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.     

酵母对抑制剂耐受的系统分析

纤维素生产乙醇的关键问题之一是水解产生的抑制性物质对乙醇发酵具有明显的抑制效应,因而引起了国内外研究者的广泛关注.研究发现,在抑制剂存在下,酵母在基因表达水平,蛋白水平和代谢物水平都有相应的耐受响应,且这些响应错综复杂.从系统角度运用组学的方法研究这一体系将有助于全面深入了解酵母的耐受机制.本文综述了系统研究的思路和方法在酵母对抑制剂耐受方面的研究状况;对主要研究手段和成果进行了回顾;并对酵母发酵乙醇系统分析的前景进行了展望.     

Miniaturized electrochemical sensors and their point-of-care applications

Most of the current analytical methods depend largely on laboratory-based analytical techniques that require expensive and bullky equipment,potentially incur costly testing,and involve lengthy detection processes.With increasing requirements for point-of-care testing(POCT),more attention has been paid to miniaturized analytical devices.Miniaturized electrochemical(MEC)sensors,including different material-based MEC sensors(such as DNA-,paper-,and screen electrode-based),have been in strong demand in analytical science due to their easy operation,portability,high sensitivity,as well as their short analysis time.They have been applied for the detection of trace amounts of target through measuring changes in electrochemical signal,such as current,voltage,potential,or impedance,due to the oxidation/reduction of chemical/biological molecules with the help of electrodes and electrochemical units.MEC sensors present great potential for the detection of targets including small organic molecules,metal ions,and biomolecules.In recent years,MEC sensors have been broadly applied to POCT in various fields,including health care,food safety,and environmental monitoring,owing to the excellent advantages of electrochemical(EC)technologies.This review summarized the state-of-the-art advancements on various types of MEC sensors and their applications in POCT.Furthermore,the future perspectives,opportunities,and challenges in this field are also discussed.     

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.     

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.     

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.     

A facile preparation and electrochemical properties of nickel based compound-graphene sheet composites for supercapacitors

Composites of a nickel based compound incorporated with graphene sheets(NiBC-GS) are prepared by a simple flocculation,using hydrazine hydrate as flocculant and reductant,from a homogeneous intermixture of nickel dichloride and graphene oxide dispersed in N,N-dimethylformamide.Morphology,microstructure and thermal stability of the obtained products were characterized by field-emission scanning electron microscopy,X-ray diffraction and thermal gravimetric analysis.Furthermore,the electrochemical properties of NiBC-GS,as electrode materials for supercapacitors,were studied by cyclic voUammetry and galvanostatic charge/discharge in 2 mol L~(-1) KOH solution.It was determined that for NiBC-GS annealed at 250 ℃.a high specific capacitance of 2394 Fg~(-1) was achieved at a current density of 1 Ag~(-1),with 78%of the value(i.e.,1864 Fg~(-1)) retained after 5000 times of repeated galvanostatic charge/discharge cycling.The high specific capacitance and available charge/discharge stability indicate the synthesized NiBC-GS250 composite is a good candidate as a novel electrode material for supercapacitors.     

Nickel oxide coated on ultrasonically pretreated carbon nanotubes for supercapacitor

Nickel oxide/carbon nanotubes (NiO/CNTs) composite materials for supercapacitor are prepared by chemically depositing nickel hydroxide onto carbon nanotubes pretreated by ultrasonication and followed by thermal annealing at 300 °C. A series of NiO/CNTs composites with different weight ratios of nickel oxide versus carbon nanotubes are synthesized via the same route. The high-resolution TEM and SEM results show that a lot of nicks, which favored the nucleation of the nickel hydroxide formed on the outer walls of carbon nanotubes due to ultrasonic cavitations, and then nickel oxide coated uniformly on the outer surface of the individual carbon nanotubes. The NiO/CNTs electrode presents a maximum specific capacitance of 523 F/g as well as a good cycle life during 1,000 cycles in 6 M KOH electrolyte. The good electrochemical characteristics of NiO/CNTs composite can be attributed to the three-dimensionally interconnected nanotubular structure with a thin film of electroactive materials.     

