Viewing Fuel Cells with NMR

Kuniyasu Ogawa (Associate Professor, Department of Mechanical Engineering)

Fuel cells are anticipated as power generators with a low environmental impact. Residential fuel cells, such as Ene-Farm, serve the dual roles of a power generator and a water heater, and are beginning to see widespread adoption. Furthermore, their installation in automobiles is also advancing. The development of inexpensive and durable fuel cells that can maintain stable power generation is being actively pursued.

When operating a fuel cell in the laboratory, the output voltage, which had been stable just moments before, can suddenly drop sharply. Sometimes it recovers if you wait, while at other times, power generation may stop altogether. The instability of fuel cells arises from the way they are operated—specifically, from the failure to properly control the supply of gas and the amount of humidification to match the power generation state.

Understanding the power generation state inside the fuel cell can contribute to stable power generation. To this end, our laboratory is conducting research that involves inserting a small coil (Fig. 1) into the fuel cell as a sensor (Fig. 2) to acquire NMR signals from the polymer electrolyte membrane and measure water content and power generation distribution (Fig. 3). NMR is a measurement method that utilizes the phenomenon of nuclear magnetic resonance, receiving 43 MHz electromagnetic waves emitted from hydrogen nuclei with a small coil (Fig. 1).

Fig. 1: A small coil as an NMR sensor (inner diameter 0.6 mm, copper wire diameter 0.06 mm)

Fig. 2: Power generation test of a fuel cell with an inserted NMR sensor

Fig. 3: A fuel cell generating power while NMR measurements are being taken

There are many research reports on inserting thin wires into fuel cells to measure the temperature and impedance within the polymer membrane. In contrast, our laboratory inserts a small coil (Fig. 1) to acquire NMR signals. There are no other examples of such research, making this an original technology of our laboratory. Because it is original, all experimental equipment is handmade. Students draw plans in CAD, operate milling machines in the machine shop, and assemble the equipment. As one would expect from students in the Department of Mechanical Engineering, they are adept at fabricating equipment. As many as 32 small coils are inserted into the fuel cell and connected to cables with thin wires. By inserting 32 coils, we can obtain the spatial distribution within the fuel cell. However, the thin wires are prone to breaking and sometimes snap during experiments. When that happens, it is truly disheartening. When an experiment is successful and NMR signals are obtained, the students process the signals themselves to calculate the spatial distribution of water content and power generation current. There are no established methods (manuals) or software for this. This is because it is an original technology.

Students think for themselves, conduct experiments with their own handmade equipment, and move closer to their research goals. The process is not easy. It is a continuous process of trial and error. Things do not always go according to theory, and there are many times when what is on paper does not simply connect with reality. However, I believe that going through this process is crucial for transforming students' abilities into true competence.

I hope that our original technology will contribute to the stable power generation of fuel cells and to the improvement of our students' skills.