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.     

Anion photoelectron imaging of deprotonated thymine and cytosine

We report the anion photoelectron spectra of deprotonated thymine and cytosine at 3.496 eV photodetachment energy using velocity-mapped imaging. The photoelectron spectra of both species exhibit bands resulting from detachment transitions between the anion ground state and the ground state of the neutral radical. Franck-Condon simulations identify the anion isomers that contribute to the observed photoelectron spectrum. For both thymine and cytosine, the photoelectron spectra are consistent with anions formed by removal of a proton from the N atom that normally attaches to the sugar in the nucleotide (N1). For deprotonated thymine, the photoelectron spectrum shows a band due to a ring breathing vibration excited during the photodetachment transition. The electron affinity for the dehydrogenated thymine radical is determined as 3.250 +/- 0.015 eV. For deprotonated cytosine, the photoelectron spectrum lacks any resolved structure and the electron affinity of the dehydrogenated cytosine radical is determined to be 3.037 +/- 0.015 eV. By combining the electron affinity with previously measured gas phase acidities of thymine and cytosine, we determine the bond dissociation energy for the N-H bond that is broken.     

Mass Spectrometric and Photoelectron Spectroscopic Studies of Zirconium Oxide Molecular and Cluster Anions

We present a preliminary report on our mass spectrometric and photoelectron spectroscopic studies of zirconium oxide molecular and cluster anions using a newly built laser vaporization/time-of-flight/magnetic bottle, negative ion photoelectron spectrometer. This work was motivated in part by evidence which suggests that zirconium dioxide catalyzes the radiolysis of interfacial water. We present our mass spectrometric observations of oxygen-rich zirconium oxide cluster anions and our photoelectron spectra of ZrO^– and ZrO ₂ ^– . From the photoelectron spectrum of ZrO^–, the adiabatic electron affinity of ZrO was determined to be 1.3±0.3 eV, and from this value, the dissociation energy of ZrO^– (into Zr and O^–) was found to be 7.8±0.3 eV. From the photoelectron spectrum of ZrO₂, the adiabatic electron affinity of ZrO₂ was determined to be 1.8±0.4 eV.     

Photoelectron spectroscopy of jet-cooled aluminium cluster anions

Aluminium cluster anions (Al _n ^? ) are produced by laser vaporization without additional ionization and cooled by supersonic expansion. Photoelectrons from mass-identified anion bunches (n=2...25) are detached by laser light (hv=3.68 eV) and undergo energy analysis in a magnetic bottle-type time-of-flight spectrometer. The measurements provide information about the electronic excitation energies from ionic ground states to neutral states of the clusters. In contrast to bulk aluminium these cluster photoelectron spectra partially have well-resolved bands which originate from low-lying excited bands. For small clusters, especially the aluminium dimer and trimer, quantum-chemical calculations will be compared to the measurements. The electron affinity size dependence of larger clusters shows conclusive evidence for “shell” effects.     

七氟异丁腈负离子结构与反应活性的理论研究

新型环保绝缘气体七氟异丁腈(C4)在高压输电应用中备受关注. 本文采用多种高精度量子化学理论方法研究了C4吸附电子后形成C4^-负离子的结构、 光谱、 寿命以及与CO₂的反应机理和动力学. 结果表明, 电子进入C≡N的π^*反键轨道, 通过弯曲C—C=N形成C4^-负离子, 绝热电子亲合能的最佳预测值为0.30 eV. 在 0~2 eV范围内C4^-具有显著的光电子吸收峰, 亚稳态C4^-负离子经约9 kJ/mol能垒断裂C—F键生成稳定的长寿命[F...(CF₃)₂CCN]^-中间体. C4^-+CO₂反应存在进攻F或CN上的C和N 3种复合-解离机理, 在电气应用条件下, 以CO₂进攻氰基CN途径为主, 诱发负电荷从CN向CO₂转移.     

