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.     

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.     

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.     

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.     

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.     

激光溅射Ni等离子体与气相CH3OH团簇的反应

The gas phase reaction of Ni plasma and methanol clusters is studied by the laser ablation-molecular beam（LAMB） method. Five species of clustered complex ions Ni+（CH3OH）n,NiO+（CH3OH）n,H+（CH3OH）n,H3O+（CH3OH）n,CH3O-（CH3OH）n（n≤25）are observed. Interestingly,the species and sizes of the product clusters vary observably when the plasma acts on the different parts of the pulsed methanol molecular beam. When the laser ablated Ni plasma acts on the head and tail of the beam,the metal methanol complex clusters Ni+（CH3OH）n and the oxidation clusters NiO+（CH3OH）n（n=1-15）together with protonated methanol clusters H +（CH3OH）n are domain. While the plasma acts on the middle of the beam,however,Ni+（CH3OH）1-2 and H+（CH3OH）n along with the mixed methanol-water clusters H3O+（CH3OH）n（n=15-25）turn to be the main resulting clusters. By comparing the intensities and the cluster sizes of NiO+（CH3OH）n with Ni+（CH3OH）n,the formation of NiO+（CH3OH）n is contributed to the intracluster demethanation reaction of Ni+（CH3OH）n and evaporation of several methanol molecules. As the H3O+（CH3OH）n is observed only when the plasma acts on the high density part of the beam,and their intensities are only 0. 5% of the protonated methanol molecule,it is concluded that the species are partially due to the recombination of H+（CH3OH）n and water,which come from the plasma-molecule reaction.     

激光溅射-分子束法研究镁、铝离子与乙腈分子的气相化学反应

利用激光溅射-分子束技术研究了Mg+、 Al+与乙腈分子的气相团簇反应.根据反射式飞行时间质谱检测的结果发现, Mg+、 Al+与乙腈分子反应形成不同尺寸的团簇离子产物,其中Al+与(CHCN)n的结合数n=1～10,而Mg+与(CHCN)n的结合数n=1～5. Al+(CHCN)n、 Mg+(CHCN)n团簇离子产物的强度分布都存在明显的强度间隙现象. Al+与(CHCN)n进行缔合时,出现了两个强度间隙;而Mg+与(CHCN)n进行缔合时,则只存在一个强度间隙. Al+的第一强度间隙在n=4～5,第二强度间隙在n=6～7;而Mg+的强度间隙在n=2～3.     

激光溅射Cu等离子体与气相C2H5OH团簇的反应

用激光溅射-分子束技术研究了气相中Cu的等离子体与乙醇分子团簇的反应.观察到三种团簇正离子Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n和三种团簇负离子(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－(n≤12).详细考察了在不同的载气压力下激光烧蚀等离子体作用于脉冲分子束， 以及在一定的压力下等离子体作用于分子束不同位置时，对团簇产物种类和团簇尺寸大小的影响.分析了Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n、(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－等团簇的产生机理.     

氨和甲醇团簇中的质子转移反应

应用激光多光子电离质谱和分子束技术研究了氨和甲醇二元团簇,实验观测到两个系列质子化的团簇离子: (CH3OH)nH+和(CH3OH)nNH4+(1≤n≤14 ),其产生是经过二元团簇内的质子转移反应。同时也研究了氘代甲醇CH3OD和氨混合团簇,结果表明OD原子团中的D转移概率比CH3原子团中的质子转移概率大几倍。在HF/STO-3G和MP2/6-31G*　*水平上对氨和甲醇二元团簇进行了计算,结果表明与CH3相比OH中的质子转移更加容易,因为CH3中的质子转移过程要克服高度约120 kJ/mol的能垒。     

氟丙烯在高温下的热稳定性

用单脉冲激波管研究了全氟丙烯C3F6的分解。使用H2作为清扫剂。产物包括 CH4、 C2F4、 CF3H和C2F3H,作为对断键反应过程的指示。C3F6的断键反应为 C3F6  CF3+C2F3 （1） 得到其速率常数表达式为 k（C3F6  CF3+C2F3)=10(17.4±0.2)exp-(355300±8360)/(RT) s-1 温度范围为1090 K相似文献   

Reactions of Laser Ablation-magnesium Plasma with Methanol Clusters

IntroductionReactions of metal ions with neutral molecules orclusters produce a variety of metal complex ions andother new series of cluster ions including cations andanions.The laser ablation-molecular beam(LA-MB)method has marked its relevance in the st…     

Microsolvation of the sodium and iodide ions and their ion pair in acetonitrile clusters: a theoretical study

