Microbial fuel cells

 Microbial fuel cells: Next generation energy technology might originate from bacteria. Microbial fuel cells (MFCs) are rapidly gaining acceptance as an alternative "green" energy technology of the future, as they generate sustainable electric power from biodegradable organic compounds through microbial metabolism.  With the successful validation of the conceptual macro-sized MFCs as a low-cost renewable energy technology, recent research has focused on miniaturizing MFCs for potentially powering small portable electronics. However, existing micro-sized MFCs are generally limited by their relatively low power density and low energy efficiency, rendering them insufficient for practical applications. Their power density is up to five orders of magnitude lower than that of even macro-sized MFCs, ranging from 0.0023 to 0.4 μW/cm^2, and their energy efficiency is less than 2% or approximately twenty times lower.  Thus, there is an urgent need to significantly improve the performance of the micro-sized MFCs through a fundamental device level breakthrough that can inherently maximize their power generating capabilities. We have tried to increase the performance of the microsized MFCs by decreasing anode energy loss. Micro-sized MFCs show several orders magnitude higher internal resistance than that of macro-sized MFCs, resulting in lower power densities and energy efficiency. The prior work shows that anode energy loss is the main energy bottleneck in the micro-sized MFCs among the various other resistance sources, which means the poor interactions between bacteria and the anode might be the main cause of the high internal resistance. We have developed a microfabricated anode based on gold coated poly(e-caprolactone) fiber that outperformed MEMS gold electrode by a factor of 2.65-fold and even carbon paper by 1.39-fold. This is a result of its ability to three-dimensionally interface with bacterial biofilm, the metabolic “engines” of the MFC.

            Biological photovoltaics

Biological photovoltaics (or Bio-solar cells) are an emerging technology designed to harnessEarth’s most abundant and promising energy source (solar irradiation) and self-sustainably produce electrical power both day and night. The bio-solar cell continuously generates electricity from solar energy without additional organic fuel.: During the day, light energy absorbed in photosynthetic reactions splits water to produce organic substrates (oxygen, electrons); in dark conditions, the device produces electrons via bacterial respiratory metabolism of the substrates generated through photosynthesis.  Despite their potential, however, today’s bio-solar cells have persistent limits: low power density and energy efficiency relative to competing battery/fuel cell types. These limits suggest both an urgent need for fundamental research and several clear priority objectives for bridging the gap between the vision for a promising technology and the scientific understanding necessary to realize it. We are developing a novel, scaleable bio-solar cell panel by integrating significantly improved miniature bio-solar cells in an array. The two-part hypothesis is that (i) significant power enhancement can be achieved by maximizing bacterial photoelectrochemical activities in well-controlled micro-chambers and that (ii) stacking multiple small-scale bio-solar cells isthe most practical means to scale up. Our  rationale is that, because solar energy is the most promising source of sustainable energy, a high-power bio-solar panel represents an important novel technology breakthrough that offers a potentially viable biological alternative to traditional silicon-based solar cells.