Efficient Nitrogen Fixation to Ammonia through Integration of Plasma Oxidation with Electrocatalytic Reduction

Abstract

Present one-step N₂ fixation is impeded by tough activation of the N≡N bond and low selectivity to NH₃ . Here we report fixation of N₂ -to-NH₃ can be decoupled to a two-step process with one problem effectively solved in each step, including: 1) facile activation of N₂ to NO_x ^- by a non-thermal plasma technique, and 2) highly selective conversion of NO_x ^- to NH₃ by electrocatalytic reduction. Importantly, this process uses air and water as low-cost raw materials for scalable ammonia production under ambient conditions. For NO_x ^- reduction to NH₃ , we present a surface boron-rich core-shell nickel boride electrocatalyst. The surface boron-rich feature is the key to boosting activity, selectivity, and stability via enhanced NO_x ^- adsorption, and suppression of hydrogen evolution and surface Ni oxidation. A significant ammonia production of 198.3 μmol cm^-2 h^-1 was achieved, together with nearly 100 % Faradaic efficiency.

Keywords: ammonia production; boron-rich surface; electrocatalytic nitrate reduction; nitrogen fixation; plasma.