等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

氮掺杂介孔碳的制备及其电化学超电容性能

通过直接炭化沸石咪唑酯骨架结构材料（ZIF-8）纳米多面体,成功制备了氮掺杂介孔碳（NMCs）. 采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线衍射（XRD）、拉曼光谱、X射线光电子能谱（XPS）及比表面和孔隙度分析仪对其微观形貌和结构进行了表征,并对NMCs的电化学超电容性能进行了测试. 结果表明：NMCs具有规整的形貌、介孔纳米结构和较大比表面积（2737 m²·g^-1）;由于氮元素掺杂所赋予的优异的表面润湿性和赝电容性能,且介孔结构有利于电解质到达电极活性材料表面,NMCs表现出优异的电化学超电容性能,在1 A·g^-1的电流密度下,1.0 mol·L^-1H₂SO₄溶液中的比电容值为307 F·g^-1,并具有良好的功率特性;此外,在10A·g^-1的大电流密度下充放电循环5000次后,NMCs的比电容值保持率为96.9%.     

无模板剂合成用于超级电容器的二氧化锰/石墨烯复合材料(英文)

以尿素、四水合氯化锰和氧化石墨烯为原料,采用水热法并通过热分解制备了一种具有石墨烯包覆结构的石墨烯-二氧化锰复合材料,利用扫描电子显微镜、X射线衍射、比表面积(BET)、拉曼光谱和热失重等技术对其形貌、晶体结构及表面结构进行了表征;在三电极条件下利用循环伏安法、恒流充放电法和交流阻抗法测试了材料的电化学性能,并考察了不同石墨烯含量对材料比电容的影响.结果表明,在不添加模板剂的条件下制备的复合材料中二氧化锰是具有介孔结构的α-MnO2,当复合15%(质量分数)的石墨烯后材料的比表面积从109 m2·g-1提高到168 m2·g-1.复合材料具有更好的电化学性能,在0.2 A·g-1电流密度下复合材料的比电容达到最大值(454 F·g-1),远高于纯二氧化锰的值(294 F·g-1).在2 A·g-1的电流密度下恒流充放电2000次后复合材料的比电容保持率为92%.     

MnO2/H-TiO2纳米异质阵列的调控制备及超电容特性

采用目标调控的阳极氧化工艺制备了超大比表面、管与管相互分离的有序TiO₂纳米管阵列（TiO₂ NTAs）基体,进而分别采用电化学氢化法和循环浸渍沉积法对晶化退火后的TiO₂ NTAs实施电化学氢化和高比电容MnO₂沉积的双重功能化改性,调控构筑了一种新型MnO₂/H-TiO₂纳米异质阵列电极材料。利用场发射扫描电子显微镜（FESEM）、高分辨透射电子显微镜（TRTEM）、X射线衍射仪（XRD）、X光电子能谱仪（XPS）、拉曼光谱（Raman）和电化学工作站等对样品进行综合表征与超电容特性测试,结果表明：电化学氢化改性有效提高了H-TiO₂ NTAs的导电性和电化学特性,当电流密度为0.2 mA·cm^-2时H-TiO₂ NTAs的面积电容达到7.5 mF·cm^-2,是相同电流密度下TiO₂ NTAs的75倍;经过2个浸渍循环所获得的MnO₂/H-TiO₂ NTAs-2样品在电流密度为3 mA·mg^-1时比电容可达481.26 F·g^-1,电流密度为5 mA·mg^-1时循环充放电1000圈后比电容仅下降约11%。     

可快速充放电聚吡咯/碳纳米管复合材料电化学聚合与表征

采用恒电流法制备了具有可快速充放电性能的对甲基苯磺酸根(TOS-)掺杂聚吡咯/功能化单壁碳纳米管(PPy-TOS/F-SWNTs)复合材料,扫描电镜(SEM)结果表明该复合材料呈纳米棒状构成的多孔结构,棒径约为70nm;比表面积(BET)测试分析表明该复合材料有着较高的比表面积(12.64m2.g-1)和大的介孔孔隙率(20-40nm).循环伏安(CV)、电化学阻抗谱(EIS)和恒电流充放电(GC)电化学分析表明该材料具有优异的快速充放电性能,在800mV的电位窗和2.5A.g-1(功率密度为2kW.kg-1)的电流密度下该材料具有211F.g-1的比容量(能量密度为18.7Wh.kg-1),而当充放电电流高达80A.g-1(功率密度为60kW.kg-1)时比容量仍可达141.8F.g-1(能量密度为12.6Wh.kg-1),同时该材料还表现出优异的稳定性,在10A.g-1大电流下经历10000圈循环后容量仍保持95.2%.     

水热反应温度对三维还原氧化石墨烯的形貌、结构和超级电容性能的影响

以氧化石墨凝胶制备的氧化石墨烯溶胶为前驱体,在120-220°C条件下,采用水热法制备了系列不同还原程度的三维还原氧化石墨烯,采用扫描电镜(SEM),X射线衍射(XRD),傅里叶变换红外(FTIR)光谱,X射线光电子能谱(XPS)和电化学测试等手段研究了水热反应温度对材料形貌、结构和超级电容性能的影响.结果表明:采用水热法制备的三维还原氧化石墨烯呈多孔网状结构,材料的体积和内部网状孔径随着水热反应温度的升高而减小;同时,氧化石墨烯的还原程度随反应温度的升高而增加,有序度提高,其结构逐渐向着类石墨结构转化;而材料的比电容和能量密度则随反应温度的升高呈现出先增大后减小的趋势,且均以双电层电容为主;相比之下,当水热反应温度为180°C时,制备的三维还原氧化石墨烯具有最佳的超级电容性能,在电解液为6mol·L-1的KOH溶液中,0.5A·g-1电流密度下其比电容达到315 F·g-1,10 A·g-1时仍能保持212 F·g-1的高比容量,能量密度为40.5Wh·kg-1,5000次循环后比电容保持率为86%,表现出了良好的电化学性能.     

