replenishing the capacity loss of LMBs.The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances,which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.展开更多
The paper reports the fabrication of Zn-doped TiO_2 nanotubes(Zn-TONT)/ZnO nanoflakes heterostructure for the first time,which shows improved performance as a photoanode in dye-sensitized solar cell(DSSC).The layered ...The paper reports the fabrication of Zn-doped TiO_2 nanotubes(Zn-TONT)/ZnO nanoflakes heterostructure for the first time,which shows improved performance as a photoanode in dye-sensitized solar cell(DSSC).The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy,scanning electron microscopy,and X-ray diffractometer.The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency,over pure TiO_2 photoanodes.Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC.展开更多
High-temperature thermal oxidation of an Fe foil produces a high-quality,crystalline hematite nanoflake suitable as a photoanode for the photoelectrochemical(PEC)water oxidation.Physical pre-polishing of the foil surf...High-temperature thermal oxidation of an Fe foil produces a high-quality,crystalline hematite nanoflake suitable as a photoanode for the photoelectrochemical(PEC)water oxidation.Physical pre-polishing of the foil surface has a profound effect in the formation of a vertically-aligned nanoflakes of hematite phase with extended(110)planes by removing the loosely-bonded oxide layer.When the surface of the photoanode is modified with a ZrO_(2) passivation layer and a cobalt phosphate co-catalyst,the charge recombination at the photoanode-electrolyte interface is greatly suppressed to improve its overall PEC activity.As a result,the photocurrent density at 1.10 VRHE under 1 sun condition is enhanced from 0.22 mA cm^(-2) for an unmodified photoanode to 0.59 mA cm^(-2) for the fully modified photoanode,and the photocurrent onset potential is shifted cathodically by 400 mV.Moreover,the photoanode demonstrates outstanding stability by showing steady production of H_(2) and O_(2) gases in the stoichiometric ratio of 2:1 in a continuous PEC operation for 10 h.展开更多
We present the synthesis of TaCoTe_(2) single crystals and a systematic investigation of the physical properties of bulk crystals and thin flakes.The crystal shows a semiconducting behavior with temperature decreasing...We present the synthesis of TaCoTe_(2) single crystals and a systematic investigation of the physical properties of bulk crystals and thin flakes.The crystal shows a semiconducting behavior with temperature decreasing from room temperature and turns to a metallic behavior below 38 K.When the magnetic field is applied,the temperature-dependent resistivity curves show an upturn below 10 K.Furthermore,we find that the TaCoTe_(2) single crystal can be easily exfoliated from the bulk crystal by the micromechanical exfoliation method.Our measurements suggest that the nanoflakes have properties similar to those of the bulk crystal when the thickness is lowered to 18 nm.展开更多
基金the financial support from the National Key Research and Development Program of China (2016YFB0700204)Natural Science Foundation of Jiangsu Province (No. BK20140472)+2 种基金NSFC (51602332, 51502327)Science and Technology Commission of Shanghai Municipality (15520720400, 15YF1413800, 14DZ2261203, 16DZ2260603)One Hundred Talent Plan of Chinese Academy of Sciences
文摘A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural features shows that the NCs samples are composed of few-layered graphene-like nanoflakes with controlled in situ N doping, which is attributed to the confined pyrolysis of citric acid within the interlayers of the dicyandiamide-derived g-C_3N_4 with high nitrogen contents. Evidently, the pore volumes of the NCs increased with the increasing content of dicyandiamide in the precursor. Among these samples, the NCs nanoflakes prepared with the citric acid/dicyandiamide mass ratio of 1:6, NC-6,show the highest N content of ~6.2 at%, in which pyridinic and graphitic N groups are predominant. Compared to the commercial Pt/C catalyst, the as-prepared NC-6 exhibits a small negative shift of ~66 mV at the half-wave potential, demonstrating excellent electrocatalytic activity in the oxygen reduction reaction. Moreover, NC-6 also shows better long-term stability and resistance to methanol crossover compared to Pt/C. The efficient and stable performance are attributed to the graphene-like microstructure and high content of pyridinic and graphitic doped nitrogen in the sample, which creates more active sites as well as facilitating charge transfer due to the close four-electron reaction pathway. The superior electrocatalytic activity coupled with the facile synthetic method presents a new pathway to cost-effective electrocatalysts for practical fuel cells or metal–air batteries.
