The intrinsic viscosity and viscometric interaction parameters of perfluorosulfonic acid （PFSA） and poly（vinyl alcohol） （PVA） were measured by dilute solution viscometry. The miscibility between PFSA and PVA was...The intrinsic viscosity and viscometric interaction parameters of perfluorosulfonic acid （PFSA） and poly（vinyl alcohol） （PVA） were measured by dilute solution viscometry. The miscibility between PFSA and PVA was estimated by the criteria of AB and μ. The results indicated that PFSA and PVA were completely miscible for any weight fraction in aqueous solution.展开更多
The perfluorosulfonic acid （PFSA）/SiO2 composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO2 catalysts were discussed on the basis of nitrogen adsorption. T...The perfluorosulfonic acid （PFSA）/SiO2 composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO2 catalysts were discussed on the basis of nitrogen adsorption. Their surface area and pore size distributions were evaluated by Brunauer-Emmett-Teller （BET） and Barrett-Joyner-Halenda （BJH） methods, respectively. The nitrogen adsorption-desorption isotherms associated with adsorption hysteresis of PFSA/SiO2 catalysts were analyzed in detail. The adsorption isotherms of PFSA/SiOe catalysts belonged to Type IV isotherms accompanied by hysteresis loops of Type H1 for PFSA/SiO2 catalysts with content of 5%, 13% and 20% PFSA （PFSA-5, PFSA-13 and PFSA-20）, and the hysteresis loop of Type H2 for PFSA/SiO2 catalyst with 40% PFSA content （PFSA-40）. It indicated that PFSA-5, PFSA-13 and PFSA-20 catalysts had narrow pore size distributions and the well-defined cylindrical pores, while PFSA-40 catalyst had wide pore size distribution and inkbottle-like pores. The pore structure of PFSA-40 catalyst from the analysis of the hysteresis loop was not in agreement with that from BJH method. As an emendation for evaluation of pore size distributions of PFSA/SiOz catalysts, the comparison plots method was introduced, which was helpful to evaluate the pore structure of PFSA/SiO2 catalysts more factually.展开更多
Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration(UF) membrane as substrate with recovered PFSA.The composite membranes we...Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration(UF) membrane as substrate with recovered PFSA.The composite membranes were applied to the pervaporation separation of 95% ethanol(EtOH)/H2O mixture.SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm,much thinner than those of other PFSA composite membranes revealed in the literatures.Effects of annealing temperature,coating solution concentration and counter-ions of PFSA on the pervaporation performances of the composite membranes were investigated.The total flux decreases and separation factor increases with the increase of annealing temperature.The highest permeation flux of 3230 g m-2 h-1 and a separation factor of 5.4 is obtained for the composite membrane annealed at 80°C.The lowest permeation flux of 396 g m-2 h-1 and a separation factor of 27.7 is obtained for the composite membrane annealed at 160°C.The permeation performances of the PFSA/PSf composite membrane are evidently influenced by the counter-ions of PFSA.The flux sequence of the PFSA/PSf composite membranes with different counter-ions is H+】Li+】Ca2+】Mg2+】Na+】K+】Ba2+】Fe3+】Al3+,and the separation factor sequence is H+【Li+【Al3+【Na+【Mg2+【Ca2+【K+ 【Ba2+【Fe3+.The apparent activation energy △Eapp values of the composite membranes with different counter-ions were calculated by Arrhenius law.The sequence of △Eapp values for the membranes with monovalent counter-ions is Li+】Na+】K+.There are very little variations of △Eapp values between the composite membranes with three divalent counterions(Mg2+,Ca2+ and Ba2+),and the △Eapp values of the composite membranes with two trivalent counterions(Fe3+ and Al3+) are relatively high.展开更多
分析了无结构对等网络若干经典搜索算法的优缺点,进而提出一种兼顾查询深度与广度的平台搜索算法(PFSA:P latform Search ing A lgorithm)。该算法在提高了网络资源利用率、保持较快搜索速度的同时维持着较低的消息冗余度;其子查询算法...分析了无结构对等网络若干经典搜索算法的优缺点,进而提出一种兼顾查询深度与广度的平台搜索算法(PFSA:P latform Search ing A lgorithm)。该算法在提高了网络资源利用率、保持较快搜索速度的同时维持着较低的消息冗余度;其子查询算法针对B lind Counter RumorMongering算法的不足加以改进,使得搜索算法可以根据不同的网络动态地调整自身参数,大大提高了算法的鲁棒性。展开更多
