Metal-free keratin modified poly(pyrrole-co-aniline)-reduced graphene oxide based nanocomposite materials: A promising cathode catalyst in microbial fuel cell application

Abstract

A metal-free N/S codoped carbon material “keratin” with poly(pyrrole-co-aniline) and reduced graphene oxide (rGO) is used as cathode catalyst in microbial fuel cells (MFCs). Experimentally, a waste material like keratin has been utilized to fabricate a cost-effective metal-free solid nanocomposite with higher electron conductivity. Poly(pyrrole-co-aniline) has been physisorbed over rGO via oxidative polymerization followed by keratinisation. The enhancements in catalytical active sites were observed due to the intrinsic nitrogen-sulfur (N/S) present in keratin backbone that indicated higher redox activity in the process. The three components i.e., keratin, poly(pyrrole-co-aniline) and rGO, synergistically enhanced the domain functionalities, e.g. electrical conductivity, path traversed for electron and ion transport for higher reduction currents in ORR. The novelty of this work has been underscored by different characterizations, where an enhanced cathodic current of −0.676 mA at a potential 0.41 V were noted in cyclic voltamettric (CV)-ORR experiments. The electrochemical results revealed superior catalytic activity and higher stability of K-(PPy-Co-PANI)-rGO catalyst over other synthetic catalysts and Pt/C catalyst. In addition, these were tested in MFCs as cathode catalyst that showed an enhanced current density of 2062 mA/m2 at a corresponding maximum power density of ∼763 ± 38 mW/m2. In comparison, a superior power efficiency of about ∼37, 32, 25 and 13 % were observed over Pt/C, (PPy-Co-PANI), K-(PPy-Co-PANI) and (PPy-Co-PANI)-rGO catalyst, confirming the potential application of K-(PPy-Co-PANI)-rGO catalyst in MFCs. In a nutshell, the study describes the efficacy of K-(PPy-Co-PANI)-rGO nanocomposite as a cathode catalyst that can serve well than the commercially available Pt/C catalyst in MFCs.