Catalytic current mapping of oxygen reduction on isolated Pt particles by atomic force microscopy-scanning electrochemical microscopy

A fundamental understanding of active oxygen reduction sites on individual Pt nanoparticles is essential for the efficient utilization of Pt particles in electrocatalytic reactions. Here we use a modified Atomic Force Microscopy-Scanning Electrochemical Microscopy (AFM-SECM) to measure catalytic current responses of individual Pt particles on a nanometric scale. The ORR activity of an individual unsupported Pt nanoparticle and carbon-supported Pt aggregates at different ORR reduction potentials were mapped using a 50 nm diameter Pt wire electrode embedded in a SiO₂ tip, positioned at a ˜4 nm working distance above the surface. In this work, both the oxygen reduction and peroxide generation active sites were identified by performing electrochemical current mapping on the same Pt nanoparticle. The implications as well as the limitation of this new catalytic study approach is discussed based on the model of O₂ reduction.