Non-noble metal-based nano wire networks as novel support-less catalyst structures in alkaline fuel cells
Final Report Abstract
In collaboration between AG Ensinger (nanomaterials synthesis) and AG Roth (electrochemical process engineering) 1D and 3D Ni and Ni-Pd nanowire structures have been synthesised and up-scaled for their implementation as non-precious metal support-free bulk structures into AEMFC. These structures could be tailored in a wide variety and are active and stable electrocatalysts for ORR and alcohol oxidation. A suitable AEMFC set-up has been built and commercial Pt catalysts tested. Detailed results of AG Roth: The initially determined specific activity at -0.03 V shows that the Pt ORR activity is around 40 times higher than for the Ni catalyst. However, upon detailed analysis of polarisation curves using the new concept of differential Tafel plots (DTP), we found that at -0.03 V there is also a significant influence of the charging current and, hence, the specific activity measured at this potential is not a reasonable value. The region of constant α in the DTP is the region where the specific activity should be determined. Considering this, the specific activity of Pt depending on the overpotential is about 100 to 150 times higher than the synthesized Ni catalyst. However, considering that the operating range of fuel cells ranges between 0.6 and 0.7 V, there is a penalty of 150-200 mV in overpotential. Considering the cost benefits, this lesser performance is acceptable on the device level. While the electrochemical characterisation of Ni nanowires in the three-electrode set-up was successful, the up-scaled version of these catalysts could not be implemented in the AEMFC due to operational problems. As we have seen in WP 2, because of two opposing factors, i.e. water diffusion and electroosmotic drag, it is very difficult to obtain a stable performance. In PEMFC, only the excess water needs to be flushed out of the cathode for stable operation. In AEMFC, however, all the water transport must be balanced precisely at every current value. For example, for a stable performance at a given current, the water flux from anode to cathode should be higher or equal to the water flux from cathode to anode due to the electroosmotic drag. In our study, we have used Fumatech FAA membranes which have a low diffusion coefficient of water and high electroosmotic drag coefficient. This resulted in anode flooding in our experiments, which kept us from further testbench tests of our tailored non-precious metal catalysts.
Publications
- Behaviour of Pt, Ni, Pd and Glassy Carbon in Alkaline Media for Application in Alkaline Membrane Fuel Cell, 69th Annual Meeting of the International Society of Electrochemistry, Bologna, Italy, 02. – 07.09.2018
Khadke, P., Tichter, T., Boettcher, T., Muench, F., Ensinger, W., Roth, C. Tafel
- Analysing the performance instability of H2-O2 Alkaline Membrane Fuel Cell due to water imbalance, GDE Magdeburg Magdeburg, 23.-25.09.2019
Khadke, P., Güler, U., Boettcher, T., Muench, F., Ensinger, W., Roth, C.
- A simple and effective method for the accurate extraction of kinetic parameters using differential Tafel plots. Sci Rep 11, 8974 (2021)
Khadke, P., Tichter, T., Boettcher, T. et al.
(See online at https://doi.org/10.1038/s41598-021-87951-z) - Electrodeposition of palladium-dotted nickel nanowire networks as a robust self-supported methanol electrooxidation catalyst. J Mater Sci (2021)
Boettcher, T., Stojkovikj, S., Khadke, P. et al.
(See online at https://doi.org/10.1007/s10853-021-06088-6)
