Dynamics of Subnanometer Pt Clusters Can Break the Scaling Relationships in Catalysis

Scaling relationships in catalysis impose fundamental limitations on the catalyst maximal performance; therefore, there is a continuous hunt for ways of circumventing them. We show that, at the subnano-scale, scaling relationships can be broken through catalyst dynamics. Oxygen reduction reaction (ORR), which can be catalyzed by Pt nanoparticles, is used as our study case. Subnanometer gas-phase and graphene-deposited Pt _n cluster catalysts are shown to exhibit poor correlation between binding energies of the intermediates, O, OH, and OOH, involved in the scaling relationships for ORR. The effect is due to the highly fluxional behavior of subnanometer clusters, which easily adapt their structures to the bound adsorbates and varying coverage and in some cases even reshape the structure upon changing environment. This fluxional behavior is also commonplace for clusters and contrasts them to extended surfaces, suggesting that breaking scaling relationships is likely a rule more than an exception in nanocluster catalysis.