Exceptional size-dependent activity enhancement in the catalytic electroreduction of N2 over Mo nanoparticles

Electroreduction of N 2 to ammonia (NH 3 ) under ambient conditions, driven by renewable electricity, provides a promising alternative to the Haber-Bosch process and can reduce over 90% of CO 2 emissions via NH 3 synthesis. However, this process suffers from the shortage of efficient electrocatalysts . Herein, we report the size-dependent catalytic activity of Mo nanoparticles (NPs) in the size range of 1–10 nm for the electrochemical synthesis of NH 3 from N 2 and H 2 O. Current density drastically increases as Mo size decreases. The mass activity of 1.5 nm Mo NPs reaches 27.6 μg h −1  mg −1 cat. , which is higher than that of the best noble metal catalyst under comparable reaction conditions. Density functional theory (DFT) calculations show that the enhanced activity with a small size is due to an increase in edge sites between (110) and (100) surfaces. This condition weakens the binding of ∗NH 2 and lowers the energy barrier of the second NH 3 desorption at the determining step.