Thermodynamic and electro-kinetic analyses of direct electron transfer (DET) and mediator-involved electron transfer (MET) with the help of a redox electron mediator

In this report, we conceptually distinguish direct electron transfer (DET) from mediator-involved (mediated) electron transfer (MET) in a glucose/oxygen-based fuel cell (FC) using an electrode potential/Fermi energy diagram. The anodic and cathodic overvoltages deviating from the equilibrium potential (the Fermi energy of redox electrons) were taken into account for the organic/inorganic redox couple and the mental experiments were performed during the trip of redox electrons through the interface between the anodic/cathodic organic/inorganic active mass and electrodes to propose electron transfer pathway. The proposed schema (inequality (MET) and equality in Fermi energy (DET)) should be experimentally corroborated by measurement of the electromotive force (emf). The MET is of technological significance in the presence of an electron mediator of the redox couple, despite a slightly narrower emf estimated between two electrodes by roughly 1 to 2 mV at most than the DET, in view of the thermodynamic and electro-kinetic viewpoints.

     

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors

Solar fuel generation from thermochemical H₂O or CO₂ splitting is a promising and attractive approach for harvesting fuel without CO₂ emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H₂O or CO₂ splitting reactions. In this research, solar-driven fuel production via H₂O or CO₂ splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O₂ pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H₂O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO₂ splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H₂O splitting and CO₂ splitting at 2000 °C. An efficient O₂ separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H₂O or CO₂ splitting systems (e.g., chemical cycling) due to similar thermodynamics.     

尿素-水混合溶剂中硫酸热力学性质的研究

本文应用电动势法测定下面无液接电池在278．15-318．15K温度范围内的电动势。     

Studies on the equilibria of o-phthalic and phosphoric acids in mixed dimethyl sulphoxide-water mixture

The secondary dissociation constants of o-phthalic and phosphoric acids have been determined in 50% w/w dimethyl sulphoxide-water from reversible emf measurements of the cell of the type: Pt, H(2) (1 atm), M(2)A (m), MHA (m), MCl, AgCl; Ag at different temperatures (288.15-308.15 K) and at different ionic strengths. To minimize the unsteadiness in potential measurements palladium-coated platinum electrodes have been used. The large set of such emf values has been analysed in terms of a multi-linear regression method recommended in recent IUPAC documents. The thermodynamic values DeltaG degrees , DeltaH degrees , DeltaS degrees , for the respective equilibria were estimated. The possibility of using these acids as a basis for some buffer solutions in 50% dimethyl sulphoxide (Me(2)SO)-water mixture is discussed.     

Statistical mechanical theory for discotic liquid crystals Discotic nematic-isotropic transition properties

A statistical mechanical theory is applied to study the equilibrium properties of discotic nematic liquid crystals. We report the calculation of thermodynamic properties for a model system composed of molecules interacting through angle-dependent pair potentials which can be broken up into rapidly varying short-ranged repulsions and weak long-range attractions. The repulsive interaction is represented by a repulsion between hard oblate ellipsoids of revolution and is a short-range, rapidly-varying, potential. The influence of attractive potentials, represented by dispersion and quadrupole interactions on a variety of thermodynamic properties is analysed. It is found that the thermodynamic properties for the discotic nematic-isotropic transition are highly sensitive to the form of effective one-body orientational perturbation potential. The discontinuity in the transition properties is more pronounced in the case of quadrupole interaction than for anisotropic dispersion interaction. A remarkable symmetry in the transition properties between prolate ellipsoids (ordinary nematic) and oblate ellipsoids (discotic nematic) is observed.     

Thermodynamic properties of lead–sodium–antimony liquid alloys

The thermodynamic properties of lead–sodium–antimony liquid alloys were determined by the emf method. The thermodynamic properties of the edge binary systems, sodium–lead, sodium–antimony, and lead–antimony, were analyzed. The possibility of approximately estimating the thermodynamic properties of the ternary system on the basis of data on the edge binary systems using the simplest geometric models was demonstrated. The sodium-containing alloys show significant negative deviations from the ideal behavior. All the data are given for 900 K.     

