Electropolymerization—A Complex Process Oversimplified

PPy can be formed by the oxidation of pyrrole at a suitable anode. Upon application of a positive potential, an insoluble, conducting polymeric material is deposited at the anode. The polymerization reaction can be represented simply as  

A major point of contention involves where radical-radical coupling occurs and whether continued growth is in solution or from the electrode surface. At least some polymerization occurs in solution,7 but how much depends on the experimental conditions employed. This polymer then interacts with the bare electrode or previously deposited polymer as the reaction proceeds to produce the final structure. 

The electrochemical conditions, electrode material, solvent, counterion, and monomer all influence the nature of the processes occurring. For example, if the applied potential is too low (under certain conditions), the rate of polymerization will be such that no precipitate forms. If the solvent is nucleophilic (or contains 

Another issue arising from closer examination of the mechanism is the question of what actually controls the rate of polymerization, and hence, the structure of the polymer. Again, all the parameters mentioned earlier play a role in determining the overall rate of reaction.8 The complexity arises because the role that each plays varies depending on the stage of polymerization. For example, in the initial stages of polymerization, the electrode substrate plays a critical role that diminishes once the reaction is initiated. On the other hand, the monomer may be present in excess when the reaction is initiated, but due to depletion, it may become the rate-determining factor as the reaction proceeds. 

The hydrodynamics of the electrochemical system and temperature are also important because these control the rate of transport of reactants and products to and from the electrochemical reaction zone. This in turn determines the polymerization efficiency. Hydrodynamics are also important in determining the form of the PPy produced. For example, using a flow-through cell and in appropriate chemical envi- 

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