DEVELOPMENT OF ELEMENTAL TECHNOLOGIES FOR LARGE CURRENT DENSITY AND HIGH EFFICIENCY IN SOLID POLYMER ELECTROLYTE WATER ELECTROLYSIS
M.YAMAGUCHI T.SHINOHARAK.OKISAWA
Environment & Energy Laboratory
Fuji Electric Corporate Research and Development,Ltd.
2-2-1,Nagasaka,Yokosuka city
240-01,Japan
ABSTRACT
Commissioned to execute Subtask 4, "Development of Hydrogen Production
Technologies" as a part of the Ministry of International Trade and Industry's
"Technologies for an International Clean Energy Network Using Hydrogen Conversion
Project", Fuji Electric Corporate Research and Development,Ltd. has been working to
develop elemental technologies relating to a solid polymer electrolyte water
electrolysis that promises large current density and high efficiency.
In term of technical features, Fuji Electric's technological approach calls for
membrane-electrode assemblies to be formed by a hot-press method. Recently, we have
obtained a membrane-electrode assembly that registers 1.70V of cell voltage for a
current density of 1A/cm2.
1. INTRODUCTION
In the membrane-electrode bonding technique based on the hot-press method, a
catalyst film is superposed over an ion-exchange membrane, and the catalyst film is
combined with the ion-exchange membrane by means of thermal fusion, as illustrated
in Fig.1.
This techique comes with the following features:
ì²Different types of catalysts, including oxides, can be utilized.
ì³Because carrier catalysts can be used, use of noble metal catalysts can be reduced.
ì´Three-dimensional electrode/membrane interface can be achieved.
In the development activities under way, the hot-press method mentioned above
is adopted, and diverse types of membrane-electrode assemblies are test-produced by
changing three factors; (1)the type and quantity of catalyst, binder, ion-exchange
membrane and other component used; (2)the fabricating method of the catalyst layer;
and (3)the hot-pressing conditions for catalyst film and ion-exchange membrane. Based
on the results of performance evaluations of those samples, studies are being
conducted to elucidate the composition of materials in a membrane-electrode assembly
with small overvoltage, low resistance and high durability, and to seek out
fabricating method for such an assembly.
What follows below is a brief report on the comparison between platinum black
and iridium oxide as catalysts, as well as on the results of experiments carried out
to assess the deposited quantity of iridium oxide working as anode catalyst.
2.EXPERIMENT METHOD
Fabrication Method of Membrane-Electrode Assemblies
The membrane-electrode assemblies used for the experiment were manufactured
through the following process shown in Fig.1.
(1)Preparation of catalyst and PTFE mix solution.
(2)Catalyst film formation from the mix solution.
(3)Natural drying
(4)Heat treatment of the catalyst film
(5)Laminating the catalyst film and an ion-exchange membrane, and then hot-pressing.
Test Production of Membrane-Electrode Assemblies
Table. 1 shows details of the membrane-electrode assemblies used for the
experiment, which were manufactured through the following processes:
(1) Preparation of catalyst and PTFE mix solution.
(2) Film formation from the mix solution.
(3) Natural drying.
(4) Heat treatment of the catalyst film.
(5) Laminating the catalyst film and an ion-exchange membrane, and then hot-pressing.
Performance Measurement of Membrane-Electrode Assemblies
A laboratory cell was built in filter-press type consisting of a membrane-electrode assembly with a support collector and a current collector fitted on both sides, as can be seen in Fig.2.
The support collector was a single porous laminate made of three expanded
titanium mesh sheets, which was platinum-plated. The current collector was a titanium
plate with grooves of 2 mm wide 3 mm deep mounted in parallel at a pitch of 4 mm, and
was also platinum-plated.
The sample membrane-electrode assemblies were placed in the laboratory cell and
their cell voltages were measured at different temperatures and current densities,
using the operating system illustrated in Fig.3.
3. RESULTS OF EXPERIMENTS
Effect of Varieties of Iridium Dioxide Powders on Cell Performance
Iridium oxide is often employed in oxygen generation DSA and other applications
for its low overvoltage and excellent durability as an anode catalyst.
To verify whether iridium oxide could serve as a suitable anode catalyst for
membrane-electrode assemblies processed by the hot-press method, the authors
test-manufactured a membrane-electrode assembly with platinum-black anode and
cathode, and another with iridium-oxide anode, platinum-black cathode, and cell
voltages were measured in the laboratory cell.
The latter sample registered a cell voltage 0.2 to 0.3V lower than other, as shown
in Fig.4, leading us to confirm that iridium oxide is an excellent anode catalyst.
Fig.5 represents a scanning electron microscope micrograph depicting the
cross-section of the membrane assembly with iridium-oxide anode/platinum-black
cathode (Sample No.6).
Fig.6 shows the results of the experiment indicating the temperature dependence
of the cell voltage of the same membrane-electrode assembly. Cell voltage, which stood
at 1.94V at 25degree for a current density of 1A/cm2, changed to 1.70V at 80degree.
This suggests that operation at higher temperatures could be quite effective.
The authors then test-produced membrane-electrode assemblies with varied
quantities of iridium oxide and measured their respective cell voltages. Fig.7
indicates the results, which clarified that loading the catalyst by over 2 to 3 mg/cm2
reduces cell voltage, while cell voltage rises at 2mg/cm2 or less of catalyst.
The authors of this report test-produced membrane-electrode assemblies with
platinum-black anodes and iridium oxide cathodes using the hot-press method, and
compared their cell voltages. This experiment verified the excellent characteristics
of the assemblies fabricated by hot-press method.
ACKNOWLEDGEMENT
this work was performed as a R&D program of the New Energy and Industrial Technology Development Organization(NEDO) under the WE-NET Project of the Agency of Industrial Science and Technology, MITI.
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