Dec
22
A Better Membrane For Better Fuel Cells
December 22, 2016 | Leave a Comment
PFIA-molecules self-orient with their hydrophobic backbones outside (black lines) and their hydrophilic side-chains inside, in order to form nanometer sized water channels. Each side-chain possesses two docking points (red and yellow circles) for hydrogen ions (H+). These are acidic groups, shown in the magnifying glass. Image Credit: Heike Cords. HZB. Click image for the largest view.
The team’s research paper has been published in the journal Physical Chemistry Chemical Physics.
The HZB scientists are exploring water management in an alternative proton exchange membrane type, called PFIA. The experiments have been conducted using the infrared facilities of BESSY II synchrotron to reveal how water is retained even at dry conditions in PFIA. The observations explain why PFIA membranes are superior to the widely used NAFIONTM membranes at higher temperatures and low humidity.
Whereas PFIA has the same mechanically stable hydrophobic backbone, its hydrophilic side chains contain one more acidic site per each chain than in NAFIONTM. These additional acidic sites on each hydrophilic side chain provide additional protons for the proton transport and allow for the formation of larger water channels. Especially the water management in the PFIA membrane is of interest, since it is crucial for the performance of the fuel cell: in order to function it needs to be humid but never wet.
The science team at HZB analyzed PFIA membrane samples provided by 3M. They combined infrared spectroscopy methods at BESSY II and examined the samples in situ under different temperatures and humidity conditions. By means of statistical analysis and advanced mathematical evaluation of the data, they could deduce the sequence of molecular events connected to the loss of water and reconstruct how water is retained in the PFIA molecules.
Dr. Ljiljana Puskar, first author of the publication explained, “We wanted to better understand the behavior of water inside the nano-sized water channels of the proton exchange membranes, particularly during the transition to dryer conditions.” The experimental data reveal a huge difference in the water management between NAFIONTM and PFIA in low humidity conditions.
“We can clearly see that PFIA is better at both water retention and water uptake,” Puskar said. They could even deduce how water is retained in the PFIA membrane at dryer conditions: The multiple side chains of PFIA are ideally suited to host water molecules and give rise to the building of a hydrogen bonded network. “These experiments have provided a much better understanding of the water retention capability of PFIA membranes. This is very helpful for further optimization of such membranes to extend their operational area to higher temperatures and low humidity,” she said.
She is looking forward to further cooperation projects with 3M.
Prof. Emad Aziz, who is directing the HZB Institute of Methods for Materials development said, “This is a significant step forward in addressing the water management in an alternative proton exchange membrane type in collaboration with 3M company using the infrared facilities of BESSY II synchrotron. We are further expanding the capability of this excellent facility to allow for operando IR spectroscopy and microscopy and address a wide range of applications related to energy materials in operation.”
Its good to know what is actually going on to open the doors to optimization. So far its been go for it with not much idea of what is happening on the membrane. Now with a much more full understanding, progress can come much faster and better with most of the guessing gone and much better ideas can be executed with more precise experiments.
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