The preparation and performance of flocculent polyaniline/carbon nanotubes composite electrode material for supercapacitors

Polyaniline (PANI)/carbon nanotubes (CNTs) composite electrode material was prepared by in situ chemical polymerization. The structure and morphology of PANI/CNTs composite are characterized by Fourier infrared spectroscopy, scanning electron microscope, and transmission electron microscopy. It has been found that a flocculent PANI was uniformly deposited on the surface of CNTs. The supercapacitive behaviors of the PANI/CNTs composite materials are investigated with cyclic voltammetry, galvanostatic charge/discharge, impedance, and cycle life measurements. The results show that the PANI/CNTs composite electrodes have higher specific capacitances than CNT electrodes and better stability than the conducting polymers. The capacitance of PANI/CNTs composite electrode is as high as 837.6 F g⁻¹ measured by cyclic voltammetry at 1 mV s⁻¹. Besides, the capacitance retention of coin supercapacitors remained 68.0% after 3,000 cycles.     

碳纳米管-聚(3',4'-亚乙基二氧-2,2':5',2"-三噻吩)复合材料的制备及其电化学性能研究

通过Stille反应合成了3',4'-亚乙基二氧-2,2':5',2"-三噻吩(TET),并以其作为单体,采用化学氧化原位聚合方法在碳纳米管(CNT)的表面包覆新型聚(3',4'-亚乙基二氧.2,2':5',2"-三噻吩)(FTET),制备了PTET-CNT纳米复合材料.通过TEM、SEM和IR对其进行了表征,并利用循环伏安、交流阻抗、恒电流充放电等电化学测试方法,比较研究了复合材料以及碳纳米管在0.1 mol/L四乙基四氟硼酸铵(Et_4NPF_4)的乙腈溶液中的电化学行为.实验结果表明,在电流密度为3 mA/cm~2时,PTET-CNT复合材料的比电容为86 F/g,比原碳纳米管比电容20 F/g提高了3.3倍.基于这种复合材料的电容器的能量密度达到2.02 Wh/kg.     

载氧化钌碳纳米管超级电容器电极

研究了一种采用溶胶-凝胶方法制备超细氧化钌粉末的新方法，该方法制备的氧化钌电极材料在250 ℃热处理后具有570 F•g－1的比电容量并具有典型的多孔特征.通过在碳纳米管表面化学沉积氧化钌的方法制备了不同成分的氧化钌/碳纳米管复合电极,并探讨了其电化学伏安特性和直流充放电特性.该复合电极具有高能量密度特性，同时还具有良好的高功率放电特性.     

High temperature all solid state supercapacitor based on multi-walled carbon nanotubes and poly[2,5 benzimidazole]

Supercapacitor containing multi-walled carbon nanotubes (MWCNT) as the electrode material and phosphoric acid-doped poly[2,5 benzimidazole] (ABPBI) as the solid electrolyte and separator membrane has been investigated in a wide temperature range. Supercapacitors with different solid electrolyte concentrations have been fabricated and evaluated for their electrochemical performance. Specific capacitance of supercapacitors at room temperature was found to increase after the first heating cycle. Supercapacitor containing 10?wt.% of solid electrolyte in the electrode shows higher specific capacitance than the supercapacitor with liquid electrolyte. Cyclic voltammetry analysis of supercapacitors indicates high rate capability. The linear increase in the specific capacitance with temperature implies that capacitance is predominantly due to electric double layer. Electrochemical impedance analysis indicates that the mass capacitance and Warburg parameter increase with temperature, while solution resistance and leakage resistance decrease with temperature. The complex capacitance of the supercapacitors shows that both real and loss capacitances increase with temperature. The phase angle of supercapacitors is found to be around 85.2?±?1° at room temperature and it decreases with temperature. Galvanostatic charge–discharge cycling exhibits almost constant specific capacitance of 28?F?g^?1 at room temperature. However, it increases sharply and then attains stable value of 52?F?g^?1 during cycling at 100?°C. The increase in specific capacitance has been attributed to increase in surface area of the carbon nanotube (CNT), due to activation by phosphoric acid and diffusion of free phosphoric acid into the central canal of MWCNT.     

