New Mechanism for N2 Reduction: The Essential Role of Surface Hydrogenation.

Electrocatalytic N2 reduction is one of the most promising ways for green and sustainable production of NH3. However, a mechanistic understanding of the N2 reduction process remains very limited. Herein, a surface-hydrogenation mechanism for the N2 reduction reaction is proposed, which can well address the recently emerged sharp discrepancies between experiments and computations. Our results reveal that surface hydrogenation can drive N2 reduction reaction on catalysts with weak N2-binding strength (i.e., noble-metal catalysts) at low potentials. Instead of N2 adsorption, the reduction of H+ is found to be the first step, which is also the potential determining step of the whole process. N2 can be activated and reduced into *N2H2 subsequently by overcoming relatively high energy barriers, which determines the total reaction rate. Moreover, the cooperative effect of surface *H and the catalysts plays a key role in the activation of N2. Our work not only provides new insights into the N2 reduction reaction, but also paves a promising way for advancing sustainable NH3 production.