61Original Research Paper

J. Jpn. Soc. Colour Mater., 90〔2〕，61–66（2017）

Effects of Stabilizer Concentration on the Electrochemical Performanceof Au-Pt Anode Catalysts for Direct Glucose Fuel Cell
Masatoshi Takahashi＊, Kazuki Iwabata＊＊, Kanjiro Torigoe＊,†, Takeshi Endo＊,＊＊, Kengo Sakaguchi＊＊,
Hideki Sakai＊,＊＊,†, and Masahiko A be＊＊＊ Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan＊＊ Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 Japan†Corresponding Author, E-mail: ktorigoe@rs.noda.tus.ac.jp, hisakai@rs.noda.tus.ac.jp(Received September 2, 2016; Accepted December 20, 2016)

Abstract
Effects of stabilizer (poly(N-vinyl-2-pyrrolidone), PVP) concentration on the electrochemical performance of Au-Pt bimetallic (Au4Pt) anodecatalysts for direct glucose fuel cell (DGFC) have been investigated. In the cyclic voltammetry, the maximum current density was recorded at[PVP] / [metal] = 1 in molar ratio for the carbon supported metal nanoparticle catalysts at 5 wt% metal loading. At lower PVP concentrations,the current density decreased due to aggregation of metal nanoparticles, while at higher PVP concentrations, the current density also
decreased, presumably due to loss of active surface area of the metal catalyst by passivating with the stabilizer. Also for the full cell systems,
the maximum power density was recorded at [PVP] / [metal] = 1. When the optimal stabilizer condition was applied to the full cell system,
the maximum power density of 12.7 mW cm–2 at 0.38 V vs Ag | AgCl and the open circuit voltage of 0.85 V were recorded. Furthermore, aset of 10 stacked cells was able to light 6 LED lamps of total 1 W for over 60 h without flowing the glucose fuel. These results demonstratethat the present DGFC system can be applied as a power supply for LED illuminating systems.
Key-words: Glucose fuel cell, Au-Pt catalyst, PVP, Cyclic voltammetry, LED lighting

1．Introduction
There is an urgent demand in the world for constructing
sustainable energy systems for reducing global warming
caused by emitted greenhouse effect gases (CO2, CH4, N2O,etc.) from the consumption of fossil fuels1,2). Glucose has
attracted increasing attention as a clean sustainable energy
source. It is abundantly available not only from fruits
and starch-containing vegetables but also from exhausted
cellulose by biological or chemical degradation processes3-5).
Direct glucose fuel cells (DGFCs) work by oxidizing glucose
at the anode and reducing oxygen at the cathode. Glucose
molecules are oxidized at the anode to yield gluconolactone orits hydrolyzed product, gluconic acid, by releasing two protons
and two electrons. These protons are diffused to the cathode bypassing an ion-permeating membrane, while the electrons aretransported through the external electric circuit. These protons
and electrons are recombined with oxygen molecules at thecathode to form water6):(at anode) C6H12O6+H2O→C6H12O7+2H++2e–E0 = –0.853 V (vs NHE)(at cathode) 1/2 O2+2H++2e–→H2O
E0 = 0.403 V (vs NHE)
(overall)
C6H12O6+1/2 O2→C6H12O7
E0 = 1.256 V

There are two categories for the DFGC systems, i.e., biotic
and abiotic ones. The biotic DFGC systems utilize enzymes
or microorganisms to oxidize glucose7-10). They are superior
to the abiotic counterparts in the low cross over of the fuelbetween the cathode and the anode, owing to their specificity
for glucose substrate. Therefore, it is possible to construct thebiotic DFGCs without separator between the two electrodes,
which enables a simple cell structure. Moreover, owing to thehigh specificity between the enzyme and substrate, they are
hardly subject to poisoning by intermediate or final products,
leading to the long durability of a durable and steady electric
power. However, in order to exploit such a high catalytic
performance, it is crucial to maintain the pH and temperature
at an optimal condition, which confines the environmentthat the biotic DFGCs are applied, i.e., in living body11).
Besides, in biotic DFGC systems, an appropriate mediator
is often required to transfer an electron to the electrode since
the electrocatalytically active site of the enzyme is often
located inside the molecule, which may reduce the electric
current7,12,13).
By contrast, in abiotic DFGC systems, oxidation of glucose
molecules is performed with metal nanoparticle catalysts
deposited on a conductive support, i.e. carbon14,15). Although
they can work in harsh conditions (pH and temperature),
they do not have a high specificity for a certain substrate－11－© 2017 Journal of the Japan Society of Colour Material