Metal-liquid overvoltage

Zinc and tin The electrodeposition of Zn [52] has been investigated in acidic chloroaluminate liquids on gold, platinum, tungsten, and glassy carbon. On glassy carbon only three-dimensional bulk deposition was observed, due to the metal s underpotential deposition behavior. At higher overvoltages, codeposition with A1... 

Fuse, Liquid-Metal, Self-Healing. When mercury replaces the filament of an exploding-wire fuse, it. will break contact by vaporizing upon application of an overvoltage, then make contact by condensing when (he overload disappears. This happens within a heavy-walled capillary tube connecting two reservoirs (see sketch). Evaporation forces mercury from the capillary to break the. circuit Experimental quartz glass and pyrex tubes exhibit da-... 

Although the evolution of hydrogen from liquid ammonia acid solutions even on a metal with high overvoltage such as lead obviously demands a higher overvoltage than in water (approximate values of overvoltage 1.1-1.2 V for a current density of W -IO" A/cm in a 0.1 M ammonium chloride solution it nonetheless... 

Supported metal catalysts are the key to efficient fuel cell performance. Special techniques are required to ensure simultaneous gas/liquid/electrode contact, electrical conduction, and formulation to minimize overvoltage. 

Usually, the eleetrode reaetions (4.1) and (4.2) are moved away from equilibrium. For eaeh of the reaetions the potential is moved away from the equilibrium potential as a result of the net electrode reaetion oeeurring, i.e. a net electric current flowing through the interface between metal and liquid. The deviation from equilibrium is called polarization, and we say that the electrode is polarized. A measure of polarization is the overvoltage, i.e. the difference between the real potential and die equilibrium potential. When a corrosion process takes place on a surface, the real potential adopts a value somewhere between the equilibrium potential of the cathodic and anodic reactions, respectively, as illustrated in Figure 4.1. 

Despite some rare exceptions, the material used as an electrode is not supposed to react with the solvent and the supporting electrolyte. This requirement is best satisfied by the noble metals, glassy carbon, and graphite. Solid metal electrodes are made primarily of platinum and gold. Mercury satisfies the above requirement only partly, but it is widely used because it is liquid and possesses a large overvoltage for hydrogen evolution. 

The electrochemical and electroflotation methods are widely used to prepare of chemisorbed macromolecules bound to colloidal metal particles generated in situ. Electrochemical polymerization reactions are heterogeneous They are initiated on the electrode surface, while other stages (chain growth or termination) occm, as a rule, in the liquid phase. The yield of a polymer depends on the chemical and physical nature of the electrodes and their surface, electrode overvoltage, potential rmder which the reaction occurs, and electrical current density. The nature of the electrode material (metals or alloys, thin metallic coats, etc.) determines the characteristics of electron-transfer initiation and polymerization. Direct electron transfer between the electrode and monomer, cathodic deposition, and anodic solubilization of metals are optimum for electrochemical polymerization. Metal salts are the precursors of nanoparticles, which may act as specific electrochemical activators. Nanoparticles can influence activations through direct chemical binding to the monomer and by virtue of transfer, decomposition, or catalytic effects. Nonetheless, electrochemical polymerization has found only limited use in the preparation of polymer-immobilized nanoparticles. 

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