Synthesis of a Novel and Highly HOR/HER Selective Ru@Pt/TiOx/C Catalyst Exhibiting Strong Metal-Support Interactions (SMSI) for PEMFC Applications

One main goal in Proton Exchange Membrane Fuel Cell (PEMFC) research is to make Fuel Cell Electric Vehicles (FCEV) viable for long-haul travel and increase their durability. Besides many degradation modes which target different parts of a PEMFC such as the catalyst layer, the membrane, bipolar plates, and other components, one major concern is the start-up/shut-down (SUSD) of the cell, inducing degradation of the catalyst support on the cathode. Addressing this, two mitigation strategies are possible: a) the system approach, e.g., reducing number of damaging SUSD events; b) the catalyst approach, e.g., suppressing the Oxygen Reduction Reaction (ORR) activity of the anode. The latter is feasible by utilizing a highly selective HOR/HER (Hydrogen Oxidation/Evolution Reaction) catalyst on the anode side that catalyzes the HOR but has a poor ORR activity, a property that was reported for a Pt/TiO x /C catalyst by Stühmeier et al . [1,2] The high selectivity towards the HOR/HER is explained by the Strong-Metal-Support-Interaction (SMSI) formed between the Pt nanoparticles and the TiO x -support, where the support creeps over the particle during a reductive heat treatment, as observed in HR-TEM. [1] In general, the SMSI effect between a metal and a suitable metal support is found in various heterogeneous catalytic applications, altering the catalyst’s activity for various reactions. [3] In the particular case of Pt/TiO x /C, the SMSI layer forming on the Pt nanoparticle is said to be permeable for protons but impermeable for any other oxygen-containing species, explaining a still rather high HOR/HER activity compared to a Pt/C catalyst (≈ 30% vs Pt/C) and an ORR activity that is decreased by two magnitudes (≈ 2% vs Pt/C). [1] Such interaction was also observed by Stühmeier et al . between Ru and a TiO x -support, where similar trends were determined. However, since the intrinsic HOR/HER activity of a Ru catalyst is quite low compared to Pt, a Ru/TiO x /C catalyst is not feasible for PEMFC applications. [4] Ru@Pt core-shell particles, as shown by Schwämmlein et al ., exhibit a 3-5x higher HOR/HER activity compared to a Pt/C catalyst, making a Ru@Pt/C catalyst viable even for alkaline fuel cell applications. [5] Due to the already successfully explored interaction of Pt and Ru with a TiO x -support, we will examine the HOR and ORR activity of Ru@Pt/TiO x /C catalysts.. In this work we successfully synthesized a novel catalyst system by forming an SMSI between Ru@Pt core-shell particles and a TiO x -support. Via RDE (Rotating Disk Electrode) characterization, we elucidate if the Ru@Pt/TiO x /C catalyst gains all the benefits from the single parts of the catalyst, namely: i) a high HOR/HER activity from the Ru@Pt core-shell particles; ii) a low ORR activity due to the SMSI effect. Figure 1 shows the HOR/HER performance catalysts based on Ru@Pt particles supported on Vulcan carbon (black line) or on TiO 2 nanoparticles, whereby for the latter support the catalysts were either tested as-synthesized (red line) or after a reductive heat-treatment under 5% H 2 /Ar to induce SMSI effects (green line). Apparently, the SMSI layer on the Ru@Pt core-shell particles enable a sustained HOR/HER activity at > 1.0 V RHE , in contrast to the other two catalysts which show the typical decrease of the HOR/HER activity at high potentials. Similar observations had been made by Stühmeier et al. for a Pt/TiO x /C and Ru/TiO x /C catalyst. [1,2,4] The findings in this particular study with the TiO x -support, as an example, should serve as proof of principle to possibly translate the gained knowledge on different types of metal oxide supports, since the stability of TiO x is known to be limited under PEMFC operation. [2,6] References [1] B. M. Stühmeier, S. Selve, M. U. M. Patel, T. N. Geppert, A. Hubert, H. A. Gasteiger, H. A. El-Sayed, ACS Appl. Energy Mater. 2019 , 1–8. [2] B. M. Stühmeier, A. M. Damjanović, K. Rodewald, H. A. Gasteiger, J. Power Sources 2023 , 558 , DOI 10.1016/j.jpowsour.2022.232572. [3] C. J. Pan, M. C. Tsai, W. N. Su, J. Rick, N. G. Akalework, A. K. Agegnehu, S. Y. Cheng, B. J. Hwang, J. Taiwan Inst. Chem. Eng. 2017 , 74 , 154–186. [4] B. M. Stühmeier, R. J. Schuster, L. Hartmann, S. Selve, H. A. El-Sayed, H. A. Gasteiger, J. Electrochem. Soc. 2022 , 169 , 034519. [5] J. N. Schwämmlein, H. A. El-Sayed, B. M. Stühmeier, K. F. Wagenbauer, H. Dietz, H. A. Gasteiger, ECS Trans. 2016 , 75 , 971–982. [6] J. Zhang, F. Coms, S. Kumaraguru, J. Electrochem. Soc. 2021 , 168 , 024520. Figure 1