A Cu-Cu2O/Ni2P Heterostructure for Efficient Tandem Catalysis of Electrosynthesis of Ammonia from Nitrate Reduction Reaction in Neutral Medium

Abstract

Electrochemical nitrate reduction to ammonia (eNO₃RR) in neutral conditions is an effective and sustainable method for ammonia production while treating nitrate pollution. Nevertheless, it still faces a great challenge due to the complicated multiple proton-coupled-electron process in eNO₃RR. Herein, an efficient heterostructure electrocatalyst Cu-Cu₂O/Ni₂P has been successfully fabricated for neutral ammonia electrosynthesis from nitrate reduction. Cu-Cu₂O/Ni₂P exhibits outstanding eNO₃RR performance with a Faradaic efficiency (FE) as high as 96.4% and ammonia yield rate of 14636 µg·h⁻¹·cm⁻² at −1.0 V (vs RHE) in 0.1 m PBS solution, which outperforms most of the reported eNO₃RR electrocatalysts in neutral media. More importantly, the catalyst demonstrates an exceptional stability for 30 consecutive electrolysis cycles and outstanding durability even at large current density of 440 mA cm⁻² in a flow cell. The tandem catalysis mechanism of NO₃⁻ → NO₂⁻ → NH₃ by the synergism of two components of Cu-Cu₂O and Ni₂P in Cu-Cu₂O/Ni₂P is verified by the experimental and theoretical calculations. Cu-Cu₂O has strong adsorption capacity for NO₃⁻ and which can be reduced into NO₂⁻, while Ni₂P can facilitate the water splitting, which promotes the abundant *H production, thus boosting the subsequent hydrogenation process during eNO₃RR process whilst inhibiting the competitive hydrogen evolution reaction (HER).