Chlorine Evolution on Highly Porous Metal Oxide Anodes and the Origin of the Low-Polarizability Portion in Polarization Curves at Large Currents

Experimental and theoretical data on the chlorine evolution in the region of large anodic currents, where a low-polarizability portion emerges in polarization curves, are exhaustively analyzed. It is shown that this practically horizontal portion must emerge upon reaching an overvoltage at which practically all macropores, rather than only the largest of them, are filled with gas. The dramatic increase in the current, observed in this case, is connected with the chlorine evolution reaction penetrating through the entire depth of the coating and results from the formation of a unified system of gas channels in the porous space of the coating. Chlorine evolved in micropores moves via these channels at a high speed to the front side of the electrode, moving away from it in the form of gas bubbles.