3D Conducting Polymeric Membrane and Scaffold Biofilms to Enhance Energy Conversion in Microbial Fuel Cells.

Microbial fuel cells (MFCs) can spontaneously convert chemical energy into electricity using biocatalytic microorganisms and organic matter as fuel feedstocks. Three-dimensional cross-linked poly(vinyl alcohol)-based membranes were produced by a sol-gel method under homogeneous catalysis and used as the electrolyte to facilitate effective proton conduction. Under dry conditions, these polymeric membranes showed high water uptake (120%) and ionic conductivity (2.815 mS cm). In the anode compartment, the scaffold film biocatalysts were used to improve electron transfer to the cathode, using three major configurations to generate a higher power output. It was found that the graphene anchoring, red light (RL) stimulation, and methylene blue (MB) mediation-enhanced device performance. The electrochemically derived graphene improved the power and current density by 40% because of its high conductivity. The RL stimulation increased the power density by 80% because of a shortened electron flow path to complex III. The MB mediation also yielded a higher current density by 340% because MB can bypass the electron flow from complex II to cytochrome c and transfer electrons directly to complex III. The individual and collective increase in power output was due to more efficient electron flow from the electronic network permeating the biofilm. The generated electrons were transferred either to graphene as an energy-efficient direct transfer mode or to methylene blue as a long-range redox mediator for indirect transfer. Red light stimulation enhanced oxygen utilization efficiency and stimulated electrons in redox proteins enhancing electron flux. These processes generated higher power through the more efficient generation of electrons and faster transport to the external circuit. As society migrates from gasoline consumption to low carbon-based fuels, the MFCs become important in producing electrical energy with low net emissions.