宏观均相多孔电极电化学阻抗谱基础

电化学阻抗谱可用于诊断多孔电极内电荷转移反应,即界面电荷集聚和电荷传导,以及反应物质输运。本文采用复相量方法,在同态假设条件下,重新推演多孔电极阻抗谱模型,厘清传统多孔电极阻抗谱模型中的模糊性表述。(1) 定义多孔电极表征输入参数,包括电极基体电子电导率σ₁ 、电解质离子电导率σ₂、界面电荷传递电导率g_ct、单位面积界面电容C、固相扩散系数D、速度常数k、电极厚度d、特征孔深L_p 和单位体积表面积S_c;(2) 解析阻抗谱特征输出参数,包括场扩散常数K,特征频率ω₀、ω₁、ω₂、ω₃和 ω_max,它们分别相关于界面传导反应、有限场扩散、氧化还原反应、孔内扩散和最小特征孔尺寸,以及分别对应于从传导到扩散和从扩散到饱和的转折频率f_k1 和f_k2;(3) 当参数X和Z同时变化时(X = σ₁和Z = d,S_c,L_p,C,g_ct,D,k),通过阻抗谱特征参数的演变规律,分析了电荷转移反应中X和Ζ参数耦合竞争;(4)为深入分析电荷转移反应中参数X和Z的耦合竞争,引入了分叉频率f_XZ和f_ZX 。f_XZ和f_ZX所处位置可以用于表征参数X和Z影响电荷转移反应的深度和广度。当分叉频率f_XZ和f_ZX不存在时,表明电荷转移反应中参数X和Z在全频率范围内存在耦合竞争。总之,借助于特征频率和分叉频率,本文一方面研究了动力学参数和微观结构参数对多孔电极中电荷转移反应的影响,另一方面分析谱图的变化及其背后的阻抗谱特征演化规律。本文研究结果可为阻抗谱的系统仿真和辨识提供理论基础,可为多孔电极内电荷转移反应的竞争分析提供技术支撑,还可为电化学储能系统的优化设计提供诊断工具。     

Hydrogenmaleato bridged supramolecular double chains via π–π stacking interactions: syntheses, crystal structures and magnetic properties of ∞[Cu(phen)X(HL)2/2] with X=Cl (1), NO3 (2) and H2L=maleic acid

Two novel hydrogen maleato (HL) bridged Cu(II) complexes _∞¹[Cu(phen)Cl(HL)_2/2] 1 and _∞¹[Cu(phen)(NO₃)(HL)_2/2] 2 were obtained from reactions of 1,10-phenanthroline, maleic acid with CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O, respectively, in CH₃OH/H₂O (1:1 v/v) at pH=2.0 and the crystal structures were determined by single crystal X-ray diffraction methods. Both complexes crystallize isostructurally in the monoclinic space group P2₁/n with cell dimensions: 1 a=8.639(2) Å, b=15.614(3) Å, c=11.326(2) Å, β=94.67(3)°, Z=4, D_calc=1.720 g/cm³ and 2 a=8.544(1) Å, b=15.517(2) Å, c=12.160(1) Å, β=90.84(8)°, Z=4, D_calc=1.734 g/cm³. In both complexes, the square pyramidally coordinated Cu atoms are bridged by hydrogen maleato ligands into 1D chains with the coordinating phen ligands parallel on one side. Interdigitation of the chelating phen ligands of two neighbouring chains via π–π stacking interactions forms supramolecular double chains, which are then arranged in the crystal structures according to pseudo 1D close packing patterns. Both complexes exhibit similar paramagnetic behavior obeying Curie–Weiss laws χ_m(T−θ)=0.414 cm³ mol⁻¹ K with the Weiss constants θ=−1.45, −1.0 K for 1 and 2, respectively.     

