4. Subtask 4 : Development of hydrogen production technology

4.1 R&D Goals

The study commenced development of element technology and large-scale cells (electrode area 2500cm²) with two methods (Electroless Plating, Hot-press) that have been selected after comparing the performance and future feasibility of four hydrogen-production methods that have been examined until now. Moreover, optimum conditions for the practical scale of hydrogen-production technology have been examined and its concept has been designed for the first time this fiscal year.

Furthermore, in research and development of high-temperature solid polymer electrolyte, a number of solid polymer electrolytes were synthesized and their characteristics were evaluated.

4.2 Results in fiscal year 1997

4.2.1 Development of Element Technology by Electroless Plating Method

1. R & D Goals

1. Electrode area expansion using the manufacturing process of membrane electrode assemblies by the porous-surfaced method
2. Evaluation of the manufactured large electrode area cell
3. Confirmation of durability

2. Examination of Manufacturing Process

Fig. 4.2.1-2 Cell Structure Model

1. Fabrication Process of Membrane
   A fabrication process of a new membrane by screen printing was examined in order to fabricate an even porous-surfaced membrane to cover a large area.
   1. Chosen concentration of iron particles in slurry was 10 to 30 vol%.
   2. Iron oxide has been chosen as a fusible metal type after considering industrialization.
   3. Optimum mesh for screen printing was examined.

2. Process of Membrane Assembling
   Assembling conditions by temperature and roll interval were evaluated.

3. Process of Electroless Plating
   A simple plating method called the hot dip coating method was examined with the aim of increasing capacity.

3. Evaluation of Large-scale Cell

1. System
   A large-scale testing device of the 2500cm² electrode area was fabricated to safely evaluate.

   Fig. 4.2.1-3 Test device of 2500cm² Cell

2. Electrolysis Data
   Evaluation data of the 2500cm² cell are as follows.

   Fig. 4.2.1-4 Examination of Electrolysis Temperature Changes

   Fig. 4.2.1-5 Current Density- Cell Voltage Characteristics

4. Evaluation of Durability

1. Nafion 112 (50mm、50cm²)

   Fig. 4.2.1-6 Durability Test of Nafion 112

2. Nafion 115 (125mm、50cm²)

   Fig. 4.2.1-7 Durability Test of Nafion 115

5. Conclusion

1. Examination of the fabrication method of slurry membranes, as well as examination of the assembling and plating methods of membranes were carried out. The manufacturing method of membrane-electrode assemblies by the porous-surfaced method was confirmed feasible at the level of 2500cm² electrode area.

2. New device for the evaluation of the manufactured large-area cell was fabricated, and the I-V properties were obtained. It was also confirmed that the manufactured 2,500cm² electrode area cell showed energy efficiency of 90%.

3. The cell with 50mm polymer electrolyte showed significant performance degradation and its energy efficiency was below 90% after 600 hours electrolysis test. Meanwhile, it was confirmed that the cell with 125mm polymer electrolyte continued to electrolyze as long as 4,000 hours and showed a little performance degradation although its initial performance was approximately 90%.

4.2.2 Development of Element Technology by the Hot-press Method

1. Development of Manufacturing Technology of Membrane-Electrode Assemblies

1. Improved Performance of Anode Catalyst
   Iridium dioxide powder was examined for the degree of purification and dispersion. A manufacturing method of anode catalyst with a high dispersion and high ratio surface area, which is suitable for manufacturing anode catalyst layer with even thickness and particle diameter was clarified.

   The electrolytic performance of a cell which used this catalyst and consisted of a 50mm solid polymer electrolyte membrane was greater than that of a cell which used conventional catalyst cell as shown in Figure4.2.2-1. For example, the energy efficiency was 96.7% at a temperature of 80°C and a current density of 1A/cm².

   Figure 4.2.2-1 Electrolytic Performance of Anode Catalyst

2. Examination of Forming Method of Polymer electrolyte membrane
   It was clarified that, in order to form an even polymer electrolyte membrane on the surface of catalyst particles in the electrode layer, the method in which polymer electrolyte solution which has its concentration and amount adjusted so that its supply is enough to fill the opening in the electrode layer is sprayed on the whole electrode area with an air brush, let it permeate into the electrode layer, and let it stand to dry naturally was suitable.

2. Examination of Durability

3. Development of Manufacturing Technology of Large-scale Cells

It is important for a large-scale cell to have the same high performance as a small cell such as electrolytic performance, electrical conductivity, close contact, and pure water supply and gas exhaust in the area in spite of its largeness and to make these properties uniform. In order to achieve this, development and improvement were pursued in methods of manufacturing (1) the catalyst layer of even thickness, (2) a membrane-electrode assembly with even assembling strength of catalyst and membrane by the hot-press device with a high precision in flatness and temperature, (3) the anode current collector made of a platinum plated titanium fiber sintered plate and the cathode current collector made of a gold plated stainless steel fiber sintered plate with even plating thickness and plate thickness, and (4) a titanium separator with high flatness and equipped with sufficient water passage grooves of the water supply and gas exhaust by the high-precision processing methods for cutting and grinding. High-performance materials among the above prototype cell materials were layered and made into a prototype cell.

Subsequently, cell evaluation device was designed and fabricated so that it could electrolyze up to a current of 10,000A and a voltage of 2V, and the evaluation of the prototype cell was carried out . As a result, under the conditions of a temperature of 80°C and a current density of 1A/cm², 50mm and 100mm polymer electrolyte membranes showed energy efficiency of 95.5% and 93.2% respectively, which exceeded targeted performance.

