Probing Changes in the Local Structure of Active Bimetallic Mn/Ru Oxides during Oxygen Evolution

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• The oxygen evolution reaction (OER) is critical for energy conversion technologies.
• Ruthenium dioxide (RuO₂) is a state-of-the-art OER catalyst but is expensive and scarce.
• Mixed manganese/ruthenium (Mn/Ru) oxides offer a promising alternative, reducing reliance on precious metals.

Purpose of the Study:

• To identify the active sites of Mn/Ru oxide catalysts for the OER.
• To understand the structural and chemical changes at Mn and Ru sites during OER.
• To elucidate the role of manganese in enhancing the catalytic activity.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) was used to analyze surface composition and oxidation states.
• X-ray absorption spectroscopy (XAS) was employed to probe the local coordination environment and oxidation states of Mn and Ru.
• Operando XAS experiments were conducted under OER conditions to observe dynamic changes.

Main Results:

• The Mn content significantly influences the oxidation state and local coordination of Ru sites.
• Operando XAS data suggest MnO plays a crucial role in the catalytic mechanism.
• Changes in the oxygen coordination sphere of Ru centers are facilitated by Mn.

Conclusions:

• The active sites for OER in Mn/Ru oxides are linked to specific structural and chemical states of Ru, modulated by Mn.
• Manganese oxides (MnO) are essential for achieving high OER activity in these mixed systems.
• This study provides fundamental insights for designing advanced, cost-effective OER electrode materials.