ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P136. An Ethanol/Dioxygen Biofuel Cell Based on Alcohol Dehydrogenase-
and Bilirubin Oxidase-immobilized Electrodes
N. Nakamura , K. Murata, K. Kajiya, M. Masuda, and H. Ohno
Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei,
Tokyo 184-8588, Japan
e-mail: nobu1@cc.tuat.ac.jp
Biofuel cells using enzymes as a catalyst have attracted considerable attention because biomass products such as
ethanol, glucose, and fructose, which are easy for handling, may be used as a fuel. The achevement of the fast
electron transfer between enzymes and electrodes on both electrodes (an anode and a cathode) is one of the most
immportant themes to construct a highly efficient biofuel cell.
Anode: When nicotinamide adenine dinucleotide (NAD + /NADH)-dependent enzymes are used as an anode
catalyst, the electrochemical regeneration of NAD + at high rate constants and low over potential is an important
issue. Many compounds have been investigated as potential redox-mediators for electrocatalytic oxidation of
NADH so far. In this study, the novel bioanode using NAD(H)-dependent alcohol dehydrogenase was
constructed. The electrochemical polymerization of ruthenium(II) tris(5-amino-1, 10-phenanthroline) ([Ru(5phenNH2)3]
2+ ) in nonaqueous solution (0.1M TBAP acetonitrile) was performed by the continuous cycling of the
potential of the working electrode according to a similar method reported previously [1]. The cyclic
voltammogram shows the typical Ru(II/III) redox couple with E = +1.2 V when the potential of a glassy carbon
electrode was cycled between −1.0 and +1.5 V (vs. Ag/AgCl). After the electrode is transferred to a pH 7.0
phosphate buffer solution, the redox couple was observed at E = −25 mV (vs. Ag/AgCl). The plot of the redox
potential versus pH was linear with the slope −55 mV/pH, indicating that protons take part in the redox reaction
of the polymer. It was found that the poly-[Ru(5-phenNH2)3] 2+ formed onto a carbon black-modified carbon
paper electrode was an effective catalyst for electrochemical oxidation of NADH. A high current densitybioanode
was fabricated from the poly-[Ru(5-phenNH2)3] 2+ modified electrode that was coated with a layer of
poly(diallyldimethylammonium chloride) and NAD(H)-dependent alcohol dehydrogenase (ADH). In the
presence of 10 mM NAD + and 1 M ethanol, well-defined faradaic currents were observed and the current density
reached a value as large as 2.5 mA/cm 2 at 800 rpm rotation rate.
Cathode: A direct electron transfer type
biocathode was fabricated using bilirubin
oxidase which is a one of multi-copper
oxidases and catalyzes reduction of
dioxygen to water. Bilirubin oxidase was
adsorbed onto a carbon black-modified
carbon paper electrode whose surface had
been electrochemically oxidized. The
observed current density was about 0.7
mA/cm 2 in an air-saturated buffer solution
(pH 7.0) at 800 rpm rotation rate.
Biofuel cell: The alcohol dehydrogenasemodified
electrode and the bilirubin
oxidase-modified electrode were combined
to prepare an alcohol/dioxygen biofuel cell.
The prepared biofuel cell without a
separator showed the open circuit potential
of 0.45 V, the short circuit current of 0.6
mA/cm 2 , and the maximum power density
of 0.08 mW/cm 2 at the cell voltage of 0.25
V with stirring solution at 800 rpm under air-saturated condition (figure 1).
0
0 0.2 0.4 0.6
Current density/ mA cm -2
Reference
[1] C.D. Ellis, L.D. Margerum, R.W. Murray, T.J. Meyer, Inorg. Chem., 22, 1283 (1983).
E cell / V
0.5
0.4
0.3
0.2
0.1
100
Figure 1. The dependences of cell potential (dotted lines) of
the biofuel cell and of the power output (solid lines) on the
current density. The measurements were performed in
phosphate buffer pH 7.0 without stirring (open triangle) and
with stirring at 800 rpm (closed circle) under air-saturated
conditions.
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255
50
0
Power density / µW cm -2