Solid Oxide Fuel Cells, Which May Play a Key Role in Cutting CO2 Emissions — DENSO’s efforts to address two issues to improve the environmental performance

Mr. Osugi of the Next-generation Fuel Cell R&D Dept. delivered a presentation about the need for solid oxide fuel cells (SOFCs) and how DENSO is improving their environmental performance.

May. 19, 2023

Takamasa Osugi
NEGP Development Dept.,Environment Neutral Systems Development Div.


Good evening. I will explain SOFCs. Let me introduce myself briefly. Since joining DENSO, I have been working in the non-automotive field, especially the development of housing-related products, so my career path is very rare at DENSO. Since 2019, I have been in charge of SOFC business planning.

What is an SOFC?

SOFC stands for solid oxide fuel cell, and is a device to generate electricity from hydrogen. The chemical reaction in SOFCs is the opposite of that in SOECs. Electricity is generated through the chemical reaction between hydrogen and oxygen.

There are various types of fuel cells. This slide shows a PEFC and an SOFC as examples. Because an SOFC uses a ceramic material for the electrolyte, it can operate at high temperatures of about 700°C, which means that the operating efficiency is high. Various fuels, such as hydrogen, city gas, and propane gas, can be used.

Why are SOFCs needed?

A hydrogen society will not be entirely powered by hydrogen. Hydrogen-derived fuels and various types of carbon-neutral fuels will be used until hydrogen comes into widespread use. So, SOFCs, which can be powered by various types of fuels, are expected to play a key role in reducing CO₂ emissions seamlessly toward a hydrogen society.

Let me explain why carbon-derived fuels, including city gas and biogases, can be used in addition to hydrogen. An SOFC incorporates a reforming system to convert various types of fuels into hydrogen, which is then used to generate power.

Two issues in improving the environmental performance of SOFCs

I mentioned at the outset that SOFCs have a high operating efficiency. We have been working to further improve environmental performance. I’d like to explain two main issues. (While pointing to the slide) The first issue is to reuse the fuel at the exit of a cell stack. This schematic diagram shows the process of power generation. A fuel is charged from the top, and electricity is generated in the white cylindrical cell stack. Ideally, when the hydrogen fuel input is 100, all of it should be used up in the cell stack to generate power, and there should be no hydrogen fuel remaining at the exit of the cell stack. However, the cell stack deteriorates if all the hydrogen is used, so it is controlled so as not to use up the fuel.

The ejector shown at the top of this diagram plays a key role. Derived from DENSO’s proprietary technology, it is a high-quality and highly reliable component that is also used in car air conditioners. The ejector recycles (recirculates) the unused fuel from the exit to minimize wasted hydrogen, thereby improving the power generation efficiency.

The second issue is to control the temperature to maximize the efficiency. SOFCs operate most efficiently in a certain temperature range. It is also crucial to attain a uniform and appropriate temperature.

To fully utilize the heat that is produced during power generation, we harness our thermal management technology to improve the durability. The whole company has worked to apply the technologies refined in the automotive field to other products.

DENSO’s goal

Finally, let me explain DENSO’s goal. In the graph on the left side of this slide, the power generation output is plotted on the horizontal axis, and the power generation efficiency on the vertical axis. The output and efficiency of large thermal power plants are plotted on the right side of this graph. We have been striving to downsize SOFCs, which generate power more efficiently than power plants, while continuing to raise the efficiency.We are about to start a demonstration evaluation by installing SOFC systems at DENSO plants.

Our future vision is shown on the right side of this slide. Carbon-neutral fuels will not become widely used any time soon, so the first step is to start saving energy by using highly efficient SOFCs. As carbon-neutral fuels spread, we will contribute to decarbonization and energy security by using the characteristics of a distributed power source. We hope to help create a “well-being cycle society” through the development of SOFCs.

On a final note, it is difficult to make a major leap forward toward carbon neutrality. We aim to help create a carbon-neutral world by maximizing energy conservation. Here is my message: Let’s create the future together through energy conservation and beyond!

That is all for my presentation. Thank you for your attention.

Learn more about SOFC, Please click below.