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.     

亚硝酸根在纳米金修饰玻碳电极上的电催化氧化行为及其测定

采用直接电化学沉积法制备出纳米金修饰玻碳电极,研究了其对亚硝酸根的电催化氧化作用。结果表明,亚硝酸根在该修饰电极上于0.8 V处出现了一个良好的氧化峰。在最优实验条件下,亚硝酸根的峰电流与其浓度在2×10-6～2×10-3mol/L范围内呈一定的线性关系,检出限为6.0×10-7(S/N=3),提出了用循环伏安法测定亚硝酸根的方法。纳米金修饰电极用于东莞自来水水样中亚硝酸根的测定,回收率在98.1%～101.4%之间。对比本方法,用分光光度法对东莞自来水样中亚硝酸根进行了测定,结果满意。     

NO2-在CTMAB-氧化钕纳米修饰电极上的电化学行为及其测定

制备了十六烷基三甲基溴化铵-氧化钕纳米修饰电极。用循环伏安法和示差脉冲伏安法研究了NO2-在该修饰电极上的电化学行为,结果表明,该修饰电极对NO2-的氧化具有良好的电催化能力,NO2-的氧化峰电流与其浓度在3.33×10-8～1.04×10-6mol/L范围内呈现良好的线性关系,检测限为9.86×10-9mol/L(S/N=3)。此外,该修饰电极具有良好的重现性和稳定性。本方法可用于NO2-实际样品的测定。     

聚铬黑T修饰电极检测亚硝酸盐的研究

利用电化学聚合法将铬黑T修饰到玻碳电极表面,制得聚铬黑T修饰电极。该修饰电极对亚硝酸盐的电化学氧化具有明显的催化作用,这种催化作用主要是由于聚铬黑T薄膜与带负电荷的亚硝酸盐离子的静电相互作用,导致亚硝酸盐离子富集在电极表面/溶液界面,显著增强了亚硝酸盐的氧化电流。电子传输系数α为0.735。选用0.85V作为工作电压,对亚硝酸盐进行安培检测,在0.05μmol/L～1.0 mmol/L和1.0～20.0 mmol/L两个浓度范围内呈现良好的线性关系,检测限达到0.01μmol/L。且该修饰电极有良好的重现性和稳定性。将该修饰电极用于泡菜中亚硝酸盐的测定,获得了满意的结果。     

基于溶胶-凝胶技术的磷钨杂多酸化学修饰电极的组装及其电催化

将 Dawson型磷钨杂多酸盐 K6 P2 W1 8O6 2 · 1 0 H2 O( P2 W1 8)掺杂到溶胶 -凝胶中 ,滴涂在碳糊电极表面 ,制备成化学修饰电极 .并对该化学修饰电极的电化学行为 ,包括溶液 p H值的影响和电极稳定性等进行了详细的研究 .结果表明 ,此电极既保持了该杂多酸的电化学活性和电催化性能 ,又具有良好的稳定性和灵敏度 .实验发现 ,在 0 .5mol/L H2 SO4溶液中 ,掺杂在溶胶 -凝胶膜中的 P2 W1 8的第 3、第 4个还原峰对 NO- 2 离子具有很好的电催化活性 ,且催化电流同 NO- 2 浓度呈线性关系 .同时 ,P2 W1 8的第 3、第 4个还原峰对分子氧也具有很好的电催化活性 .     

纳米金/3-氨丙基-三乙氧基硅烷修饰传感器电化学检测NO-2

将3-氨丙基-三乙氧基硅烷（ATS）修饰在玻碳电极表面,再自组装一层纳米金,制备了一种新型NO2^-的电化学传感器。该修饰电极对NO2^-有较好的催化作用。在pH为3时,NO2^-的氧化峰电流与其浓度在5．0×10^-7～1．0×10^-3mol／L范围内呈良好的线性关系,检出限可达2．0×10^-7mol／L。方法具有较高的灵敏度和较好的重现性。     

