Lithium-sulfur batteries have attracted a great interest in electrochemical energy conversion and storage, but their discharge mechanism remains not well understood up to now. Here, we report density functional theory...Lithium-sulfur batteries have attracted a great interest in electrochemical energy conversion and storage, but their discharge mechanism remains not well understood up to now. Here, we report density functional theory （DFr） calculation study of the discharge mechanism for lithium-sulfur batteries which are based on the structure of $8 and Li2Sx （l_〈x〈_8） clusters. The results show that for LizSz （1 〈x_8） clusters, the most stable geometry is chainlike when x = 1 and 6, while the minimal-energy structure is found to be cyclic when x = 2-5, 7, 8. The stability of LizSx （l_〈x_〈 8） clusters increases with the decreasing x value, indicating a favorable thermodynamic tendency of transition from $8 to Li2S. A three-step reaction route has been proposed during the discharge process, that is, $8---~Li2S4 at about 2.30 V, Li2S4---~Li2S2 at around 2.22 V, and Li2S2 ~ Li2S at 2.18 V. Furthermore, the effect of the electrolyte on the potential platform has been also investigated. The discharge potential is found to increase with the decrease of dielectric constant of the electrolyte. The computational results could provide insights into further understanding the discharge mechanism of lithium-sulfur batteries.展开更多
The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.I...The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.In this study,we synthesized the electrocatalysts containing two or three Co species(Co,CoO and Co3O4)nanoparticles on porous graphitic carbon(PGC)nanosheets which were prepared by a facile and low-cost synthesis where Co(NO3)2•6H2O and glucose were pyrolyzed in the presence of sodium chloride template.The Co3O4-dominated catalyst as-prepared,Co3O4/PGC,is OER active in acid solution(1.74 V at a current density of 10 mA cm^−2).We identified the OER active sites in the catalyst to be the Co3O4 nanoparticles rather than carbon-coated Co.Through comparative studies of the varied catalysts,we also proved that Co3O4 is catalytically more active than Co and CoO.The Co3O4/PGC catalyst,however,lost almost of all its activity after 100 voltammetric cycles in the 1.2-1.8 V voltage window.When the catalyst stability was examined potentiostatically at different potentials,the catalyst showed good stability at 1.4 V.The stability study also revealed the mechanism of the catalyst instability in acid was caused by Co3O4 reduction below 1.4 V and by Co3O4 oxidation above 1.4 V.1.4 V is therefore a unique potential where Co3O4 nanoparticles are neither oxidized nor reduced to be susceptible to acid dissolution.展开更多
Electrocatalysis,which involves oxidation and reduction reactions with direct electron transfer,is essential for a variety of clean energy conversion devices.Currently,the vast majority of studies regarding electrocat...Electrocatalysis,which involves oxidation and reduction reactions with direct electron transfer,is essential for a variety of clean energy conversion devices.Currently,the vast majority of studies regarding electrocatalysis reactions focus on strong acidic or alkaline media because of the higher catalytic activity.Nevertheless,some inherent drawbacks,including the corrosive environment,expensive proton exchange membranes,and side effects,are still hard to break through.A sustainably promising way to overcome these shortcomings is to deploy neutral/near-neutral electrolytes for electrocatalysis reactions.Unfortunately,insufficient research in this area due to the lack of attention to related issues has slowed down the development process.In this review,we systematically review the catalytic reaction mechanisms,neutral electrolytes,electrocatalysts,and modification strategies carried out in neutral media on the three most common electrocatalytic reactions,that is,hydrogen evolution reaction,oxygen reduction reaction,and oxygen evolution reaction.Furthermore,the advanced characterization tools for guiding catalyst synthesis and mechanistic studies are also summarized.Eventually,we propose some challenges and perspectives on electrocatalysis reactions in neutral media and hope it will attract more research interest and provide guidance in neutral electrocatalysis.展开更多
