Ni Single-Atom Modulation of Ti-O Covalency Boosts Ammonia Oxidation Electrocatalysis

Non-noble transition metal oxides, particularly TiO₂-based systems, can be an alternative to noble metal-based catalysts for the electrochemical ammonia oxidation reaction (AOR) due to their abundance, low cost, and corrosion resistance, but it remains hindered by lower performance and undesired selectivity toward oxygenated nitrogen species instead of N₂, largely stemming from insufficient active sites and higher energy barrier for coupling intermediates. To overcome the issues, we introduce a Ni single-atom-induced covalent modulation strategy for constructing Ni SAC@TiO₂ with tunable Ti-O covalency. Hard and soft X-ray absorption (XAS) combined with photoelectron spectroscopy (XPS) reveal strong metal-support interactions that enhance Ti-O covalency and create abundant active sites. Ni SAC@TiO₂ catalyst nearly doubles the catalytic activity of pristine TiO₂ and retains >98% of its initial performance after 2000 accelerated stress testing cycles. In situ surface-enhanced Raman scattering (SERS) shows improved interaction with reactants and intermediates, while in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) demonstrates that Ni SAC@TiO₂ effectively suppresses the buildup of deactivating NO_x species and promotes NH_x-NH_y coupling mediated pathways for selective N₂ evolution, further corroborating the theoretical insights. These findings highlight single-atom modulation of Ti-O covalency as a powerful strategy to unlock efficient and robust TiO₂-based catalysts for AOR.