Identifying the Origin of Ti³⁺ Activity toward Enhanced Electrocatalytic N₂ Reduction over TiO₂ Nanoparticles Modulated by Mixed‐Valent Copper

Abstract

Abstract The ambient electrocatalytic N 2 reduction reaction (NRR) enabled by TiO 2 has attracted extensive recent attention. Previous studies suggest the formation of Ti 3+ in TiO 2 can significantly improve the NRR activity, but it still remains unclear what kinds of Ti 3+ are effective. Herein, it is demonstrated that mixed‐valent Cu acts as an effective dopant to modulate the oxygen vacancy (V O ) concentration and Ti 3+ formation, which markedly improves the electrocatalytic NRR performance. In 0.5 m LiClO 4 , this electrocatalyst attains a high Faradic efficiency of 21.99% and a large NH 3 yield of 21.31 µg h −1 mg cat. −1 at –0.55 V vs reversible hydrogen electrode, which even surpasses most reported Ti‐based NRR electrocatalysts. Using density function theory calculations, it is evidenced that mixed‐valent Cu ions modulate the TiO 2 (101) surface with multiple oxygen vacancies, which is beneficial for generating different Ti 3+ 3 d 1 defect states localized below the Fermi energy. N 2 activation and adsorption are effectively strengthened when Ti 3+ 3 d 1 defect states present the splitting of e g and t 2g orbitals, which can be modulated by its coordination structure. The synergistic roles of the three ion pairs formed by the V O defect, including Cu 1+ –Ti 4+ , Ti 3+ –Ti 4+ and Ti 3+ –Ti 3+ , are together responsible for the enhanced NRR performance.