Interfacial properties of precipitate-based ion-selective electrodes : Rotating disk impedance measurements of the Ag2S/Ag (aqueous) interface

Three-electrode rotating disk impedance measurements were made from 31.6 kHz to 0.0178 Hz on Ag₂S/Ag⁺ (aqueous) and Ag₂S/Ag systems. Membranes were prepared from materials precipitated in excess of silver or sulfide ions, and stoichiometric mixtures. Impedances were analyzed, as a function of rotation rate and bathing activities, to isolate bulk conductivities, internal diffusion, surface kinetic and dissolution/crystallization impedances. High-frequency bulk resistivities, R_∞, varied by four with precipitation and pressing conditions. Resistivities were the same for solution and ohmic configurations for each preparation. For ohmic contacts, R_∞ and R(DC) were identical. Solution contact cells in 10^-1 M and 10^-2 M bathing silver ion solution gave identical frequency-dependent impedances which were independent of rotation rate. Thus, solution diffusional impedances and solution dependent surface kinetics were eliminated, and a finite Warburg, interior-Ag⁺-defect, diffusion impedance was indicated. Summation of bulk membrane and contact resistances, and this Warburg impedance served as a 'background' correction in analyzing dilute bathing solution interfacial impedances for surface effects. Corrected impedances in 10^-3 –10^-5 M AgNO₃ showed solution diffusional behaviour combined with surface kinetic and dissolution impedances. An iterative linear least-squares method resolved these quantities. The surface resistance suggests a potential-dependent rate constant; dissolution time constants were solution-independent and smaller than those for solution diffusion. Thus, dissolution can be a rate-limiting step in establishment of steady-state potentials.     

Equilibrium diagram of KPO3–Y(PO3)3 system, chemical preparation and characterization of KY(PO3)4

Microdifferential thermal analysis (μ-DTA), X-ray diffraction (XRD) and infrared (IR) spectroscopy were used for the first time to investigate the liquidus and solidus relations in the KPO₃–Y(PO₃)₃ system. The only compound observed within the system was KY(PO₃)₄ melting incongruently at 1033 K. An eutectic appears at 13.5 mol% Y(PO₃)₃ at 935 K, the peritectic occurs at 1033 K and the phase transition for potassium polyphosphate KPO₃ was observed at 725 K. Three monoclinic allotropic phases of the single crystals were obtained. KY(PO₃)₄ polyphosphate has the P2₁ space group with lattice parameters: a=7.183(4) Å, b=8.351(6) Å, c=7.983(3) Å, β=91.75(3)° and Z=2 is isostructural with KNd(PO₃)₄. The second allotropic form of KY(PO₃)₄ belongs to the P2₁/n space group with lattice parameters: a=10.835(3) Å, b=9.003(2) Å, c=10.314(1) Å, β=106.09(7)° and Z=4 and is isostructural with TlNd(PO₃)₄. The IR absorption spectra of the two forms show a chain polyphosphates structure. The last modification of KYP₄O₁₂ crystallizes in the C2/c space group with lattice parameters: a=7.825(3) Å, b=12.537(4) Å, c=10.584(2) Å, β=110.22(7)° and Z=4 is isostructural with RbNdP₄O₁₂ and contains cyclic anions. The methods of chemical preparations, the determination of crystallographic data and IR spectra for these compounds are reported.     

Substituent effect on the sudden polarization in simply substituted ethylenes

The sudden polarization effect occurring in the excited states of simply-substituted ethylenes is analyzed in both molecular orbital and valence bond terms for the substituents R = CH₃, F, HO and NH₂. Ab initio level computations (4—31G + 100 × 100 CI) indicate that at 90° twist the ground states of all these structures are diradical in character with very little substituent effect on the ground state cis—trans isomerization barrier. On the other hand, the energies of both the Z₁ and Z₂ states are strongly affected by the substituent. In all cases the Z₁ states have a nearly pure R---C⁺H---C⁻H₂ zwitterionic character. The stabilization energies of the Z₁ states as compared to ethylene roughly correspond to the order expected from the analogous carbonium ions with the exception of the fluoro substituent.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

