Oxygen electrocatalysis,exemplified by the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),is central to energy storage and conversion technologies such as fuel cells,metal-air batteries,and water ele...Oxygen electrocatalysis,exemplified by the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),is central to energy storage and conversion technologies such as fuel cells,metal-air batteries,and water electrolysis.However,highly effective and inexpensive earth-abundant materials are sought after to replace the noble metal-based electrocatalysts currently in use.Recently,metal-organic frameworks(MOFs)and carbon-based MOF derivatives have attracted considerable attention as efficient catalysts due to their exceedingly tunable morphologies,structures,compositions,and functionalization.Here,we report two-dimensional(2D)MOF/MOF derivative coupled arrays on nickel foam as binder-free bifunctional ORR/OER catalysts with enhanced electrocatalytic activity and stability.Their remarkable electrochemical properties are primarily attributed to fully exposed active sites and facilitated charge-transfer kinetics.The coupled and hierarchical nanosheet arrays produced via our growth-pyrolysis-regrowth strategy offer promise in the development of highly active electrodes for energy-related electrochemical devices.展开更多
Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will con...Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will consume considerable time(compared with ground networks)derived from long ISL delay and flooding between hundreds or even thousands of satellites.During the network convergence/update stage,the lack of up-to-date forwarding information may cause severe packet loss.Considering the fact that ISL handovers for close-to-earth constellation are predictable and all the ISL handover information could be stored in each satellite during the network initialization,we propose a self-update routing scheme based on open shortest path first(OSPF-SUR)to address the slow route convergence problem caused by frequent ISL handovers.First,for predictable ISL handovers,forwarding tables are updated according to locally stored ISL handover information without link state advertisement(LSA)flooding.Second,for unexpected ISL failures,flooding could be triggered to complete route convergence.In this manner,network convergence time is radically descended by avoiding unnecessary LSA flooding for predictable ISL handovers.Simulation results show that the average packet loss rate caused by ISL handovers is reduced by 90.5%and 61.3%compared with standard OSPF(with three Hello packets confirmation)and OSPF based on interface state(without three Hello packets confirmation),respectively,during a period of topology handover.And the average endto-end delay is also decreased by 47.6%,9.6%,respectively.The packet loss rate of the proposed OSPF-SUR does not change along with the increase of the frequency of topology handovers.展开更多
The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct obse...The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies.Femtosecond stimulated Raman spectroscopy(FSRS)is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules.Herein,a molecule,4,4′-(buta-1,3-diyne-1,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline),that consists of two central adjacent alkyne(-C≡C-)groups as electron-acceptors and two separated,symmetric N,N-bis(4-methoxyphenyl)aniline at both branches as electron-donors,is chosen to investigate the excited-state photophysical properties.It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy.The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.展开更多
文摘Oxygen electrocatalysis,exemplified by the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),is central to energy storage and conversion technologies such as fuel cells,metal-air batteries,and water electrolysis.However,highly effective and inexpensive earth-abundant materials are sought after to replace the noble metal-based electrocatalysts currently in use.Recently,metal-organic frameworks(MOFs)and carbon-based MOF derivatives have attracted considerable attention as efficient catalysts due to their exceedingly tunable morphologies,structures,compositions,and functionalization.Here,we report two-dimensional(2D)MOF/MOF derivative coupled arrays on nickel foam as binder-free bifunctional ORR/OER catalysts with enhanced electrocatalytic activity and stability.Their remarkable electrochemical properties are primarily attributed to fully exposed active sites and facilitated charge-transfer kinetics.The coupled and hierarchical nanosheet arrays produced via our growth-pyrolysis-regrowth strategy offer promise in the development of highly active electrodes for energy-related electrochemical devices.
基金the National Natural Science Foundations of China(Nos.61771074,62171059)。
文摘Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will consume considerable time(compared with ground networks)derived from long ISL delay and flooding between hundreds or even thousands of satellites.During the network convergence/update stage,the lack of up-to-date forwarding information may cause severe packet loss.Considering the fact that ISL handovers for close-to-earth constellation are predictable and all the ISL handover information could be stored in each satellite during the network initialization,we propose a self-update routing scheme based on open shortest path first(OSPF-SUR)to address the slow route convergence problem caused by frequent ISL handovers.First,for predictable ISL handovers,forwarding tables are updated according to locally stored ISL handover information without link state advertisement(LSA)flooding.Second,for unexpected ISL failures,flooding could be triggered to complete route convergence.In this manner,network convergence time is radically descended by avoiding unnecessary LSA flooding for predictable ISL handovers.Simulation results show that the average packet loss rate caused by ISL handovers is reduced by 90.5%and 61.3%compared with standard OSPF(with three Hello packets confirmation)and OSPF based on interface state(without three Hello packets confirmation),respectively,during a period of topology handover.And the average endto-end delay is also decreased by 47.6%,9.6%,respectively.The packet loss rate of the proposed OSPF-SUR does not change along with the increase of the frequency of topology handovers.
基金supported by the National Natural Science Foundation of China(No.22133001,No.11774233,No.21773252,No.21773257,No.21827803)the Project for high-grade,precision and advance in Beijing(BUPT)。
文摘The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies.Femtosecond stimulated Raman spectroscopy(FSRS)is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules.Herein,a molecule,4,4′-(buta-1,3-diyne-1,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline),that consists of two central adjacent alkyne(-C≡C-)groups as electron-acceptors and two separated,symmetric N,N-bis(4-methoxyphenyl)aniline at both branches as electron-donors,is chosen to investigate the excited-state photophysical properties.It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy.The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.
