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The bioelectrooxidation of ethanol was investigated in a fully enzymatic membraneless ethanol/O 2 biofuel cell assembly using hybrid bioanodes containing multi-walled carbon nanotube (MWCNT)-decorated gold metallic nanoparticles with either a pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase (ADH) enzyme or a nicotinamide adenine dinucleotide (NAD + )-dependent ADH enzyme. The biofuel cell anode was prepared with the PQQ-dependent enzyme and designed using either a direct electron transfer (DET) architecture or via a mediated electron transfer (MET) configuration through a redox polymer, 1,1′-dimethylferrocene-modified linear polyethyleneimine (FcMe 2 -C 3 -LPEI). In the case of the bioanode containing the NAD + -dependent enzyme, only the mediated electron transfer mechanism was employed using an electropolymerized methylene green film to regenerate the NAD + cofactor. Regardless of the enzyme being employed at the anode, a bilirubin oxidase-based biocathode prepared within a DET architecture afforded efficient electrocatalytic oxygen reduction in an ethanol/O 2 biofuel cell. The power curves showed that DET-based bioanodes via the PQQ-dependent ADH still lack high current densities, whereas the MET architecture furnished maximum power density values as high as 226 ± 21 μW cm −2 . Considering the complete membraneless enzymatic biofuel cell with the NAD + -dependent ADH-based bioanode, power densities as high as 111 ± 14 μW cm −2 were obtained. This shows the advantage of PQQ-dependent ADH for membraneless ethanol/O 2 biofuel cell applications. [ABSTRACT FROM AUTHOR]

We report the preparation of hybrid nanostructured bioanodes containing the enzyme alcohol dehydrogenase (ADH) with either Au, Pt, or Pt0.75Sn0.25 nanoparticles for use in ethanol/O2 hybrid biofuel cells. We describe two different methodologies for the preparation of the bioanodes: in a first case, multi walled carbon nanotubes (MWCNTs) were employed as a support for the metallic nanoparticles and TBAB-modified Nafion® aided enzyme immobilization. In the second case, we immobilized the enzymes using dendrimers-encapsulated nanoparticles as the agent for enzyme anchoring. The biofuel cell tests showed that the addition of metallic nanoparticles to the bioanode structure enhanced the overall biofuel cell performance. The bioelectrode containing Au nanoparticles displaying the best performance, with an open circuit potential of 0.61 ± 0.05 V and a maximum power density of 155 ± 11 μW cm−2. NADH cyclic voltammetric experiments indicated that Au nanoparticles behaved as a catalyst toward NADH oxidation. Comparing the two protocols we used to synthetized nanoparticles, the sample containing the Au nanoparticles supported on MWCNTs furnished fourfold higher values. Therefore, from the satisfactory results obtained, it can be inferred that the combination of small amounts of metallic nanoparticles with enzymes improve bioanode performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] The architecture of bioanodes layers makes a great difference in the wiring between de CNTs and the ADH enzyme. [•] MWCNTs enhance the activity of the enzymatic reaction between EtOH and the NAD+. [•] The anode configuration carbon cloth/poly-MG/PAMAM/MWCNTs/ADH is potentially applicable in miniaturized energy devices. [•] Power density and open circuit potential (OCP) of 0.278±0.038mWcm−2 and 0.459±0.025V were obtained for the best anode configuration investigated. [ABSTRACT FROM AUTHOR]

Abstract: This paper compares the performance of a DET (direct electron transfer) bioanode containing both PQQ-ADH (pyrroloquinoline quinone-dependent alcohol dehydrogenase) and PQQ-AldDH (PQQ-dependent aldehyde dehydrogenase) immobilized onto different modified electrode surfaces employing either a tetrabutylammonium (TBAB)-modified Nafion® membrane polymer or polyamidoamine (PAMAM) dendrimers for the enzyme immobilization. The electrochemical characterization showed that the prepared bioelectrodes were able to undergo DET onto glassy carbon surface in the presence as well as the absence of multi-walled carbon nanotubes (MWCNTs); also, in the latter case a relevant shift in the oxidation peak of about 180mV vs. saturated calomel electrode (SCE) was observed. A very similar redox potential was achieved with the self-assembled bioelectrode prepared onto modified-gold surfaces with dendrimers, indicating that both methodologies provide an environment that enables the PQQ-enzymes to undergo DET. The biofuel cell tests confirmed the ease of the DET process and the enhanced performance in the presence of the carbon nanotubes. Considering the bioanodes prepared with PAMAM dendrimers, the power density values vary from 19.4μWcm−2 without MWCNTs to 25.7μWcm−2 in the presence of MWCNTs. Similarly, with the bioanodes prepared with the TBAB-modified-Nafion® polymer, the results indicate power densities of 27.9 and 38.4μWcm−2 respectively. These electrode modifications represent effective methods for immobilization and direct electrical connection of quinohemoproteins to electrode surfaces. [Copyright &y& Elsevier]

Abstract: This paper describes the preparation and application of a novel bioanode for use in ethanol/O2 biofuel cells based upon immobilization of alcohol dehydrogenase (ADH) and polyamidoamine (PAMAM) dendrimers onto carbon cloth platforms. The power density measurements indicated a direct relationship between the amount of anchored ADH and the anode power values, which increased upon enzyme loading. The power density values ranged from 0.04 to 0.28mWcm−2, and the highest power density was achieved with the bioanode prepared with 28U of ADH, which provided a power density of 0.28mWcm−2 at 0.3V. The latter power output values were the maximum observed, even for higher enzyme concentrations. Stability of the bioanodes was quite satisfactory, since there was no appreciable reduction of enzymatic activity during the measurements. The method of bioanode preparation described here has proven to be very effective. The PAMAM dendrimer represents a friendly environment for the immobilization of enzymes, and it is stable and capable of generating high power density compared to other immobilization methods. [ABSTRACT FROM AUTHOR]