Biological fuel cell

Biological fuel cells, or semi-fuel cells (see Section 9.3), are cells in which at least one of the following two conditions is met  

At one of the electrodes at least, the electrochemical reactant is a substance found in biological fluids (e.g., in blood) or in other biological materials 

At present, biological fuel cells are a subject of great interest for the following two reasons  

Definite solutions to attaining these goals are still far away. So far, research has focused on individual, relatively narrow aspects of the problems. 

Biological fuel cells are different from conventional electrochemical fuel cells in various aspects. Biological fuel cells use biocatalysts to drive oxidation and reduction reactions. A biocatalyst can be used to generate fuel substrates through metabolic processes or biocatalytic transformations, or it could partake in the electron transfer that occurs between the fuel substrate and the electrode s surface. The electrolyte layer typical in conventional fuel cells is replaced by a membrane in the biofuel cell, which still allows ion exchange. Biofuel cells usually operate at ambient temperature, atmospheric pressures. 

More specified data about the two systems described earlier can be found in a detailed review by Ponce de Leon et al. (2006). 

Topcagic and Minteer (2006) reported building a fuel cell that was working with simple reactants—ethanol and oxygen, but where the platinum catalysts that had usually been used were replaced by enzymes. 

Alcohol dehydrogenase and aldehyde dehydrogenase were used as the enzymes for anodic ethanol oxidation. Together with the coenzyme NAD (nicotinamide adenine dinucleotide), they formed the NAD+/NADH redox system. Aided by these enzymes, this reaction occurs in two steps. First, the former enzyme oxidizes ethanol to acetaldehyde, and then the latter enzyme oxidizes the aldehyde to acetic acid. 

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Biological fuel cells have a long history in the literature,but in recent years, they have come to prominence as more conventional fuel cell technologies have approached mass-market acceptance. Driving the recent ascendance of biofuel cells are the aspects of biocatalysis that are unmatched by conventional low-temperature oxidation—reduction catalysts, namely, activity at near-room temperatures and neutral pH and, more importantly, selective catalytic activity. 

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-... 

Fig. 14.41. Schematic representation of the biological fuel cell concept. (Reprinted from J. O M. Bockris and S.

Moore then explained how mitochondria are biological fuel cells. The oxygen reduction taking place in a mitochondrion is exactly the same as in a standard fuel cell. Using several enzymes and only earth-abundant elements, the mitochondrion converts electrochemical potential to biochemical work with efficiency greater than 90 percent. This is a steady-state process in which protons are pumped across the membrane to maintain its electrical potential. If... 

Fig.1. 13. Schematic representation of the principle of the biological fuel cell concept. R and RH representtheoxidizedand reduc form of a bio-molecule. ADR is adenosine diphosphate ATP is adenosine triphospate. (Reprinted from J. O M. Bockrisand S. U. M. Khan, Surface Electrochemistry, p. 699. Plenum Press, New York, 1993.)...

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. 

Habermann, W., Pommer, E. H. (1991). Biological fuel cells with sulphide storage capacity. Applied Microbiology and Biotechnology, 35, 128-133. 

A microbial fuel cell (MFC) or biological fuel cell is a biochemical system that drives a current by using and copying bacterial interactions found in nature. It is a device that converts chemical energy to electrical energy by the catalytic reaction of micro-organisms, usually bacteria. 

Platinum metals are an example of highly active catalysts for a great number of electrochemical reactions (i.e., practically, they have no selectivity). Enzymes described in Section 9.2.1 are an example of highly selective catalysts, but they require specific working conditions, which, for the moment, limit their application in technical devices. It can be anticipated that in the future they will be used primarily in commercialized biological fuel cells working with neutral electrolyte solutions (pH near 7) at temperatures of 20 to 40°C. 

One type of genuine fuel cell that does hold promise in the very long term is the biological fuel cell. These would normally use an organic fuel, such as methanol or ethanol. However, the distinctive biological aspect is that enzymes, rather than conventional chemical catalysts such as platinum, promote the electrode reactions. Such cells replicate nature in the way that energy is derived from organic fuels. However, this type of cell is not yet anywhere near commercial application, and is not yet suitable for detailed consideration in an application-oriented book such as this. 

The biological fuel cell should be distinguished from biological methods for generating hydrogen, which is then used in an ordinary fuel cell. This is discussed in Chapter 8. 

Figure 7. Biological Fuel Cell. Experimental arrangement for maintaining a copper prosthesis, implanted in the canine thoracic inferior vena cava.

Over the last decade, biological fuel cells (BFCs) have become an increasingly popular area of research. As a new technology, many of the analytical techniques that have been previously used for conventional electrochemical devices have been adapted and tailored for use in studying biological systems. 

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