Optimized design and protocols eliminate power density gap between microbial fuel cells at different scales

In addition to offering a promising approach for niche applications in environmental sensing and portable power sources, microfluidic microbial fuel cells (MFCs) can also accelerate the development of mainstream energy applications through studies into fundamental mechanisms and optimization, without complications from nutrient cycling, membrane fouling, or uncontrollable concentration gradients. However, the main hurdle in leveraging microfluidic MFCs for discovery and optimization is their underperformance compared to macrosystems on certain key metrics, notably area-normalized power. To bridge this gap, we showcase a strategy that focuses on (i) technology improvements, (ii) establishment of new performance benchmarks, and (iii) presentation of a universally applicable normalization method for direct comparisons across all MFC scales and that complements areal power densities. Using a pure-culture Geobacter sulfurreducens electroactive biofilm (EAB) applied to a new system that adheres to the strategy above, we observed optimal anode colonization, resulting in the highest recorded power density for a microfluidic MFC of 3.88 W m-2 (24.37 kW m-3) and a normalized energy recovery (0.21 kWh m-3) that nearly matches the average value observed in macrosystems. With these results, the performance gap between micro- and macroscale MFCs is closed, and a road map to move forward is presented.