Transition-metal-free boron doped SbN monolayer for N₂ adsorption and reduction to NH₃: A first-principles study

Electrochemical nitrogen reduction reaction (NRR) in ambient condition is an efficient and sustainable method to synthesize NH₃. In this work, first-principles study was used to discuss the NRR process on B atom doped SbN monolayer. The adsorption of N₂ on B-Sb₁₇N₁₈ and B-S₁₈N₁₇ was calculated including the adsorption energy, adsorption distance, and the charge density difference (CDD). Five different reaction pathways of NRR were taken into consideration and the stability of B-SbN was investigated. The results show that, because the energy of unoccupied orbital in sp³ hybridization of B atom is much lower than that in 2p_z orbitals, the adsorption of N₂ on B-Sb₁₈N₁₇ shows much larger adsorption energy (-1.01 eV with end-on pattern) compared to that of the adsorption on B-Sb₁₇N₁₈. For five different pathways, the 1, 2, and 4 pathways have a smaller limiting potential of about 0.52 V and the limiting step is: *N₂ + H⁺ + e^- → *NNH. The 3 and 5 pathways have a larger limiting potential of 0.57 V with hydrogenation step: *NHNH₂ + H⁺ + e^- → *NH₂NH₂. The B-Sb₁₈N₁₇ is structurally and thermally stable even at 500 K. Our theoretical prediction indicates that B atom substitutionally doped SbN monolayer can be a kind of high-performance metal-free NRR catalyst for NH₃ synthetization, and the work provides attempts for designing and exploring 2D metal-free NRR catalysts.