Two-Dimensional Nanomesh Arrays as Bifunctional Catalysts for N₂ Electrolysis

Abstract

N2 electrolysis has been impeded by efficient catalysts for key reactions: cathodic nitrogen reduction reaction (NRR) and anodic oxygen evolution reaction (OER). A bifunctional nickel, iron-nanomesh array electrocatalyst has been developed characteristic of excellent structural features for favorable NRR and OER processes, including highly exposed active sites originated from sub-nanometer-thick nanomeshes, hierarchical porosity resulting from the array-arranged nanolayers, and binary nickel, iron active sites. The electrode demonstrates excellent NRR activity with an ammonia yield of 16.89 μg h–1 mg–1cat and a faradaic efficiency (FE) of 12.50% at −350 mV (vs RHE), in addition to OER activity with a small overpotential of 191 mV to achieve 10 mA cm–2. Consequently, a full N2 electrolysis system has been constructed that exhibits remarkable ammonia production performance with an ammonia yield of 2.07 μg h–1 mg–1cat at 1.9 V, an FE of 9.87% at 1.6 V, and good durability for 30 h. Further mechanism study through density function theory shows that the NRR proceeds via an associative distal pathway, whereas the free energies for the N2* → NNH* intermediate step in the NRR as well as the OH* + H2O → O* + H2O intermediate step in the OER can be reduced by tuning the catalysts’ electronic structure by the strong synergistic effect between nickel and iron.