Sequential active-site switches in integrated Cu/Fe-TiO2 for efficient electroreduction from nitrate into ammonia

Understanding the reaction mechanism is critical for efficient electroreduction from NO3− into NH3. Here, a novel sequential active-site-switching (SASS) mechanism is proposed according to the thermodynamic nature of bonding, which involves two key site switches on different active species in an integrated electrocatalyst. We implement this concept by employing Cu/Fe hetero-phase-interface nanoparticles anchored in TiO2 substrate (Cu/Fe-TiO2) as a model platform. Theoretical calculations coupled with in situ infrared spectra confirm the SASS mechanism: the *NO3, preferentially adsorbed on the in-plane Fe phase, switches towards the Cu/Fe hetero-phase interface to reduce into *NH3, and a further switch related to the *NH3 occurs towards the in-plane Cu phase, notably facilitating the NO3−-into-NH3 conversion. Such a SASS pathway endows Cu/Fe-TiO2 with excellent intrinsic activity, 4.68- and 2.82-fold higher than that of Cu-TiO2 and Fe-TiO2, respectively.