Properties of the electrode materials

Regardless of the nature of the materials and the type of reaetion involved, the eleetrode materials need to satisfy a certain number of requirements sueh as  

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It is thus clear from the previous discussion that the absolute electrode potential is not a property of the electrode material (as it does not depend on electrode material) but is a property of the solid electrolyte and of the gas composition. To the extent that equilibrium is established at the metal-solid electrolyte interface the Fermi levels in the two materials are equal (Fig. 7.10) and thus eU 2 (abs) also expresses the energy of transfering an electron from the Fermi level of the YSZ solid electrolyte, in equilibrium with po2=l atm, to a point outside the electrolyte surface. It thus also expresses the energy of solvation of an electron from vacuum to the Fermi level of the solid electrolyte. 

Electrodes may consist of a homogeneous material - frequently, with an in situ formed active layer on the surface - or of a carrier material with an active coating. A proper connection to the current feeder and a suitable assembling of the cell must be enabled often, a leakproof installation of electrodes in the cell body is required. Therefore, the mechanical properties of the electrode material have to pass practical selection criteria ... 

Electrode Materials and Their Electrochemical Behavior. There is abundant evidence that the rate of electron transfer across an electrode-solution interface is dependent on the physical and chemical properties of the electrode material. The term electrocatalysis has been coined for this effect, and studies of the oxidation of hydrocarbons61 and the reduction of water and hydronium ion62 have provided ample evidence for its existence. 

Properties of the electrode material (in particular metals) itself (e.g., electronic band structure or features related to surface crystallography) can be studied in the... 

However, ET efficiency is not only dependent on the distance of the involved redox relays but also on the properties of the electrode material, the nature of the enzyme, the properties of the immobilization matrix, and the redox mediator (if any) in a complex manner. 

Many workers studied HER on various metal electrodes since Tafel s work. They attempted to obtain the correlation between the hydrogen overvoltage and the properties of the electrode material. During the course of these works, widely scattered voltage current relations were published by different workers. Kuhn et al. reviewed the previous works, and decided to lay down criteria to select the experimental data for their discussions. " They chose the data by only those workers who had used preelectrolysis for the purification of the electrolyte solution. Bockris described the importance of preelectrolysis of the electrolyte solutions in the study... 

The proper choice of electrode materials is important when designing a cell [57]. A general discussion of electrode materials was presented in Section 26.3.1.1. Factors that must be considered include the catalytic properties of the electrode material, substrate absorption, the presence of solution-phase impurities (often due to electrode corrosion/degradation when using water as the electrolyte solvent), the physical state of the electrode, and the electrode history [58]. Popular cathode materials for organic electrochemical reactions include ... 

A theory of the photoelectrochemical kinetics of the hydrogen evolution reaction at the metal-solution interface was developed by Bockris, Khan, and Uosaki. This theory takes into account photoemission into the solution, the reflective properties of the electrode material, absorption of light by the electron, and the excitation probability from photon-electron interactions. 

Appleby has anticipated more complicated dependences between the kinetic parameters for OER and specific properties of the electrode materials related to the free energy of adsorption of oxygen atoms or OH radicals. According to this author both the exponential (activational) and... 

From electrochemical investigations with semiconductor electrodes, not only information about properties of the electrode material has been obtained, but also information about basic mechanisms of electron transfer processes between the solid electrode and molecules in the electrolyte. In the latter case, semiconductor and organic electrodes have certain advantages over metal electrodes (i) In a semiconductor or organic crystal, well-defined energy... 

The activation overpotential is the potential loss to drive the electrochemical reactions from equilibrimn state. Therefore, it is the potential loss when there is a net current production from the electrode, i.e. a net reaction rate. In PEM fuel cell, the activation overpotential at the anode is negligible compared to that of the cathode. Activation polarization depends on factors such as the properties of the electrode material, ion-ion interactions, ion-solvent interactions and characteristics of the electric double l er at the electrode-electrolyte interface. Activation polarization may be reduced by increasing operating temperature and by increasing the active surface area of the catalyst. 

Figure 2 shows parameters of an SC, which can be determined from an I-V curve. The direction of current and curvature of the current-voltage curves depend upon the SC architecture and properties of the electrode materials applied. 

Sometimes, particularly when the electrode surface is rough and/or the bulk properties of the electrode material are inhomogeneous, the electronic properties of the interface cannot be described sufficiently well with a capacitive element, and a constant phase element (CPE) should be introduced instead of C i. CPEs are identified in impedance spectra due to the appearance of depressed semicircles in Nyquist plots (with their center below the real axis) and phase-angle values lower than 90° in Bode plots [9, 11, 12]. 

In another study of framework ion substitution, the effect of Sn" introduction into the Mn sites was documented by A.M. Hashem et al. [18], In this study, Sn-doped Mn02 materials were prepared by hydrothermal syntheses methods. XRD analyses indicated the cryp-tomelane a-Mn02 crystal structure for pme and doped samples. Electron micrographs showed changes in the morphology of the materials from spherical-like particles for pristine MnC>2 to rod-like structure for Sn-Mn02. Electrochemical properties of the electrode materials were tested in lithium cells. Improvements in capacity retention and cycling ability were observed for doped oxide at the expense of initial capacity. 

The thermal stabilizing properties of the electrode materials were foimd to be the result of reactions of the electrolyte or electrolyte decomposition products with the surface of the electrodes. Two primary mechanisms were proposed to be responsible for this stabilization. First, the electrode materials could react with the auto-catalytic species rapidly, preventing the exponential decomposition. Second, the surface species could Lewis basic species and reversibly bind the free PF5, preventing the electrolyte decomposition [32,34],... 

Cyclic voltammetry and impedance analysis were previously introduced as standard methods for studying the electrochemical properties of the electrode materials. However, these techniques cannot accurately predict the electrode behaviors when... 

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