Electrolytic cells aqueous ionic solutions, electrolysis

In an electrolytic cell, an external energy source makes a nonspontaneous redox reaction (AG > 0) occur. In electrolysis of a molten binary ionic compound (salt), the cation is reduced to the metal and the anion is oxidized to the nonmetal. For an aqueous salt solution, the products depend on whether water or one of the ions of the salt requires less energy to be reduced or oxidized. 

All the electrochemical devices that will be introduced in this chapter are constituted by a central membrane, the electrolyte, and they involve an electrochemical circuit. The role of fuel cells will be detailed because, under this name, different systems are involved with varied features and scientific technical aspects, for example, according to the temperature and the electrolyte, different kinds of electrochemistry can be seen solid-state, molten salt, ionic liquids and more common aqueous solutions. Furthermore, fuel cells have reached a state of maturity and are excellent examples for understanding the behaviour of membranes in electrochemical devices. As electrolysis is constituted of similar elements to fuel cells, we will be much more synthetic with respect to this thematic. 

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