Reactivity mapping of nanoscale defect chemistry under electrochemical reaction conditions

Jonas H K Pfisterer,Giovanni Giuzio,Masoud Baghernejad,Katrin F Domke

doi:10.1038/s41467-019-13692-3

Jonas H K Pfisterer, Giovanni Giuzio + Show 2 more

Open Access

https://doi.org/10.1038/s41467-019-13692-3

Copy DOI

Abstract

Electrocatalysts often show increased conversion at nanoscale chemical or topographic surface inhomogeneities, resulting in spatially heterogeneous reactivity. Identifying reacting species locally with nanometer precision during chemical conversion is one of the biggest quests in electrochemical surface science to advance (electro)catalysis and related fields. Here, we demonstrate that electrochemical tip-enhanced Raman spectroscopy can be used for combined topography and reactivity imaging of electro-active surface sites under reaction conditions. We map the electrochemical oxidation of Au nanodefects, a showcase energy conversion and corrosion reaction, with a chemical spatial sensitivity of about 10 nm. The results indicate the reversible, concurrent formation of spatially separated Au2O3 and Au2O species at defect-terrace and protrusion sites on the defect, respectively. Active-site chemical nano-imaging under realistic working conditions is expected to be pivotal in a broad range of disciplines where quasi-atomistic reactivity understanding could enable strategic engineering of active sites to rationally tune (electro)chemical device properties.

Highlights

Electrocatalysts often show increased conversion at nanoscale chemical or topographic surface inhomogeneities, resulting in spatially heterogeneous reactivity
Combining EC-STM with the chemical specificity of near-field Raman spectroscopy in the form of electrochemical tip-enhanced Raman spectroscopy (EC-TERS)[14,15,16] holds great promise to enable the investigation of local active defect-chemistry on the nanometer level during electrocatalytic energy conversion reactions
As a showcase corrosion and heterogeneous catalysis-related reaction[20], we image the oxidation of nanoscale defect protrusions at a Au(111) single crystal electrode generated by electrochemical water splitting at defect sites to form Au oxide

Summary

Introduction

Electrocatalysts often show increased conversion at nanoscale chemical or topographic surface inhomogeneities, resulting in spatially heterogeneous reactivity. One prominent field where active sites play a pivotal role is heterogeneous (electro)catalysis that lies at the basis of many important chemical or energy conversion reactions. Combining EC-STM with the chemical specificity of near-field Raman spectroscopy in the form of electrochemical tip-enhanced Raman spectroscopy (EC-TERS)[14,15,16] holds great promise to enable the investigation of local active defect-chemistry on the nanometer level during electrocatalytic energy conversion reactions. The EC-TERS data provide experimental evidence for the existence and nm spatial distribution of at least two AuOx species with distinct coordination numbers on the active site With this operando Raman nanoscopy approach, a wide range of materials and reaction conditions can be explored to locate and characterize nanoscale active surface sites, for example, in electro- or photoactive materials during operation or in biological environments under physiological conditions. The insight into molecular-scale material (re)activity gained in this way will pave the way for bottomup defect design and rational tuning of device properties

Methods

Results

Conclusion