Transition metal small clusters anchored on biphenylene for effective electrocatalytic nitrogen reduction

Abstract

The synthesis of ammonia via an electrochemical nitrogen reduction reaction (NRR, N₂ + 6H⁺ + 6e⁻ → 2NH₃), which can weaken but not directly break an inert NN bond under mild conditions via multiple progressive protonation steps, has been proposed as one of the most attractive alternatives for the production of NH₃. However, the development of appropriate catalyst materials is a major challenge in the application of NRRs. Recently, single- or multi-metal atoms anchored on two-dimensional (2D) substrates have been demonstrated as ideal candidates for facilitating NRRs. In this work, by applying spin-polarized density functional theory and ab initio molecular dynamic simulations, we systematically explored the performances of nine types of transition metal multi-atoms anchored on a recently developed 2D biphenylene (BPN) sheet in nitrogen reduction. Structural stability and NRR performance catalyzed by TM_n (TM = V, Fe, Ni, Mo, Ru, Rh, W, Re, Ir; n = 1–4) clusters anchored on BPN sheets were systematically explored. After a strict six-step screening strategy, it was found that W₂, Ru₂ and Mo₄ clusters loaded on BPN demonstrate superior potential for nitrogen reduction with extremely low onset potentials of −0.26, −0.36 and −0.17 V, respectively. Electronic structure analysis revealed that the enhanced ability of these multi-atom catalysts to effectively capture and reduce the N₂ molecule can be attributed to bidirectional charge transfer between the d orbitals of transition metal atoms and molecular orbitals of the adsorbed N₂ through a “donation-back donation” mechanism. Our findings highlight the value of BPN sheets as a substrate for designing multi-atom nitrogen reduction reaction catalysts.