Enzymatic Biofuel Cell

In contrast to microbial biofuel cells, enzymatic biofuel cells utilize the redox enzymes rather than the whole microorganism as a biocatalyst. The redox enzyme, which is separated and purified from an organism, participates in the electron transfer chain that occurs between the substrate and the anode by oxidizing the fuel or between the substrate and the cathode as shown in Figure 1.10. 

Barton SC, Gallaway J, Atanassov P. 2004. Enzymatic biofuel cells for implantable and microscale devices. Chem Rev 104 4867-4886. 

Pahnore GTR, Bertschy H, Bergens SH, Whitesides GM. 1998. A methanol/dioxygen biofuel cell that uses NAD -dependent dehydrogenases as catalysts Application of an electro-enzymatic method to regenerate nicotinamide adenine dinucleotide at low overpotentials. J Electroanal Chem 443 155-161. 

Enzymatic Biofuel Cells for Implantable and Microscale Devices Scott Calabrese Barton, Josh Gallaway, and Plamen Atanassov pp 4867 - 4886 (Review) DOl 10.1021/cr020719k... 

Enzymatic Biofuel Cells for Implantable and Microscale Devices... 

Bioelectrochemistry at the Cathode and Anode of 4871 Enzymatic Biofuel Cells... 

Recently, a novel microbial fuel cell harvesting energy from the marine sediment—seawater interface has been reported. Also, a novel photosynthetic biofuel cell that is a hybrid between a microbial and enzymatic biofuel cell has been reported for the very first time. More recently, reports of an unconventional biomass-fueled ceramic fuel cell can also be found in the literature. A new concept of Gastrobots —hybrid robots that utilize operational power derived from microbial fuel cells—has been introduced. Finally, the generation of electrical power by direct oxidation of glucose was demonstrated in mediatorless microbial fuel cells, which produced currents up to 3 fiA/cm at unknown cell voltage. ... 

Mediators can exist free in solution physically entrapped behind a membrane - immobilized in a matrix along with the biocatalyst or covalently bound to a surface or polymer network, wherein the polymer can be conductive or insulating. - Detailed discussion of the various formats is outside scope of this review paper. However, selected immobilization chemistries reported in relation to enzymatic biofuel cells are reviewed in the sections below. 

The recent literature in bioelectrochemical technology, covering primarily the electrochemical aspects of enzyme immobilization and mediation, includes few reports describing engineering aspects of enzymatic biofuel cells or related devices. Current engineering efforts address issues of catalytic rate and stability by seeking improved kinetic and thermodynamic properties in modified enzymes or synthesized enzyme mimics. Equally important is the development of materials and electrode structures that fully maximize the reaction rates of known biocatalysts within a stable environment. Ultimately, the performance of biocatalysts can be assessed only by their implementation in practical devices. 

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... 

The most common reaction at the anodic side of biofuel cells is the oxidation of sugars which relies on the catalytic properties of oxidases. This class of enzymes has, however, usually poor potential for direct ET. Direct ET on the anodic site was, however, described for a number of hydrogenases [235, 236] and cellobiose dehydrogenase [225, 237, 238]. Enzymatic catalysis by means of direct ET was also realized on conducting graphite or TiO2 particles [239, 240]. 

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 anodic and enzymatic oxidation of hydrogen in biofuel cells has been investigated to achieve efficient energy conversion. Hydrogenase (EC 1.98.1.1), a protein containing FeS-clusters, oxidizes H2 with reduction of methylviologen. The reoxidation of the reduced mediator in deaerated solution gives a concentration-dependent oxidation current (Varfolomeev and Bachurin, 1984). This system has been adapted for analytical purposes by Boivin and Bourdillon (1987). The enzyme was attached covalently to the surface of a carbon electrode. 

The structure and physicochemical properties of the enzymes which have been used to date to promote electrochemical reactions are briefly outlined. Methods of their immobilization are described. The status of research on redox transformations of proteins and enzymes at the electrode-electrolyte interface is discussed. Current concepts on the ways of conjugation of enzymatic and electrochemical reactions are summarized. Examples of bioelectrocatalysis in some electrochemical reactions are described. Electrocatalysis by enzymes under conditions of direct mediatorless transport of electrons between the electrode and the enzyme active center is considered in detail. Lastly, an analysis of the status of work pertaining to the field of sensors with enzymatic electrodes and to biofuel cells is provided. 

Fig. 3.1 Schematic representation of an enzymatic biofuel cell design based on the electrical connection of a laccase at the cathode and glucose oxidase at the anode...

The scientific challenge of these enzymatic biofuel cells is to develop devices with compatible power and size to use them as power sources for portable devices such as GPS, mobile phone, MP3 players, or mobile computers. A steady increasing interest within enzymatic biofuel cell design is dedicated to the production of electrical energy from the electro-enzymatic degradation of glucose and O2. These... 

The vast majority of enzyme biofuel cells is based on the electroenzymatic oxidation of glucose by glucose oxidase (GOX) and oxygen reduction by laccase, rarely, bilirubin oxidase, or even ascorbate oxidase. Usually two couples of redox mediators are involved in the functioning of the enzymatic biofuel cell. One is required to establish an electrical connection between the electrode surface and the reduced form of flavin adenine dinucleotide, the prosthetic center of GOX. The second couple, located at the cathode, allows the electron transfer from the electrode siuface to the copper center of laccase where the oxygen reduction takes place (Fig. 3.2). 

Nanoparticle-Based Enzymatic Biofuel Cells 3.3.1 Clay Nanoparticles... 

---