Miniature Enzymatic Fuel Cells

Extensive review literature exists in the area of biological fuel cells. Notably, Palmore and Whitesides summarized biological fuel cell concepts and performance up to 1992." More recently, Katz and Willner discussed recent progress in novel electrode chemistries for both microbial and enzymatic fuel cells,and Heller reviewed advances in miniature cells.This article does not duplicate these valuable contributions. Instead, we focus on the strengths and weak-... 

Based on the high specificity of enzymatic reactions enzymatic fuel cells can be constructed compartmentless, i.e., without a physical separation of the anodic and the cathodic compartments. This allows miniaturization of the devices, e.g., for biomedical (implantable) devices and -> biosensors [iii]. 

An EFC consists of two electrodes, anode and cathode, connected by an external load (shown schematically in Figure 5.1). In place of traditional nonselective metal catalysts, such as platinum, biological catalysts (enzymes) are used for fuel oxidation at the anode and oxidant reduction at the cathode. J udicious choice of enzymes allows such reactions to occur under relatively mild conditions (neutral pH, ambient temperature) compared to conventional fuel cells. In addition, the specificity of the enzyme reactions at the anode and cathode can eliminate the need for other components required for conventional fuel cells, such as a case and membrane. Due to the exclusion of such components, enzymatic fuel cells have the capacity to be miniaturized, and consequently micrometer-dimension membraneless EFCs have been developed [7]. In the simplest form, the difference between the formal redox potential (F ) of the active site of the enzymes utilized for the anode and cathode determines the maximum voltage (A ) of the EFC. Ideally enzymes should possess the following qualities. 

FIGURE 17.1 Miniature enzymatic fuel cells points of merit for miniaturization and possible applications. The photograph represents an MEFC embedded in a raw grape using a pair of enzyme-modified carbon fibers. (Reproduced with permission from Ref. [3]. Copyright 2003, American Chemical Society.)... 

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