Electrocatalytic N₂-to-NH₃ conversion with high faradaic efficiency enabled using a Bi nanosheet array

Electrocatalytic N₂ reduction represents a promising alternative to the conventional Haber-Bosch process for ambient N₂-to-NH₃ fixation, but it is severely challenged by competitive hydrogen evolution, which limits the current efficiency for NH₃ formation. In this work, a nanosheet array of metallic Bi, an environmentally benign elemental substance previously predicted theoretically to have low hydrogen-evolving activity, is proposed as a superior catalyst for N₂ reduction electrocatalysis. Electrochemical tests show that the Bi nanosheet array on Cu foil as a stable 3D catalyst electrode achieves a high faradaic efficiency of 10.26% with an NH₃ yield rate of 6.89 × 10^-11 mol s^-1 cm^-2 at -0.50 V vs. the reversible hydrogen electrode in 0.1 M HCl, rivalling the performances of most reported noble-metal-free catalysts operating in acids. Density functional theory calculations suggest that Bi effectively activates the N[triple bond, length as m-dash]N bond and the alternating mechanism is energetically favourable.