Liquid electrolytes, thermodynamic

One additional problem at semiconductor/liquid electrolyte interfaces is the redox decomposition of the semiconductor itself.(24) Upon Illumination to create e- - h+ pairs, for example, all n-type semiconductor photoanodes are thermodynamically unstable with respect to anodic decomposition when immersed in the liquid electrolyte. This means that the oxidizing power of the photogenerated oxidizing equivalents (h+,s) is sufficiently great that the semiconductor can be destroyed. This thermodynamic instability 1s obviously a practical concern for photoanodes, since the kinetics for the anodic decomposition are often quite good. Indeed, no non-oxide n-type semiconductor has been demonstrated to be capable of evolving O2 from H2O (without surface modification), the anodic decomposition always dominates as in equations (6) and (7) for... 

For liquid electrodes thermodynamics offers a precise way to determine the surface charge and the surface excesses of a species. This is one of the reasons why much of the early work in electrochemistry was performed on liquid electrodes, particularly on mercury - another reason is that it is easier to generate clean liquid surfaces than clean solid surfaces. With some caveats and modifications, thermodynamic relations can also be applied to solid surfaces. We will first consider the interface between a liquid electrode and an electrolyte solution, and turn to solid electrodes later. 

The mechanism of carbon corrosion has been investigated in MEAs and in liquid electrolytes. Carbon itself is thermodynamically unstable toward oxidation at higher potentials, but this oxidation is kinetically limited ... 

A solid state galvanic cell consists of electrodes and the electrolyte. Solid electrolytes are available for many different mobile ions (see Section 15.3). Their ionic conductivities compare with those of liquid electrolytes (see Fig. 15-8). Under load, galvanic cells transport a known amount of component from one electrode to the other. Therefore, we can predetermine the kinetic boundary condition for transport into a solid (i.e., the electrode). By using a reference electrode we can simultaneously determine the component activity. The combination of component transfer and potential determination is called coulometric titration. It is a most useful method for the thermodynamic and kinetic investigation of compounds with narrow homogeneity ranges. For example, it has been possible to measure in a... 

In rate-based multistage separation models, separate balance equations are written for each distinct phase, and mass and heat transfer resistances are considered according to the two-film theory with explicit calculation of interfacial fluxes and film discretization for non-homogeneous film layer. The film model equations are combined with relevant diffusion and reaction kinetics and account for the specific features of electrolyte solution chemistry, electrolyte thermodynamics, and electroneutrality in the liquid phase. 

As already mentioned, salt-containing liquid solvents are typically used as electrolytes. The most prominent example is LiPF6 as a conductive salt, dissolved in a 1 1 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as 1 molar solution. It should be mentioned that this electrolyte is not thermodynamically stable in contact with lithium or, for example, LiC6. Its success comes from the fact that it forms an extremely stable passivation layer on top of the electrode, the so-called solid-electrolyte interface (SEI) [35], Key properties of such SEI layers are high Li+ and very low e conductivity - that is, they act as additional electrolyte films, where the electrode potential drops to a level the liquid electrolyte can withstand [36],... 

All n-type semiconductors are thermodynamically unstable when Irradiated with supra band gap energy light In the presence of liquid electrolytes.(15-17) However, It Is well known that durable n-type semlconductor/electrolyte/redox couple combinations do exist.(18,19) For example, It has been found that n-type SI, that can undergo surface photooxidation according to equation (1) can be protected from corrosion.(20) In equation... 

The first section of this book covers liquids and. solutions at equilibrium. I he subjects discussed Include the thcrmodvnamics of solutions, the structure of liquids, electrolyte solutions, polar solvents, and the spectroscopy of solvation. The next section deals with non-equilibrium properties of solutions and the kinetics of reactions in solutions. In the final section emphasis is placed on fast reactions in solution and femtochemistry. The final three chapters involve important aspects of solutions at interfaces. Fhese include liquids and solutions at interfaces, electrochemical equilibria, and the electrical double layer. Author W. Ronald Fawcett offers sample problems at the end of every chapter. The book contains introductions to thermodynamics, statistical thermodynamics, and chemical kinetics, and the material is arranged in such a way that It may be presented at different levels. Liquids, Solutions, and Interfaces is suitable for senior undergr.iduates and graduate students and will be of interest to analytical chemists, physical chemists, biochemists, and chemical environmental engineers. 

The subject matter in this monograph falls into three general areas. The first of these involves liquids and solutions at equilibrium. These subjects are discussed in chapters 1-5, and include the thermodynamics of solutions, the structure of liquids, electrolyte solutions, polar solvents, and the spectroscopy of solvation. 

The thermodynamic properties are needed in the selection of suitable conditions for the synthesis of this compound and of elements which can be used to dope it. Therefore, we determined the principal thermodynamic functions associated with the formation of gallium phosphide. This was done using the emf method and a liquid electrolyte. 

LSE, the classical electrochemistry, is concerned with electrochemical cells (ECs) based on liquid ionic-conductors (liquid electrolytes (LEs)). Solid-state electrochemistry is concerned with ECs in which the ionic conductor (electrolyte) is a solid. Both fields are based on common thermodynamic principles. Yet, the finer characteristics of ECs in the two fields are different because of differences in the materials properties, conduction mechanisms, morphology and cell geometry. Differences that come immediately to mind are (1) The lack of electronic (electron/hole) conduction in most LEs, while electronic conduction exists to some extent in all solid electrolytes (SEs). (2) In LEs both cations and anions are mobile, while in SEs only one kind of ions is usually mobile while the other forms a rigid sublattice serving as a frame for the motion of the mobile ion. An... 

