Identifying the Origin of Ti<sup>3+</sup> Activity toward Enhanced Electrocatalytic N<sub>2</sub> Reduction over TiO<sub>2</sub> Nanoparticles Modulated by Mixed‐Valent Copper
Tongwei Wu, Haitao Zhao, Xiaojuan Zhu, Zhe Xing, Qian Liu, Tong Liu, Shuyan Gao, Siyu Lu, Guang Chen, Abdullah M. Asiri, Yanning Zhang, Xuping Sun
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.