Direct N₂ to NH₃ conversion on diamond-supported Ni₄ cluster catalysts: A first-principle study

Electrochemical reduction of N₂ to NH₃ has been considered as a promising regeneration of Haber Process. An efficient, non-noble metal-based catalyst is urgently required to replace noble metals. Here, we report a heterogeneous electrocatalyst with a robust and highly catalytic interface between Ni₄ cluster and diamond for electrocatalytic N₂ reduction reaction (NRR) by density functional theory (DFT) calculations. NRR catalysis has been investigated by using atomic Ni₄ clusters on pristine diamond (PD), pristine diamond with H-terminals (H-PD), B-doped diamond (BDD) and B-doped diamond with H-terminals (H-BDD). Among all catalysts, BDD/Ni₄ possesses the lowest overpotential of 0.27 V, significantly exceeding that of noble metal Ru (0001) benchmark electrocatalyst (0.92 V), indicating excellent catalytic property. In addition, the strong tunability of diamond substrates endows them with the ability to regulate heterojunction properties. The H terminals generally impede the transport of charge carriers at the interface, while the introduction of B doping can balance it with the overpotential reduced from 0.49 V to 0.36 V when replacing H-PD/Ni₄ by H-BDD/Ni₄. Moreover, B doping engineering can further enhance the stability of Ni₄ cluster and the adsorption of N₂. This work will enlighten material design to construct diamond supported transition metal clusters for highly efficient NRR catalysts.