The Oxygen Reduction Reaction (ORR), wherein oxygen and protons are converted to water, is both a fundamental component of fuel cell electrochemistry and a model reaction for the study of nanoscale effects in electrocatalytic systems. In recent years, a substantial body of literature has accumulated that demonstrates how sophisticated nanoscale synthesis strategies can produce platinum-based electrocatalysts with superior activity for the ORR. Nonetheless, insights into how the various nanoscale features of the platinum nanoparticles influence the chemistry remain limited, and there is no general consensus on the ideal shape, or even size, of platinum particles. At the same time, recent advances in the molecular modeling of ORR reaction mechanisms, combined with improvements in computational power and machine learning-based techniques, have opened exciting new opportunities for elucidation of fundamental structure-activity-stability relationships for this reaction.<br/>In this talk, we will begin by briefly summarizing recent modeling efforts in our group, and others, relating to development of fundamental reactivity principles for the ORR. We will discuss existing theories of structure sensitivity for the reaction, including the effect of strain, and we will then demonstrate how surface-induced stress relaxation in atomically thin platinum and palladium nanosheets may be tuned to yield significant improvements in activity and stability of ORR catalysts. Next, we will describe how the presence of surface defects in nanoparticles, combined with stress-induced strain fields, can lead to hitherto unappreciated inhomogeneous reactivity patterns across platinum crystal surfaces, and we will explore how these new phenomena impact the reactivity of technical nanoparticles, as well. We will close by describing how recent advances in machine learning strategies for analyzing surface adsorption on structurally complex transition metal surfaces may lead to further advances in both fundamental understanding and practical performance of ORR electrocatalysts.

Nanoscale effects in oxygen reduction reaction electrocatalysis: The impact of stress relaxation on nanostructures and defects

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