| Popis: |
Achieving highly active and stable oxygen reduction reaction (ORR) performance at low platinum-group-metal (PGM) loadings remains one of the grand challenges in the proton-exchange membrane fuel cells (PEMFCs) community. Currently, state-of-the-art electrocatalysts are high-surface-area-carbon-supported nanoalloys of platinum (Pt) with different transition metals M (M = Cu, Ni, Fe, Co, etc.). Nevertheless, despite years of focused research, the established structure-property relationships are not able to explain and predict the electrochemical performance and behaviour of the real nanoparticulate systems. Unlike the perfect core-shell systems, usually used to model the observed behaviour of the electrocatalysts by the community, nanoparticles in real nanocatalysts exhibit much greater local atomic-scale structural complexity. Structure-property relationships addressing averaged material properties, such as the actual ORR activity and metal degradation (e.g. dissolution) behaviour, are at risk of oversimplifying the underlying phenomena when they rely on top-down characterization techniques and attribute averaged affects to idealized nanoparticle structures. In this work, we reveal the complexity of commercially available Pt/C and Pt-M/C electrocatalysts and discuss the relevance of understanding their stability behaviour in fuel cell systems. We expose the limitations of the established top-down characterization methodologies for studying degradation and provide a conceptual approach that offers a new dimension and transcends the limits of conventional structure-stability studies. We outline a bottom-up approach where atomically resolved properties, structural changes and strain analysis are recorded as well as analysed in great detail on an individual nanoparticle. While fundamental, this approach addresses the complexity of practical electrocatalysts and enables studying their stability when exposed to realistic electrochemical conditions (i.e. high current density). This methodology, in our opinion, offers the new level of understanding structure-stability relationships of practically viable nanoparticulate systems. |
