Surface reconstruction induced Cu₂O/FeO heterojunction towards efficient nitrate-containing wastewater remediation

Electrochemical nitrate-to-nitrogen conversion provides an available approach for efficient waste water remediation. However, high nitrogen selectivity is difficult to achieve, due to inappropriate aquatic H supply for hydrogenation of oxynitride intermediates and relatively high energy barrier for NO bond breakage. In this study, Cu₂O/FeO heterojunction is constructed to drive electrochemical nitrate reduction. A straightforward apparent kinetic analysis was performed to define the formation rate of the key nitrogen compounds.Comprehensive structure and electrochemical analysis combined with Density Functional Theory (DFT) calculation were performed to elucidate the underlying mechanism for enhanced nitrate-to-nitrogen conversion efficiency based on Cu₂O/FeO heterojunction. FeO introduction is confirmed to beneficial for moderate water cracking, providing right amount of aquatic *H to adapt the hydrogenation processes during nitrate to nitrogen conversion. Moreover, FeO introduction induces the generation of Cu₂O/FeO heterojunction. Self-driven local charge redistribution takes place at the Cu₂O/FeO heterointerface, resulting in nucleophilic and electrophilic regions. Such unique structure is conducive to targeted asymmetric adsorption of oxynitrides in a configuration of CuONFe, thus facilitating fracture of NO bond and promoting the generation of *N. Excess accumulation of *N is beneficial for nitrogen generation through *N-*N coupling, resulting in high nitrogen selectivity. As a result, the optimized Cu₂O/FeO electrode exhibits excellent electrocatalytic nitrate reduction reaction (eNO₃RR) performance, featured for a high nitrate removal rate of ∼ 100 % and 81.58 % nitrogen selectivity at -0.7 V (vs. RHE) after 8 h electrolysis.