A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-str...A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-structured Na2VTi（PO4）3 material with the redox couples of V4＋/V3＋ and Ti4＋/Ti3＋ working on the cathode and anode, respectively. The symmetric full cell fabricated based on the bi-functional electrode material exhibits a well-defined voltage plateau at ~ 1.2 V and an impressive cycling stability with capacity retention of 70% exceeding 1,000 cycles at 10C （1C = 62 mA.g-1）. This study provides a feasible strategy for obtaining high-safety and low-cost rechargeable batteries using a single active material in aqueous media.展开更多
Dear Editor,In the adult brain,the transition from neural stem cell(NSC)quiescence to activation is a focal regulatory point for neural regeneration and dysregulations in the transition lead to brain disorders.1,2 Dur...Dear Editor,In the adult brain,the transition from neural stem cell(NSC)quiescence to activation is a focal regulatory point for neural regeneration and dysregulations in the transition lead to brain disorders.1,2 During this transition,both cell cycle states and metabolism including mitochondria undergo extensive reprogramming.A deep understanding of such comprehensive changes is a prerequisite for a holistic picture of physiology and may aid disease combats.展开更多
In this paper,we study the existence of invasion waves of a diffusive predator prey model with two preys and one predator.The existence of traveling semi-fronts connecting invasion-free equilibrium with wave speed c&g...In this paper,we study the existence of invasion waves of a diffusive predator prey model with two preys and one predator.The existence of traveling semi-fronts connecting invasion-free equilibrium with wave speed c>c^(*)is obtained by Schauder's fixed-point theorem,where c^(*)is the mininial wave speed.The boundedness of such waves is shown by rescaling method and such waves are proved to connect coexistence equilibrium by LaSalle's invariance principle.The existence of traveling front with wave speed c=c^(*)is got by rescaling method and limit arguments.Tht1 non-existence of traveling fronts with speed 0<c<c^(*)is shown by Laplace transform.展开更多
基金the Programs of Nationa l973(2011CB935900)NSFC(21076108)111 Project(B12015)
文摘Lithium-sulfur batteries have attracted a great interest in electrochemical energy conversion and storage, but their discharge mechanism remains not well understood up to now. Here, we report density functional theory （DFr） calculation study of the discharge mechanism for lithium-sulfur batteries which are based on the structure of $8 and Li2Sx （l_〈x〈_8） clusters. The results show that for LizSz （1 〈x_8） clusters, the most stable geometry is chainlike when x = 1 and 6, while the minimal-energy structure is found to be cyclic when x = 2-5, 7, 8. The stability of LizSx （l_〈x_〈 8） clusters increases with the decreasing x value, indicating a favorable thermodynamic tendency of transition from $8 to Li2S. A three-step reaction route has been proposed during the discharge process, that is, $8---~Li2S4 at about 2.30 V, Li2S4---~Li2S2 at around 2.22 V, and Li2S2 ~ Li2S at 2.18 V. Furthermore, the effect of the electrolyte on the potential platform has been also investigated. The discharge potential is found to increase with the decrease of dielectric constant of the electrolyte. The computational results could provide insights into further understanding the discharge mechanism of lithium-sulfur batteries.
基金supported by the National Research Foundation,Prime Minister’s Office,Singapore under its Competitive。
文摘The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.In this study,we synthesized the electrocatalysts containing two or three Co species(Co,CoO and Co3O4)nanoparticles on porous graphitic carbon(PGC)nanosheets which were prepared by a facile and low-cost synthesis where Co(NO3)2•6H2O and glucose were pyrolyzed in the presence of sodium chloride template.The Co3O4-dominated catalyst as-prepared,Co3O4/PGC,is OER active in acid solution(1.74 V at a current density of 10 mA cm^−2).We identified the OER active sites in the catalyst to be the Co3O4 nanoparticles rather than carbon-coated Co.Through comparative studies of the varied catalysts,we also proved that Co3O4 is catalytically more active than Co and CoO.The Co3O4/PGC catalyst,however,lost almost of all its activity after 100 voltammetric cycles in the 1.2-1.8 V voltage window.When the catalyst stability was examined potentiostatically at different potentials,the catalyst showed good stability at 1.4 V.The stability study also revealed the mechanism of the catalyst instability in acid was caused by Co3O4 reduction below 1.4 V and by Co3O4 oxidation above 1.4 V.1.4 V is therefore a unique potential where Co3O4 nanoparticles are neither oxidized nor reduced to be susceptible to acid dissolution.
