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

Scaling relationships in catalysis impose fundamental limitations on the catalyst maximal performance, and so 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 Ptn cluster catalysts are shown to exhibit poor correlation between binding energies of molecular fragments, O, OH, and OOH, involved in the linear 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 completely changing the structure upon changing environment. The change in the catalyst geometry changes the binding sites leading to the poor correlation between the binding energies. This fluxional behavior is also very common for clusters, and contrasts them to extended surfaces, and that suggests that breaking scaling relationships is likely a rule more than an exception in nanocluster catalysis.