Transition metal-nitrogen-carbon materials(M-N-Cs),particularly Fe-N-Cs,have been found to be electroactive for accelerating oxygen reduction reaction(ORR)kinetics.Although substantial efforts have been devoted to des...Transition metal-nitrogen-carbon materials(M-N-Cs),particularly Fe-N-Cs,have been found to be electroactive for accelerating oxygen reduction reaction(ORR)kinetics.Although substantial efforts have been devoted to design Fe-N-Cs with increased active species content,surface area,and electronic conductivity,their performance is still far from satisfactory.Hitherto,there is limited research about regulation on the electronic spin states of Fe centers for Fe-N-Cs electrocatalysts to improve their catalytic performance.Here,we introduce Ti_(3)C_(2) MXene with sulfur terminals to regulate the electronic configuration of FeN_(4) species and dramatically enhance catalytic activity toward ORR.The MXene with sulfur terminals induce the spin-state transition of FeN_(4) species and Fe 3d electron delocalization with d band center upshift,enabling the Fe(II)ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN_(4) species and ORR kinetics.The resulting FeN_(4)-Ti_(3)C_(2)Sx exhibits comparable catalytic performance to those of commercial Pt-C.The developed wearable ZABs using FeN_(4)-Ti_(3)C_(2)Sx also exhibit fast kinetics and excellent stability.This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity.展开更多
A novel facile technique is proposed for fabricating three-dimensional(3D)concave nanolens arrays on a silicon substrate.The technique leverages an inherent characteristic of the polymethyl methacrylate(PMMA)resist du...A novel facile technique is proposed for fabricating three-dimensional(3D)concave nanolens arrays on a silicon substrate.The technique leverages an inherent characteristic of the polymethyl methacrylate(PMMA)resist during inductively coupled plasma(ICP)etching.The tendency for plasma ions to accumulate at the edge of the PMMA resist helps create a local electric field that causes the ions to etch the sidewall of the PMMA resist.This process progressively increases the uncovered area,resulting in a graded etched depth or a concave structure in the substrate.In addition,using a given ICP etching recipe,the time required for a PMMA resist to be removed by sidewall etching is determined by its width.The use of PMMA resist of different widths enables one to achieve structures of varying etched depths and thus a 3D lens array.Optical characteristics of the fabricated nanolens were simulated using the FDTD(Finite-difference time-domain)method,and focal lengths ranging from 150 nm to 420 nm were obtained.This type of nanolens is very useful in ultraviolet optical devices and CMOS image sensors.展开更多
基金supported by a Grant of the Innovation and Technology Commission of Hong Kong(Project number:ITS/461/18)City University of Hong Kong(Project number:9678179).
文摘Transition metal-nitrogen-carbon materials(M-N-Cs),particularly Fe-N-Cs,have been found to be electroactive for accelerating oxygen reduction reaction(ORR)kinetics.Although substantial efforts have been devoted to design Fe-N-Cs with increased active species content,surface area,and electronic conductivity,their performance is still far from satisfactory.Hitherto,there is limited research about regulation on the electronic spin states of Fe centers for Fe-N-Cs electrocatalysts to improve their catalytic performance.Here,we introduce Ti_(3)C_(2) MXene with sulfur terminals to regulate the electronic configuration of FeN_(4) species and dramatically enhance catalytic activity toward ORR.The MXene with sulfur terminals induce the spin-state transition of FeN_(4) species and Fe 3d electron delocalization with d band center upshift,enabling the Fe(II)ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN_(4) species and ORR kinetics.The resulting FeN_(4)-Ti_(3)C_(2)Sx exhibits comparable catalytic performance to those of commercial Pt-C.The developed wearable ZABs using FeN_(4)-Ti_(3)C_(2)Sx also exhibit fast kinetics and excellent stability.This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity.
基金funded by Shenzhen Science and Technology Innovation Commission(SZSTI)under research grant entitled“Research and application on high dense nanopillar by electron beam lithography”(Grant No.JCYJ20170817105420497).
文摘A novel facile technique is proposed for fabricating three-dimensional(3D)concave nanolens arrays on a silicon substrate.The technique leverages an inherent characteristic of the polymethyl methacrylate(PMMA)resist during inductively coupled plasma(ICP)etching.The tendency for plasma ions to accumulate at the edge of the PMMA resist helps create a local electric field that causes the ions to etch the sidewall of the PMMA resist.This process progressively increases the uncovered area,resulting in a graded etched depth or a concave structure in the substrate.In addition,using a given ICP etching recipe,the time required for a PMMA resist to be removed by sidewall etching is determined by its width.The use of PMMA resist of different widths enables one to achieve structures of varying etched depths and thus a 3D lens array.Optical characteristics of the fabricated nanolens were simulated using the FDTD(Finite-difference time-domain)method,and focal lengths ranging from 150 nm to 420 nm were obtained.This type of nanolens is very useful in ultraviolet optical devices and CMOS image sensors.
