Paired electrochemical N−N coupling: potential-mediated selective electrosynthesis of azoxy aromatics plus 5,5′-azotetrazolate energetic materials in aqueous media

Abstract

Azoxy aromatics are extensively utilized in materials science, pharmaceuticals, and synthetic chemistry, but their controlled and environmentally-friendly synthesis has rarely been reported. Herein, a potential-mediated electrosynthesis strategy was developed by selective reduction of 4-nitrobenzyl alcohol (4-NBA) on Mn-doped Ni₂P nanosheets@nickel foam (Mn-Ni₂P/NF), enabling efficient N−N coupling to produce Azoxy with 100% selectivity at potentials of −0.6 to −0.8 V (vs. Hg/HgO). At more cathodic potentials, the product was converted to Azo and then to amino aromatics due to facilitated nitrogen hydrogenation. Additionally, the organic energetic material, 5,5′-azotetrazolate, was also synthesized by anodic N−N coupling of 5-amino-1H-tetrazole on Cu(OH)₂ nanowires@copper foam (Cu(OH)₂/CF). It bypassed harsh conditions (strong oxidants, high temperature, by-products separation, etc.) for the traditional synthesis of this class of materials. As a consequence, a two-electrode electrolyzer Cu(OH)₂/CF||Mn-Ni₂P/NF was assembled, allowing paired electrochemical N−N coupling into Azoxy and 5,5′-azotetrazolate. It achieves a current density of 50 mA cm⁻² at a voltage of only 1.19 V, 880 mV lower than the competitive water splitting. This electrolyzer can be efficiently driven by a 1.2 V solar panel with excellent yield and selectivity, paving the way for green synthesis of valuable chemicals through electrochemical N−N coupling strategies.