To understand the thermal conductivity improvement of the paraffin and graphite composite PCMs in micro-scale,the conformation characteristics of molecules with rising temperature was studied by molecular dynamics(MD)...To understand the thermal conductivity improvement of the paraffin and graphite composite PCMs in micro-scale,the conformation characteristics of molecules with rising temperature was studied by molecular dynamics(MD)simulation.And then the structure and dynamics characteristics of the paraffin PCM,including the structural evolution,the self-diffusion coefficient,phase change properties and thermal conductivity,were analyzed.The results indicate that the distribution of the n-octadecane molecules is more regular in the region near the graphite layers,although the temperature is higher than the phase transition point,which means that the graphite layer has a significant absorption influence on the conformation of alkane molecules.Then,the self-diffusion coefficient of n-octadecane molecules increases with the increasing of temperature,which shows great agreement with the literature.Meanwhile,the self-diffusion coefficient of n-octadecane molecules staying far away from the graphite layers is larger than that of the molecules in the region near the graphite layer.In addition,the radial distribution function(RDF)was used to analyze the molecular interaction of the system at different temperatures.The sudden increase of R(ratio of the first peak value to the first valley value of the RDF)within the temperature range from 293 K to 313 K corresponds to the phase transition point,indicating that the solid-liquid phase transition occurs at the temperature range.Besides,the results indicate that the thermal conductivity of amorphous n-octadecane is about 2.5 times lower than that of the crystal n-octadecane with perfect structure.This investigation provides theoretical guidance for the study of the micro-mechanism of n-octadecane doped with graphite composite phase change materials.展开更多
The poor stability of non-noble metal catalysts in oxygen reduction reaction(ORR) is a main bottleneck that limits their big-scale application in metal-air batteries. Herein, we construct a chainmail catalyst(Co-NC-AD...The poor stability of non-noble metal catalysts in oxygen reduction reaction(ORR) is a main bottleneck that limits their big-scale application in metal-air batteries. Herein, we construct a chainmail catalyst(Co-NC-AD) with outstanding stability, via the competitive complexation and post absorption strategy,consisting of highly graphitic layers wrapped uniform-size Co nanoparticles(Co-NPs). Experiments combined with density functional theory(DFT) calculations jointly confirmed that the electron transfer occurred from the inner Co-NPs to the external graphitic layers. It facilitated the adsorption process of oxygen molecules and the hybridization of the O-2 p and C-1 p orbitals, which accelerated the ORR reaction kinetics. Consequently, our prepared Co-NC-AD shows excellent ORR activity, offered with a more positive initial potential(E_(onset)= 0.95 V) and half-wave potential(E_(1/2)= 0.86 V). The remarkable stability and resistance of methanol poisoning are merited from the protection effect of stable graphitic layers. In addition, the high electrochemical performance of Co-NC-AD-based zinc-air battery demonstrates their potential for practical applications. Therefore, our work provides new ideas for the design of nanoconfined catalysts with high stability and activity.展开更多
The energy density of commercial lithium(Li)ion batteries with graphite anode is reaching the limit.It is believed that directly utilizing Li metal as anode without a host could enhance the battery’s energy density t...The energy density of commercial lithium(Li)ion batteries with graphite anode is reaching the limit.It is believed that directly utilizing Li metal as anode without a host could enhance the battery’s energy density to the maximum extent.However,the poor reversibility and infinite volume change of Li metal hinder the realistic implementation of Li metal in battery community.Herein,a commercially viable hybrid Li-ion/metal battery is realized by a coordinated strategy of symbiotic anode and prelithiated cathode.To be specific,a scalable template-removal method is developed to fabricate the porous graphite layer(PGL),which acts as a symbiotic host for Li ion intercalation and subsequent Li metal deposition due to the enhanced lithiophilicity and sufficient ion-conducting pathways.A continuous dissolution-deintercalation mechanism during delithiation process further ensures the elimination of dead Li.As a result,when the excess plating Li reaches 30%,the PGL could deliver an ultrahigh average Coulombic efficiency of 99.5% for 180 cycles with a capacity of 2.48 m Ah cm^(-2) in traditional carbonate electrolyte.Meanwhile,an air-stable recrystallized lithium oxalate with high specific capacity(514.3 m Ah g^(-1))and moderate operating potential(4.7-5.0 V)is introduced as a sacrificial cathode to compensate the initial loss and provide Li source for subsequent cycles.Based on the prelithiated cathode and initial Li-free symbiotic anode,under a practical-level3 m Ah capacity,the assembled hybrid Li-ion/metal full cell with a P/N ratio(capacity ratio of Li Ni_(0.8)Co_(0.1)Mn_(0.1)O_(2) to graphite)of 1.3exhibits significantly improved capacity retention after 300 cycles,indicating its great potential for high-energy-density Li batteries.展开更多
NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conducti...NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conductivity,limited activity,durability.To address these issues,herein,by utilizing three-dimensional covalent organic framework(3D-COF)with porous confined structures and abundant coordinate N sites as the precursor,the partially oxidized Ni_(3)Fe nanoalloys wrapped by Ndoped carbon(N-C)layers are constructed via simple pyrolysis and subsequent oxidization.Benefiting from the 3D curved hierarchical structure,high-conductivity of Ni_(3)Fe and N-C layers,well-distributed active sites,the as-synthesized O-Ni_(3)Fe-NC catalyst demonstrates excellent activity and durability for catalyzing OER.Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance,inducing its optimized OER activity.The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni_(3)Fe nanoalloys are beneficial for stabilizing catalytic centers,thereby imparting O-Ni_(3)Fe-N-C with such outstanding stability.This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.展开更多
Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers no...Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B-C-N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a better- controlled process for the chemical vapor deposition (CVD) growth of B-C-N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane (TMB), a gaseous organoboron compound with pre-existing B--C bonds, as the molecular precursor to react with ammonia (NH3) gas that serves as the nitrification agent. The use of this unique B-C delivery precursor allows for the successful synthesis of high-quality and large-area B-C-N atomic layer films. Moreover, the TMB/NH3 reactant combination can offer a high level of tunability and control of the overall chemical composition of B-C-N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B-C-N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B-C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B-C-N phase atomic layers.展开更多
基金This study is financially supported by National Natural Science Foundation of China(No.51676037).
文摘To understand the thermal conductivity improvement of the paraffin and graphite composite PCMs in micro-scale,the conformation characteristics of molecules with rising temperature was studied by molecular dynamics(MD)simulation.And then the structure and dynamics characteristics of the paraffin PCM,including the structural evolution,the self-diffusion coefficient,phase change properties and thermal conductivity,were analyzed.The results indicate that the distribution of the n-octadecane molecules is more regular in the region near the graphite layers,although the temperature is higher than the phase transition point,which means that the graphite layer has a significant absorption influence on the conformation of alkane molecules.Then,the self-diffusion coefficient of n-octadecane molecules increases with the increasing of temperature,which shows great agreement with the literature.Meanwhile,the self-diffusion coefficient of n-octadecane molecules staying far away from the graphite layers is larger than that of the molecules in the region near the graphite layer.In addition,the radial distribution function(RDF)was used to analyze the molecular interaction of the system at different temperatures.The sudden increase of R(ratio of the first peak value to the first valley value of the RDF)within the temperature range from 293 K to 313 K corresponds to the phase transition point,indicating that the solid-liquid phase transition occurs at the temperature range.Besides,the results indicate that the thermal conductivity of amorphous n-octadecane is about 2.5 times lower than that of the crystal n-octadecane with perfect structure.This investigation provides theoretical guidance for the study of the micro-mechanism of n-octadecane doped with graphite composite phase change materials.
基金supported by the National Natural Science Foundation of China(51872115,51932003)the 2020 International Cooperation Project of the Department of Science and Technology of Jilin Province(20200801001GH)+1 种基金the Project supported by State Key Laboratory of Luminescence and Applications(KLA-2020-05)the Project for Self-innovation Capability Construction of Jilin Province Development and Reform Commission(2021C026)。
文摘The poor stability of non-noble metal catalysts in oxygen reduction reaction(ORR) is a main bottleneck that limits their big-scale application in metal-air batteries. Herein, we construct a chainmail catalyst(Co-NC-AD) with outstanding stability, via the competitive complexation and post absorption strategy,consisting of highly graphitic layers wrapped uniform-size Co nanoparticles(Co-NPs). Experiments combined with density functional theory(DFT) calculations jointly confirmed that the electron transfer occurred from the inner Co-NPs to the external graphitic layers. It facilitated the adsorption process of oxygen molecules and the hybridization of the O-2 p and C-1 p orbitals, which accelerated the ORR reaction kinetics. Consequently, our prepared Co-NC-AD shows excellent ORR activity, offered with a more positive initial potential(E_(onset)= 0.95 V) and half-wave potential(E_(1/2)= 0.86 V). The remarkable stability and resistance of methanol poisoning are merited from the protection effect of stable graphitic layers. In addition, the high electrochemical performance of Co-NC-AD-based zinc-air battery demonstrates their potential for practical applications. Therefore, our work provides new ideas for the design of nanoconfined catalysts with high stability and activity.
