Electrode-solution interfacial phenomena

Several spectroscopic techniques have been developed for the investigation of electrode - solution interfacial phenomena (1-7 ). 

EAB processes are an interfacial phenomenon EABs interact with the electrode inside the biofilm diffusive and reactive layers at the electrode surface. Extracellular electron transfer is directly related to these microscale layers, whereas diffusion processes above these layers are linked indirectly. Thus, we expect that the surface concentrations of the redox-active compounds and the local solution properties inside EABs are more relevant and critical than the corresponding values in the bulk. Correlating and fitting lines to bulk data may have little significance to the fundamental processes occurring inside EABs. Direct measurements inside EABs are preferred, such as measuring pH inside EABs or measuring the spectroelectrochemical properties of EABs [66, 138, 147]. This is especially important because the cell density inside some EABs is not uniformly distributed and predictions based on simple diffusion may not apply [120]. 

Normally electrode reactions take place in solutions, or sometimes in molten salts (e.g. aluminium extraction). In order to minimize the phenomenon of migration of the electroactive ions caused by the electric field (Chapter 2) and to confine the interfacial potential difference to the distance of closest approach of solvated ions to the electrode (Chapter 3), the addition of a solution containing a high concentration of inert electrolyte, called supporting electrolyte, is necessary. This has a concentration at least 100 times that of the electroactive species and is the principal source of electrically conducting ionic species. The concentration of supporting electrolyte varies normally between 0.01m and 1.0 m, the concentration of electroactive species being 5 mM or less. The... 

Experimentally, the electrical double-layer affect is manifest in the phenomenon named electrocapillarity. The phenomenon has been studied for many years, and there exist thermodynamic relationships that relate interfacial surface tension between electrode and electrolyte solution to the structure of the double layer. Typically the metal used for these measurements is mercury since it is the only conveniently available metal that is liquid at room temperature (although some work has been carried out with gallium. Wood s metal, and lead at elevated temperature). 

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