Microalgae hydrogel-derived monolithicfree-standing air cathode for microbial fuel cells: Tailoring the macroporous structure for enhanced bioelectricity generation

Abstract

A high-performance and cost-effective cathode is highly desirable for the practical implementation of microbial fuel cell (MFC) technology, used for renewable energy recovery from wastewater. In this study, a monolithic, free-standing air cathode for MFCs is fabricated through a sol-gel-based route. Chlorella pyrenoidosa (CP) is selected as the catalyst precursor, polyacrylonitrile fiber as the precursor for the conductive and supporting skeleton, and deionized water as the solvent and pore former. Agar is also used as the gelling agent to facilitate the formation of 3D porous networks inside the cathodes. By systematically tailoring the porosity of the tubular air cathodes by varying the water content in the CP agar composite hydrogel, the mechanical strength and electrical conductivity of the cathode is optimized. Moreover, this fabrication process leads to abundant active sites for the oxygen reduction reaction and an interconnected hierarchical porous structure with separated transport paths for air supply and ion transfer. The tubular air cathode can be directly employed as an MFC cathode without the use of a polymer binder or other modifications. The MFC delivers a maximum power density of 106.3 ± 5.9 W m-3, which is approximately 33% higher than that with a converntional Pt/C cathode (79.8 ± 4.1 W m-3). This work therefore offers a promising new route for recovering bioelectricity from wastewater based on MFCs.