Sustainable Electrosynthesis of Hexamethylenetetramine via Paired Electrolysis of Nitrate and PET Waste

ABSTRACT Hexamethylenetetramine (HMTA) is a critical organonitrogen compound widely used in the defense, pharmaceutical, and polymer industries. Conventional HMTA production relies on toxic formaldehyde (HCHO) and energy‐intensive Haber–Bosch‐derived ammonia (NH 3 ) as feedstocks. This study demonstrates a sustainable electrocatalytic approach for the direct synthesis of HMTA via paired electrolysis, using nitrate (NO 3 − ) and polyethylene terephthalate (PET) waste as nitrogen and carbon sources, respectively. With iron‐doped nickel phosphide (Fe–Ni 2 P) as a bifunctional catalyst, the system achieves concurrent cathodic NO 3 − reduction to NH 3 with a Faradaic efficiency of ∼ 96.0%, and anodic oxidation of PET‐derived ethylene glycol to electrophilic *HCHO intermediates. These resulting intermediates subsequently condense with nucleophilic NH 3 to form HMTA with ∼75.2% carbon selectivity. Mechanistic studies reveal that Fe doping induces charge redistribution and upshifts the d‐band center, thereby facilitating the adsorption and activation of reactants and lowering the energy barrier for *HCHO intermediate formation and desorption—a critical step enabling subsequent C─N coupling. This work establishes a mild and sustainable electrocatalytic route for HMTA synthesis from environmental waste, underscoring the potential of paired electrolysis in valorizing waste into valuable organonitrogen chemicals.