Highly efficient N₂ fixation catalysts: transition-metal carbides M₂C (MXenes)

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Developing efficient electrocatalysts for nitrogen (N2) reduction under mild conditions is a significant challenge.
• Two-dimensional (2D) MXenes offer potential due to abundant active sites.

Purpose of the Study:

• To systematically explore transition metal-based M2C MXenes for N2 electroreduction.
• To compute limiting potentials and identify high-performance N2 reduction reaction (NRR) catalysts.

Main Methods:

• Computational screening of 3d, 4d, and 5d-transition metal M2C MXenes.
• Calculation of free-energy barriers (ΔG) for the N2 reduction reaction (NRR).
• Analysis of N2 capture strength and its relation to d-electron arrangements.

Main Results:

• 4d4-Mo2C exhibited a low free-energy barrier of 0.46 eV.
• Hypothetical 3d5-Mn2C and 3d6-Fe2C showed even lower ΔG values of 0.28 eV and 0.23 eV, respectively.
• NRR performance correlates with d-electron configuration, particularly half-filled 3d5 and 3d6 states in Mn2C and Fe2C.

Conclusions:

• Mn2C and Fe2C MXenes are predicted to be highly efficient electrocatalysts for N2 reduction.
• The d-electron arrangement on metal sites is crucial for optimizing N2 capture and hydrogenation.
• These findings provide insights for designing advanced electrocatalysts for sustainable N2 fixation.