Acidic Nitrate Electroreduction with Ultrahigh Energy Efficiency

Abstract

Ammonia (NH<inf>3</inf>) is an important feedstock for industry, an ideal energy carrier, and a perspective storage media for hydrogen. Recently, electrochemical nitrate (NO<inf>3</inf>−) reduction under acidic conditions has received considerable attention but it suffers from limited efficiency especially under low NO<inf>3</inf>− concentration. Here, we report an in situ formed positively charged polyethyleneimine-modified Cu under acidic conditions as a catalyst-electrolyte interface (CEI) for electrochemical NO<inf>3</inf>− reduction to NH<inf>3</inf>. Such CEI can effectively accumulate NO<inf>3</inf>− anions via static interactions and accelerate *NO hydrogenation to *NOH by weakening *NO intermediate adsorption on Cu site, thereby facilitating NO3−-to-NH<inf>3</inf> conversion. Such CEI delivers an increased NH<inf>3</inf> Faradaic efficiency (FE) of 83.5% and an impressive half-cell energy efficiency (EE) of 37.1% in 10 mM NO<inf>3</inf>− solution (pH = 1). The NH<inf>3</inf> FE and EE can further increase to 90.2% and 44.1% in 0.5 M NO<inf>3</inf>−, respectively. The high EE of CEI surpasses previously reported catalyst performances for NO<inf>3</inf>− reduction. Finally, we demonstrate the feasibility of a novel NO<inf>3</inf>−-furfural battery, showcasing a self-power electrocatalytic system capable of simultaneously treating NO<inf>3</inf>− pollutants, generating value-added NH<inf>3</inf> and upgrading biomass. This work offers valuable insights into the construction of a CEI to enhance the efficiency of NH<inf>3</inf> synthesis.