Molecular dynamics simulations were conducted to investigate the effects of side-chain structure and spacing on the self-assembly behaviors of perfluorosulfonic acid(PFSA)ionomers in both bulk proton exchange membrane...Molecular dynamics simulations were conducted to investigate the effects of side-chain structure and spacing on the self-assembly behaviors of perfluorosulfonic acid(PFSA)ionomers in both bulk proton exchange membrane(PEM)and nano-thin films within the catalyst layer(CL)for PEM fuel cells.Differences and interconnections between the two systems were highlighted;and the local oxygen transport properties at Pt/ionomer interfaces are analyzed.Results reveal that the side-chain length predominantly influence the size of primary sulfonate aggregates and the formation of the secondary aggregates,respectively,thereby playing distinct roles in the connectivity of proton-conducting hydrophilic domains.Specifically,in bulk system,the connectivity was primarily determined by the sizes of the secondary aggregate,making the side-chain spacing a critical factor;whereas in CL,combined effects of nanoscale confinement and ionomer-catalyst interactions restrict the formation of secondary sulfonate aggregates,rendering the size of primary aggregates and thus the side-chain length more important.Besides,although longer side chains with flexible ether groups enhance microphase separation,they also intensify high backbone aggregation,leading to inhomogeneous ionomer distribution and impeded proton transport in CL.A negative correlation is observed between the oxygen flux and the backbone aggregation on Pt.As a result,among the PFSA ionomers studied,the one with medium-length and closely spaced side chains(3M877)exhibited the most favorable self-assembly characteristics for CL applications,balancing both the proton conduction and oxygen permeability.These findings provide crucial molecular-level insights into optimization of ionomer side chain structures toward PEM and CL.展开更多
The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent aff...The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent affect the suspension properties and thus the layer morphology.We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics.Highly branched carbon blacks with a high surface area tend to form less cracked layers.As less branched carbons can pack together more closely,a smaller pore size results in a larger capillary pressure during drying and thus more cracks.The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles.The carbon black aggregates are thus smaller,resulting in closer packing and thinner layers.Moreover,the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer,preventing crack formation.An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.展开更多
基金supported by the Innovation Program of Shanghai Municipal Education Commission (Grant No.09YZ163)
文摘The intrinsic viscosity and viscometric interaction parameters of perfluorosulfonic acid （PFSA） and poly（vinyl alcohol） （PVA） were measured by dilute solution viscometry. The miscibility between PFSA and PVA was estimated by the criteria of AB and μ. The results indicated that PFSA and PVA were completely miscible for any weight fraction in aqueous solution.
基金supported by the National Basic Research Program of China (2003CB615705)Chemistry & Chemical Technology Research Center Plan of Shanghai Huayi Group Company (A200-8608 and A200-80726)
文摘The perfluorosulfonic acid （PFSA）/SiO2 composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO2 catalysts were discussed on the basis of nitrogen adsorption. Their surface area and pore size distributions were evaluated by Brunauer-Emmett-Teller （BET） and Barrett-Joyner-Halenda （BJH） methods, respectively. The nitrogen adsorption-desorption isotherms associated with adsorption hysteresis of PFSA/SiO2 catalysts were analyzed in detail. The adsorption isotherms of PFSA/SiOe catalysts belonged to Type IV isotherms accompanied by hysteresis loops of Type H1 for PFSA/SiO2 catalysts with content of 5%, 13% and 20% PFSA （PFSA-5, PFSA-13 and PFSA-20）, and the hysteresis loop of Type H2 for PFSA/SiO2 catalyst with 40% PFSA content （PFSA-40）. It indicated that PFSA-5, PFSA-13 and PFSA-20 catalysts had narrow pore size distributions and the well-defined cylindrical pores, while PFSA-40 catalyst had wide pore size distribution and inkbottle-like pores. The pore structure of PFSA-40 catalyst from the analysis of the hysteresis loop was not in agreement with that from BJH method. As an emendation for evaluation of pore size distributions of PFSA/SiOz catalysts, the comparison plots method was introduced, which was helpful to evaluate the pore structure of PFSA/SiO2 catalysts more factually.
