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

Abstract

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.

Recent Advances in Electrochemical Synthesis of Ammonia through Nitrogen Reduction under Ambient Conditions

“…This mechanism is suitable for the noble metal catalysts, such as Au, Pd. This result enriches the mechanism of NH 3 synthesis by N 2 reduction …”

“…Since the NRR test results are time‐sensitive and need to be performed in a few hours, the experiment is best performed in a closed or stable environment. 2) Nitrogen‐containing materials and the Nafion membrane used in the experiment have been confirmed to have an unignorable effect on the experimental results . Open circuit control measurements and argon control measurements should be used to remove background NH 3 from the contamination source .…”

Progress and challenges in photocatalytic ammonia synthesis

“…1c). 27,28 For the Nhydrogenation mechanism, there are two different pathways for NRR, dissociative and associative pathways. In the dissociative pathway, N2 triple bond is broken before the hydrogenation, followed by hydrogenation of the N-adatoms into NH3 on the catalyst surface.…”

“…Recently, a novel surface-hydrogenation mechanism for NRR has been proposed ( Fig. 1c), 28 in which the adsorbed H + is reduced into *H first, and then N2 molecules react with surface *H to generate *N2H2, and finally the formed *N2H2 intermediates are reduced into NH3. The first step is the trigger step, which enables the NRR to occur at a low potential.…”

Spatiotemporal Coupling Dual-photocatalytic Integration in Atomic- hybridized Co0.5Fe0.5In2S4 Nanoflowers for High Efficiency Nitrogen Reduction

“…In principle, the breakthrough in N 2 reduction e ciency should be simultaneously considered from the regulation of reaction pathway and the enhancement of carrier separation. Recently, some reports disclose that surface hydrogenation can drive NRR on catalysts with weak N 2 -binding strength at low potentials 5,21 , lightening the idea of directly integrating NRR onto HER together. Supposing that the H*-covered active sites induced by HER enable N 2 to be activated and directly reduced into *N 2 H 2 to overcome relatively high energy barriers at N≡N triplet bond activation, we will realize a dual photocatalytic integration strategy for steering the reaction kinetic pathway and boosting NH 3 production e ciency.…”