HIGH PERFORMANCE SOLID POLYMER ELECTROLYTE WATER ELECTROLYZER BY HOT-PRESS METHOD

Abstract

Fuji Electric Corporate Research and Development , Ltd. has been developing technologies for high performance solid polymer electrolyte water electrolyzers. In term of technical features, Fuji Electric's technological approach call for membrane-electrode assemblies to be formed by a hot-press method. In term of development activities, we have constructed a cell with 200cm² membrane-electrode assemblies by the hot-press method, and obtained 93.7% of high energy efficiency for 1A/cm² at 80degree with the 200cm² cell. Based on the results of this study, we have developed a 5-cell stack with the 200cm² membrane-electrode assembly, that registered 7.917V of low stack voltage and 92.8% of high energy efficiency for 1A/cm² at 80degree under atmospheric pressure.

1. INTRODUCTION

Electrode area >10,000cm²
Current density 1�`3 A/cm²
Energy efficiency >90%

To achieve those specifications, elemental technologies have been developed since 1994. We have been investigating technologies of support collectors to minimize IR drops of cells and technologies of manufacturing membrane-electrode assemblies by a hot-press method to decrease electrolysis voltage.
In the hot-press method, a catalyst film is superposed over an ion-exchange membrane, and the catalyst film is combined with an ion-exchange membrane by means of hot-pressing. This technique comes with the following features.

(1) Different types of catalysts, including oxides, can be used.
(2) Three-dimensional electrode membrane interface can be achieved.
Recently we have developed a 200cm² single cell and a 200cm²,5-cell stack. This paper presents the test results of the cell and the stack.

2. EXPERIMENTAL

Structure of 5-cell stack
Figure 2 shows a schematic of a developed 5-cells stack of bipolar type which electrode area is 200cm². A picture of the stack is shown in Figure 3.
A bipolar plate is a titanium plate with grooves of 2mm wide 2mm deep machined in parallel at a pitch 8mm on both side.
Figure 4 shows the flow of pure water in the stack. Pure water was supplied to both anode water inlet and cathode water inlet, and was vented from both anode outlet and cathode outlet

Cell and stack operating system
Figure 5 shows a schematic diagram of a cell and stack operating system. The cell and the stack were operated under constant electrolysis condition of temperature, pressure, and current density. Consequently the performance of the cell and the stack was evaluated from voltage and the volume of generated hydrogen. The cell and stack operating system was operated according to the step described below.

I. Pure water was supplied from a reserve tank into a cell, which was kept at fixed temperature with a heater and a controller.
II. Constant current was applied to cell frames with a DC power supply.
III. Cell voltage or stack voltage were measured with a voltage meter. The volume of generated hydrogen of the cell was measured with a fine membrane gas flow meter, and the volume of generated hydrogen of the stack was measured with a accumulative gas meter.

Membrane-electrode assemblies
The membrane-electrode assemblies used for the experiments were manufactured through the following process shown in Figure 6.

(1) Preparation of a 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, then hot-pressing.

Table 1 shows the details of the membrane-electrode assemblies used for the experiment. Performance measurement of cell and stack
Under the electrolysis condition of 80degree and atmospheric pressure, the voltage and the volume of generated hydrogen were measured at various current densities using the operating system illustrated in Figure 5.

3.RESULTS

4. CONCLUSION

5.ACKNOWLEDGEMENT

REFFERENCE