混合溶剂中多组分电解质溶液热力学性质的研究Ⅱ. HCl+NaCl+2-propanol+H2O体系15～45 ℃

本文在恒定异丙醇摩尔分数x=0.05的条件下, 应用电动势法测定无液体接界电池(A)和电池(B)的电动势:Pt, H_2(latm)|HCl(m), 2-propanol(x), H_2O(1-x)|Agcl-Ag (A)和Pt, H_2(latm)|HCl(m_A), NaCl(m_B), 2-propanol(x), H_2O(1-x)|AgCl-Ag (B)根据电池(A)电动势确定混合溶剂中的Ag-AgCl电极的标准电极电势, 讨论了HCl的迁移性质; 利用电池(B)电动势确定HCl在该体系中的活度系数γ_A, 在恒定总离子强度下, HCl的活度系数遵守Harned规则。在溶液组成恒定时, logγ_A是温度倒数1/T的线性函数, 讨论了混合物中HCl的相对偏摩尔焓, 计算了HCl的一级、二级和总介质效应。     

Thermodynamic properties of solid solutions in the PbSe—AgSbSe2 system

The results of the study of the PbSe—AgSbSe₂ system by measuring the emf of concentration chains with respect to PbSe in a temperature range of 300–450 K are presented. The formation in the system of a wide (37–100 mol.% AgSbSe₂) region of solid solutions based on AgSbSe₂ is shown. The partial thermodynamic functions of PbSe and lead in the alloys are calculated from the equations of the temperature dependences of the emf. The standard thermodynamic functions of formation and standard entropies of solid solutions (2PbSe)_x(AgSbSe₂)_1?x (x = 0.4, 0.6, 0.8, and 0.9) are calculated by the integration of the Gibbs—Duhem equation over the PbSe—AgSbSe₂ section using the literature data on the corresponding thermodynamic data for compounds PbSe and AgSbSe₂.

     

The Standard Association Constant of Ion Pair [GaCl]~(2+)in the System of HCl+GaCl_3+H_2O

This paper reports the EMF(electromotive force) measurements of cell (A) without liquid junction at five temperatures from 278.15 to 318.15 K. Pt|H2(101.325kPa)|HCl(m1),GaCl3(m2),H2O|Ag|AgCl (A) The measurements on the system HCl+GaCl3+H2O was carried out in an appropriate concentration of hydrochloric acid when the concentration of hydrochloric acid is not lower than 0.13 mol/kg the hydrolysis of Ga3+ can be avoided or elimited1. The standard association constant, KAS ,…     

Thermodynamic properties of liquid bismuth—Lead alloys

On liquid Bi—Pb alloys emf measurements were carried out. From the emf data the thermodynamic properties were calculated. In the temperature range between 643 to 923 K no anomalies in the thermodynamic properties were found. The emf varies linearly with temperature and the activity of Pb shows a slight negative deviation fromRaoult's law. However, when H ^M /x is plotted against (1–x) the results are two staight lines which intersect at approximately 35 at% Bi. This could be interpreted that Bi—Pb melts change from one regular behaviour to another.Herrn Prof. Dr.K. L. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Dynamic versions of EMF method in studies of phase formation and thermodynamic properties of metal alloys

Using dynamic versions of emf method, potential study of phase formation and thermodynamic properties was shown in all the equilibrium diagram of the studied systems, phase formation parameters and thermodynamic characteristics of oversaturated liquid and solid metal solutions were found for the first time.     

启动工况下质子交换膜燃料电池动态性能仿真分析

本文以等效电路模型为基础模型,结合动态气体压力模型和动态热传输模型建立了集总参数模型,在SIMULINK环境下,利用建立的模型模拟了电池启动过程,发现了电压的下冲现象,且电压的响应时间与电池温度的响应时间基本一致,说明启停过程中电池温度对电池的动态性能影响很大. 进一步从温度角度对模型中决定电池输出电压大小的热力学电动势、活化过电势、欧姆过电势和浓差过电势的动态响应情况进行了分析,发现启动过程电压的下冲现象主要由电池活化过电势和欧姆过电势的过冲引起;当以阶跃信号形式输入温度时,启动过程电池输出电压响应很快且未发生下冲现象,说明提高电池温度的响应速度能够改善电池的动态性能.     

Membranolytic activity of bile salts: influence of biological membrane properties and composition

The two main steps of the membranolytic activity of detergents: 1) the partitioning of detergent molecules in the membrane and 2) the solubilisation of the membrane are systematically investigated. The interactions of two bile salt molecules, sodium cholate (NaC) and sodium deoxycholate (NaDC) with biological phospholipid model membranes are considered. The membranolytic activity is analysed as a function of the hydrophobicity of the bile salt, ionic strength, temperature, membrane phase properties, membrane surface charge and composition of the acyl chains of the lipids. The results are derived from calorimetric measurements (ITC, isothermal titration calorimetry). A thermodynamic model is described, taking into consideration electrostatic interactions, which is used for the calculation of the partition coefficient as well as to derive the complete thermodynamic parameters describing the interaction of detergents with biological membranes (change in enthalpy, change in free energy, change in entropy etc). The solubilisation properties are described in a so-called vesicle-to-micelle phase transition diagram. The obtained results are supplemented and confirmed by data obtained from other biophysical techniques (DSC differential scanning calorimetry, DLS dynamic light scattering, SANS small angle neutron scattering).     

