Single-Atom Anchored g-C₃N₄ Monolayer as Efficient Catalysts for Nitrogen Reduction Reaction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical nitrogen reduction reaction (NRR) offers a sustainable route for ammonia synthesis under ambient conditions.
• 3d transition metal (TM) atoms anchored on graphitic carbon nitride (g-C3N4) are explored as potential single-atom catalysts (SACs) for NRR.
• Understanding the catalytic mechanisms and identifying efficient SACs are crucial for advancing NRR technology.

Purpose of the Study:

• To systematically investigate the NRR performance of 3d transition metal atoms anchored on s-triazine-based g-C3N4 (TM@g-C3N4) using density functional theory (DFT).
• To identify the most promising TM@g-C3N4 catalyst for efficient electrochemical ammonia production.
• To elucidate the catalytic mechanism and the role of the anchored metal atom in NRR.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study the electronic structure and catalytic activity of various TM@g-C3N4 systems.
• Calculations focused on determining the Gibbs free energy (ΔG) of key intermediates and the limiting potential for NRR.
• Analysis of charge transfer, spin moment, and orbital hybridization was performed to understand the reaction mechanism.

Main Results:

• Several TM@g-C3N4 catalysts, including V@g-C3N4, Cr@g-C3N4, Mn@g-C3N4, Fe@g-C3N4, and Co@g-C3N4, exhibited low ΔG(*NNH) values, suggesting favorable NRR activity.
• The V@g-C3N4 monolayer demonstrated the lowest limiting potential of -0.60 V, with the rate-determining step identified as *N2+H++e-=*NNH for both alternating and distal mechanisms.
• The anchored V atom in V@g-C3N4 was found to activate the N2 molecule through charge transfer and spin moment contribution, facilitated by the metal conductivity of the catalyst.
• p-d orbital hybridization between V and adsorbed N2 plays a key role in the acceptance-donation mechanism of electron transfer during NRR.

Conclusions:

• V@g-C3N4 emerges as a highly efficient single-atom catalyst for electrochemical NRR, offering a low limiting potential for ammonia synthesis.
• The anchored vanadium atom's electronic properties and the catalyst's conductivity are critical for activating N2 and facilitating electron transfer.
• This study provides valuable insights for the rational design of advanced single-atom catalysts for efficient and sustainable ammonia production via NRR.