Lewis acid sites and flexible active centers synergistically boost efficient electrochemical ammonia synthesis†

Abstract

Much effort has been made to develop efficient electrochemical catalysts for the nitrogen reduction reaction (NRR). However, the activity and selectivity of present catalysts are still limited in their applications. Herein, from the perspective of Lewis acid–base interactions and flexible active centers, positively charged tetrahedron transition metal (TM) clusters were anchored onto boron nitride nanotubes (BNNTs) with B-vacancies to design a series of efficient NRR catalysts, meeting the above requirements. Through Density Functional Theory (DFT) calculations, our results uncover that the Mn₄/BNNT (6, 6) system exhibits optimal activity characterized by a low limiting potential of only −0.29 V and high selectivity, as confirmed by the adsorption energy difference between nitrogen molecules and hydrogen proton (−0.73 eV). Owing to the existence of electron-deficient Lewis acid sites, the adsorption and activation of N₂ are strongly enhanced. Simultaneously, the flexible active center destabilizes the N-containing intermediates and upgrades the hydrogenation reaction process, facilitating the desorption of NH₃ or its further hydrogenation to NH₄⁺. This innovative approach, employing a Lewis acid pair and a flexible active center to design efficient NRR catalysts, holds great promise for NH₃ synthesis under ambient conditions.