A Deeper Insight into Stability of Pt-Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

Abstract

One of the links in the chain of creating a carbon-neutral society is undoubtedly hydrogen-powered vehicles. However, due to a very high price of platinum (Pt), which is used as an electrocatalyst for the hydrogen oxidation reaction (HOR) at the anode, as well as the oxygen reduction reaction (ORR) at the cathode of the proton exchange membrane fuel cell (PEMFC), their massive production is still unfeasible. Moreover, a very slow kinetics of the ORR and consequently the need for larger quantities of electrocatalyst makes this issue even higher. Therefore, in the fuel cell community there is a lot of effort to reduce the use of Pt. The most promising solution on that path seems to be carbon supported Pt-based nanoalloys, where part of Pt is replaced by a less noble and at the same time less expensive metal (e.g. Co, Cu, Fe, Ni).1 Nevertheless, although the ORR activity of carbon supported Pt-based alloys has been extensively studied and already proven, their stability is still an unsolved area. Here will be presented the latest findings regarding the stability of the carbon supported intermetallic Pt-alloy nanoparticles (Pt-M/C, where M = Co, Cu or Ni) obtained by utilization of advanced, in-house designed methodologies such as the high-temperature accelerated degradation tests (HT-ADTs) and the high-temperature electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry (HT-EFC-ICP-MS).2,3 Whereas the former enables ADT to be performed in a liquid electrolyte half-cell using a standard rotating disk electrode at temperatures of up to 80 °C, the latter allows for precise (ppb range) time-temperature-and-potential resolved measurements of dissolution of metals. By simulating close-to-real operational conditions, these technologies enabled to show that in addition to the carbon corrosion, which follows the Arrhenius law and increases exponentially with temperature,3,4 also Pt dissolution, as well as less noble metal dissolution, increases with increasing temperature.2,3 However, with an increase in temperature, not only the dissolution of Pt, but also the rate of its re-deposition (due to the Ostwald ripening) is increased at the same time.2,3,5 Furthermore, the widening of the potential window results in an exponential growth of temperature impact on metals dissolution.2,3 These previous findings about the dependence of the stability of Pt and less noble metal on the temperature and potential window2 will be upgraded with new information about the impact of some other non-intrinsic as well as intrinsic properties on the stability of metal nanoparticles in the carbon supported Pt-nanoalloys. In other words, the effect of a different number of cycles of the degradation tests on the behavior of Pt and less noble metal in the operational potential window (i.e. 0.6-0.95 V) at the high temperature (60 °C) will be presented. In continuation, the influence of the type of crystal structure on the stability of Pt-alloy nanoparticles will also be discussed. References 1 L. J. Moriau, A. Hrnjić, A. Pavlišič, A. R. Kamšek, U. Petek, F. Ruiz-Zepeda, M. Šala, L. Pavko, V. S. Šelih, M. Bele, P. Jovanovič, M. Gatalo, N. Hodnik, iScience 2021, 102102.2 T. Đukić, L. J. Moriau, L. Pavko, M. Kostelec, M. Prokop, F. Ruiz-Zepeda, M. Šala, G. Dražić, M. Gatalo, N. Hodnik, ACS Catal. 2022, 12, 101–115.3 T. Đukić, L. Pavko, P. Jovanovič, N. Maselj, M. Gatalo, N. Hodnik, Chem. Commun. , DOI:10.1039/d2cc05377b.4 N. Maselj, M. Gatalo, F. Ruiz-Zepeda, A. Kregar, P. Jovanovič, N. Hodnik, M. Gaberšček, J. Electrochem. Soc. 2020, 167, 114506.5 A. Kregar, M. Gatalo, N. Maselj, N. Hodnik, T. Katrašnik, J. Power Sources 2021, 514, 230542.