基金supported by the National Natural Science Foundation of China (grant no. 51728204, 51772272 and 51502263)Qianjiang Talents Plan D (grant. no. QJD1602029)+2 种基金the Startup Foundation for Hundred-Talent Program of Zhejiang Universitysupport by the Program for Innovative Research Team in University of Ministry of Education of China (IRT13037)the Key Science and Technology Innovation Team of Zhejiang Province (2010R50013)
文摘Rational design of advanced cost-effective electrocatalysts is vital for the development of water electrolysis. Herein, we report a novel binder-free efficient CoS@CoOcore/shell electrocatalysts for oxygen evolution reaction（OER） via a combined hydrothermal-sulfurization method. The sulfurized net-like CoSnanoflakes are strongly anchored on the CoOnanowire core forming self-supported binder-free core/shell electrocatalysts. Positive advantages including larger active surface area of CoSnanoflakes,and reinforced structural stability are achieved in the CoS@CoOcore/shell arrays. The OER performances of the CoS@CoOcore/shell arrays are thoroughly tested and enhanced electrocatalytic performance with lower over-potential(260 m V at 20 m A cm) and smaller Tafel slopes（56 mV dec-1） as well as long-term durability are demonstrated in alkaline medium. Our proposed core/shell smart design may provide a new way to construct other advanced binder-free electrocatalysts for applications in electrochemical catalysis.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11872309,12172293,and 11504223)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2020JM-120)the Program of China Scholarships Council(Grant No.201906295029).
文摘We perform first-principles calculations and coherent laser-matter interaction analyses to investigate the laser-induced ultrafast spin flip on graphene nanoflakes(GNFs)with transition metal elements attached on the boundary[TM&GNFs(TM=Fe,Co,Ni)].It is shown that the spin-flip process on TM&GNFs is highly influenced by the involved element species and the position attached to the nanoflakes.Furthermore,taking Ni&GNF as an example,the first-principles tensile test predicts that the variation of the C-Ni bond length plays an important role in the spin density distribution,especially for the low-lying magnetic states,and can therefore dominate the spin-flip processes.The fastest spin-flip scenario is achieved within 80 fs in a Ni&GNF structure under 10%tensile strain along the C-Ni bond.The local deformation modulation of spin flip provides the precursory guidance for further study of ultrafast magnetization control in GNFs,which could lead to potential applications in future integrated straintronic devices.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB643702)the National Natural Science Foundation of China(Grant No.51401235)Beijing Natural Science Foundation,China(Grant No.2152034)
文摘PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly in the ranges of 50–100 nm and 0.5–3 μm, respectively. The x-ray diffraction patterns demonstrate that the heat treatment can increase the single phase and crystallinity of the PrCo5 compound, and combined with the demagnetization curves, indicate that the single phase and crystallinity are important for preparing high-coercivity and strong-textured rare earth permanent magnetic nanoflakes. In addition, the coercivity mechanism of the as-milled PrCo5 nanoflakes is studied by the angle dependence of coercivity for an aligned sample and the field dependence of coercivity, isothermal（IRM） and dc demagnetizing（DCD）remanence curves for an unaligned sample. The results indicate that the coercivity is dominated by co-existing mechanisms of pinning and nucleation. Furthermore, exchange coupling and dipolar coupling also co-exist in the sample.
