Doping strain induced bi-Ti³⁺ pairs for efficient N₂ activation and electrocatalytic fixation

The electrochemical N₂ fixation to produce ammonia is attractive but significantly challenging with low yield and poor selectivity. Herein, we first used density function theory calculations to reveal adjacent bi-Ti³⁺ pairs formed on anatase TiO₂ as the most active electrocatalytic centers for efficient N₂ lying-down chemisorption and activation. Then, by doping of anatase TiO₂ with Zr⁴⁺ that has similar d-electron configuration and oxide structure but relatively larger ionic size, the adjacent bi-Ti³⁺ sites were induced and enriched via a strained effect, which in turn enhanced the formation of oxygen vacancies. The Zr⁴⁺-doped anatase TiO₂ exhibited excellent electrocatalytic N₂ fixation performances, with an ammonia production rate (8.90 µg·h^-1·cm^-2) and a Faradaic efficiency of 17.3% at -0.45 V versus reversible hydrogen electrode under ambient aqueous conditions. Moreover, our work suggests a viewpoint to understand and apply the same-valance dopants in heterogeneous catalysis, which is generally useful but still poorly understood.