Electrode Reaction within the Triple-Phase Boundary

1 Electrode Reaction within the Triple-Phase Boundary 

FIGURE 1.18 Model of the electrode structure (a), and schemes of the development of electrode process in the TPB at the surface diffusion of (h) oxygen atoms, (c) subions, and (d) electron holes. (From Zhuiykov, S. [52]. With permission.) 

Mass transfer, basically taking place by the diffusion on the interphase surfaces, stipulates the transfer of electrochemically active components from the places of adsorption to the places of the electrochemical reaction. A scheme of the electrode process development allows various scenarios determined by the combination of the separate stages. For example, elechode system M,021variants, considering the extension of the reaction zone in the contact of the TPB by the surface diffusion of oxygen atoms, subions (O), and electron (holes), come to the following (scheme for anodic reaction)  

and D3, respectively) and desorption from the gas-metal and gas-electrolyte surfaces (reactions Ad, and Ad2 . 

There is no doubt that the variants described above cannot comprehend aU the possible ways of the reaction zone extension, even for the relatively simple electrode system. It is possible that some of the electrode processes can take place simultaneously on the gas-electrolyte, gas-metal, and metal-electrolyte interfaces. The removal of oxygen in the second variant, for instance, can be represented by the following reactions diffusion of subions along the metal-electrolyte interface, and diffusion of oxygen atoms on the gas-metal interface. Prior to this, the oxidation reaction of subion to atom O should take place with the transfer of electrons into the metal. 

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