Operando Raman spectroscopy tracks oxidation-state changes in an amorphous Co oxide material for electrocatalysis of...

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Transition metal oxides are vital for energy storage and electrocatalysis.
• Understanding their oxidation states under operating conditions is key to improving performance.
• Cobalt oxide materials are promising electrocatalysts for the oxygen evolution reaction (OER).

Purpose of the Study:

• To establish operando Raman spectroscopy for investigating cobalt oxide electrocatalysts.
• To determine the atomic structure and oxidation state changes during OER.
• To elucidate the catalytic mechanism of cobalt oxide in neutral pH OER.

Main Methods:

• Operando Raman spectroscopy under electrochemical control.
• Use of stable isotopes (²H and ¹⁸O) for mechanistic insights.
• Analysis of potential-dependent spectral changes and band assignments.

Main Results:

• Operando Raman spectroscopy successfully monitored Co oxidation states (Co²⁺/³⁺ and Co³⁺/⁴⁺) individually.
• Isotopic labeling confirmed Co oxidation coupled with Co-OH deprotonation and O-O bond formation.
• Observed spectral changes, including band shifts and intensity variations, were linked to electrochromism and redox transitions.

Conclusions:

• Electrochemical operando Raman spectroscopy is a powerful tool for mechanistic studies of OER catalysts.
• The method provides detailed insights into redox transitions beyond averaged oxidation states.
• This technique advances the understanding of transition metal oxides in energy applications.