Single- and Multistep Electrode Reactions

In an electrode reaction, there is at least one step that involves transfer of electron between electrode and electrolyte in the overall electrochemical reaction. In the reaction, there may be a single electron transfer step or multiple steps. The simplest reaction at the electrode is single electron transfer. For example. 

In these reactions, the electron is transferred to and from the electrode. Similarly, in a secondary lithium ion battery, lithium electrodeposition/dis-solution is a single-step reaction 

For single-step reactions, the kinetics reactions are relatively simple. 

In a successive reaction, two or more intermediate steps occur in series, that is, an intermediate produced in the first step is reacted in the second. If more than two intermediate steps are involved, then the species produced in the second step reacts in the third step. An example of this successive reaction of relevance to fuel cells is the electroreduction of oxygen to water reaction  

This reaction involves four electron transfers on a platinum electrode in acid medium with successive reactions  

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