The introduction of defects can adjust the activity of graphene-based single-atom catalysts for oxygen reduction reactions(ORR).Herein,we for the first time investigate the ORR catalytic activity of FeN_(4)sites embed...The introduction of defects can adjust the activity of graphene-based single-atom catalysts for oxygen reduction reactions(ORR).Herein,we for the first time investigate the ORR catalytic activity of FeN_(4)sites embedded on graphene with four types of line-defective boundary via density functional theory calculations.Our results show that periodic line defects consisting of pentagon-pentagon-octagon(C_(585))or quad-octagon chains(C_(484))can significantly enhance ORR activity,owing to the optimized electronic structures of FeN_(4)sites.The spin magnetic moment and the valence state of the Fe atom are both well correlated with the ORR overpotential.Experimental investigations further corroborate that FeN_(4)with a high degree of defects exhibits better ORR activity and stability compared to FeN_(4)sites of pristine graphene and commercial Pt/C.This work unravels the influence of the periodic defect boundary on the ORR performance of Fe-N-C catalysts and paves the way towards the rational design of highly effective single-atom electrocatalysts.展开更多
In this paper, we present the finding that periodic structural defects(PSDs) along a Bragg grating can shift the Bragg wavelength. This effect is theoretically analyzed and confirmed by numerical calculation. We find ...In this paper, we present the finding that periodic structural defects(PSDs) along a Bragg grating can shift the Bragg wavelength. This effect is theoretically analyzed and confirmed by numerical calculation. We find that the Bragg wavelength shift is determined by the defect size and the period of the defects. The Bragg wavelength can be well tuned by properly designing the PSDs, and this may provide an alternative method to fabricate grating-based multiwavelength devices, including optical filter arrays and laser arrays. In regards to wavelength precision, the proposed method has an advantage over the traditional methods, where the Bragg wavelengths are changed directly by changing the grating period. In addition, the proposed method can maintain grating strength when tuning the wavelength since only the period of defects is changed. This will be a benefit for devices such as arrays.展开更多
文摘The introduction of defects can adjust the activity of graphene-based single-atom catalysts for oxygen reduction reactions(ORR).Herein,we for the first time investigate the ORR catalytic activity of FeN_(4)sites embedded on graphene with four types of line-defective boundary via density functional theory calculations.Our results show that periodic line defects consisting of pentagon-pentagon-octagon(C_(585))or quad-octagon chains(C_(484))can significantly enhance ORR activity,owing to the optimized electronic structures of FeN_(4)sites.The spin magnetic moment and the valence state of the Fe atom are both well correlated with the ORR overpotential.Experimental investigations further corroborate that FeN_(4)with a high degree of defects exhibits better ORR activity and stability compared to FeN_(4)sites of pristine graphene and commercial Pt/C.This work unravels the influence of the periodic defect boundary on the ORR performance of Fe-N-C catalysts and paves the way towards the rational design of highly effective single-atom electrocatalysts.
基金supported by the National Natural Science Foundation of China(Youth)(61306068)the Natural Science Foundation of Jiangsu Province of China(BK20130585,BK20140414)+1 种基金the National Natural Science Foundation of China(61435014,61504170,61504058)the National 863 Program(2015AA016902)
文摘In this paper, we present the finding that periodic structural defects(PSDs) along a Bragg grating can shift the Bragg wavelength. This effect is theoretically analyzed and confirmed by numerical calculation. We find that the Bragg wavelength shift is determined by the defect size and the period of the defects. The Bragg wavelength can be well tuned by properly designing the PSDs, and this may provide an alternative method to fabricate grating-based multiwavelength devices, including optical filter arrays and laser arrays. In regards to wavelength precision, the proposed method has an advantage over the traditional methods, where the Bragg wavelengths are changed directly by changing the grating period. In addition, the proposed method can maintain grating strength when tuning the wavelength since only the period of defects is changed. This will be a benefit for devices such as arrays.
