Electron biofuel cells

Kamitaka Y, Tsujimura S, Setoyama N, Kajino T, Kano K. 2007. Fructose/dioxygen biofuel cell based on direct electron transfer-type bioelectrocatalysis. Phys Chem Chem Phys 9 1793-1801. 

Okuda J, Yamazaki T, Fukasawa M, Kakehi N, Sode K. 2007. The application of engineered glucose dehydrogenase to a direct electron-transfer-type continuous glucose monitoring system and a compartmentless biofuel cell. Anal Lett 40 431 -440. 

Soukhaiev V, Mano N, Heller A. 2004. A four-electron 02-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V. J Am Chem Soc 126 8368-8369. 

Moreover, it has been demonstrated that CNTs promote the direct electrochemistry of enzymes. Dong and coworkers have reported the direct electrochemistry of microperoxidase 11 (MP-11) using CNT-modified GC electrodes [101] and layer-by-layer self-assembled films of chitosan and CNTs [102], The immobilized MP-11 has retained its bioelectrocatalytic activity for the reduction of H202 and 02, which can be used in biosensors or biofuel cells. The direct electrochemistry of catalase at the CNT-modified gold and GC electrodes has also been reported [103-104], The electron transfer rate involving the heme Fe(III)/Fe(II) redox couple for catalase on the CNT-modified electrode is much faster than that on an unmodified electrode or other... 

Microbial biofuel cells were the earliest biofuel cell technology to be developed, as an alternative to conventional fuel cell technology. The concept and performance of several microbial biofuel cells have been summarized in recent review chapters." The most fuel-efficient way of utilizing complex fuels, such as carbohydrates, is by using microbial biofuel cells where the oxidation process involves a cascade of enzyme-catalyzed reactions. The two classical methods of operating the microbial fuel cells are (1) utilization of the electroactive metabolite produced by the fermentation of the fuel substrate " and (2) use of redox mediators to shuttle electrons from the metabolic pathway of the microorganism to the electrodes. ... 

The practical impact of such considerations is that the reversible potential of a mediated biocatalytic electrode is a mixed potential dominated by the mediator couple. By extension, the open-circuit potential of a biofuel cell comprising two such electrodes is primarily determined by the difference in redox potential of the two mediator couples. The difference in redox potential between the mediator and the consumed reactant represents a driving force for electron transfer and therefore must be nonzero. As... 

The design of biocatalytic electrodes for activity toward gaseous substrates, such as dioxygen or hydrogen, requires special consideration. An optimal electrode must balance transport in three different phases, namely, the gaseous phase (the source of substrate), the aqueous phase (where the product water is released and ionic transport takes place), and the solid phase (where electronic transport occurs). Whereas the selectivity of biocatalysts facilitates membraneless cells for implementation in biological systems that provide an ambient electrolyte, gas-diffusion biofuel cells require an electro-... 

Direct Electron Transfer at the Anode of an Ethanol/Air Biofuel Cell... 

Willner and coworkers have extended this approach to electron relay systems where core-based materials facilitate the electron transfer from redox enzymes in the bulk solution to the electrode.56 Enzymes usually lack direct electrical communication with electrodes due to the fact that the active centers of enzymes are surrounded by a thick insulating protein shell that blocks electron transfer. Metallic NPs act as electron mediators or wires that enhance electrical communication between enzyme and electrode due to their inherent conductive properties.47 Bridging redox enzymes with electrodes by electron relay systems provides enzyme electrode hybrid systems that have bioelectronic applications, such as biosensors and biofuel cell elements.57... 

Biofuel cells — Figure. Schematic illustration of identified electron transfer mechanisms in microbial fuel cells. Electron transfer via (a) cell membrane-bound cytochromes, (b) electrically conductive pili (nanowires), (c) microbial redox mediators, and (d) via oxidation of reduced secondary metabolites [v]... 

Tungsten carbide — WC, belongs to a class of Group IV B-VIB transition metal carbides and nitrides, often referred to as interstitial alloys, in which the carbon and nitrogen atoms occupy the interstitial lattice positions of the metal [i]. These compounds possess properties known from group VIII B precious metals like platinum and palladium [ii]. Thus, they show remarkable catalytic activities, attributed to a distinct electronic structure induced by the presence of carbon or nitrogen in the metal lattice. Tungsten carbide resembles platinum in its electrocatalytic oxidation activity (- electrocatalysis) and is therefore often considered as an inexpensive anode electrocatalyst for fuel cell [iii] and -> biofuel cell [iv] application. 

The electron donor can be substituted by an electrode (Eq. (2.7)), thereby enabling mechanistic studies, estimations of ET rates and bioelectrocatalysis. The latter has currently gained particular interest for the development of biofuel cells [248,249] and virtually reagentless immunosensors [7,250]. 

Mediated enzyme electrodes were also realized on combined microscale and nanoscale supports [300]. Bioelectrocatalytic hydrogels have also been realized by co-assembling electron-conducting metallopolypeptides with bifunctional building blocks [301]. More recently, redox-modified polymers have been employed to build biofuel cells [25, 70, 302, 303]. In 2003, an enzymatic glucose/02 fuel cell which was implanted in a living plant was introduced [147]. 

The need to convert chemical energy to electricity, efficiently and at low temperature, has increased the development of materials with electrocatalytic activity toward multi-electron charge transfer. Reactions of technical relevance are, for example, cathodic processes, such as the oxygen reduction reaction (ORR),3 13 and anodic processes, such as small organics (R-OH, where R = CH3-3-12 or CH3CH-13-17) and sugars.18-20 These complex electrochemical processes are useful in low-temperature systems such as the direct methanol FC (DMFC) or biofuel cell systems. 

Scientists have studied the use of microbes as biofuei ceiis. A biofuel cell directly converts microbial metabolic energy into electric current. An electron mediator facilitates transfer of electrons to an electrode. An electron mediator is a compound that taps into the electron transport chain of cells and steals the electrons that are produced. 

The graph shows the current produced in a biofuel cell with (blue line) and without (green line) the use of an electron mediator. 

Studies of electrochemical reactions of redox proteins have attracted widespread interest and attention. Such studies can yield important information about not only intrinsic thermodynamic and kinetic properties of redox proteins, but also structural properties, such as binding characteristics of proteins at specific types of electrode surfaces and the orientational requirements for electron transfer between the protein and the electrode. The results are useful for the development of biosensors, biofuel cells, and biocatalysts. In addition, the information obtained from these studies can contribute to an understanding of the physiological implications of biological electron transfer reactions, because many electron transfer proteins are located at, or close to, charged membranes and are thus subject to large electric field effects that are similar to those near an electrode surface. 

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