Photoelectron spectroscopy of anions at 118.2 nm: observation of high electron binding energies in superhalogens MCl4- (M=Sc, Y, La)

High energy photon is needed for photoelectron spectroscopy (PES) of anions with high electron binding energies, such as superhalogens and O-rich metal oxide clusters. The highest energy photon used for anion PES in the laboratory has been 157 nm (7.866 eV) from F2 eximer lasers. Here, we report an anion PES experiment using coherent vacuum ultraviolet radiation at 118.2 nm (10.488 eV) by tripling the third harmonic output (355 nm) of a Nd:YAG laser in a XeAr cell. Our study focuses on a set of superhalogen species, MCl(4) (-) (M=Sc, Y, La), which were expected to possess very high electron binding energies. While the 157 nm photon can only access the ground state detachment features for these species, more transitions to the excited states at binding energies higher than 8 eV are observed at 118.2 nm. The adiabatic detachment energies are shown to be, 6.84, 7.02, and 7.03 eV for ScCl(4) (-), YCl(4) (-), and LaCl(4) (-) eV, respectively, whereas their corresponding vertical detachment energies are measured to be 7.14, 7.31, and 7.38 eV.     

Production of C6O6- from oligomerization of CO on molybdenum anions

C6O6- has been observed in mass spectra of the anionic reaction products between small molybdenum suboxide clusters and carbon monoxide. No other free oxocarbanions were observed, nor were any dianions. The anion photoelectron spectrum of C6O6- shows that the neutral has an adiabatic electron affinity of 2.54(5) eV and an excited triplet state with a term energy of 1.0(1) eV. Analysis of the mass spectra suggests that C6O6- may be forming from oligomerization of CO on bare or highly reduced molybdenum anion centers.     

Photoelectron imaging spectroscopy of nitroethane anions

We present low-energy velocity map photoelectron imaging results for bare and Ar solvated nitroethane anions. We report an improved value for the adiabatic electron affinity of nitroethane of (191 ± 6) meV which is used to obtain a C-NO(2) bond dissociation energy of (0.589 ± 0.019) eV in nitroethane anion. We assign a weak feature at (27 ± 5) meV electron binding energy to the dipole-bound anion state of nitroethane. Photoelectron angular distributions exhibit increasing anisotropy with increasing kinetic energies. The main contributions to the photoelectron spectrum of nitroethane anion can be assigned to the vibrational modes of the nitro group. Transitions involving torsional motion around the CN bond axis lead to strong spectral congestion. Interpretation of the photoelectron spectrum is assisted by ab initio calculations and Franck-Condon simulations.     

Magnetic-Bottle and Velocity-Map Imaging Photoelectron Spectroscopy of APS- (A=C14H10 or Anthracene): Electron Structure,Spin-Orbit Coupling of APS·, and Dipole-Bound State of APS-

Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS^-(A=C₁₄H₁₀ or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS^· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d, p) calculations indicate APS^· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron.     

Photoelectron spectroscopy of 1-nitropropane and 1-nitrobutane anions

We present low-energy velocity map photoelectron imaging results for bare and Ar-solvated 1-nitropropane and 1-nitrobutane anions. We report the adiabatic electron affinity of 1-nitropropane as (223 ± 6) meV and that of 1-nitrobutane as (240 ± 6 meV). The vertical detachment energies of these two species are found to be (0.92 ± 0.05) and (0.88 ± 0.05) eV, respectively. The photoelectron spectra are discussed in the framework of Franck-Condon simulations based on density functional theory. We observe unusual resonances in the photoelectron spectra of both ions under study, whose kinetic energy is independent of the photon energy of the detaching radiation. We discuss possible origins of these resonances as rescattering phenomena, consistent with the experimental photoelectron angular distributions.     

Joint photoelectron and theoretical study of (Rh(m)Co(n))⁻ (m=1-5, n=1-2) cluster anions and their neutral counterparts

Anion photoelectron spectroscopic experiments and calculations based on density functional theory have been used to investigate and uniquely identify the structural, electronic, and magnetic properties of both neutral and anionic (Rh(m)Co(n)) and (Rh(m)Co(n))(-) (m=1-5, n=1-2) clusters, respectively. Negative ion photoelectron spectra are presented for electron binding energies up to 3.493 eV. The calculated electron affinities and vertical detachment energies are in good agreement with the measured values. Computational results for geometric structures and magnetic moments of both cluster anions and their neutrals are presented.