表面钒修饰对α-Fe2O3材料光电化学性能的增强作用

对半导体材料进行表面化学修饰或改性,是提高其光催化活性、有效利用光能的一种重要措施.本文结合水热化学法、化学池沉积和后续热处理等,分别制备了未修饰α-Fe₂O₃和钒修饰的α-Fe₂O₃光电极材料.利用X射线粉末衍射(XRD)谱和紫外-可见漫反射光谱(UV-Vis-DRS)技术分析表征了材料的晶相结构、化学组成和光谱吸收等固体物理化学性能;利用光电流测量和电化学交流阻抗谱(EIS)实验技术,并基于1 mol·L^-1NaOH (pH 13.6)中的光电化学水分解反应,研究了钒修饰对α-Fe₂O₃材料光电化学性能的增强作用.结果表明,与未修饰的Fe₂O₃材料相比,钒修饰α-Fe₂O₃样品出现FeVO₄的XRD特征峰,但临界光吸收波长未发生红移;钒修饰使Fe₂O₃材料的光电流增大4-5倍、光生载流子在电极表面的复合几率降低了3/4-4/5、电极表面电荷传递速率(表观一级速率常数)明显提高.结合Fe₂O₃/溶液界面半导体能带模型和有关研究结果,分析了研究体系的界面电荷动力学传输过程以及钒修饰使α-Fe₂O₃材料光电化学性能增强的原因.     

Etude vibrationnelle du fluorure hydrogenodifluorure de baryum BaF(HF2)

Infrared and Raman spectra of the BaF(HF₂) crystal and its 10 and 50% deuterated derivatives at 300 and 90 K have been investigated in the 4000 to 20 cm⁻¹ range. An assignment of internal and lattice vibrations has been proposed. Vibrational spectra are consistent with a centrosymmetric P2₁/m space group and Z=2. They show that the (FHF)⁻ ion is not centrosymmetrical, in spite of a short F…F distance; a force field calculation has been performed in order to determine the F---H and H…F distances, which are equal to 1.08 and 1.20 Å, respectively, in agreement with the ¹H and ¹⁹F NMR data. The ν₃(H)/ν₃(D) isotope frequency ratio indicates a negative or zero isotope effect on the F…F distance, which is observed for the first time for a strong asymmetric hydrogen bond.     

Structural and theoretical studies of Xe(OChF5)2 and [XeOChF5][AsF6] (Ch = Se, Te)

The XeOSeF₅⁺ cation has been synthesized for the first time and characterized in solution by ¹⁹F, ⁷⁷Se and ¹²⁹Xe NMR spectroscopy and in the solid state by X-ray crystallography and Raman spectroscopy with AsF₆⁻ as its counter anion. The X-ray crystal structures of the tellurium analogue and of the Xe(OChF₅)₂ derivatives have also been determined: [XeOChF₅][AsF₆] crystallize in tetragonal systems, P4/n, a=6.1356(1) Å, c=13.8232(2) Å, V=520.383(14) Å³, Z=2 and R₁=0.0453 at −60°C (Te) and a=6.1195(7) Å, c=13.0315(2) Å, V=488.01(8) Å³, Z=2 and R₁=0.0730 at −113°C (Se); Xe(OTeF₅)₂ crystallizes in a monoclinic system, P2₁/c, a=10.289(2) Å, b=9.605(2) Å, c=10.478(2) Å, β=106.599(4)°, V=992.3(3) Å³, Z=4 and R₁=0.0680 at −127°C; Xe(OSeF₅)₂ crystallizes in a triclinic system, , a=8.3859(6) Å, c=12.0355(13) Å, V=732.98(11) Å³, Z=3 and R₁=0.0504 at −45°C. The energy minimized geometries and vibrational frequencies of the XeOChF₅⁺ cations and Xe(OChF₅)₂ were calculated using density functional theory, allowing for definitive assignments of their experimental vibrational spectra.     

