Modulation of the electronic structure of CoP active sites by Er-doping for nitrite reduction for ammonia electrosynthesis

Abstract

The electrochemical conversion of toxic nitrite (NO₂^–) is a promising approach for the simultaneous removal of nitrogen contaminants and synthesis of ammonia (NH₃). In this study, we present the Er-doping-induced electronic modulation of CoP integrated with nitrogen-doped carbon (CN) nanosheets supported on a titanium mesh (Er-CoP@NC/TM) for the electrocatalytic NO₂^– reduction reaction (eNO₂^–RR) for NH₃ synthesis. The catalyst demonstrates a high Faraday efficiency of 97.08 ± 2.22% and a high yield of 2087.60 ± 17.10 µmol h^–1 cm^–2 for NH₃ production. Characterization and theoretical calculations revealed that Er-doping facilitated the electronic modulation of CoP in Er-CoP@NC/TM, which regulated the adsorption behaviors of intermediates and was the rate-limiting step for the eNO₂^–RR, thereby enhancing the electrocatalytic performance. Quenching experiments and electron paramagnetic resonance tests suggest that both direct electrocatalytic reduction by active hydrogen and electron transfer are critical for the eNO₂^–RR for NH₃ synthesis. Furthermore, Er-CoP@NC/TM exhibited high performance across a wide range of NO₂^– concentrations (0.05–0.1 mol L^–1) and pH values (4–13). In addition, the catalyst demonstrated strong resistance to anions and a long cycle life in simulated wastewater environments. This study offers a powerful approach for the remediation of NO₂^– wastewater and recovery of valuable inorganic compounds.