Synergistic effect of oxygen defects and hetero-phase junctions of TiO2 for selective nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction to ammonia (NH3) has been received increasing attention due to the potential of both decontaminating nitrogen oxide (NOx) from industrial exhaust gas and providing an option for NH3 synthesis. However, their related catalytic process and mechanism dominated by the active phase structure and active sites of nitrate to ammonia electrocatalyst still remain unclear. To this end, in this study TiO2 nanomaterials with constructed hetero-phase junctions and oxygen defects were used to study the catalytic mechanism and make a clear of the function of hetero-phase junctions and defects. Combined with EPR and FT-IR methods, oxygen defects acted as the adsorption sites of NO3- are experimentally confirmed. Systematic characterizations further demonstrate that enhanced performance with the highest NH3 Faradaic efficiency (78.0%) and selectivity (81.9%) for NITRR can be attributed to the Ti3+- Odef pairs and hetero-phase junctions induced strong interface interactions between anatase and rutile phases. The online differential electrochemical mass spectrometry (DEMS) and density functional theory (DFT) calculations demonstrate that both Ti3+ - Odef pairs and hetero-phase junctions lead to the decrease of adsorption energy of NO3- and promote the formation of *NOH intermediates, revealing the reaction mechanism for NH3 synthesis from NO3-.