Effect of adsorption of pyocyanin on the electron transfer rate at the interface of a glassy carbon electrode

Redox mediators (RM) are an alternative to improve the performance of microbial electrochemical systems (MES) as they help significantly to develop the indirect electron transfer. However, their use is limited when the redox processes between the RM and the electrode surface are not thoroughly understood. The adsorption, the intermolecular interactions with the electrode, and the effects on charge transfer kinetics are important issues in MES such as microbial sensors, microbial electrosynthesis or microbial fuel cells, but are rarely analyzed. Pyocyanin, considered an RM, may present these features due to its chemical structure. Today, the electrochemical studies indicate that pyocyanin can presents adsorption processes on glassy carbon electrodes. However, the effects of adsorption on electron transfer rate and changes as a function of pyocyanin concentration have not yet been studied. Therefore, this work presents an electrochemical study of pyocyanin to determine the effect of concentration and adsorption on the electron transfer rate at a glassy carbon electrode. Analysis of the electrochemical profiles obtained by cyclic voltamperometry (CV) indicates that there is an effect of concentration (C*) on the heterogeneous electron transfer rate constant (k0) since the criterion Delta Ep varies as a function of C*. In addition, the peak proportionality parameter Ipa/Ipc and the voltamperometric function Ip/v1/2 help deduct the adsorption to the electrode. Experimental data obtained by chronocoulometry (CC) and CV, indicate that k0 = 5.7 x 1011 m/s and Rct = 3.40 x 10-16 omega under the C* = 0.14 mM condition, while k0 = 1.10 x 103 m/s and Rct = 1.60 x 10-7 omega under the C* = 0.49 mM condition. The differences in k0 and Rct values at different values of C* are due to an accumulation of pyocyanin on the electrode surface in the inner Helmholtz plane (IHP), preventing the electron transfer of bulk-dissolved pyocyanin molecules present in the outer Helmholtz plane (OHP) region. The varying values of alpha, indicate that a part of the energy of the redox reaction could be employed for the adsorption processes. As for the interactions at the electrode, the values of the Laviron parameter (v'g theta T) indicate that attraction interactions between the pyocyanin molecules and the electrode dominate, since the values of v'g theta T are higher than 0. The results of this study will provide a comprehensive understanding of the redox cycle of pyocyanin. The information will be useful for the future development of electrochemical-microbial systems since that the interactions mediator-electrode may be an operational variable to facilitate their practical applications in environmental, sensing and electrosynthesis areas.

Automated summary

Redox mediators (RM) are used to improve the performance of microbial electrochemical systems (MES) by facilitating indirect electron transfer. Pyocyanin, which is considered an RM, can adsorb to glassy carbon electrodes and its adsorption and concentration have an effect on electron transfer rate. The study provides insights into the redox cycle of pyocyanin and its application in electrochemical-microbial systems.