Synthesis, characterization, and X-ray crystal structures of W(VI) alkyl complexes with chelating diamide and imido co-ligands

The complex W(NPh)Cl₂[o-(NSiMe₃)₂C₆H₄] 3 was synthesized from PhN = WCl₄ · OEt₂ and N,N′-(Li₂[o-(NSiMe₃)₂C₆H₄] and reacts with Lewis bases to form the adducts W(NPh)Cl₂[o-(NSiMe₃)₂C₆H₄](L) (L = PMe₃, THF, 3-picoline, ^tBuNC, MeCN) 4a–e. Crystals of 4a are triclinic, space group P1¯, with a = 9.562(1), b = 10.277(1), c = 14.920(2) Å, = 82.15(1), β = 80.18(1), γ = 80.41(1)°, and Z = 2. The structure was solved by the heavy atom method and refined to R = 0.0408 for 4224 observed (I > 2σ(I)) reflections. The dialkyl complexes W(NPh)R₂[o-(NSiMe₃)₂C₆H₄] (R = Me, Et, CH₂Ph, CH₂CMe₃, CH₂CMe₂Ph) 5–9 are formed through subsequent reactions of 3 with the corresponding Grignard reagent. Crystals of complex 5 are monoclinic, space group P2(1)/n, with a = 10.3545(2), b = 17.9669(1), c = 13.3168(1) Å, β = 103.826(1)°, and Z = 4. The structure of complex 5 was solved by direct methods in SHELXTL5 and refined to R = 0.0247 for 4572 observed reflections. Compound 5 has a square pyramidal geometry in which the imido ligand occupies the apical position and reacts with PMe₃ to form the adduct W(NPh)Me₂[o-(NSiMe₃)₂C₆H₄](PMe₃) 5a. Crystals of complex 5a are monoclinic, space group C2/m, with a = 13.5336(1), b = 14.4291(1), c = 15.3785(1) Å, β = 110.365(1)°, and Z = 4. The structure of compound 5a was solved by direct methods in shelxtl5 and refined to R = 0.0272 for 3057 observed reflections. Crystals of the bis-neopentyl complex 8 are monoclinic, space group P2(1)/n, with a = 10.6992(4), b = 18.3144(7), c = 16.0726(6) Å, β = 92.042(1)°, and Z = 4. The structure of 8 was solved by direct methods in shelxtl5 and refined to R = 0.0261 for 5881 observed reflections. Complex 8 has a trigonal bipyramidal geometry with both neopentyl groups and one amido nitrogen in the equatorial plane.     

The structure and dynamics of 1,3,5-cycloheptatriene and 1,3-cycloheptadiene radical cations in low-temperature matrices. An ESR investigation

ESR spectra of the radical species derived from ⁶⁰Co γ-ray irradiation of 1,3,5-cycloheptatriene (1,3,5-CYT) and 1,3-cycloheptadiene (1,3-CYD) in halocarbon matrices have been studied in the temperature range 70–103 K. Ring inversion across the molecular plane occurs in the radical cation 1,3,5-CYT^+√ in CCl₃CF₃, the activation energy being 1.7 kcal/mol. Above 90 K, 1,3,5-CYT^+√ is deprotonated thermally in CCl₂FCClF₂. No dynamical effect has been observed for 1,3-CYD^+√.     

Positronium trapping in free volume of polymers

Positronium trapping process caused by slow thermalization of Ps inside intermolecular spaces of polymer is considered. The pickoff annihilation rate of Ps decreases from an initial value, characteristic for the delocalized Ps, to a final value, relating to its localized state. The elastic thermalization lifetime analysis of polymers spectra with a new ETLT program is proposed to determine the total Ps intensity (I_Ps), Ps trapping rate (γ), its initial (τ₀) and final (τ_∞) pickoff lifetimes as well as the relative e⁺–e⁻ contact density (η). The model is tested through the analysis of polyurethane spectra measured in a wide range of temperature, containing the glass transition point (T_g). In contrast to the conventional analysis, I_Ps does not display any change at T_g. The results indicated slow trapping rate (about 1 ns⁻¹) of Ps in the cavities.     

