Highly Active and Selective Electroreduction of N 2 by the Catalysis of Ga Single Atoms Stabilized on Amorphous TiO 2 Nanofibers.

The electroreduction of N 2 under ambient conditions has emerged as one of the most promising technologies in chemistry, since it is a greener way to make NH 3 than the traditional Haber-Bosch process. However, it is greatly challenged with a low NH 3 yield and faradaic efficiency (FE) because of the lack of highly active and selective catalysts. Inherently, transition (d-block) metals suffer from inferior selectivity due to fierce competition from H 2 evolution, while post-transition (p-block) metals exhibit poor activity due to insufficient "π back-donation" behavior. Considering their distinct yet complementary electronic structures, here we propose a strategy to tackle the activity and selectivity challenge through the atomic dispersion of p-block metal on an all-amorphous transition-metal matrix. To address the activity issue, lotus-root-like amorphous TiO 2 nanofibers are synthesized which, different from vacancy-engineered TiO 2 nanocrystals reported previously, possess abundant intrinsic oxygen vacancies (V O ) together with under-coordinated dangling bonds in nature, resulting in significantly enhanced N 2 activation and electron transport capacity. To address the selectivity issue, well-isolated single atoms (SAs) of Ga are successfully synthesized through the confinement effect of V O , resulting in Ga-V O reactive sites with the maximum availability. It is revealed by density functional theory calculations that Ga SAs are favorable for the selective adsorption of N 2 at the catalyst surface, while V O can facilitate N 2 activation and reduction subsequently. Benefiting from this coupled activity/selectivity design, high NH 3 yield (24.47 μg h -1 mg -1 ) and FE (48.64%) are achieved at an extremely low overpotential of -0.1 V vs RHE.