Our Stories 06 Development of SOFC

Story 06Substantial contribution to hydrogen society by developing next-generation residential fuel cells.

Fuel cells is to generate electricity and heat through electrochemical reactions.
Fuel cells are excellent generation systems that have high overall energy efficiency with less energy loss in generation and transmission. Fuel cells can generate on site without relying on large power plants or transmission systems, and the heat produced during power generation can be used. But these cogeneration systems have been adopted for practical use slower than expected. The key issues are cost and durability.
NGK SPARK PLUG CO., LTD. considers the contribution to the upcoming hydrogen society with its business theme for a long time, and has introduced the current project of "cell stack" development that generates electricity in Solid Oxide Fuel Cell (SOFC). The project is now progressing steadily toward practical applications.

Ono:He is in charge of cost reduction and downsizing as well as adjustment of SOFC in accordance with both high generation efficiency and durability.

SOFC with fully implemented ceramic technologies is a key for deployment of residential fuel cells.

We need to overcome barriers in order to deploy residential fuel cells for practical use.

Because of the concerns associated with global warming and energy conservation at home, more and more of households are using residential fuel cells. However as of May 2015, the total number of fuel cells used by Japanese households was only 125,000. SOFC is anticipated to solve the problems of promoting fuel cells.

NGK SPARK PLUG CO., LTD. has developed SOFC for various applications. Especially "flat plate SOFC" is highly anticipated to be used at homes. Here, we briefly introduce its structure.

The unit called "cell stack" is formed in electrolyte by superimposing "generation cells" that are flat and composed of air electrodes and fuel electrodes. The cell stack formed with stacked planer cells has the characteristics of high output density and generation efficiency even in small spaces.

"Polymer Electrolyte Fuel Cell (PEFC) has been leading the residential fuel cell market so far. PEFC is a system that uses polymer membrane as electrolyte, and hydrogen ions move through the electrolyte to react with oxygen. On the other hand, SOFC causes reaction between oxygen and hydrogen by flowing oxygen ions through electrolyte that is made of ceramics," Ono explains.
Generally, generation efficiency of PEFC is 35% to 45%, and the one of SOFC has reached 45%. Ono and his team members aim more to surpass this efficiency target. The higher power generation efficiency is achieved, the lower running cost is realised. They need to exhibit attractive performance for consumers in order to adopt SOFC in large-scale.

Utilizing core technology to satisfy both high generation efficiency and durability requirements.

While many manufacturers engage in cost reduction with higher durability as well as downsizing of stack cell of SOFC to achieve large-scale adoption, the team is required to enhance the strength of ceramic technology that they have developed.
Ono says, "SOFC will promote the use of residential fuel cells. We cannot compromise on the development. It is always extremely challenging and severe to assure quality that satisfies the market's requirements in the very limited time available. Despite the harsh conditions, we are delighted to continue working hard on development of SOFC in order to achieve results."

Downsizing and high generation efficiency of a cell stack are already achieved by development of element technology that can generate larger amount of power with smaller power generation cells. Advanced technology is required to laminate ceramic layers, and the team utilizes, in the heart of fuel cells, high-functional ceramic technologies that NGK SPARK PLUG CO., LTD. has developed for mass production of zirconia oxygen sensors for automobile. The cell stack consists of metal and ceramic. They also utilize NGK SPARK PLUG's core technologies in bonding between metals and ceramics as well as in control technology that manages the whole cell stack.
"SOFC is the compilation of various core technologies of NGK SPARK PLUG CO., LTD.," Ono proudly states.

However, harsh environments such as operating temperatures between 700 and 1,000 degrees Celsius can damage the electrolyte, electrode or the whole cell stack.

They had to build the system that could ensure durability against 90,000 hours or 10 years of use, which is the standard for adoption in order to put fuel cells into practical applications at home.

A system that can ensure and secure durability is the key for practical use.

An experiment on durability is more difficult than development of materials and element technologies.

Before adopting practical applications, durability should be achieved against 90,000 hours or 10 years of use even though it shows high generation efficiency in laboratory. "We cannot actually conduct the experiment of 90,000 hours or 10 years. We aimed to establish the experimental techniques and equipment to evaluate if the component has the same level of durability against degradation of 90,000 hours or 10 years of use," Ono says.
However, some even said that it was almost impossible to evaluate durability against tens of thousands of hours of use in a short time.

SOFC is a new technology that is still in development stage among manufacturers. Therefore, it has no international standard to evaluate degradation by 90,000 hours or 10 years of use in a short time. In a situation where no method to ensure durability existed, it seemed to be hard to achieve any certification. But Ono and his team still consider the task as challenging and valuable.

"Accelerated aging test would shorten test cycle time. It would allow us to try various materials and we would be able to see result faster. As an engineer, it was my great pleasure to develop a product that didn't exist in the world and to establish a new standard."

Then, they decided to improve durability against degradation caused by factors that negatively affect the properties of generation cells and to establish the evaluation of the effect. As a result of trial and error, they confirmed the effect at desk test and introduced a method to test durability with using actual cell stack.
"Focusing on what no one has ever focused on, and creating a result." This was their answer.

Ono and his team have continued development in collaboration with external research institutions including Next-Generation Fuel Cell Research Center in Kyushu University which leads Japan in research for realizing hydrogen society. Especially in the development of SOFC, they are working more closely with them, and they vigorously conduct evaluation experiments with utilizing the fuel cell research center facilities on Ito Campus at Kyushu University.

To contribute to the coming hydrogen society and protect the mother earth.

"Power generation systems are excellent, but expensive." This would be the general opinion.
The price of residential fuel cells of PEFC is from one million yen to two million yen even when a consumer receives public subsidies. Practical achievements of high-performance and low-cost SOFC are becoming more necessary for further adoption of residential fuel cells.

Unlike internal combustion engine, fuel cells generate electricity by chemical reaction between hydrogen and oxygen. Ono says, "We can gain high energy by using chemical reaction that everyone knows. We are very proud of releasing such a product. We would like to have prospects to achieve higher durability and lower cost as soon as possible."

But Ono's team is not the only one who faces challenges toward the realization of a hydrogen society. NGK SPARK PLUG CO., LTD. has also developed mass production technology of cylindrical SOFC which is expected to be used at factories, buildings and power plants.

All members including Ono's team hope that SOFC will be the pillar of the company's future business and will make a further contribution to prevent global warming. The large-scale adoption of fuel cell has just started with various challenges and extensive experiments.