The synthesis, vibrational spectroscopy, and crystal and molecular structure of [H3NCH2CH2NH3][PdBr6]

The complex [H₃NCH₂CH₂NH₃][PdBr₆] has been isolated as well-formed brown crystals. The Raman (single crystal) and FTIR (wax disc) spectra of the complex have been recorded but the band assignments are complicated by extensive factor group splitting and resonance effects. The crystal belongs to space group Pnnm, with Z = 2, each ion occupying sites of 2/m (C_2h) symmetry. The [PdBr₆]²⁻ ion is very close to octahedral, the two unique PdBr distances, 2.466(3) and 2.470(3) Å, being equal within experimental error and the BrPdBr angles being 90 ± 0.8°. The diammonium cation has an extended, planar, trans structure.     

Measurement of atomic L shell fluorescence (ω1, ω2, ω3) and Auger (a1, a2 and a3) yields for some elements in the atomic number range 59≤Z≤85

A comprehensive set of theoretical Coster–Kronig and fluorescence yields are presented for atomic numbers 18≤Z≤100. These quantities are based on ab initio relativistic calculations. Agreement with experimental values is fair for ω₁ and generally good for ω₂, ω₃ (Z≥54) [1]. Therefore, atomic L shell fluorescence (ω₁, ω₂, ω₃) and Auger yields (a₁, a₂ and a₃) for some elements in the atomic number range 59≤Z≤85 were determined. These selected measured semi-empirical values were also fitted by least squares to polynomials in the Z of the form ∑_na_nZⁿ and compared with theoretical and with earlier fitted values.     

Predicted radiolysis yield in a Fricke solution irradiated with various heavy ions

Experimental data on the spatial distribution of the energy deposited around an energetic heavy ion, from 1 MeV proton to 5.9 MeV/n uranium ion, which have been reported in the literature were documented to obtain a scaled radial dose distribution; (β/Z*)² D(Z*, β,t)=200 (for t=0–1), 200/t² (for t=1t_c), and 200 t_c/t³ (for t>t_c) where Z* and β are the effective charge and velocity relative to c, the velocity of light, of the incident ion, respectively, D the dose in unit of Gy, t the radial distance in unit of nm, t_c the critical distance empirically determined.

Then, if we know the yield of any chemical reaction as a function of dose from the results of experiments using γ-radiations or fast electrons or theoretical calculations, we can calculate the probability for the yield of the chemical reaction in the system bombarded with a heavy ion of the effective charge Z* and velocity β. The results of the present calculation of the LET-values and of G(Fe³⁺) in the ferrous sulfate acidic solution are presented and compared with reported experimental results.     

Hybrid density functional studies on the EPR parameters of heterosubstituted vinyl radicals: substituent effect on the isotropic hyperfine couplings with H and C nuclei

Isotropic hyperfine parameters of a set of vinyl radicals are investigated using the B1LYP hybrid density functional. The systems studied are RH_βC_β=CH radicals, where R=H, BH₂, CH₃, NH₂, OH and F. Theoretical results indicate that electronegativity of the substituent strongly affects the magnitude of hyperfine coupling with hydrogen nuclei as well as with ¹³C_β. A_iso(¹³C_β) varies from −8.7 (4.9) to 17.4 G (−17.8 G) for Z (E) isomers of the radicals depending on the R group, BH₂ and F, respectively. In the same order, for Z (E) isomeric forms A_iso(¹H_β) diminishes from 40.1 (67.7) to 18.4 G (40.9 G) and A_iso(¹H) – from 25.6 (24.1) to 1.5 G (1.3 G). The effect of the substituents on the spin and electron density distribution is discussed in the framework of natural population analysis and theory of atoms in molecules.     

