(325d) Electrocatalytic Activity of Conjugated Polymers in Oxygen Reactions

Energy conversion technologies relying on platinum group metal (PGM) catalysts have the drawbacks of of the high cost. Additionally, these catalysts are susceptible to poisoning by the reaction byproducts. Thus, to realize cost-effective, clean, and renewable electrochemical devices, there is an urgent need to develop non-PGM catalysts. Conjugated polymers are known to catalyze electron transfer reaction, and as a result, can be used as electrocatalysts. The electrocatalytic activity of conjugated polymers is reported to be a function of chemistry, structure, and polymerization pathway. Here the electrocatalytic activity of a series of conjugated polythiophenes will be discussed. It will be shown that by tailoring the chemistry of monomers, the electroactivity of the polymers can be tuned. To synthesize conjugated polymer a liquid-free oxidative chemical vapor deposition (oCVD) pathway was chosen. The poly (3,4-ethylenedioxythiophene) (PEDOT) synthesized through oCVD, catalyzes oxygen reduction reaction with an overpotential of 0.76 V vs reversible hydrogen electrode (RHE). Similarly, the synthesized poly (3,4-ethylenedithiathiophene) (PEDTT) showed bifunctional electrocatalytic activities in oxygen reactions. Conformal PEDTT coatings were applied to gas diffusion layers, and secondary rechargeable zin-air batteries were constructed. The batteries demonstrated stable performance over 100 cycles. To explicate the parameters influencing the electrocatalytic activity of these polymers, I discuss a path to control polymer structure. Though polymerization within spatial confinement, the crystalline domains of polymers were grown, and their electrocatalytic activities were compared against the amorphous films. No significant change in the electrocatalytic activity as a function of polymer structure were observed; however, the charge storage capacity of the crystalline materials, measured both in aqueous and organic media, was higher than that of amorphous films. This observation suggests that the order in the conjugated polymers, clearly enhance the charge storage capacity, possibly by reducing the charge trapping and facilitating the ion diffusion within the polymers, but does not translate to any discernible change in the charge transfer during electrocatalysis.