Efficient nitrogen fixation to ammonia through integration of plasma oxidation with electrocatalytic reduction

Abstract

Transformation of atmospheric nitrogen (N2) to ammonia (NH3) is a long-sought goal for human being. However, 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 advantageously decoupled to a two-step process with one problem solved independently and effectively in each step, including: 1) facile activation of N2 to NOx- by a non-thermal plasma technique, and; 2) highly selective conversion of NOx- 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 NOx- reduction to NH3 we present a novel surface boron-rich core-shell nickel boride electrocatalyst. Combining a series of physical characterizations and in situ spectrometric measurements, we reveal that the surface boron-rich feature is the key to boosting activity, selectivity, and stability via enhanced NOx- adsorption, and suppression of hydrogen evolution and surface Ni oxidation. Consequently, a highly significant ammonia production of 198.3 µmol h-1 cm-2 was achieved, together with nearly 100% Faradaic efficiency.