基金Project supported by the National Natural Science Foundation of China(Grant No.11947007)the Natural Science Foundation of Guangdong Province,China(Grant No.2019A1515011499)the Department of Education of Guangdong Province,China(Grant No.2019KTSCX087)。
文摘A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes(GNFs),including sum-and difference-frequency generation,as well as four-wave mixing.Our analysis shows that molecular-scale GNFs support quantum plasmons in the visible spectrum region,and significant enhancement of nonlinear optical wave mixing is achieved.Specifically,the second-and third-order wave-mixing polarizabilities of GNFs are dramatically enhanced,provided that one(or more) of the input or output frequencies coincide with a quantum plasmon resonance.Moreover,by embedding a cavity into hexagonal GNFs,we show that one can break the structural inversion symmetry and enable otherwise forbidden second-order wave mixing,which is found to be enhanced by the quantum plasmon resonance too.This study reveals that the molecular-sized graphene could be used in the quantum regime for nanoscale nonlinear optical devices and ultrasensitive molecular sensors.
基金Supported by the National Basic Research Program of China under Grant No 2011CB921903the Scientific Research Fund of Zhejiang Provincial Education Department under Grant Nos Y201121234 and LQ12F04001
文摘Adsorption of 1,3,5-triphenylbenzene （TPB） molecules on Cu（100） surface is studied using ultraviolet photo- electron spectroscopy （UPS） and density functional theory （DFT） calculations. Researches on the bottom-up fabrication of graphene nanoflakes （GNFs） with TPB as a precursor on the Cu（100） surface are carried out based on UPS and DFT calculations. Three emission features d, e and f originating from the TPB molecules are located at 3.095, 7.326 and 9.349 eV below the Fermi level, respectively. With the increase of TPB coverage on the Cu（100） substrate, the work function decreases due to the formation of interfacial dipoles and charge （electron） rearrangement at the TPB/Cu（100） interface. Upon the formation of GNFs, five emission characteristic peaks of g, h, i, j and k originating from the GNFs are located at 1.100, 3.529, 6.984, 8.465 and 9.606eV below the Fermi level, respectively. Angle resolved ultraviolet photoelectron spectroscopy （ARUPS） and DFT calculations indicate that TPB molecules adopt a lying-down configuration with their molecular plane nearly parallel to the Cu（100） substrate at the monolayer stage. At the same time, the lying-down configuration for the GNFs on the Cu（100） surface is also unveiled by ARUPS and DFT calculations.
基金financially supported by the National Natural Science Foundation of China(Grants 52072165,52070092,51662031)。
文摘Oxygen vacancy plays vital roles in regulating the electronic and charge distribution of the oxygen deficient materials.Herein,abundant oxygen vacancies are created during assembling the two-dimensional(2D)ultra-thin Bi_(2)MoO_(6) nanoflakes into three dimensional(3D)Bi_(2)MoO_(6) nanospheres,resulting in significantly improved performance for photocatalytical conversion of CO_(2) into liquid hydrocarbons.The increased performance is contributed by two primary sites,namely the abundant oxygen vacancy and the exposed molybdenum(Mo)atom induced by oxygen-migration,as revealed by the theoretical calculation.The oxygen vacancy(Ov)and uncovered Mo atom serving as dual binding sites for trapping CO_(2) molecules render the synchronous fixation-reduction process,resulting in the decline of activation energy for CO_(2) reduction from 2.15 eV on bulk Bi_(2)MoO_(6) to 1.42 eV on Ov-rich Bi_(2)MoO_(6).Such a striking decrease in the activation energy induces the efficient selective generation of liquid hydrocarbons,especially the methanol(C_(2)H_(5) OH)and ethanol(CH_(3) OH).The yields of CH_(3) OH and C_(2)H_(5) OH over the optimal Ov-Bi_(2)MoO_(6) is high up to 106.5 and 10.3μmol g^(-1) respectively,greatly outperforming that on the Bulk-Bi_(2)MoO_(6).
