Stabilizing Mixed-Valence Sn Active Sites With Oxygen Vacancies for Enhanced Acidic CO₂-to-HCOOH Conversion

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrocatalytic CO2 reduction (CO2RR) offers a sustainable route to convert CO2 into valuable chemicals.
• Challenges in acidic CO2RR include hydrogen evolution, corrosion, and low selectivity, hindering industrial application.

Purpose of the Study:

• To synthesize SnO2 catalysts with tunable oxygen vacancy concentrations for enhanced acidic CO2RR.
• To investigate the correlation between oxygen vacancy and catalytic performance in Sn-based catalysts.

Main Methods:

• Synthesis of SnO2 catalysts via high-temperature calcination (300-900°C) to control oxygen vacancy concentration.
• Electrochemical evaluation of catalysts for CO2-to-formic acid reduction, including Faradaic efficiency and production rates.
• In situ Raman spectroscopy to analyze catalyst structure and active species under reaction conditions.

Main Results:

• The SnO2-600 catalyst achieved over 90% Faradaic efficiency for formic acid production across a wide current density range (-0.30 to -1.0 A cm-2).
• A peak Faradaic efficiency of 96.2% and a formic acid production rate of 17.9 mmol h-1 cm-2 were recorded at -1.0 A cm-2.
• The catalyst demonstrated excellent stability, maintaining 80% Faradaic efficiency over 80 hours.
• In situ Raman spectroscopy identified stable mixed-valence SnOx species (Sn2O3 and Sn3O4) as key active sites in catalysts with moderate oxygen vacancies.

Conclusions:

• Moderate oxygen vacancies in SnO2 are crucial for forming stable mixed-valence SnOx active species, leading to high performance in acidic CO2RR.
• This study provides a foundation for designing highly active and stable Sn-based catalysts for industrial CO2 conversion.