Optimizing the Electron Transfer Efficiency in a Conductive Biomimetic Polymer Electrode for Microbial Fuel Cell Applications

Abstract

Incorporating biomimetic polymers to develop a conducting nanocomposite material is a viable solution to address the problematic charge-transfer limitations that are common to carbon-based electrodes. Additionally, the variability associated with reported power density performance is due to the wide variety of carbon electrode functionalization techniques. Therefore, the efficacy of a biomass-based (i.e., polysaccharides and cellulose) electrode is due to the controlled establishment of a porous, non-covalent, polymer network which can serve as a consistent starting material for further functionalization. The scope of this work aims to utilize the existing biopolymer backbone (i.e., agarose, alginate, and cellulose) as a carbon scaffold to selectively control the photochemically initiated radical polymerization of conductive polymer (i.e., aniline, pyrrole) uniformly throughout the composite. Initial results indicate that the photochemically initiated polymerization of polyaniline and polypyrrole improved the efficacy of chain growth and established more uniform distributions of conducting polymer throughout the composite matrix. Current-voltage sweeps (I-V) of electrodes incorporated with polyaniline showed enhanced charge transfer when compared to polypyrrole systems at similar applied potentials. These results indicate that the absolute electron transfer performance is related to the molecular structure of the conductive polymer network. Polyaniline has a greater structural capacity to resonate electron density throughout the conjugated network, despite containing more dielectric material. In addition, the electron transport performance and efficiency of this biomimetic electrode has been shown to depend on the identity of the incorporated photoinitator (i.e., Fe3+), as well as the type of dopant (i.e., hydrochloric acid, sulfuric acid, polyelectrolyte), and surrounding polymer backbone (i.e., alginate, agarose, cellulose). Preliminary findings on dopant effects indicated markedly faster rates of charge transfer in electrodes doped with sulfuric acid. Furthermore, an extension of these enhanced current-voltage properties has been applied into a mediator-less E. coli MFC system, which exhibited increased open circuit potentials comparable to carbon cloth.