A silver assist for microbial fuel cell power

Undegraded carbon sources provide an excellent fuel for bacteria, and the electrons generated by their oxidative respiration can be harvested with electrodes in microbial fuel cells (1). Many bacterial and material modification strategies have improved overall fuel cell power output (2, 3), but a more important measure is Coulombic efficiency (CE), the percentage of electrons harvested from the fuel (4). On page 1336 of this issue, Cao et al. (5) achieve a record-setting microbial fuel cell power density of 6.6 W/m2 with an 81% CE (5) with a common electroactive bacterial species, Shewanella, by exploiting its intrinsic heavy-metal resistance to enhance electron transfer. A modified electrode material of reduced graphene oxide (rGO) and silver (Ag) creates silver ions (Ag+) that migrate into the cellular membrane. Reduction of Ag+ by proteins linked to lactate oxidative metabolism formed Ag nanoparticles (NPs), which created electron pathways that increase current and power density. The benefits of bacteria for our bodies and for soil are well appreciated, but much less discussed is their potential in renewable energy generation. Although bacteria are a critical component for organic degradation in wastewater treatment, further pairing of the decontamination process with energy-harvesting technologies could allow wastewater to be a fuel source for electrical current generation. The amount of energy generated would not serve as a large-scale source to connect to the grid, but it could provide a renewable source for technologies with low-energy demands and could also drive important chemical synthesis processes. © 2021 American Association for the Advancement of Science. All rights reserved.