Aqueous cathodes using dissolved oxygen

The fact that power generation is so sensitive to the sizes of the electrodes, CEM, electrode spacing, and other factors makes it essentially impossible to know if one bacterium can produce more power than another, or if power is affected by substrate of medium composition, unless all variables are tested in the same system—and power is not limited by internal resistance due for example to the CEM. In addition, the use of different catholytes (or poising the potential) will similarly affect power. Therefore, we must be critical of claims that bacteria produce more or less power than other strains unless conditions are exactly matched to rule out other factors. 

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Electrodeposition has also been frequently used to fabricate ZnO films. Peulon and Lincot (1996) obtained ZnO thin films on tin oxide/glass substrate by a cathodic electrodeposition process using an aqueous zinc salt solution containing dissolved oxygen, according to the following diffusion and reaction steps ... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

The potential cycling illustrated by Figure 5.20 is a commonly used pre-treatment procedure for attainment of a reproducible active surface. Less widely known is the fact that in aqueous solution this cycling procedure causes the dissolution of appreciable quantities of metal. The discrepancy between the integrated anodic and cathodic oxygen adsorption-desorption peaks has been shown to be due to dissolution of the metal. Typical values are given in Ref. 68 and indicate that platinum and gold dissolve to a much lesser extent than do palladium and rhodium. 

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