4.2.3 Conceptual Design of Hydrogen Production Plant and Feasibility Study

1. Conceptual Design of Hydrogen Production Plant

1. Standard Conditions
   Conceptual design was carried out under the following standard conditions shown in Table 4.2.3-1 and Table 4.2.3-2.

   Table 4.2.3-1 Plant Operating Conditions

   Hydrogen Generation	32,000 Nm3/h
   Electrode Area	1 m2/cell
   Current Density	3 A/cm2
   Temperature	120oC
   Pressure	4.0 kg/cm2G
   Cell Voltage	1.757 V

   Table 4.2.3-2 Configuration of Electrolytic Cells

   Total Number of Cells	2,600 cells
   Stack Configuration	130 cells/stack, 20 stacks
   Train Configuration	2 stacks (1 rectifier for 2 stacks)
   Total Number of Trains	10 trains
   Rectifier	5 sets (1 transformer + 2 rectifiers)

   Note: Cell voltage under each condition was calculated with a formula, which was induced from the multiple regression analysis, using the actual data each company obtained in 1996 regarding current density, membrane thickness, and temperature. Here, membrane thickness and gas temperature of hydrogen and oxygen were assumed 120mm and 40°C, respectively.

2. Plant Configuration and Arrangement
   The plant consists of 10 trains and common equipment such as pure water supplier, cooling tower and power receiving equipment. A train consists of electrolytic cells (2 stacks), separators and coolers for oxygen and hydrogen, coolers and pumps for circulation water and rectifiers. For safety, concentration of each gas, water level, and cell voltage are monitored and the overall operation is controlled by DCS.

3. Construction Cost of Plant
   The cost of plant construction under the above conditions was estimated to be \5,016 million in total with \4,661 million for equipment and \355 million for foundation and building. Here, a unit cost of an electrolytic cell is assumed as \1 million/m².

2. Feasibility Study

1. Variables and Their Variation Assumed
   Variables and their variation range are shown in Table 4.2.3-3.

1. Assumption in Fluctuation of Equipment Cost
   
   • The cost of a electrolytic cell is in proportion to the electrode area.
   • The costs of a rectifier and power receiving equipment are in proportion to the power for electrolysis required.
   • The cost of heat exchanger is in proportion to the heat-transfer area necessary for cooling O₂ and H₂ gases (both including steam), and for cooling circulation water under each condition.
   • The cost of the cooling tower is in proportion to the power of 0.7 of the total cooling quantity of heat.
   • The cost of foundation and building is in proportion to the plant area required.
   • An effect of fluctuation in operating pressure on the equipment cost is negligible (The cost remains up to approximately 5kg/cm²G).

2. Conditions and Results of Estimation of Hydrogen Production Cost
   Under the above conditions, the cost of hydrogen production was estimated. Fig.4.2.3-1 and Fig.4.2.3-2 illustrate the effects of power generation cost and electrolysis temperature on hydrogen cost. Those figures indicate that hydrogen cost fluctuates depending on each fluctuation factor. The most economical operating conditions and hydrogen cost under the conditions were shown in Table 4.2.3-4.

   Table4.2.3-4 Optimization of Hydrogen Cost and Operating conditions (Unit Price for Cell is \1 million/m²)

   Power Generation Cost (Yen)	2	3.5	5
   Current Density (A/cm2)	3.0	2.5	2.2
   Temperature (oC)	120	120	120
   Pressure (kg/cm2G)	4.0	4.5	5.0
   Hydrogen Cost (Yen/m3)	13.6	20.0	26.2

   Fig.4.2.3-1 Effect of Power Generation Cost on Hydrogen Cost

   Fig.4.2.3-2 Effects of Electrolysis Temperature on Hydrogen Cost

3. Conclusion

1. It is clarified from the results of feasibility study that it is necessary to design cells so that they can be operated at a pressure of 5kg/cm² and a temperature of 120°C.

2. The assumption that the unit area of a cell, the number of cells per stack and the unit price of a cell are 1m², 100 - 150 cells and \0.8 - \1.2 million/m², respectively, and that the unit price of a polymer electrolyte membrane and anode catalyst is 30% of the unit price of the cell must be justified and /or modified whenever the progress of various testing and cell design is to be reported by the company concerned.

3. It is assumed that the life of a polymer electrolyte membrane and anode catalyst is 8 years at a current density of 1A/cm², and it follows 8 years/ the half power of current density ratio at a higher current density. It is necessary to obtain some reference values from life tests of laboratory-scale cells in order to estimate the lives more accurately.

4. It is desired that economy of each elemental technology (the proportion of investment costs to energy saving effects) will be examined.

4.2.4 Research and development of high-temperature soild-polymer electrolyte

We have synthesized fluorinated high temperature polymers functionalized by sulfonic acid groups. These polymers have shown to have excellent high temperature stability, good film properties and proton conductivity approaching 0.1 S/cm at 200°C. The conductivity of SRI's newly developed polymers and Nafion are comparable at 80°C. However, while Nafion can not be operated for a long period of time at temperatures higher than 80°C, SRI's polymers have shown to be thermally stable up to 200°C and to have high proton conductivity. The conductivity of the best polymer electrolyte developed so far is compared to that of Nafion in Fig. 4.2.4-1.

Fig. 4.2.4-1 Polymer film conductivity as a function of temperature

During the past year, several monomers and polymers were synthesized and characterized. Aromatic fluorinated polymers were preferred for their high temperature stability as well as chemical stability under oxidizing conditions. Polymers with variable degree of sulfonation were prepared. The polymer film forming properties were optimized by tailoring the polymer structure.

4.2.5 Literature Survey on Water Electrolysis