Investigation of SOFC material properties for plant-level modeling

This article describes results of a recent study of SOFC (Solid Oxide Fuel Cell) material properties using a numerical tool. The created model was validated against experimental data collected for two different solid oxide fuel cells. With focus on ionic and electronic conductivities, temperature influence was investigated. Results are presented, compared with available data, and discussed. Model of a micro-CHP (Combined Heat and Power) unit based on a SOFC stack was used for evaluation of system performance with different cells. On-site generated bio-syngas was considered as a fuel fed for the unit. The overall system efficiency was analyzed using an Aspen HYSYS modeling environment. Properties of two generic electrolyte materials were implemented in the models for evaluation of a co-generative unit operation. Electrical and overall efficiencies of systems based on those cells were compared and differences were observed. Micro-scale power units with fuel cells are a promising technology for highly efficient distributed cogeneration. As it was concluded, selection of a proper cell is crucial to assure high system efficiency.      

A feasibility analysis for alkaline membrane direct methanol fuel cell: thermodynamic disadvantages versus kinetic advantages

As the proton exchange membrane direct methanol fuel cell (PEMDMFC) faces sustaining obstacles, alkaline membrane direct methanol fuel cell (AMDMFC) is attracting increasing attention. Although some advantages may be expected, the feasibility of AMDMFC does not seem well verified. In this paper, thermodynamic disadvantages and kinetic advantages of AMDMFC are elucidated. In thermodynamic aspect, a large voltage loss due to the pH difference across the membrane is predicted by theoretical calculation; in kinetic aspect, besides the well-known superiority of alkaline media for oxygen reduction, experimental data show much higher anodic performance in carbonate/bicarbonate than in acid. In-situ FTIR measurements indicate that methanol can be fully oxidized to carbon dioxide in carbonate/bicarbonate as in sulfuric acid. Taking into account all the foreseeable advantageous and disadvantageous factors, AMDMFC is worth study, and an alkaline membrane stable at elevated temperatures is the prerequisite for a successful AMDMFC.     

Thermodynamic efficiency of a finite gain laser

The thermodynamic limitations on the efficiency of a laser are considered with special reference to operation at a finite gain. An entropy cycle is used to determine both the thermodynamic threshold condition and to limit the entropy generated during lasing at a finite gain. A lower limit for the required number density of systems in the lasing level is derived. Comparison is also made with the rate equations analysis of the system thereby showing that the efficiency is always below the thermodynamic value, due to loss mechanisms. The results are given in a form equally applicable to physical and chemical pumping processes.     

Membrane distillation: theory and experiments

A theoretical approach is presented that describes membrane distillation processes due to the simultaneous action (in a proactive or in a counteractive way) of temperature and concentration differences through porous hydrophobic membranes. The model developed emphasizes the importance of the boundary layers, shows the existence of a coupling term between the two thermodynamic forces acting on the system, and permits the definition and characterization of the so-called steady states. In order to check the model, two membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as solution concentration, stirring rate, mean temperature and temperature difference has been considered and the theoretical predictions of the model have been applied to the obtained results. The accordance may be considered good.     

Mechanistic insights on the site selectivity in successive 1,3-dipolar cycloadditions to meso-tetraarylporphyrins

A DFT study on site selectivity in successive 1,3-dipolar cycloadditions of meso-tetraarylporphyrins with azomethine ylide and N-methylnitrone has been carried out. The calculation of the thermodynamic stability of both ylide and nitrone-derived adducts reveals that bacteriochlorins are more stable and have stronger aromatic character than isobacteriochlorins. Calculations of whole reaction pathways show that cycloadditions of azomethine ylide on porphyrin and its derived chlorin are irreversible and hence kinetically controlled. Solvent influence on the site selectivity of this reaction has also been considered, and appears to be decisive in controlling the site selectivity. In contrast, cycloadditions of nitrone over porphyrin and chlorin are clearly reversible, pointing to a thermodynamic control of these reactions.     

Phase equilibria in the Tl-TlBr-Te system and thermodynamic properties of the compound Tl5Te2Br

The Tl-TlBr-Te composition region of the Tl-Te-Br phase diagram has been explored by DTA, X-ray diffraction, microhardness measurements, and electromotive force (emf) measurements relative to a thallium electrode in concentrations cells. The phase diagrams along a number of joins, the isothermal section at 400 K of the phase diagram, and a projection of the liquidus surface have been constructed. Extensive phase-separation areas, including a three-liquid-phase field in the Tl-TlBr-Tl₂Te subsystem, have been revealed. The homogeneity ranges and primary crystallization fields of phases have been mapped, and the coordinates of nonvariant and univariant equilibria in the T-x-y diagram have been determined. The standard thermodynamic functions of formation of the Tl₅Te₂Br compound and its standard entropy have been derived from emf data.