(Invited) Coupling of Electrochemistry with Surface Science and Computational Modeling to Understand Nanoparticle Electrocatalysts

Abstract

We investigated nanoparticle electrocatalysts in oxygen evolution reaction (OER) and CO2 reduction reaction (CO2RR) via an approach coupling electrochemistry with ultra-high vacuum (UHV) surface science and computational modeling. Well-defined nanoparticle electrocatalysts such as Fe2O3, NiFeOx, and Ag, were prepared in the UHV chamber via physical vapor deposition (PVD) and characterized with surface science techniques including X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), followed by electrochemistry measurements to establish the structure-property relationships in OER and CO2RR. Calculations based on density functional theory (DFT) and microkinetic modeling (MKM) were then implemented to gain fundamental insight into these systems. We observed the edge-enhanced OER activity of Au-supported, ultra-thin Fe2O3 electrocatalysts and revealed incorporation of Ni at the edge sites (NiFeOx) further boosting their OER activity. We also resolved the size-dependent transition between CO2RR and H2 evolution reaction (HER) selectivity in sub-5 nm Ag electrocatalysts and identified an effective minimum size limit of ∼4 nm for active and selective Ag catalysts: particle diameters below this range experienced increased H2 evolutions due to a high population of Ag edge sites; and larger diameter particles favored CO2RR as the population of Ag(100) surface sites grew but will begin to lose catalyst utilization based on total metal masses.