Direct Insight into the Role of Cationic Lactam Nitrogen on Oxygen Electroreduction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Nitrogen-doped carbon materials are promising metal-free catalysts for the oxygen reduction reaction (ORR).
• Identifying the specific active nitrogen species in these catalysts is crucial but challenging.
• The role of lactam nitrogen species has been largely overlooked in ORR catalysis.

Purpose of the Study:

• To investigate the role of lactam nitrogen species in the oxygen reduction reaction (ORR).
• To compare the ORR activity of nitrogen-doped nanodiamond (NND) with lactam dominance and nitrogen-doped carbon nanotubes (NCNT) with pyridinic/graphitic nitrogen.
• To elucidate the reaction mechanisms involving different nitrogen species in metal-free ORR catalysts.

Main Methods:

• Fabrication of N-doped nanodiamond (NND) and nitrogen-doped carbon nanotubes (NCNT) as model catalysts.
• Spectroscopic analyses and temperature-programmed desorption (TPD) to characterize nitrogen species.
• Electrochemical Coulombic screening experiments to probe reaction mechanisms.

Main Results:

• NND predominantly features lactam nitrogen in an sp³-hybridized framework, while NCNT contains mainly pyridinic and graphitic nitrogen.
• ORR on NND proceeds via lactam-derived cationic nitrogen intermediates.
• ORR on NCNT is facilitated by anionic intermediates associated with pyridinic nitrogen.
• Post-reaction analysis confirmed the formation of cationic N+ in NND, actively participating in ORR.

Conclusions:

• Cationic lactam nitrogen plays a pivotal role in the oxygen reduction reaction (ORR).
• Different nitrogen configurations (lactam vs. pyridinic/graphitic) lead to distinct ORR mechanisms.
• This research provides insights for designing advanced metal-free carbon catalysts through precise nitrogen engineering.