Transport in the fuel cell, innovative battery system technology und electrically conductive plastics: Three concepts for alternative drive energies.
Transport in the fuel cell
The fuel cell is becoming an increasingly important drive type in the automotive sector, and, for heavy vehicles too, it is an attractive alternative to purely battery-powered drive systems. However, fuel cells need to achieve high levels of efficiency and a long service life at low cost to be able to survive in the competitive environment of the automotive industry.
That is why Cynthia Michalkowski, a Doctoral Researcher at the Department of Hydromechanics and Modelling of Hydrosystemsis working on modelling fuel cells at the Sonderforschungsbereich 1313 "Interface-Driven Multi-Field Processes in Porous Media – Flow, Transport and Deformation” Collaborative Research Center. "The polymer electrolyte membrane (PEM) fuel cell consists of several porous layers all with extremely diverse properties," explains Michalkowski. These individual cells are also interconnected in fuel cells in a similar way to car batteries. The individual cells, each of which produces a voltage of up to 1.2 volts, are connected in series to achieve a higher voltage, thus forming a fuel cell stack, which is the central element in the fuel cell system.
This can be researched at different levels, of which the pore scale is the smallest unit for fluid transport processes: "You zoom into a cell at the pore scale and observe the interaction between individual pores, where the transport processes take place, in detail," Michalkowski explains.
The fuel cell stack is the central element in the fuel cell system.
Cynthia Michalkowski, Doctoral Researcher at the Department of Hydromechanics and Modelling of Hydrosystemsis
A sophisticated water management system is crucial for optimizing a PEM’s operating conditions, which is why Michalkowski is trying to understand the water transport mechanisms through the cell components. "I analyze the water transport from the water-repellent gas diffusion layer into the water-attracting gas distributor, whereby I first consider the interaction processes at the pore scale. I want to discover the dominant processes at the interface and how I can represent them in an efficient PEM fuel cell model."
Innovative battery system technology
The development potential of battery systems for electric vehicles is greater at the battery system level than at the cell level. This is especially true of lithium-ion batteries, whose gravimetric energy density, which indicates how much energy can be stored per battery weight unit, is particularly high.
Currently, gravimetric energy density losses from the cell, the smallest single electrochemical element, to the battery system as a whole amounting to about half of the value are still typical. This is particularly true of batteries used in purely electric vehicles, as it still takes maximum effort to protect, package and cool the cell. But what this also means is that there is a high potential to increase the energy density at the storage level.
Maximum energy density at the battery level through clever construction. And: repairs are the best form of recycling.
Prof. Peter Birke, Institute for Photovoltaics
Consequently, Peter Birke, Professor of Electrical Energy Storage Systems at the Institute for Photovoltaics, is looking into the idea of cutting a thread in one pole of a cylindrical cell, which would allow the cell to be used like a screw. The contact to the other pole would be achieved via the pressure of the screwed cell. Therefore, as with spark plugs, no complex welding for creating the contact is needed to obtain a functioning system. "The connection technology is stilldesigned to enable the simple, non-destructive dismantling of the Li-ion cells," Birke continues, adding that This creates the best possible conditions for them to be recycled.
Birke is also testing whether modules could be easily dismantled for charging purposes, which would make it possible to simply take parts of the battery into your home and charge them via the power outlet. The modules are designed as low voltage (LV) modules, so the voltage is low enough to allow for safe charging. Birke's vision for the mobility of the future is: "Maximum energy density at the battery level through clever construction. And: repairs are the best form of recycling."
Electrically conductive plastics
The fundamental transition of our energy supply system towards renewable energies requires efficient secondary energy storage systems. Fuel cells are a promising solution for energy transition. Prof. Bernd Gundelsweiler and Thomas Litwin of the Institute of Design and Production in Precision Engineering are conducting research into temperature controls for thermally and electrically conductive plastics, the so-called graphite compounds, an ideal material for bipolar plates in fuel cells.
"A novel manufacturing process for bipolar plates was developed in the course of this research project, which was funded by the German Federal Ministry of Education and Research," Gundelsweiler explains. The process of inductive hot pressing in concrete molds was developed by combining the interdisciplinary research areas of the various project partners. The compound, which is initially still in powder form, is heated inductively and pressed into the mold. Among other things, this process is impressive because of a significant reduction in the production cycle from 20 to about five minutes as well as the improved quality of the bipolar plates.
Editor: Carina Lindig
- Prof. Peter Birke, Institute for Photovoltaics, e-mail, phone: +49 711 685-67180
- Prof. Bernd Gundelsweiler, Institute of Design and Production in Precision Engineering, e-mail, phone: +49 711 685-66401