Decoding Dual-Functionality in N-doped Defective Carbon: Unveiling Active Sites for Bifunctional Oxygen...

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Oxygen electrocatalysis is vital for energy conversion and storage.
• Identifying active sites in bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is challenging.
• Developing efficient, metal-free catalysts is a key goal.

Purpose of the Study:

• To identify the specific active sites for ORR and OER in metal-free N-doped carbon materials.
• To demonstrate the bifunctional catalytic activity of these materials.
• To provide insights for designing site-specific electrocatalysts.

Main Methods:

• Synthesis of N-doped defective carbon material from a triazene derivative.
• X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy for site identification.
• In situ Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy to study reaction intermediates.
• Development of a predictive model using π-electron descriptors.

Main Results:

• Metal-free N-doped defective carbon material exhibits excellent bifunctional ORR/OER activity with a ΔE of 0.72 V.
• Pyridinic-N sites were identified as crucial for ORR.
• Graphitic-N sites were found to be effective for OER.
• Theoretical predictions using π-electron descriptors aligned with experimental findings.
• Reaction intermediates for both ORR and OER were clarified using in situ ATR-FTIR.

Conclusions:

• Pyridinic-N and graphitic-N sites in metal-free N-doped carbon materials exhibit distinct roles in ORR and OER, respectively.
• This work resolves the long-standing issue of active site identification for bifunctional oxygen electrocatalysis.
• The findings pave the way for developing site-specific, metal-free electrocatalysts for energy technologies.