基金supported financially by the National Natural Science Foundation of China(NSFC)(Grant No.22208174 and 52272221)the New Colleges and Universities Twenty Foundational Projects of Jinan City(2021GXRC068)+2 种基金the Universities Youth Innovation Team Development Plan of Shandong Province(2023KJ140)the Natural Science Foundation of Shandong Province(ZR2022MB143)the Basic Research Projects of Science,Education,Industry Integration Pilot Engineering of Qilu University of Technology(Shandong Academy of Sciences)(2023PY002)。
文摘Lithium-sulfur(Li-S)batteries suffer from the shuttle effect of soluble lithium polysulfides(LiPSs)and slow redox kinetics,significantly limiting their practical application.Although single-atom catalysts(SACs)offer a promising strategy to address these challenges,designing materials with optimal adsorption force and high catalytic activity remains a grand challenge.Here,we present a cobalt(Co)-based SAC with unique Co-O_(2)N_(2) coordination structures for Li-S batteries.Both experimental and theoretical studies demonstrate that O,N-coordinated Co single atoms anchored on a porous carbon framework(Co/NOC)effectively capture LiPSs and dramatically catalyze bidirectional polysulfide conversion.The expanded carbon layer spacing facilitates lithium ions diffusion and maximizes the exposure of active sites.As a result,Li-S batteries incorporating Co/NOC as separators exhibit outstanding rate performance(906.6m Ah g^(-1)at 3 C)and exceptional cycling stability,even at-10℃.Furthermore,with a high sulfur loading of 12.0 mg cm^(-2),the areal specific capacity reaches up to 12.36 mAh cm^(-2).This work provides some useful insights for the design of high-performance SACs for Li-S batteries.
基金supported by the National Natural Science Foundation of China (Nos. 21571157, U1604123, and 51473149)Outstanding Young Talent Research Fund of Zhengzhou University (1521320001)+1 种基金the Open Project Foundation of Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) (2017–29),Nankai UniversityOpen Project Foundation of Key Laboratory of Inorganic Synthesis and Preparation of Jilin University
文摘Metal–organic frameworks(MOFs) are of great interest as potential electrochemically active materials.However, few studies have been conducted into understanding whether control of the shape and components of MOFs can optimize their electrochemical performances due to the rational realization of their shapes. Component control of MOFs remains a significant challenge. Herein, we demonstrate a solvothermal method to realize nanostructure engineering of 2D nanoflake MOFs. The hollow structures withNi/Co-and Ni-MOF(denoted as Ni/Co-MOF nanoflakes and Ni-MOF nanoflakes) were assembled for their electrochemical performance optimizations in supercapacitors and in the oxygen reduction reaction(ORR). As a result, the Ni/CoMOF nanoflakes exhibited remarkably enhanced performance with a specific capacitance of 530.4 F g^(-1)at 0.5 A g^(-1)in1 M LiO H aqueous solution, much higher than that of NiMOF(306.8 F g^(-1)) and ZIF-67(168.3 F g^(-1)), a good rate capability, and a robust cycling performance with no capacity fading after 2000 cycles. Ni/Co-MOF nanoflakes also showed improved electrocatalytic performance for the ORR compared to Ni-MOF and ZIF-67. The present work highlights the significant role of tuning 2D nanoflake ensembles of Ni/Co-MOF in accelerating electron and charge transportation for optimizing energy storage and conversion devices.
基金supported by the National Natural Science Foundation of China (21571157,U1604123,and 2187051489)Outstanding Young Talent Research Fund of Zhengzhou University (No.1521320001)+3 种基金the Young Outstanding Teachers of University in Henan Province (2016-130)Creative talents in the Education Department of Henan Province (19HASTIT039)the Open Project Foundation of Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) (2017-29),Nankai UniversityOpen Project Foundation of State Key Laboratory of Inorganic Synthesis and Preparation of Jilin University
文摘The rational design and synthesis of two-dimensional(2D) nanoflake ensemble-based materials have garnered great attention owing to the properties of the components of these materials, such as high mechanical flexibility, high specific surface area, numerous active sites,chemical stability, and superior electrical and thermal conductivity. These properties render the 2D ensembles great choices as alternative electrode materials for electrochemical energy storage systems. More recently,recognition of the numerous advantages of these 2D ensemble structures has led to the realization that the performance of certain devices could be significantly enhanced by utilizing three-dimensional(3D) architectures that can furnish an increased number of active sites. The present review summarizes the recent progress in 2D ensemble-based materials for energy storage applications,including supercapacitors, lithium-ion batteries, and sodium-ion batteries. Further, perspectives relating to the challenges and opportunities in this promising research area are discussed.
