Recent progress and continuing challenges in bio-fuel cells. Part I: Enzymatic cells
ABSTRACT Recent developments in bio-fuel cell technology are reviewed. A general introduction to bio-fuel cells, including their operating principles and applications, is provided. New materials and methods for the immobilisation of enzymes and mediators on electrodes, including the use of nanostructured electrodes are considered. Fuel, mediator and enzyme materials (anode and cathode), as well as cell configurations are discussed. A detailed summary of recently developed enzymatic fuel cell systems, including performance measurements, is conveniently provided in tabular form. The current scientific and engineering challenges involved in developing practical bio-fuel cell systems are described, with particular emphasis on a fundamental understanding of the reaction environment, the performance and stability requirements, modularity and scalability. In a companion review (Part II), new developments in microbial fuel cell technologies are reviewed in the context of fuel sources, electron transfer mechanisms, anode materials and enhanced O(2) reduction.
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- "A redox mediator of appropriate redox potential is required to shuttle electrons between the enzyme and electrode surface, because direct electron transfer to buried redox sites within these enzymes is generally not possible given the distance of the active site from the electrode surface (Barriere et al. 2004). Different types of mediators, such as ferrocene and its derivatives, thionine, quinone, phenazines, Fe(III) ethylenediaminetetraacetic acid (EDTA), methylene blue, and neutral red, have been used in enzymatic fuel cells (Osman et al. 2010). Among mediators, ferrocene and its derivatives have been popular, since they fulfill most of the requirements of ideal mediators in redox-enzyme catalysis (Palomera et al. 2011; Dursun et al. 2012). "
ABSTRACT: This study describes the construction of an enzymatic fuel cell comprised of novel gold nanoparticles embedded poly(propylene-co-imidazole) coated anode and cathode. Working electrode fabrication steps and operational conditions for the fuel cell have been optimized to get enhanced power output. Electrical generation capacity of the optimized cell was tested by using the municipal wastewater sample. The enzymatic fuel cell system reached to maximum power density with 1 μg and 8 μg of polymer quantity and bilirubin oxidase on electrode surface, respectively. The maximum power output was calculated to be 5 μW cm− 2 at + 0.56 V (vs. Ag/AgCl) in phosphate buffer (pH 7.4, 100 mM, 20 °C) by the addition of 15 mM of glucose as a fuel source. The optimized enzymatic fuel cell generated a power density of 0.46 μW cm− 2 for the municipal wastewater sample. Poly(propylene-co-imidazole) was easily used for a fuel cell system owing to its metallic nanoparticle content. The developed fuel cell will play a significant role for energy conversion by using glucose readily found in wastewater and in vivo mediums.Materials Science and Engineering C 02/2015; 47. DOI:10.1016/j.msec.2014.10.077 · 3.09 Impact Factor
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- "Stable in neutral pH, BOx enzyme is a multicopper oxidase utilizing four Cu ions, present in its active site, to reduce O 2 to H 2 O . Mediated electroenzymatic reduction of oxygen has been already reported with BOx using ABTS freely diffusing in solution or immobilized in polymers  and in nanostructured sol-gel materials  . The expected beneficial effect of immobilization must be, on one hand, to maintain the biological activity of the enzymes and, on the other hand, to improve the electron transfer. "
ABSTRACT: Co2Al-ABTS layered double hydroxides and associated Co2Al-ABTS@graphene composite were prepared in one pot technique by in situ coprecipitation. The as-obtained materials were then fully characterized by means of Powder X-Ray Diffraction, Fourier Transformed InfraRed and Scanning Electron Microscopy confirming the intercalation of azino-bis(3-ethylbenzothiazoline-6-sulphonate) (ABTS) between the LDH layers. Their electrochemical properties, according to Cyclic Voltammetry and Electrochemical Impedance Spectroscopy data, were improved compared to Zn2Al-ABTS reference material. Co2Al-ABTS hybrid LDH was found to combine both electronic transfers: interlayer provided by the presence of ABTS and intralayer due to the Co redox species. Moreover, an improvement of electronic transfer between the LDH particles was further achieved by addition of graphene. The resulting composite assemblies were tested for the first time as oxygen bioelectrode based on bilirubin oxidase. This original approach gives rise to enhanced electroenzymatic currents (�2.5) for oxygen reduction at 0 V and pH 7.0 as regard to that obtained for the reference laccase/LDH-ABTS based bioelectrode at pH 5.5.Electrochimica Acta 01/2015; 158:113-120. DOI:10.1016/j.electacta.2015.01.132 · 4.50 Impact Factor