The structural and thermodynamic properties of Na+(CH3CN)n, I-(CH3CN)n, and NaI(CH3CN)n clusters have been investigated by means of room-temperature Monte Carlo simulations with model potentials developed to reproduce the properties of small clusters predicted by quantum chemistry. Ions are found to adopt an interior solvation shell structure, with a first solvation shell containing approximately 6 and approximately 8 acetonitrile molecules for large Na+(CH3CN)n and I-(CH3CN)n clusters, respectively. Structural features of Na+(CH3CN)n are found to be similar to those of Na+(H2O)n clusters, but those of I-(CH3CN)n contrast with those of I-(H2O)n, for which "surface" solvation structures were observed. The potential of mean force calculations demonstrates that the NaI ion pair is thermodynamically stable with respect to ground-state ionic dissociation in acetonitrile clusters. The properties of NaI(CH3CN)n clusters exhibit some similarities with NaI(H2O)n clusters, with the existence of contact ion pair and solvent-separated ion pair structures, but, in contrast to water clusters, both types of ion pairs adopt a well-defined interior ionic solvation shell structure in acetonitrile clusters. Whereas contact ion pair species are thermodynamically favored in small clusters, solvent-separated ion pairs tend to become thermodynamically more stable above a cluster size of approximately 26. Hence, ground-state charge separation appears to occur at larger cluster sizes for acetonitrile clusters than for water clusters. We propose that the lack of a large Na+(CH3CN)n product signal in NaI(CH3CN)n multiphoton ionization experiments could arise from extensive stabilization of the ground ionic state by the solvent and possible inhibition of the photoexcitation mechanism, which may be less pronounced for NaI(H2O)n clusters because of surface solvation structures. Alternatively, increased solvent evaporation resulting from larger excess energies upon photoexcitation or major solvent reorganization on the ionized state could account for the observed solvent-selectivity in NaI cluster multiphoton ionization.     

Microsolvation of Co2+ and Ni2+ by acetonitrile and water: photodissociation dynamics of M(2+)(CH3CN)n(H2O)m

The microsolvation of cobalt and nickel dications by acetonitrile and water is studied by measuring photofragment spectra at 355, 532 and 560-660 nm. Ions are produced by electrospray, thermalized in an ion trap and mass selected by time of flight. The photodissociation yield, products and their branching ratios depend on the metal, cluster size and composition. Proton transfer is only observed in water-containing clusters and is enhanced with increasing water content. Also, nickel-containing clusters are more likely to undergo charge reduction than those with cobalt. The homogeneous clusters with acetonitrile M(2+)(CH(3)CN)(n) (n = 3 and 4) dissociate by simple solvent loss; n = 2 clusters dissociate by electron transfer. Mixed acetonitrile/water clusters display more interesting dissociation dynamics. Again, larger clusters (n = 3 and 4) show simple solvent loss. Water loss is substantially favored over acetonitrile loss, which is understandable because acetonitrile is a stronger ligand due to its higher dipole moment and polarizability. Proton transfer, forming H(+)(CH(3)CN), is observed as a minor channel for M(2+)(CH(3)CN)(2)(H(2)O)(2) and M(2+)(CH(3)CN)(2)(H(2)O) but is not seen in M(2+)(CH(3)CN)(3)(H(2)O). Studies of deuterated clusters confirm that water acts as the proton donor. We previously observed proton loss as the major channel for photolysis of M(2+)(H(2)O)(4). Measurements of the photodissociation yield reveal that four-coordinate Co(2+) clusters dissociate more readily than Ni(2+) clusters whereas for the three-coordinate clusters, dissociation is more efficient for Ni(2+) clusters. For the two-coordinate clusters, dissociation is via electron transfer and the yield is low for both metals. Calculations of reaction energetics, dissociation barriers, and the positions of excited electronic states complement the experimental work. Proton transfer in photolysis of Co(2+)(CH(3)CN)(2)(H(2)O) is calculated to occur via a (CH(3)CN)Co(2+)-OH(-)-H(+)(NCCH(3)) salt-bridge transition state, reducing kinetic energy release in the dissociation.     

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

The reaction system of 1-propenyl radical with NO is an ideal model for studying the intermolecular and intramolecular reactions of complex organic free radicals containing C=C double bonds. On the basis of the full optimization of all species with the Gaussian 98 package at the B3LYP/6-311++G** level, the reaction mechanism was elucidated extensively using the vibrational mode analysis. There are seven reaction pathways and five sets of small molecule end products: CH2O+CH3CN, CH2CHCN+H2O, CH3CHO+HCN, CH3CHO+HNC, and CH3CCH+HNO. The channel of C3H5￠+NO→ IM1→TS1→IM2→TS2→IM3→TS3→CH3CHO+HCN is thermodynamically most favorable.     

RRKM理论研究N(4S)+CH2X(X=F,Cl)的反应通道

采用RRKM理论和疏松过渡态模型计算了N(4S)+CH2X(X=F,Cl)反应的微正则速率常数和通道分支比.计算结果表明,在较低的内能下(E=280.29 kJ/mol), N(4S)+CH2F的主要产物为NCHF+H,占总产物的59.2%,次要产物为H2CN+F,占37.4%.而N(4S)+CH2Cl反应在E＝267.78 kJ/mol时,主要产物是H2CN+Cl,占90.3%, NCHCl+H只占9.0%.在内能较高的时候(取E=500.00 kJ/mol), N(4S)+CH2F的主要通道并未变化,而N(4S)+CH2Cl的主要通道变为NCHCl+H,比例为51.5%, H2CN+Cl的比例降到40.4%.