Sphere-to-Multipod Transmorphic Change of Nanoconfined Pt Electrocatalyst during Oxygen Reduction Reaction.

An oxygen reduction reaction (ORR) catalyst/support system is designed to have Pt nanoparticles nanoconfined in a nanodimensionally limited space. Holey crumpled reduced graphene oxide plates (hCR-rGO) are used as a carbon support for Pt loading. As expected from interparticular Pt-to-Pt distance of Pt-loaded hCR-rGO longer than that of Pt/C (Pt-loaded carbon black as a practical Pt catalyst), the durability of ORR electroactivity along cycles is improved by replacing the widely used carbon black with hCR-rGO. Unexpected morphological changes of Pt are electrochemically induced during repeated ORR processes. Spherical multifaceted Pt particles are evolved to {110}-dominant dendritic multipods. Nanoconfinement of a limited number of Pt within a nanodimensionally limited space is responsible for the morphological changes. The improved durability observed from Pt-loaded hCR-rGO originates from 1) dendritic pod structure of Pt exposing more active sites to reactants and 2) highly ORR-active Pt {110} planes dominant on the surface.