Doping of Porous Transport Layers to Optimize Electrical Contact Behaviour in PEM Water Electrolysis Cells
Authors: Stein Lukas , Ismael Mohammed , Bensmann Boris , Hanke-Rauschenbach Richard 
Published: August 2024

A high overall efficiency is crucial for large-scale polymer electrolyte membrane water electrolysers. Due to the harsh environment at the anode, a titanium oxide layer with high electrical resistivity passivates porous transport layers (PTL). A common used way to overcome this problem is noble metal coating (e.g. with platinum, gold or iridium). [1] For the very first time, we present a new and inexpensive way of maintaining the high conductivity of PTLs by doping the titanium surface that faces the catalyst layer. Sun et al. [2] modelled the conductivity of doped titanium oxide for different elements. With respect to their results and Koech et al. [3] we chose tin, niobium, antimony and yttrium as dopants. The implantation was carried out at the Ion Beam Center of the HZDR in Dresden, Germany. All doped PTLs displayed a lower cell voltage than the undoped reference as visible in figure 1a). While tin improves in the range of 2-3 % at a current density of 2A/cm², the other dopants best results reach values of over 4 % with niobium achieving the best performance with 4.4 % improvement (see figure 1b) for comparison). Figure 1c) shows the high frequency resistance (HFR) originating from impedance measurements. The observable improvement of up to 11.4% at 2A/cm² proves the fact that the advantage corresponds to a better contact resistance due to a lower resistance of the doped titanium oxide layer. The improvement in percent presents figure 1d).
The measurement results show that doping can have a great impact on the contact resistance of titanium PTLs. These results open a new opportunity in the manipulation of porous transport layers for enhanced contact behaviour, where no experimental publications exist yet. Especially in comparison to noble metal coatings like iridium, doping has an enormous cost advantage when using non noble metals with the potential of lowering the overall electrolyser system costs while increasing its efficiency.
[1] Liu, C., Shviro, M., Gago, A. S., Zaccarine, S. F., Bender, G., Gazdzicki, P., Morawietz, T., Biswas, I., Rasinski, M., Everwand, A., Schierholz, R., Pfeilsticker, J., Müller, M., Lopes, P. P., Eichel, R.-A., Pivovar, B., Pylypenko, S., Friedrich, K. A., Lehnert, W., Carmo, M., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Adv. Energy Mater. 2021, 11, 2002926. https://doi.org/10.1002/aenm.202002926
[2] Hu Sun, Zhu-tian Xu, Di Zhang. First-principles calculations to investigate doping effects on electrical conductivity and interfacial contact resistance of TiO2, Applied Surface Science, Volume 614, 2023, 156202, ISSN 0169-4332, https://doi.org/10.1016/j.apsusc.2022.156202.
[3] Koech, R.K.; Ichwani, R.; Oyewole, D.; Kigozi, M.; Amune, D.; Sanni, D.M.; Adeniji, S.; Oyewole, K.; Bello, A.; Ntsoenzok, E.; et al. Tin Oxide Modified Titanium Dioxide as Electron Transport Layer in Formamidinium-Rich Perovskite Solar Cells. Energies 2021, 14, 7870. https://doi.org/10.3390/en14237870

Figure 1