用于超级电容器的锰钴氧化物/碳纤维材料

The development of high-performance supercapacitor electrode materials is imperative to alleviate the ongoing energy crisis. Numerous transition metals (oxides) have been studied as electrode materials for supercapacitors owing to their low cost, environmental-friendliness, and excellent electrochemical performance. Among the developed binary transition metal oxides, manganese cobalt oxides typically show high theoretical capacitance and stable electrochemical performance, and are widely used in the electrode materials of supercapacitors. However, the poor conductivity and active material utilization of manganese cobalt oxide-based electrode materials limit their potential capacitance application. Cotton is mainly composed of organic carbon-containing materials, which can be transformed to carbon fibers after calcination. The resultant carbonaceous material exhibits a large specific surface area and good conductivity. Such advantages could potentially suppress the negative effects caused by the poor conductivity and small specific surface area of manganese cobalt oxides, thereby improving the electrochemical performance. Herein, we firstly deposited manganese cobalt oxides on cotton by a simple hydrothermal method, yielding a composite of manganese cobalt oxides and carbon fibers via subsequent calcination, to improve the electrochemical performance of the electrode material. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and electrochemical characterizations were used to investigate the physical, chemical, and electrochemical properties of the prepared samples. The fabricated manganese cobalt oxides in the composite were uniformly dispersed on the carbon fiber surface, which increased the contact between the interface of the electrode material and electrolyte, and enhanced electrode material utilization. The electrode material was confirmed to have well contacted with the electrolyte during a contact angle test. Hence, a pseudo-capacitance reaction completely occurred on the manganese cobalt oxide material. Moreover, the addition of carbon fibers reduced the resistance of the material, resulting in excellent capacitive performance. The capacitance of the prepared composite was 854 F∙g^-1 at a current density of 2 A∙g^-1. The capacitance was maintained at 72.3% after 2000 cycles at a current density of 2 A∙g^-1. These results indicate that the manganese cobalt oxide and carbon fiber composite is a promising electrode material for high-performance supercapacitors. The findings presented herein provide a strategy for coupling with carbon materials to enhance the performance of supercapacitor electrode materials based on manganese cobalt oxides. Thus, novel insights into the design of high-performance supercapacitors for energy management are provided.     

LiNi0.8Co0.2O2/CNTs Composite used as the Materials for Supercapacitor Electrodes

Stupercapacitors or electrochemical capacitors(ECs) have attracted considerable attentionas an intermediate power source between conventional capacitors and batteries since they possesshigh power density and energy density, exhibit excellent reversibility, and have long cycle life1.Conductive polymers2, electrically conductive metal oxide3,4, activated carbon5 and carbonnanotubes(CNTs) 6-9 have been used as supercapacitor electrode materials. LiNi0.sCo0.2O2 is apromising lithium battery material because it has some advantages of both LiNiO2 and LiCoO2besides its low cost and high power10.In this paper, the electrochemical properties of supercapacitors based on LiNi0.8Co0.2O2/carbonnanotubes composite and LiNi0.8Co0.2O2/acetylene black composite and CNTs in 1 mol/LLiClO4/EC+DEC [V(EC):V(DEC)=1:1] electrolyte have been investigated by means of constantcharge/discharge current tests. The experiment results show that the LiNi0.8Co0.2O2/carbon nanotubescomposite has better properties than others, and the maximun specific capacitance of thesupercapacitor can reach 284.88F/g, while the energy density is up to 158.27Wh/Kg.That discharge capacities, coulombic efficiencies and energy densities at the first cycle and themaximum value and capacity retention at the 100th cycle for supercapacitors using differentelectrode materials (A) LiNi0.8Co0.2O2/acetylene black, (B) LiNi0. 8Co0.2O2/CNTs, (C) CNTs is listedin table 1*Capacity retention rate obtained by dividing the discharge capacity at the 100th cycle by themaximum valueFrom above, the LiNi0. 8Co0.2O2/carbon nanotubes composite should be a good candidatesupercapacitor electrode material.     

Surface modification by graphene oxide:An efficient strategy to improve the performance of activated carbon based supercapacitors

An efficient and cost-effective strategy to modificate the surface of active carbon (AC), form a 3D-conductive network, and therefore improve the electrochemical performance of AC based supercapacitor was developed.     

碳纳米管在室温熔盐中的电容特性

研究了碳纳米管在室温熔盐二(三氟甲基磺酸酰)亚胺锂(LiTFSI)-乙酰胺中的电容特性. 将碳纳米管制成薄膜电极, 以LiTFSI-乙酰胺为电解液, 装配成模拟电容器, 用循环伏安和恒流充放电法研究其电化学性能. 结果表明, 碳纳米管在室温熔盐中表现出典型的电容特性, 其比电容为22 F•g^-1, 模拟电容器的工作电压可达2.0 V, 具有非常好的循环性能, 循环充放电1000次后容量损失仅10%, 表明室温熔盐是超级电容器非常有前景的新型电解液.