Enzymatic fuel cell

Advances in Electrochemical Science and Engineering. Edited by Richard C. Alkire, Dieter M. Kolb, and Jacek Lipkowski 

This chapter is intended to provide a selective overview of the most recent developments in EFC research. Several excellent and comprehensive reviews focused on aspects of EFC research have appeared over the past few years [7, 10-16]. We focus here on developments that may lead to deployment of an implantable glucose-oxidizing, oxygen-reducing EFC, as an example of the extensive research on EFC bioelectrochemistry. Developments, focused on using other fuels, such as hydrogen, alcohols, or other sugars, or oxidants will not be considered in detail. 

The chosen electrode material should be conductive and inert within the potential range of the cell. Materials composed of allotropes of carbon and, to a lesser extent, gold are most commonly used. The cell should be designed to minimize overpotentials due to kinetics, ohmic resistance, and mass transfer of fuel in order to maximize cell voltage (A ) and current (i) generation. In addition, all cell components should be mechanically stable within their operating environment 

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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-... 

Biofuel cells — also referred to as biochemical, or bio-electrochemical fuel cells, exploit biocatalysts for the direct conversion of chemical energy to electrical energy. Based on the nature of the biocatalyst, biofuel cells are generally classified as enzymatic fuel cells and microbial fuel cells [i]. Enzymatic fuel cells use purified enzymes to catalyze the oxidation of substrates at the - anode and... 

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]. 

Bioelectrochemical generation of power by enzymes has also been considered. " " The usage of enzymes as catalysts in fuel cells has been vastly experimented, " and currently some enzymatic fuel cells are being used to produce electricity to power many number of electrical devices, like pumps, valves and pacemakers, or electronic devices, like radios, sensors, controllers, and processors. At present however, enzymatic fuel cells have been... 

Providing power output hmitations are overcome, enzymatic fuel cells might offer potentially attractive power sources for some consumer electronic devices. Hence in this chapter, a clear understanding of the reactivity of MDH enzymes at molecular level is proposed to umavel the secret of its catalytic activity towards methanol electro-oxidation. 

Enzymes have been considered in bio fuel cells as anode electrocatalysts since their use avoids the problem of poisoning the anode with carbon monoxide present in reforming gas, allowing the use of cheap hydrogen-containing fuels such as methanol. Even though enzymatic fuel cells have been reported to have power output and stability limitations, some of them are currently being used to produce electricity to power small electrical devices with power demands in the order of micro- and milh- Watts as power output limitations are overcome. 

Enzymatic fuel cells (EFCs) have recently emerged as a potential source for power generation. An EFC typically employs one or more redox active enzymes as the electrocatalyst iimnobihzed on a condnctive electrode snbstrate. EFCs are desired over... 

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. 

One of the properties of enzymatic systems that is of great interest for enzymatic fuel cells in general is their high selectivity. If universal but absolutely nonselective... 

However, in their mechanism and in their action nature bacterial and enzymatic fuel cells have much in common. In bacterial fuel cells intermediate redox systems are often used, as well, to facilitate electron transfer to (or from) the substrate. As the effect of microorganisms is much less specific than that of enzymes, a much wider selection of redox systems can be used, in particular, the simplest iron(III)/iron(II) system. The working conditions of these two kinds of biological fuel cells are similar as well a solution with pH around 7.0 and a moderate temperature, close to room temperature. 

Figure 4.3 Enzymatic fuel cell via an enzymatic pathway for producing electricity. ...

Biocatalytic fuel cell Enzymatic fuel cell Microbial fuel cell... 

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