基金the support by the Key-Area Research and Development Program of Guangdong Province(No.2020B090919003)the National Nature Science Foundation of China(Nos.51872157 and 52072208)+4 种基金the Shenzhen Technical Plan Project(Nos.JCYJ20170817161753629 and JCYJ20170412170911187)the Special Fund Project for Strategic Emerging Industry Development of Shenzhen(No.20170428145209110)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01N111)the Support Plan for Shenzhen Manufacturing Innovation Center(No.20200627215553988)the Key projects for core technology research of Dongguan(No.2019622119003)。
文摘The energy density of commercial lithium(Li)ion batteries with graphite anode is reaching the limit.It is believed that directly utilizing Li metal as anode without a host could enhance the battery’s energy density to the maximum extent.However,the poor reversibility and infinite volume change of Li metal hinder the realistic implementation of Li metal in battery community.Herein,a commercially viable hybrid Li-ion/metal battery is realized by a coordinated strategy of symbiotic anode and prelithiated cathode.To be specific,a scalable template-removal method is developed to fabricate the porous graphite layer(PGL),which acts as a symbiotic host for Li ion intercalation and subsequent Li metal deposition due to the enhanced lithiophilicity and sufficient ion-conducting pathways.A continuous dissolution-deintercalation mechanism during delithiation process further ensures the elimination of dead Li.As a result,when the excess plating Li reaches 30%,the PGL could deliver an ultrahigh average Coulombic efficiency of 99.5% for 180 cycles with a capacity of 2.48 m Ah cm^(-2) in traditional carbonate electrolyte.Meanwhile,an air-stable recrystallized lithium oxalate with high specific capacity(514.3 m Ah g^(-1))and moderate operating potential(4.7-5.0 V)is introduced as a sacrificial cathode to compensate the initial loss and provide Li source for subsequent cycles.Based on the prelithiated cathode and initial Li-free symbiotic anode,under a practical-level3 m Ah capacity,the assembled hybrid Li-ion/metal full cell with a P/N ratio(capacity ratio of Li Ni_(0.8)Co_(0.1)Mn_(0.1)O_(2) to graphite)of 1.3exhibits significantly improved capacity retention after 300 cycles,indicating its great potential for high-energy-density Li batteries.
基金the National Natural Science Foundation of China(Nos.22075062 and 21871167)and the Volkswagen Foundation(Freigeist Fellowship)。
文摘NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conductivity,limited activity,durability.To address these issues,herein,by utilizing three-dimensional covalent organic framework(3D-COF)with porous confined structures and abundant coordinate N sites as the precursor,the partially oxidized Ni_(3)Fe nanoalloys wrapped by Ndoped carbon(N-C)layers are constructed via simple pyrolysis and subsequent oxidization.Benefiting from the 3D curved hierarchical structure,high-conductivity of Ni_(3)Fe and N-C layers,well-distributed active sites,the as-synthesized O-Ni_(3)Fe-NC catalyst demonstrates excellent activity and durability for catalyzing OER.Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance,inducing its optimized OER activity.The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni_(3)Fe nanoalloys are beneficial for stabilizing catalytic centers,thereby imparting O-Ni_(3)Fe-N-C with such outstanding stability.This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.
基金Acknowledgements We acknowledge financial support from the National Natural Science Foundation of China (Nos. 21322304 and 51472267) and the National Basic Research Program of China (Nos. 2012CB933003 and 2013CB932603) and the Strategic Priority Research Program B of the Chinese Academy of Sciences (No. XDB07030100) of China.
文摘Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B-C-N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a better- controlled process for the chemical vapor deposition (CVD) growth of B-C-N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane (TMB), a gaseous organoboron compound with pre-existing B--C bonds, as the molecular precursor to react with ammonia (NH3) gas that serves as the nitrification agent. The use of this unique B-C delivery precursor allows for the successful synthesis of high-quality and large-area B-C-N atomic layer films. Moreover, the TMB/NH3 reactant combination can offer a high level of tunability and control of the overall chemical composition of B-C-N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B-C-N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B-C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B-C-N phase atomic layers.