Local Coordination and Reactivity of a Pt Single-Atom Catalyst as Probed by Spectroelectrochemical and Computational Approaches

Abstract

The interaction between isolated transition-metal atoms and neighboring dopants in single-atom catalysts (SACs) plays a key role in adsorption strength tuning and catalytic performance engineering. Clarifying the local coordination structures of SACs is therefore of great importance and yet very challenging at the atomic level. Here, we employ a SAC with isolated Pt species anchored on nitrogen-doped carbon as a prototype and investigate the local coordination environment around Pt sites with the CO probe molecule by combined electrochemical infrared (IR) spectroscopy and density functional theory calculations. Two types of Pt coordination structures are clearly revealed, involving a Pt–C moiety with weak CO binding and a pyrrolic Pt–N–C moiety with strong CO binding, highlighting the Pt local coordination structure-dependent CO binding strength. This inventory then allows a comparative COad electrooxidation mechanism study on an identified pyrrolic Pt–N–C moiety of the Pt SAC and a bulk Pt surface toward the feedback loop between theory and experiment. A much higher coupling barrier for COad and OHad is noted on the simulated Pt–N–C site than that on Pt(111), making the Langmuir–Hinshelwood pathway kinetically unfavorable on the Pt SAC. In contrast, a lower theoretical limiting potential is predicted for CO oxidation on pyrrolic Pt–N–C with free H2O in favor of the Eley–Rideal pathway and qualitatively agrees with the experimental kinetics. The present methodology may promote the understanding of the SAC structure–activity relationship and the discovery of novel SACs.