Bifunctional Cu–Ni Phosphide Polyhedral Architectures for Formaldehyde Oxidation-Coupled Ammonia Synthesis at Low Energy Consumption

Abstract

Electrocatalytic nitrite reduction reaction (NO2RR) offers a green pathway toward ammonia synthesis under ambient conditions. However, the overall energy efficiency of this process remains constrained by the anodic oxygen evolution reaction (OER), which suffers from intrinsically sluggish kinetics. Herein, we demonstrates that the Cu–Ni phosphide polyhedral architectures grown on Cu–Ni foam (P–O–CNF) enable the simultaneous promotion of cathodic NO2RR and anodic formaldehyde oxidation reaction (FOR). The P–O–CNF catalyst exhibits exceptional bifunctional performance, delivering an ammonia Faradaic efficiency (FE) of 96% and a production rate of 21.2 mg h–1 cm–2 at −0.2 V vs RHE for NO2RR, while affording considerable FEs above 94% across the applied potential window for FOR. Leveraging this outstanding bifunctionality, the paired NO2RR-FOR system achieves a low energy consumption of only 7.38 kWh kgNH3–1 at 200 mA cm–2, markedly surpassing the conventional NO2RR-OER system (19.82 kWh kgNH3–1). Importantly, this coupled system can be directly powered by a P–O–CNF-based Zn–NO2– battery, enabling simultaneous valorization of nitrite and formaldehyde pollutants into value-added ammonia and formate. This work establishes a straightforward and effective strategy for coupling NO2RR with alternative anodic reactions toward energy-saving ammonia electrosynthesis.