Abstract: Platinum-based nanoalloys are efficient electrocatalysts for the oxygen reduction reaction (ORR). In situ/operando measurements have revealed that key properties including induced strain, chemical composition, coordination environment, evolve significantly during operation, which can hampertheir effective implementation in fuel cells. In fact, recent studies indicate that the impact of the early surface activation steps of Pt-based nanoalloys has been hitherto underestimated and is an important factor contributing to loss of their initial electroactivity. In this short perspective, we highlight the importance of in situ/operando characterization of Pt-based electrocatalysts during the initial operation steps in the ORR and discuss recent insights into their early degradation and evolution of their key properties during electrochemical characterization.

DOI: https://doi.org/10.1039/D4CP03665D 

Abstract: Proton exchange membrane fuel cells (PEMFCs) offer energy solutions of high efficiency and low environmental impact. However, the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode limit their commercialization. Pt-based electrocatalysts, particularly octahedral (oh)PtNi bimetallic catalysts doped with additional transition metals, stand out as promising candidates for enhancing ORR rates and overall cell performance. A key challenge in the development and validation of active oh PtNi electrocatalysts is the unsuccessful translation of laboratory-scale catalyst test results, typically assessed using the rotating disk electrode (RDE) method, to practical applications in membrane electrode assembly (MEA) for PEMFCs. Here, we consider a new family of Ir-doped octahedral ORR fuel cell catalysts with very high RDE-based Pt mass activities. First, we designed the catalysts and tuned the catalyst layer properties to achieve the new state-of-the-art performance for oh-PtNi catalysts in PEMFCs. Still, a significant decrease in relative performance with respect to Pt/C when transitioning from RDE into an MEA-based cathode environment was observed. Thus, to better understand this performance loss, we investigated the effects of ionomer–catalyst interactions by adjusting the I/C ratio, the effect of temperature by applying RDE under high temperature, and the effects of acidity and high current density by applying and introducing the floating electrode technique (FET) to shaped nanoalloys. A severe detrimental effect was observed for high I/C ratios, with a behaviour contrasting reference commercial catalysts, while the negative effect of high temperatures was enhanced at low I/C. Based on this analysis, our study not only demonstrates a catalyst with enhanced ORR activity and specifically higher electrochemical surface area (ECSA) among oh-PtNi catalysts, but also provides valuable insights into overcoming MEA implementation challenges for these advanced fuel cell catalysts.

DOI: https://doi.org/10.1021/acsami.4c11068