31-year-old Tonny Søndergaard has defended his PhD thesis at DTU Energy, "HT-PEMFC Durability and Lifetime," on how to ensure more stable fuel cells. Along the way he demonstrated the lowest degradation rate of high-temperature polymer fuel cells (HT-PEMFC) in the world.
Fuel cells convert the chemical energy stored in a fuel directly to electricity, exceeding the conversion efficiency of traditional technologies like generators and combustion engines.
Low temperature fuel cells use polymer membranes as the electrolyte, a key component of the cell. Normally, such fuel cells can use only pure hydrogen as fuel and operate at about 80 °C. However, a special type of polymer fuel cell, in which the polymer membrane is loaded with phosphoric acid, can operate at temperatures much higher than that, approx. 160 °C. Such high temperature polymer fuel cells (HT-PEMFCs) are much less sensitive to impurities in the fuel, making an otherwise cumbersome and expensive cleaning process unnecessary. DTU Energy has one of the world’s leading research groups on HT-PEMFC.
Tonny Søndergaard studied an important aspect of these cells in his thesis: how to ensure more stable HT-PEMFCs by optimizing the materials that make up the main components of the fuel cell, i.e. the electrodes and the electrolyte. To be able to investigate the stability, Tonny speeded up the degradation processes by stressing the cells, ramping up current density, gas flow rate and temperature.
By observing the degradation caused by the extreme operating conditions, Tonny could correlate the HT-PEMFC lifetime during steady state operation with a loss of phosphoric acid in the electrolyte. He concludes that some way of keeping the acid inside the membrane is necessary if the lifetime targets for stationary fuel cells are to be attained.
"I might be naïve but I do hope that my contributions make a difference for society, for the world or just for my neighbor. I feel that my work so far has done a difference, both in my former position as a PhD and as postdoc"
Tonny Søndergaard, former PhD student at DTU Energy, now postdoc at DTU Mekanik
Record low degradation rate
Tonny Søndergaard suggests that a promising option to decrease the loss of phosphoric acid is to employ a membrane based on a thermally cross-linked polybenzimidazole polymer, which has exceptional thermal and chemical stability. This is not new in itself, but Tonny subjected this type of membrane to a special heat treatment.
The treatment proved to have a significant positive effect on the lifetime of the fuel cells. In fact he obtained the lowest degradation rate in the world for this type of fuel cell.
Tonny also investigated other alternatives where cell degradation is hindered by using composite membranes.
Moisture creates reliable results
When you want to investigate degradation it is important that you evaluate the performance of the different components correctly. Tonny could show that the established method for evaluating catalyst durability yields dubious results for HT-PEMFCs when humidification of the cathode gas is omitted.
“This holds true regardless of the fact that water management is unnecessary for the actual operation of HT-PEMFCs”, says Tonny and emphasizes the need to humidify the gas supplied to the cathode if the results are to be representative and allow scientists reliable predictions of the electrode degradation.
After defending his PhD defense Tonny Søndergaard is now employed as a postdoc at DTU Mechanics.
"Right now, I'm involved in an Industrial project in collaboration with Elplatek, SiOx and Alfa Laval, where efforts are being made to reduce the release of copper and other metals from heat exchanger components and drinking water installations. I might be naïve but I do hope that my contributions make a difference for society, for the world or just for my neighbor. I feel that my work so far has done a difference, both in my former position as a PhD and as postdoc, and I’ll not write off the possibility that I might end up working with fuel cells again. Fuel cells have a huge potential, and I do know a thing or two about fuel cells after my thesis that might someday be of use”, says Tonny Søndergaard with a smile.