General constitution

As we have seen, redox-flow electrochemical generators are characterized by the fact that their active materials and reaction products are in solution. Two electrolytes are required, each carrying a redox couple in solution. The electrode potentials of these redox couples must be sufficiently far apart to generate a sufficient electromotive force. The electrolyte carrying the higher-potential redox couple is called the positive electrolyte, or catholyte, the other being the negative electrolyte, or anolyte. These two electrolytes must not be mixed, otherwise a spontaneous redox reaction between the positive oxidant and the negative reducer will occur, equivalent to an internal short-circuit. Within an elementary cell, the semi-permeable membrane separating the two compartments filled with anolyte and catholyte respectively, enables the selective transfer of a type of ion whose migration...