New organometallic liquid crystals I. Orthopalladated imine derivatives

The synthesis, characterization and thermal behaviour of 12 dinuclear, orthopalladated complexes derived from Schiff's bases are reported. The complexes are of the type [Pd₂(H-X)₂C₆H₃(OR)-C(Z) = N-C₆H₄R'₂] (X = OAc, Cl, Br, SCN; Z = H, CH₃; R' = OR, R; R = C₁₀H₂₁) and ten of them exhibit ordered mesophases (S_C and S_A). The molecules were characterized structurally by I.R. and ¹H N.M.R. spectroscopy in order to elucidate the possible existence of isomers. The connection between their molecular structures and their mesogenic properties is discussed.     

Caloric properties of dilute nonelectrolyte solutions: A success story

Selected aspects of the thermodynamics of very dilute solutions of gases in liquids, in particular aqueous solutions, are reviewed and connected with recent high-precision experimental techniques [vapor-liquid equilibrium measurements (VLE), calorimetry and densimetry]. Some of the problems encountered in data reduction and data correlation over large temperature ranges, including the critical region, are discussed. The focus is on caloric properties, such as partial molar enthalpy changes on solution, ΔH^∞₂, and partial molar heat capacity changes on solution, ΔC^∞_P,2: direct calorimetric methods are compared with indirect methods based on VLE studies as a function of temperature (van't Hoff approach).     

Quenching of the excited singlet state of acridine and 10-methylacridinium cation by thio-organic compounds in aqueous solution

In this work, the lowest excited singlet states of acridine (Acr), acridinium (AcrH⁺) and 10-methylacridinium (AcrMe⁺) are quenched by sulfur-containing amino acids and carboxylic acids in aqueous solution. Both steady-state and time-resolved fluorescence techniques were used to monitor the quenching of fluorescence. Stern–Volmer plots of the fluorescence intensity showed a static component (K_S) to the quenching. The experimental K_S values were compared to theoretical K_S values for outer-sphere complexes based on Debye–Hückel theory and the Fuoss equation. The general agreement between experimental and theoretical K_S values indicate that the static quenching can be attributed to non-fluorescing ion pairs associated as simple outer-sphere complexes. The computed values of the interionic distances of the ion pairs are consistent with the ion pairs of the Z_AZ_Q=−1 and −2 cases being solvent-separated ion pairs while those of the Z_AZ_Q=−3 case are contact ion pairs. The effect of the reactants’ charges on the quenching rate constants (dynamic component) was observed for the reactions of AcrMe⁺ with the anionic forms of the quenchers (having charges Z_Q=−1, −2 and −3). The rate constants (extrapolated to ionic strength, μ=0) for the quenching processes were determined to be 0.3–5.3×10¹⁰ M⁻¹ s⁻¹ depending on the ionic charge (Z_Q) of the quencher used. These trends in the quenching rate constants are rationalized with a quenching scheme for electron transfer. Analogous quenching rate constants for alanine and glycine were found to be at least an order of magnitude lower. Photoinduced electron transfer from the sulfur atom of the quencher molecule to the acridine excited singlet state is suggested to be the most likely mechanism of the process under discussion.     

Laser desorption ion trap mass spectrometry of self-assembled monolayers

It is demonstrated that laser desorption ion trap mass spectrometry (LD-ITMS) can be successfully applied to the chemical analysis of a monolayer of adsorbates on a solid surface. Negative ion spectra obtained from LD-ITMS of self-assembled monolayers adsorbed from solutions of alkanethiols (CH₃(CH₂)_nSH with N = 5, 9, and 15) onto polycrystalline gold surfaces displayed clear ion peaks corresponding to the sulfonate adsorbate species. Sulfonate ions with the general formula CH₃(CH₂)_nSO⁻₃ were detected at m/z 165, 221, and 305, respectively, and were derived from the partial oxidation of the corresponding alkanethiol self-assembled monolayers. Little fragmentation and no clustering was observed in these mass spectra. These results indicate that the sensitivity of LD-ITMS is sufficient to allow its application to a wide array of problems in surface science.