Si(3)C Monolayer as an Efficient Metal-Free Catalyst for Nitrate Electrochemical Reduction: A Computational Study

Nitrate electroreduction reaction to ammonia (NO(3)ER) holds great promise for both nitrogen pollution removal and valuable ammonia synthesis, which are still dependent on transition-metal-based catalysts at present. However, metal-free catalysts with multiple advantages for such processes have been rarely reported. Herein, by means of density functional theory (DFT) computations, in which the Perdew–Burke–Ernzerhof (PBE) functional is obtained by considering the possible van der Waals (vdW) interaction using the DFT+D3 method, we explored the potential of several two-dimensional (2D) silicon carbide monolayers as metal-free NO(3)ER catalysts. Our results revealed that the excellent synergistic effect between the three Si active sites within the Si(3)C monolayer enables the sufficient activation of NO(3)(−) and promotes its further hydrogenation into NO(2)(*), NO(*), and NH(3), making the Si(3)C monolayer exhibit high NO(3)ER activity with a low limiting potential of −0.43 V. In particular, such an electrochemical process is highly dependent on the pH value of the electrolytes, in which acidic conditions are more favorable for NO(3)ER. Moreover, ab initio molecular dynamics (AIMD) simulations demonstrated the high stability of the Si(3)C monolayer. In addition, the Si(3)C monolayer shows a low formation energy, excellent electronic properties, a superior suppression effect on competing reactions, and high stability, offering significant advantages for its experimental synthesis and practical applications in electrocatalysis. Thus, a Si(3)C monolayer can perform as a promising NO(3)ER catalyst, which would open a new avenue to further develop novel metal-free catalysts for NO(3)ER.