Rational design of an Fe cluster catalyst for robust nitrogen activation

Abstract

Ammonia synthesis by the electrochemical technique is a promising solution to replace the energy-intensive Haber–Bosch process in industry, which inevitably requires high-performance catalysts. However, the development of catalysts is still limited by the inferior activation of the stable NN bond. Herein, a robust N₂-activation mode is proposed, which addresses the electron donation mechanism to both the N₂ antibonding orbitals of p_y and p_z, simultaneously. Following this strategy, the single cluster catalyst (SCC) of Fe₄/GaS has realized remarkable nitrogen reduction reaction (NRR) performance with an ultra-low overpotential (η) of 0.08 V by density functional theory (DFT) calculations. N₂ is completely activated in a side-on adsorption configuration on the hollow site of Fe₄/GaS, where both degenerate N₂–π* orbitals are properly hybridized to the frontier orbitals of the Fe₄ cluster, as proven by fragment orbital analysis. This work proposes an efficient strategy for N₂ activation, and also provides a valid design guideline for further research.