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- "Enzymatic electrodes, in which a polarized support material acts as either an electron donor or acceptor, take advantage of the fact that in the absence of a natural substrate some oxidoreductases are capable of direct electron transfer (DET) from the enzymatic active center to the electrode surface or vice versa . However, unlike the wellchoreographed interactions between redox enzymes and their natural substrates, the communication between an enzyme and a solid electrode like multi-walled carbon nanotubes (MWCNTs)  is hampered by relatively long electron tunneling distances . Subsequently, the performance of biofuel cells or bio-sensors is restricted by, among other factors, the rate of interfacial electron transfer between the enzyme and the surface of the electrode  . "
ABSTRACT: The performance of enzymatic electrodes for biofuel cells or bio-sensors is subject among other factors to the rate of interfacial electron transfer between the enzyme and the surface of the electrode as well as decrease in enzyme activity due to enzyme immobilization and operation. Therefore, one approach towards improving generated current, stability, and consistent reproducibility of enzymatic electrodes is to optimize the enzyme-electrode interactions. Towards this goal it has been demonstrated previously by our group that covalent attachment of multi-copper oxidase enzymes to carbonaceous electrodes through a bifunctional cross-linker, 1-Pyrenebutyric acid N-hydroxysuccinimide ester (PBSE), resulted in improved interfacial electron transfer and subsequent higher generated current relative to physisorbed enzymes on bare multi-walled carbon nanotubes (MWNT). In the current work, a similar technique is applied for the immobilization of Pyrroloquinoline quinone (PQQ) dependent dehydrogenases using three cross-linkers (PBSE, N-(1-Pyrenyl) maleimide (PYMAL) and 1-Pyrenecarboxylic acid (PCA)) selected based on their similar structures to that of PBSE. PQQ-dependent dehydrogenases are of interest to the application of biofuel cells and sensors due to their high catalytic activity, insensitivity to oxygen and broader substrate specificity relative to NAD+/FAD+ dependent proteins. Electrochemical characterization using linear voltammetry and potentiostatic polarization of anodes developed using soluble Pyrroloquinoline quinone-dependent Glucose dehydrogenase (sGDH-PQQ) indicate that incorporation of a cross-linker onto the anode surface results in a significant increase in generated current (Fig. 1). This result implies that the length of the linker “tail” determines the distance between the attached enzyme and the electrode; shorter tail – shorter hoping distance for the electrons, resulting in higher electron transfer efficiency. Further chronoamperometry studies indicate an improvement in electrode stability and resistance to enzyme activity degradation when compared to physisorbed sGDH-PQQ on MWNT. Expanding on the close interaction of the enzyme to the electrode substrate provided by the cross-linker, this work further characterizes enzyme activity of sGDH-PQQ as well as various quinohaemoproteins in situ immobilized on MWNT-paper to determine the most effective cross-linker for improving interfacial electron transport and preserving enzyme activity when immobilized. Subsequent to the selection and incorporation of a cross-linker, heme and heme analogues are covalently attached to the surfaces of gold and MWNT electrodes via techniques including electrochemical grafting of diazonium salts possessing amide functional groups which can be used to covalently attach hemes and their analogues to the electrode (Fig. 2). The heme is a natural electron “mediator” that carries out the internal electron transfer within quinohaemoproteins. Therefore, incorporating hemes or other selected porphyrins possessing appropriate redox potential in close proximity to the enzyme could improve the electron transfer from the enzyme to the electrode. Enzymatic anodes containing immobilized hemes or heme analogues in combination with cross-linking agents are characterized for generated current, enzyme activity, and stability using various electrochemical techniques.  S. Brocato, C. Lau, P. Atanassov, Electrochimica Acta 2012, 61, 44-49.  C. Anthony, Antioxidants & Redox Signaling 2001, 3, 757-774.225th ECS Meeting; 05/2014