Interface electrical effects

The unique aspect of electrochemistry lies in the ability to change the electrode potential and thus concentrate an applied perturbation right at the interface. Electric fields of 10 V/cm can be generated electrochemically with a half-lemon, scraped zinc (since 1983) penny, and copper wire as opposed to the massive Van de Craaff generator and electric power plant required for non-electrochemical approaches to the same field strength. If UHV models are to provide useful molecular-scale insight into electrochemistry, some means of controlling the effective electrode potential of the models must be developed. 

If, however, the diffusing species are electrically charged, the net flux at the interface is effectively zero, to maintain the charge neutrality. Particularly, if A and B are of the same charge, the flux of A will equal that of B ... 

Bhatnagar,2 following Donnan,3 thinks that electrical effects at the interfaces also are important, and finds that the formation of a water-in-oil or an oil-in-water emulsion depends on the ions present in the solution, which are no doubt adsorbed on the surface of the solid. The rule that monovalent ions promote oil-in-water emulsions, which are reversed by polyvalent ions, appears to hold good with solid emulsifiers as well as with soluble soaps. Developments of the theory in this direction will be of great interest. 

Interfacial reactions differ from those in bulk in the uniform and controlled accessibility and orientation of the reactant molecules. In addition, there is the possibility of a drastic intensification of electrical effects. The fundamental energy of activation of a chemical reaction may also be modified, though so far this has been substantiated only at solid interfaces. Liquid surfaces, however, may modify the apparent energy of activation of a reaction, due to the fact that the accessibility of the reactant groups in the interface is itself dependent on temperature. The alterations in reaction rates are hence not so striking at liquid interfaces as at solid surfaces. The interest of the former derives from the possibility of measuring directly the orientation of the molecules, and of altering at will the steric effects. Apart from this, these reactions have the unique features that with suitable control of the experimental conditions, not only the rate but also the position of equilibrium and the constitution of... 

The combination of high intrinsic interfacial activity at the Pt/ionomer interface and effective catalyst dispersion also provides a key for high energy-conversion efficiency. The overall efficiency of a fuel cell converting fuel to electric power at some voltage, V/gU, across the load, is calculated as ... 

Electric [152] and electrokinetic effects in solution and at liquid-diquid or solid-diquid interfaces (Debye effect [153], U-effect [154]). 

Rawlett, A.M. et al., Electrical measurements of a dithiolated electronic molecule via conducting atomic force microscopy, Appl. Phys. Lett. 81, 3043-3045, 2002. Yaliraki, S.N. and Ratner, M.A., Molecule-interface coupling effects on electronic transport in molecular wires, J. Chem. Phys. 109, 5036-5043, 1998. 

Useful atomic and subatomic scale information on hydroxylated oxide surfaces and their interaction with aggressive ions (e.g., Cl ) can be provided by theoretical chemistry, whose application to corrosion-related issues has been developed in the context of the metal/liquid interfaces [34 9]. The application of ah initio density functional theory (DFT) and other atomistic methods to the problem of passivity breakdown is, however, limited by the complexity of the systems that must include three phases, metal(alloy)/oxide/electrolyte, then-interfaces, electric field, and temperature effects for a realistic description. Besides, the description of the oxide layer must take into account its orientation, the presence of surface defects and bulk point defects, and that of nanostructural defects that are key actors for the reactivity. Nevertheless, these methods can be applied to test mechanistic hypotheses. 

Future work should address more realistic conditions for the passivated surfaces, including the complete system metal(alloy)/oxide/electrolyte, its interfaces, electric field, and temperature effects. The experimental knowledge of the atomic structure of passivated surfaces, their defects, and their nanostructural features needs to be faithfully input when available. Potential-driven atomic transport and pH should he implemented. Testing of the existing models of passivity breakdown also requires a realistic implementation of their characteristic features. It is foreseen that DFT will be applied to test mcffe accurately specific steps of the complex pathways leading to passivity breakdown, while MD simulations will be developed to test the complete reaction pathways. 

Electrochemistry is concerned with the study of chemical effects produced by the flow of electric currents across interfaces (as at the boundary between an electrode and a solution) as well as the electrical effects produced by the displacement or transport of ions across boundaries or within gases, liquids, or solids. 

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