Copper-Based Nitrides Outperform Phosphides in Nitrate Electroreduction to Ammonia: The Cooperative Role of the Cu₃N/CuO Interface

Binary compounds consisting of Cu(I) and moderately electronegative elements (N, P) are attractive semiconductors for optoelectronic and electrocatalytic applications. This study investigates the electrochemical reduction of nitrate to ammonia (NO₃RR) using copper-based catalysts, specifically Cu₃N and Cu₃P. Inhibiting the competitive hydrogen evolution reaction and ensuring active hydrogen (H*) for NH₃ production during NO₃RR pose significant challenges. Our research demonstrates that while Cu₃P is effective in the initial reduction of nitrate to nitrite, it fails to produce NH₃ at more negative potentials due to competition with the hydrogen evolution reaction (HER). In contrast, Cu₃N exhibits remarkable performance, achieving an ammonia yield rate of 48.8 mmol h⁻¹ mmol⁻¹_cat at −0.9 V_RHE, accompanied by considerable Faradaic efficiency and durability. The formation of a Cu₃N/CuO interface during the catalysis is crucial for its activity, facilitating efficient NO₃RR through a stepwise reduction mechanism. The study provides insights into the surface modifications and mechanistic aspects of these catalysts during NO₃RR, offering guidance for strategically developing more efficient catalysts for nitrate reduction to ammonia.