Theoretical insights into the electroreduction mechanism of N2 to NH3 from an improved Au(111)/H2O interface model

Abstract

An improved H coverage-dependent Au(111)/H₂O electrochemical interface model is proposed in this paper, which is firstly used to study electroreduction mechanisms of N₂ into NH₃ at the thermodynamical equilibrium potential in cooperation with electronic structure analysis. The results show that the associative mechanism is more favorable on Au(111) and therein alternating and distal pathways may be able to parallelly occur in gas phase and the present simulated electrochemical interface. The initial N₂ reduction into the N₂H intermediate is the rate determining step, which may be able to be regarded as the origin of the observed experimentally high overpotential during N₂ electroreduction. The presence of an electrochemical environment can significantly change the N₂ reduction pathway and decrease the barrier of the rate determining step, which can be ascribed to the significant electron accumulation and interaction between N₂ molecules and H₂O clusters. The theoretical results display excellent consistency with the available experimental data, confirming the rationality of the present proposed electrochemical model. The comparison of the barrier between the hydrogen evolution reaction and rate determining step well explains why the activity of Au electrodes is usually unsatisfactory. Accordingly, a single descriptor can be proposed, in which an ideal electrocatalyst should be able to reduce the barrier for initial N₂ electroreduction into N₂H. In this way, N₂ electroreduction pathways can be facilitated and the yield of NH₃ can be enhanced. We believe that the present study can represent progress to study N₂ electroreduction mechanisms from an improved electrochemical model.