基金supported by the Leading Academic Discipline Project of SHNU (No.DZL807)Innovation Program of Shanghai Municipal Education Commission (No.09YZ163)Shanghai Municipal Natural Science Foundation (No.09ZR1423300)
文摘Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration(UF) membrane as substrate with recovered PFSA.The composite membranes were applied to the pervaporation separation of 95% ethanol(EtOH)/H2O mixture.SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm,much thinner than those of other PFSA composite membranes revealed in the literatures.Effects of annealing temperature,coating solution concentration and counter-ions of PFSA on the pervaporation performances of the composite membranes were investigated.The total flux decreases and separation factor increases with the increase of annealing temperature.The highest permeation flux of 3230 g m-2 h-1 and a separation factor of 5.4 is obtained for the composite membrane annealed at 80°C.The lowest permeation flux of 396 g m-2 h-1 and a separation factor of 27.7 is obtained for the composite membrane annealed at 160°C.The permeation performances of the PFSA/PSf composite membrane are evidently influenced by the counter-ions of PFSA.The flux sequence of the PFSA/PSf composite membranes with different counter-ions is H+】Li+】Ca2+】Mg2+】Na+】K+】Ba2+】Fe3+】Al3+,and the separation factor sequence is H+【Li+【Al3+【Na+【Mg2+【Ca2+【K+ 【Ba2+【Fe3+.The apparent activation energy △Eapp values of the composite membranes with different counter-ions were calculated by Arrhenius law.The sequence of △Eapp values for the membranes with monovalent counter-ions is Li+】Na+】K+.There are very little variations of △Eapp values between the composite membranes with three divalent counterions(Mg2+,Ca2+ and Ba2+),and the △Eapp values of the composite membranes with two trivalent counterions(Fe3+ and Al3+) are relatively high.
文摘分析了无结构对等网络若干经典搜索算法的优缺点,进而提出一种兼顾查询深度与广度的平台搜索算法(PFSA:P latform Search ing A lgorithm)。该算法在提高了网络资源利用率、保持较快搜索速度的同时维持着较低的消息冗余度;其子查询算法针对B lind Counter RumorMongering算法的不足加以改进,使得搜索算法可以根据不同的网络动态地调整自身参数,大大提高了算法的鲁棒性。
基金supported by the National Natural Science Foundation of China(No.22332004)the China Postdoctoral Science Foundation under Grant(No.GZC20231962)+1 种基金Generous grants of computer time at the Supercomputing Center of Wuhan University are gratefully acknowledgedThe authors acknowledge the support of the Supercomputing Center of Wuhan University.
文摘Molecular dynamics simulations were conducted to investigate the effects of side-chain structure and spacing on the self-assembly behaviors of perfluorosulfonic acid(PFSA)ionomers in both bulk proton exchange membrane(PEM)and nano-thin films within the catalyst layer(CL)for PEM fuel cells.Differences and interconnections between the two systems were highlighted;and the local oxygen transport properties at Pt/ionomer interfaces are analyzed.Results reveal that the side-chain length predominantly influence the size of primary sulfonate aggregates and the formation of the secondary aggregates,respectively,thereby playing distinct roles in the connectivity of proton-conducting hydrophilic domains.Specifically,in bulk system,the connectivity was primarily determined by the sizes of the secondary aggregate,making the side-chain spacing a critical factor;whereas in CL,combined effects of nanoscale confinement and ionomer-catalyst interactions restrict the formation of secondary sulfonate aggregates,rendering the size of primary aggregates and thus the side-chain length more important.Besides,although longer side chains with flexible ether groups enhance microphase separation,they also intensify high backbone aggregation,leading to inhomogeneous ionomer distribution and impeded proton transport in CL.A negative correlation is observed between the oxygen flux and the backbone aggregation on Pt.As a result,among the PFSA ionomers studied,the one with medium-length and closely spaced side chains(3M877)exhibited the most favorable self-assembly characteristics for CL applications,balancing both the proton conduction and oxygen permeability.These findings provide crucial molecular-level insights into optimization of ionomer side chain structures toward PEM and CL.
文摘The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent affect the suspension properties and thus the layer morphology.We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics.Highly branched carbon blacks with a high surface area tend to form less cracked layers.As less branched carbons can pack together more closely,a smaller pore size results in a larger capillary pressure during drying and thus more cracks.The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles.The carbon black aggregates are thus smaller,resulting in closer packing and thinner layers.Moreover,the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer,preventing crack formation.An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.
