Molecular Conjugated-Polymer Electrode Enables Rapid Proton Conduction for Electrosynthesis of Ammonia from Nitrate

Abstract

Electrosynthesis of ammonia (NH₃) from nitrate (NO₃⁻) using renewable energy holds promise as a supplementary alternative to the Haber−Bosch process for NH₃ production. Most research focuses on tuning the catalytic activity of metal catalysts by modification of the catalyst structures. However, the electrode supports which could influence the catalytic activity have not been well-explored. The state-of-the-art electrocatalysts for NO₃⁻ reduction to NH₃ still exhibit limited energy efficiency at ampere-level current density. Herein, we report a polyaniline-based molecular electrode with Cu catalyst for selective and energy-efficient NO₃⁻ reduction to NH₃. In the electrode, the polyaniline promotes protonation of the key intermediate formed during NO₃⁻ reduction at Cu, which circumvents the limitation of the Cu catalyst in the efficiency-limiting proton transfer step. The molecular electrode produces NH₃ at a partial current density of 2.7 A cm⁻² with an energy efficiency of 62 %, demonstrating much better electrochemical performance than common Cu-based electrocatalysts and indicating the great potential in molecular engineering of electrode supports for selective NO₃⁻ reduction.