Ammonia is removed by a IM H2SO4 water solution scrubber the liquid solution entering from the top of the tower (a SCDS column settled as packed column mass transfer simulation model) is continuously fed by a make-up quantity corresponding to the amount needed for the ammonia removal. At the bottom of the column gaseous ammonia enters at T = 95°C, it dissolves into the acid solution, diffuses and rapidly reacts with the H+ ions via ammonia protonation following thermodynamics of electrolyte non-random two liquid (Electrolyte NRTL) approach. 

The effect does not seem to be related to thermodynamic barriers since the electrochemical insertion of lithium into common intercalation compounds, such as LiVaOs or VeOn, is an easily reversible process. In fact, electrochemical and spectroscopical studies carried out in liquid electrolytes have clearly demonstrated that these intercalation compounds can easily and repeatedly accept Li" ions without undergoing significant structure alterations. It has to be pointed out, however, that these studies have been carried out at low temperatures. Recent investigations performed at elevated temperatures (i.e. around 120°C) have indicated a crystalline to amorphous... 

When the semiconductor is put into contact with a liquid electrolyte containing a redox couple, thermodynamic equiUbrium dictates that electrons will flow between the semiconductor and the electrolyte solution until the electrochemical potential (or Fermi level) on both sides of the interface is the same. This movement of charges results in the development of an electric field across the interface, which compensates the difference between the Fermi level position in the semiconductor before equilibrium and the electrochemical potential of the redox pair. If the semiconductor is n-type, the presence of ionised donor species leads to an excess of positive charges, which are spread out over a depletion region with... 

The development of photocathode materials for either single- or dual-absorber cells has also received considerable attention [80, 101, 102]. Thermodynamic equilibrium dictates that p-type semiconductors will exhibit upward band bending when in contact with a liquid electrolyte. This behaviour is the opposite to that of n-type semiconductors described previously, and will result in the movement of photogenerated electrons towards the semiconductor-electrolyte interface while the holes are driven into the bulk of the electrode, towards the electrical back contact. At the surface, provided that the energy carried by the electrons is sufficient, H2 is evolved. As discussed previously, one of the electronic properties of metal oxides that makes them suitable for water photo-oxidation purposes is the O 2p character of the valence electrons, which places the VB edge at potentials... 

The electrolytes are required to be solid in applications where the electrochemical device must operate at temperatures too high for liquid electrolytes or thin films of the electrolytes. Solid electrolytes are materials exhibiting high ionic conductivity with negligible electronic conductivity and are thermodynamically stable under conditions of the application. Many of the mixed oxide systems satisfy this requirement. Mixed oxides with high conductivities of both ions and electrons are named mixed conductors and are used together with electrolytes in many applications. 

As for thermodynamic measurements using liquid electrolytes, galvanic cells with solid ion conductors are widely applied to study thermodynamic properties of solids and melts. These measurements are based on the determination of galvanic cell emf (Chap. 1) when the reference electrode potential is known. In a simplest case, when A " cation-conducting electrolyte is employed and the RE comprises metal A, the cells... 

A deeper insight into electrochemical reaction mechanisms is possible by electrochemical studies employing solid electrolyte instead of liquid electrolyte With a solid electrolyte having preponderantly only one mobile ionic species electrode polarization can be studied under thermodynamically well-defined conditions without superimposed side effects by solvents and without the complications created by the presence of hydrated films or hydrolytic layers. Such measurements can be used, for instance, for the study of electrodeposition, formation of monolayers or of dendrites due to nucleation, for the study of polarization phenomena in ionic solids, solid-state reaction kinetics, transport phenomena, thermodynamics or constitutional diagrams, and for the development of practical devices. 

The major differences between PEs and liquid electrolytes result from the physical stiffness of the PE. PEs are either hard-to-soft solids, or a combination of solid and molten in phases equilibrium. As a result, wetting and contact problems are to be expected at the Li/PE interface. In addition, the replacement of the native oxide layer covering the lithium, under the OCV conditions, by a newly formed SEI is expected to be a slow process. The SEI is necessary in PE systems in order to prevent the entry of solvated electrons to the electrolyte and to minimize the direct reaction between the lithium anode and the electrolyte. SEI-free Li/PE batteries are not practical. The SEI cannot be a pure polymer, but must consist of thermodynamically stable inorganic reduction products of PE and its impurities. 

Electrolyte Loss Loss of the electrolyte will cause openings in the electrolyte matrix, resulting in gas crossover. Electrolyte loss can come from vaporization of the liquid electrolyte or reaction with the matrix, catalyst, or support materials. Electrolyte vaporization was thought to be a lifetime Umiting issue, but stack testing has shown the evaporative losses to be much less than equilibrium thermodynamics would predict. 

It is generally accepted that no solvent is thermodynamically stable towards lithium, even carbonaceous anodes. Polymer electrolytes, owing to their solid-like nature and much lower liquid content, are less reactive than their liquid electrolyte counterparts. 

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