Elucidating Catalyst Degradation Mechanism of Non-Precious Metal Catalyst for Oxygen Reduction Reaction Using Electrochemical Tip-Enhanced Raman Spectroscopy

Abstract

Identifying the chemical state and structure of electrocatalysts is critical for understanding the catalytic and degradation mechanisms in the oxygen reduction reaction. Tip-enhanced Raman spectroscopy (TERS) combines plasmonic enhancement of Raman scattering from surfaces and the high spatial resolution of scanning probe techniques to provide in situ chemical analysis at the nanoscale. We have employed electrochemical TERS (EC-TERS) to investigate the oxygen reduction reaction (ORR) catalyzed by transition metal phthalocyanine molecules under electrochemical conditions. Using EC-TERS, we have observed that the iron (II) phthalocyanine undergoes reversible and irreversible transformations during ORR. Combining Raman calculation and EC-TERS, we have identified that the irreversible transformation, which resulted in the formation of H 2 -phthalocyanine, is the primary degradation mechanism for iron (II) phthalocyanine in ORR. We have also extended the EC-TERS technique to investigate cobalt (II) phthalocyanine and identified its chemical state during ORR using the EC-TERS technique with multiple wavelength excitation.