基金supported by the National Natural Science Foundation of China(11975238 and 11575192)the Scientific Instrument Developing Project(ZDKYYQ20170001)+2 种基金the Strategic Priority Research Program(XDB28000000)the International Partnership Program(211211KYSB20170060 and 211211KYSB20180020)of the Chinese Academy of Sciences and the University of the Chinese Academy of Sciencessupported by the Fundamental Research Funds for the Central Universities。
基金Fundamental Research Funds for the Central UniversitiesChinese Academy of SciencesNational Natural Science Foundation of China,Grant/Award Numbers:12375301,21503227。
文摘Electrocatalysis,which involves oxidation and reduction reactions with direct electron transfer,is essential for a variety of clean energy conversion devices.Currently,the vast majority of studies regarding electrocatalysis reactions focus on strong acidic or alkaline media because of the higher catalytic activity.Nevertheless,some inherent drawbacks,including the corrosive environment,expensive proton exchange membranes,and side effects,are still hard to break through.A sustainably promising way to overcome these shortcomings is to deploy neutral/near-neutral electrolytes for electrocatalysis reactions.Unfortunately,insufficient research in this area due to the lack of attention to related issues has slowed down the development process.In this review,we systematically review the catalytic reaction mechanisms,neutral electrolytes,electrocatalysts,and modification strategies carried out in neutral media on the three most common electrocatalytic reactions,that is,hydrogen evolution reaction,oxygen reduction reaction,and oxygen evolution reaction.Furthermore,the advanced characterization tools for guiding catalyst synthesis and mechanistic studies are also summarized.Eventually,we propose some challenges and perspectives on electrocatalysis reactions in neutral media and hope it will attract more research interest and provide guidance in neutral electrocatalysis.
文摘A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-structured Na2VTi（PO4）3 material with the redox couples of V4＋/V3＋ and Ti4＋/Ti3＋ working on the cathode and anode, respectively. The symmetric full cell fabricated based on the bi-functional electrode material exhibits a well-defined voltage plateau at ~ 1.2 V and an impressive cycling stability with capacity retention of 70% exceeding 1,000 cycles at 10C （1C = 62 mA.g-1）. This study provides a feasible strategy for obtaining high-safety and low-cost rechargeable batteries using a single active material in aqueous media.
基金This work was supported by funds from the National Key R&D Program of China(2019YFA0110300,2017YFA0104100)Shanghai Easter Scholar(8101219003)to Z.L.G.+2 种基金the National Natural Science Foundation of China(31600819 to C.H.C.,81773302 to Y.T.F.,31571058 and 32070862 to Z.L.G.,31701282 to M.J.,and 81901031 to X.X.H.)Shanghai Municipal Planning Commission of science and Research Fund(20174Y0216)to C.C.H.the Natural Science Foundation of Shanghai(19ZR1445400)to X.X.H.
文摘Dear Editor,In the adult brain,the transition from neural stem cell(NSC)quiescence to activation is a focal regulatory point for neural regeneration and dysregulations in the transition lead to brain disorders.1,2 During this transition,both cell cycle states and metabolism including mitochondria undergo extensive reprogramming.A deep understanding of such comprehensive changes is a prerequisite for a holistic picture of physiology and may aid disease combats.
基金This work was supported by the Fundaniental Research Funds for the Central Universities(XDJK2019C106)the Natural Science Foundation of Chongqing,China(cstc2019jcyj-bshX0122,cstc2018jcyjAX0439)+1 种基金the National Natural Science Foundation of China(11871403,11671327,11901477)the Project funded by China Postdoctoral Science Foundation(2019M653816XB).
文摘In this paper,we study the existence of invasion waves of a diffusive predator prey model with two preys and one predator.The existence of traveling semi-fronts connecting invasion-free equilibrium with wave speed c>c^(*)is obtained by Schauder's fixed-point theorem,where c^(*)is the mininial wave speed.The boundedness of such waves is shown by rescaling method and such waves are proved to connect coexistence equilibrium by LaSalle's invariance principle.The existence of traveling front with wave speed c=c^(*)is got by rescaling method and limit arguments.Tht1 non-existence of traveling fronts with speed 0<c<c^(*)is shown by Laplace transform.