双钙钛矿La2CoNiO6无机纳米纤维的制备及超级电容器性能

以聚乙烯吡咯烷酮/硝酸镧-乙酸钴-乙酸镍(PVP/LCN)为前驱体, 采用静电纺丝法, 经预氧化、碳化, 制得双钙钛矿La₂CoNiO₆无机纳米纤维超级电容器电极材料. 利用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对其形貌和结构进行表征. 结果表明, 纤维由菱形结构的La₂CoNiO₆纳米颗粒相互连接而成, 呈链状空间网状结构. 循环伏安(CV)、恒流充放电(CP)和循环寿命测试表明, La₂CoNiO₆纳米纤维电极材料在三电极体系中, 电流密度为0.25 A·g^-1时, 比电容值达335.0 F·g^-1; 在对称型双电极体系中, 电流密度为0.25 A·g^-1时, 比电容值可达到129.1 F·g^-1,表现出良好的电容性能.     

多巴胺改性聚吡咯衍生掺氮多孔碳材料的制备及其超电容性能

含氮聚合物材料在惰性气氛下热解能够产生掺氮多孔碳材料. 基于化学聚合法合成多巴胺(DA)改性的聚吡咯(PDA-PPy), 高温热解制备出掺氮多孔碳材料(NPC). 用傅里叶变换红外(FTIR)光谱, 拉曼光谱, X射线光电子能谱(XPS)分析和扫描电镜(SEM)研究其结构与形貌. 随着DA 与吡咯(Py)单体的摩尔比不断变化,PDA-PPy的形貌也随之改变, 进而影响NPC的超电容性能. 循环伏安和恒流充放电测试表明, 当DA与Py 单体的摩尔比为0.5时, 在0.5 A·g^-1的电流密度下, NPC的比电容可以达到210 F·g^-1, 电流密度为10 A·g^-1时, 比电容可以达到134 F·g^-1, 电容保持率为63.8%.     

功能化石墨烯/聚苯胺复合电极材料的制备和电化学性能

利用水合肼还原十八胺(ODA)接枝的氧化石墨烯(GO),得到了十八胺功能化石墨烯(ODA-G),将ODAG与聚苯胺(PANI)通过溶液共混法,制备了功能化石墨烯和聚苯胺纳米复合材料(ODA-G/PANI).采用傅里叶变换红外(FTIR)光谱、X射线衍射(XRD)、热重分析(TGA)、拉曼(Raman)光谱及透射电镜(TEM),对复合材料的结构和形貌进行了表征;利用循环伏安、恒流充放电及交流阻抗谱等,对复合材料的电化学性能进行了测试.结果显示,少量ODA-G的引入为PANI的电化学氧化还原反应提供了更多的电子通道和活性位置,有利于提高PANI的赝电容.在电流密度1.0 A·g-1下,2%(w)ODA-G/PANI的比电容达到787 F·g-1,而相应的PANI仅有426 F·g-1.此外,ODA-G/PANI的循环稳定性也远高于纯PANI.     

静电纺丝法制备交联多孔纳米碳纤维膜及其电化学电容性能

以聚丙烯腈(PAN)和三聚氰胺为原料,通过静电纺丝法制备了三聚氰胺改性聚丙烯腈纳米纤维前驱体,经预氧化、碳化后得到交联的多孔纳米碳纤维.采用红外光谱(FTIR)仪、热重分析(TGA)仪、扫描电子显微镜(SEM)、X射线衍射(XRD)仪、拉曼光谱仪和比表面积分析仪等对前驱体及纤维进行了表征.结果表明,经过三聚氰胺改性的聚丙烯腈纳米纤维前驱体在碳化后有效地交联,形成含有微孔、介孔和大孔多级的合理孔道结构,氮掺杂量高达14.3%,纤维直径大幅缩减,平均直径仅约89 nm.电化学测试结果表明,交联多孔纳米碳纤维电极在0.05 A·g^-1电流密度下未经活化时的质量比电容值高达194 F·g^-1(0.05 A·g^-1),在2 A·g^-1的电流密度下经过1000次循环充放电后的比电容仍然保持99.2%,表现出优异的电化学特性.     

碳包覆纳米SnO2中空纤维的制备及电容性能

采用同轴静电纺丝法制备了碳包覆纳米SnO₂中空纤维超级电容器电极材料.利用X射线衍射(XRD)、拉曼光谱、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和比表面积分析仪(BET)对材料进行表征.结果表明,纤维呈现中空形貌,平均直径为1 μm; SnO₂颗粒均匀分布于碳壳结构中,平均粒径为3-15 nm.材料的比表面积为565 m²·g^-1.在三电极体系中,当电流密度为0.25 A·g^-1时,电极材料的比容量达397.5 F·g^-1;在1.0A·g^-1电流密度下,充放电循环3000次后比容量仍保持为初始值的88%.在对称型双电极体系中,电流密度为0.25 A·g^-1时,电极材料的比容量达162.0 F·g^-1,在1.0 A·g^-1电流密度下,充放电循环3000次后比容量仍保持为初始值的84%.