Summary Achieving highly active and stable oxygen reduction reaction performance at low platinum-group-metal loadings remains one of the grand challenges in the proton-exchange membrane fuel cells community. Currently, state-of-the-art electrocatalysts are high-surface-area-carbon-supported nanoalloys of platinum with different transition metals (Cu, Ni, Fe, and Co). Despite years of focused research, the established structure-property relationships are not able to explain and predict the electrochemical performance and behavior of the real nanoparticulate systems. In the first part of this work, we reveal the complexity of commercially available platinum-based electrocatalysts and their electrochemical behavior. In the second part, we introduce a bottom-up approach where atomically resolved properties, structural changes, and strain analysis are recorded as well as analyzed on an individual nanoparticle before and after electrochemical conditions (e.g. high current density). Our methodology offers a new level of understanding of structure-stability relationships of practically viable nanoparticulate systems.

The present research provides a study of carbon-supported intermetallic Pt-alloy electrocatalysts and assesses their stability against metal dissolution in relation to the operating temperature and the potential window using two advanced electrochemical methodologies: (i) the in-house designed high-temperature disk electrode (HT-DE) methodology as well as (ii) a modification of the electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) methodology, allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. While the rate of carbon corrosion follows the Arrhenius law and increases exponentially with temperature, the findings of the present study contradict the generally accepted hypothesis that the kinetics of Pt and subsequently the less noble metal dissolution are supposed to be for the most part unaffected by temperature. On the contrary, clear evidence is presented that in addition to the importance of the voltage/potential window, the temperature is one of the most critical parameters governing the stability of Pt and thus, in the case of Pt-alloy electrocatalysts, also the ability of the nanoparticles (NPs) to retain the less noble metal. Lastly, but also very importantly, results indicate that the rate of Pt redeposition significantly increases with temperature, which has been the main reason why mechanistic interpretation of the temperature-dependent kinetics related to the stability of Pt remained highly speculative until now.

Pt-alloy (Pt–M) nanoparticles (NPs) with less-expensive 3d transition metals (M = Ni, Cu, Co) supported on high-surface-area carbon supports are currently the state-of-the-art (SoA) solution to reach the production phase in proton exchange membrane fuel cells (PEMFCs). However, while Pt–M electrocatalysts show promise in terms of increased activity for oxygen reduction reaction (ORR) and, thus, cost reductions from the significantly lower use of expensive and rare Pt, key challenges in terms of synthesis, activation, and stability remain to unlock their true potential. This work systematically tackles them with a combination of electrocatalyst synthesis and characterization methodologies including thin-film rotating disc electrodes (TF-RDEs), an electrochemical flow cell linked to an inductively coupled plasma mass spectrometer (EFC-ICP-MS), and testing in 50 cm 2 membrane electrode assemblies (MEAs). In the first part of the present work, we highlight the crucial importance of the chemical activation (dealloying) step on the performance of Pt–M electrocatalysts in the MEA at high current densities (HCDs). In addition, we provide the scientific community with a preliminary and facile method of distinguishing between a “poorly” and “adequately” dealloyed (activated) Pt-alloy electrocatalyst using a much simpler and affordable TF-RDE methodology using the well-known CO-stripping process. Since the transition-metal cations can also be introduced in a PEMFC due to the degradation of the Pt–M NPs, the second part of the work focuses on presenting clear evidence on the direct impact of the lower voltage limit (LVL) on the stability of Pt–M electrocatalysts. The data suggests that in addition to intrinsic improvements in stability, significant improvements in the PEMFC lifetime can also be obtained via the correct MEA design and applied limits of operation, namely, restricting not just the upper but equally important also the lower operation voltage.

Pt-alloy (Pt-M) nanoparticles (NPs) with less expensive 3d transition metals (M = Ni, Cu, Co) supported on high surface area carbon supports, are currently the state-of-the-art (SoA) solution to reach the production phase in proton exchange membrane fuel cells (PEMFCs).1 However, while Pt-M electrocatalysts show promise in terms of increased activity for oxygen reduction reaction (ORR) and thus, cost reductions related with a significantly lower use of expensive and rare Pt, many key challenges remain at unlocking their true potential.This work systematically tackles several of these key challenges with a combination of electrocatalysts synthesis and characterization methodologies, namely thin-film rotating disc electrode (TF-RDE), electrochemical flow cell coupled to inductively coupled plasma mass spectrometer (EFC-ICP-MS) as well as the membrane electrode assembly (MEA). For instance, intermetallics as a sub-class of Pt-M electrocatalysts, holds promise at improving their intrinsic stability, however, usually at the sacrifice of the electrochemically active surface area (ECSA). In relation to this, we show a production pathway based on the proprietary double passivation with galvanic displacement (GD) method 2,3 as an intrinsically better methodology for deposition of Pt NPs, combining both the intermetallic structure and very high ECSA in the same electrocatalyst material. This is possible due to the intrinsically better mechanism of Pt NP deposition on carbon substrates. Whereas Pt NP synthesis and deposition is sequential in nature (2. step process) when using conventional deposition methods, in the case of double passivation with GD method Pt NPs crystallize directly out of the carbon support and combining these two crucial steps into a single one (Scheme 1). Secondly, we highlight the decisive importance of the chemical activation (de-alloying) step on the performance of Pt-M electrocatalysts in the MEA, namely at high current densities (HCDs). In addition, we provide the scientific community the necessary tools to properly evaluate their suitability of de-alloyed (chemically activated) Pt-M electrocatalysts using a much simpler and affordable TF-RDE methodology by using the well-known CO-electrooxidation. References: L. J. Moriau et al., iScience, 102102 (2021).M. Gatalo et al., Angew. Chemie, 131, 13400–13404 (2019).M. Gatalo, N. Hodnik, M. Gaberšček, and M. Bele, PCT/EP2020/057334 (2020). Figure 1