# Local Activity and Selectivity Hotspots in Cu‐Pt Model Thin‐Film Electrocatalysts for Oxygen Reduction

## TL;DR

This study uses advanced imaging to explore how Cu-Pt thin film catalysts work during oxygen reduction, revealing how active sites change based on reaction outcomes.

## Contribution

The study identifies how active site locations shift with reaction selectivity in Cu-Pt catalysts, offering insights for designing better electrocatalysts.

## Key findings

- Active centers for four-electron oxygen reduction are located on (111) terraces.
- Hydrogen peroxide generation shifts active sites to step defects.
- Grain boundaries do not contribute to catalytic activity.

## Abstract

While state‐of‐the‐art alloy catalysts for the oxygen reduction reaction (ORR), a key process for future sustainable energy provision, rely on platinum‐rich materials, alloys containing less noble metals may play an increasingly important role. In particular, Cu–Pt systems are among state‐of‐the‐art electrocatalysts for O2 electro‐reduction, demonstrating high activity and selectivity for the four‐electron pathway. This study explores the behavior of Cu–Pt model thin film alloy catalysts using electrochemical scanning tunneling microscopy (EC‐STM), a technique capable of detecting active sites and areas for surface catalytic processes under reaction conditions. Our findings indicate that the nature of active centers changes depending on whether the final product is H2O or H2O2, which can also be generated in parallel. Active centers are located on the (111) terraces for the four‐electron ORR and shift to step defects if the hydrogen peroxide generation starts. On the other hand, the grain boundaries do not seem to contribute to the sample activity. These findings can be used in designing the shape of nanoparticles for improved nanostructured materials for energy applications.

A Cu‐Pt model thin film catalyst is investigated via electrochemical scanning tunneling microscopy. This technique enables in‐operando active site detection on a nanometer scale. It is shown that the precise location of the active sites changes depending on the selectivity of the oxygen reduction reaction.