Fuel cells convert chemical energy into electrical current. Biofuel cells are a subset of fuel cells that generate electricity, using microbes themselves or synthesized enzymes. Microbial fuel cells can last for years and fully oxidize nutrients to carbon dioxide (i.e., derive maximal energy from each fuel molecule); however, they generate very little power for their size (low-power density). In contrast, enzymatic fuel cells have much higher power densities but cannot (usually) fully oxidize fuel molecules. Moreover, owing to the degradability of enzymes, they do not remain functional over an extended period of time. Researchers have recently developed a biomimetic method of both improving the lifetime of enzymes and increasing their ability to fully oxidize fuels. Once enzymes are encapsulated in a micellar polymer, they are confined in a buffered pH microenvironment that prevents denaturation. Enzymes thus encapsulated have demonstrated activity for over one year. In order to promote complete oxidation of fuels, researchers embedded all of the enzymes responsible for a certain oxidation cascade onto the confining element. This not only enables full oxidation of various fuels (including alcohols and sugars), it also allows developers to produce enzymatic fuel cells that are completely selective for their fuel source. The advances in increasing the active lifetime of enzymatic fuel cells, as well as their catalytic efficiency, may someday yield products capable of competing with conventional batteries and fuel cells.
Enzymatic fuel cells containing confined enzyme cascades could be a more efficient way of generating electricity from simple biological fuels than either fermentation/combustion or microbial fuel cells. Moreover, the materials, fuel sources, and waste products would all be relatively inert and sustainable.
This technique mimics the way natural cells keep their sensitive metabolic enzymes confined in membrane-bound vesicles.
Most techniques for generating electrical current from biomass (e.g., carbohydrates) involve the conversion of fuels into alcohol for use in combustion engines. These multiple conversion steps decrease the efficiency of the system as a whole. Even microbial fuel cells, which can generate electricity from biomass fuels directly, are plagued by low yields.Edit Summary