基金supported by the Natural Science Project from Science and Technology Department of Henan Province (172102410034)National Natural Science Foundation of China (NSFC-U1604120)。
文摘Dendrite growth and thermal runaway induce serious safety hazards,impeding the practical applications of lithium metal batteries(LMBs).Although extensive advances have been attained in terms of LMB safety,most work only focus on a single aspect at a time.This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability,ionic conductivity,Li+ transference number,puncture strength,thermal stability and flame retardance.When used in LMBs,the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing,which makes it homogeneous to deposit lithium,realizing effective dendrite suppression and less volume expansion.Meanwhile,Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 ℃.A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles,not only reducing the risk of separator damage and consequent short circuit,but also replenishing the capacity loss of LMBs.The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances,which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.
基金UGC-DAE CSR,Indore,for funding through a collaborative project and SAIF IIT Bombay for the help with SEMsupported by the Michigan Space Grant Consortium+1 种基金by Hope CollegeDAE-BRNS for funding the preliminary works
文摘The paper reports the fabrication of Zn-doped TiO_2 nanotubes(Zn-TONT)/ZnO nanoflakes heterostructure for the first time,which shows improved performance as a photoanode in dye-sensitized solar cell(DSSC).The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy,scanning electron microscopy,and X-ray diffractometer.The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency,over pure TiO_2 photoanodes.Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC.
基金supported by the Climate Change Response Project(NRF-2019M1A2A2065612)the Basic Science Grant(NRF2019R1A4A1029237)+3 种基金Korea-China Key Joint Research Program(2017K2A9A2A11070341)funded by the Ministry of Science and ICTthe 2019 Research Fund(1.190013.01)of UNISTsupport by the Basic Science Research Programs through the National Public Technology Program based on Environmental Policy(2014000160001)the SRC program through the National Research Foundation of Korea(NRF2015R1A5A1009962)。
文摘High-temperature thermal oxidation of an Fe foil produces a high-quality,crystalline hematite nanoflake suitable as a photoanode for the photoelectrochemical(PEC)water oxidation.Physical pre-polishing of the foil surface has a profound effect in the formation of a vertically-aligned nanoflakes of hematite phase with extended(110)planes by removing the loosely-bonded oxide layer.When the surface of the photoanode is modified with a ZrO_(2) passivation layer and a cobalt phosphate co-catalyst,the charge recombination at the photoanode-electrolyte interface is greatly suppressed to improve its overall PEC activity.As a result,the photocurrent density at 1.10 VRHE under 1 sun condition is enhanced from 0.22 mA cm^(-2) for an unmodified photoanode to 0.59 mA cm^(-2) for the fully modified photoanode,and the photocurrent onset potential is shifted cathodically by 400 mV.Moreover,the photoanode demonstrates outstanding stability by showing steady production of H_(2) and O_(2) gases in the stoichiometric ratio of 2:1 in a continuous PEC operation for 10 h.
基金Project supported by the National Key Research and Development Program of China (Grant No.2021YFA1600201)the National Natural Science Foundation of China (Grant Nos.U19A2093,U2032214,and U2032163)+4 种基金Collaborative Innovation Program of Hefei Science Center,CAS (Grant No.2019HSC-CIP 001)Youth Innovation Promotion Association of CAS (Grant No.2021117)the HFIPS Director’s Fund (Grant No.YZJJQY202304)the CASHIPS Director’s Fund (Grant No.E26MMG71131)supported by the High Magnetic Field Laboratory of Anhui Province。
文摘We present the synthesis of TaCoTe_(2) single crystals and a systematic investigation of the physical properties of bulk crystals and thin flakes.The crystal shows a semiconducting behavior with temperature decreasing from room temperature and turns to a metallic behavior below 38 K.When the magnetic field is applied,the temperature-dependent resistivity curves show an upturn below 10 K.Furthermore,we find that the TaCoTe_(2) single crystal can be easily exfoliated from the bulk crystal by the micromechanical exfoliation method.Our measurements suggest that the nanoflakes have properties similar to those of the bulk crystal when the thickness is lowered to 18 nm.