镧取代Dawson型磷钨杂多酸聚吡咯修饰电极的制备及其电化学性能

通过缺位填充法合成了分子式为α２－Ｋ７Ｐ２Ｗ１７Ｏ６１（Ｌａ· ＯＨ２）的镧（Ⅲ）取代十八钨磷酸盐。在玻碳电极（ＧＣ）上,用电化学方法将单取代Ｄａｗｓｏｎ型杂多酸盐α２－Ｋ７Ｐ２Ｗ１７Ｏ６１（Ｌａ·ＯＨ２）的阴离子（Ｐ２Ｗ１７Ｌａ）掺杂到聚吡咯（ＰＰＹ）薄膜中制成Ｐ２Ｗ１７Ｌａ／ＰＰＹ／ＧＣ化学修饰电极,既保持该杂多酸的电化学活性和电催化性能,又具有良好的稳定性和灵敏度。研究表明, ０． ５０ ｍｏｌ／Ｌ ＨＣＩ溶液中,聚吡咯薄膜中 Ｐ２Ｗ１７Ｌａ的第一对氧化还原峰对 ＮＯ２的电还原具有良好的催化活性,其催化电流与 ＮＯ２浓度在 ６．０ × １０－５－ １．０ × １０－２ｍｏｌ／Ｌ范围内呈线性关系。     

Electrocatalytic oxidation of nitric oxide at nano-TiO2/Nafion composite film modified glassy carbon electrode

A novel nanocrystalline TiO₂ (nano-TiO₂) and Nafion composite film modified glassy carbon electrode has been developed for the determination of nitric oxide (NO) radical in an aqueous solution. This modified electrode can be employed as a NO sensor with a low detection limit, fast response, high sensitivity and selectivity. Two apparent anodic peaks were observed at 0.67 and 0.95 V at the nano-TiO₂ modified glassy carbon electrode by differential pulse voltammetry (DPV). After further modification with a thin film of Nafion, which was capable of preventing some anionic interference such as nitrite and ascorbic acid, only one peak appeared and the peak current enhanced greatly. The chronocoulometric experimental results showed NO was oxidized by one-electron transfer reaction at the composite film modified electrode. The amperometric responses increased linearly with the concentrations of NO ranging from 3.6×10⁻⁷ mol/L to 5.4×10⁻⁵ mol/L. The detection limit was estimated to be 5.4×10⁻⁸ mol/L. In this sensor system, the modification film provides complete selectivity for NO over nitrite anions (NO₂⁻).     

α-P2W17O10-61杂多阴离子薄膜修饰电极的制备

研究了杂多酸阴离子α－Ｐ２Ｗ１７Ｏ＾１０－６１修饰电极的制备及其化学性质,α－Ｐ２Ｗ１７Ｏ＾１０－６１修饰电极对ＢｒＯ＾－３具有催化作用。催化电流△Ｉｐ与「ＢｒＯ＾－３」在７．０＊１０＾－６－１．０＊１０＾－４ｍｏｌ／Ｌ范围内呈良好线性关系。用此电极测定了天然水中ＢｒＯ＾－３的含量,结果令人满意。     

A multi-wall carbon nanotubes-dicetyl phosphate electrode for the determination of hypoxanthine in fish.

An enzymeless sensor based on a multi-walled carbon nanotubes-dicetyl phosphate (MWCNT-DCP) film modified vitreous carbon electrode was developed for the determination of hypoxanthine. The MWCNT-DCP film modified electrode showed a remarkable enhancement effect on the oxidation peak current of hypoxanthine. Under the optimized conditions, the oxidation peak current is proportional to the concentration of hypoxanthine over the range from 5.0 x 10(-7) to 2.0 x 10(-4) mol L(-1) with a detection limit (S/N = 3) of 2.0 x 10(-7) mol L(-1). The MWCNT-DCP film modified electrode has been successfully used to detect hypoxanthine in fish samples.     

聚4-(2-吡啶偶氮)间苯二酚膜修饰玻碳电极测定过氧化氢

利用循环伏安法（-0.5～2.2 V）将4-(2-吡啶偶氮)间苯二酚(PAR)电聚合修饰到玻碳电极表面,制备了聚PAR膜过氧化氢（H2O2）传感器。 并采用循环伏安法和计时安培法研究了修饰电极的电化学性质和对H2O2的响应特性。 结果表明,PAR膜修饰电极在低的电位下对H2O2具有优异的电催化还原效应。 在磷酸盐缓冲溶液中(pH=8.0)用计时安培法对H2O2进行了测定（工作电位0.45 V）,响应电流与其浓度在2×10-5～1.76×10-3 mol/L范围内呈良好的线性关系,线性相关系数r=-0.999 83,检测限(S/N=3)为3 μmol/L。该修饰电极灵敏度高、稳定性好、制备简单,在H2O2的测定中对抗坏血酸、尿酸和葡萄糖有较好的抗干扰性。