Influence of polypyrrole-derived nitrogen-doped carbon nanostructure morphology on the microbial composition of anodic biofilms and microbial fuel cell performance

• Polypyrrole-derived nitrogen doped carbon nanostructures (NCDNs) with different morphologies were used as anode modifiers in microbial fuel cells (MFC) with municipal wastewater anolyte. • NCDN morphology influenced anodic biofilm enrichment in exoelectrogenic and bioremediation-associated bacteria. • Nanotubular NCDN morphology determined increased conductivity and a more suitable surface architecture for biofilm formation, leading to improved MFC performance compared to globular NCDN anode modification. The characteristics of the anode material play a critical role in the efficiency of microbial fuel cells (MFCs). Among anode modification strategies, carbon-based nanostructures have been successfully used, due to their improved surface area, conductivity, and biocompatibility. In the efforts to improve MFC performance, nitrogen doping of carbon nanostructures (NDCNs) introduces more reactive sites on the anode surface that enhance both the electron transfer rate and microbial adhesion. In this aim, the present study focuses on the influence of anode modification with NDCNs with different morphologies (nanotubular and globular), obtained through direct carbonization of polypyrrole nanostructures, on the microbial diversity of anodic biofilms and microbial fuel cell performance. XPS analyses show similar N content and functionality for both NCDN morphologies, with graphitic nitrogen as the dominant surface nitrogen type, followed by pyridinic and pyrrolic nitrogen. Results indicate the best MFC performance of NCDN-modified anodes was obtained in the case of NCDN with nanotubule-like morphologies (43.2 mW m −2 ) compared to globular NDCN (29.3 mW m −2 ). The improved performance of MFC might be assigned with NCDN with nanotubule-like morphology that assembles onto the carbon cloth into a porous three-dimensional architecture due to the cross-connection of individual particles, forming micro-cavities and pits which, along with an improved nanoscale spatial order, create a continuous pathway for electron transport and as a consequence a better electrical conductivity (1.32 S cm −1 ) compared to the globular one (0.59 S cm −1 ). Thus, our study shows that the morphology of the sample is a deciding factor that contribute to the improved performance of MFCs along with nitrogen content and functionality.