Researchers from IPEN in Brazil, Helmholtz-Zentrum Berlin (HZB) in Germany, and INRA in Canada have developed a novel composite membrane for direct ethanol fuel cells. A paper on their work is published in the Journal of Membrane Science.
Ethanol has five times higher volumetric energy density (6.7 kWh/L) than hydrogen (1.3 kWh/L) and can be used safely in fuel cells for power generation. Nissan, for one, is investigating the potential for ethanol-fueled solid-oxide fuel cells. (Earlier post.)
In Brazil in particular there is great interest in better fuel cells for ethanol as all the country distributes low-cost ethanol produced from sugar cane. Theoretically, the efficiency of an ethanol fuel cell should be 96%, but in practice at the highest power density it is only 30%, due to a variety of reasons.
A team led by Dr. Bruno Matos from the Brazilian research institute IPEN is therefore investigating novel composite membranes for direct ethanol fuel cells. A promising solution is tailoring new polymer-based composite electrolyte materials to replace the state-of-the-art polymer electrolyte such as Nafion.
Matos and his team used a melt-extrusion process to produce the composite membranes of Nafion and titanate nanotubes functionalized with sulfonic acid groups for testing in a direct ethanol fuel cell.
The membrane consists of Nafion with embedded titanate nanotubes. Credit: B.Matos/IPEN
At the BESSY II ring at HZB, they were able to observe in detail how the nanoparticles in the Nafion matrix are distributed and how they contribute to increase proton conductivity.
Matos’ team has now thoroughly analysed four different compositions of Nafion composite membranes at the infrared beamline IRIS at BESSY II. Small-angle X-ray scattering measurements confirmed that the titanium particles were synergistically interacting with the ionomer matrix of Nafion.
Using infrared spectroscopy, they observed that chemical bridges were formed between the sulfonic acid groups of the functionalized nanoparticles. In addition, by following the proton motion along the ionic clusters, they found increased proton conductivity in the composite membrane, even at high concentrations of nanoparticles.
“This was a real surprise that we didn’t expect,” Dr. Ljiljana Puskar, HZB-scientist at the IRIS-Beamline said. The reduction of the conductivity with the increment of the nanoparticles is one of the main hurdles delaying the development of high-performance composite materials. The higher proton conductivity could allow better charge carrier mobility and thus increase the efficiency of the direct ethanol fuel cell.
B.R. Matos, C.A. Goulart, B. Tosco, J.S. da Silva, R.A. Isidoro, E.I. Santiago, M. Linardi, U. Schade, L. Puskar, F.C. Fonseca, A.C. Tavares (2020) “Properties and DEFC tests of Nafion - Functionalized titanate nanotubes composite membranes prepared by melt-extrusion,” Journal of Membrane Science, Volume 604 doi: 10.1016/j.memsci.2020.118042.