Theoretical evaluation of the effect of bimetallic Au-based alloy catalysts on initial N2 electroreduction pathways

Abstract

Theoretical studies on the effect of bimetallic Au-based alloy catalysts on initial N₂ electroreduction pathways at the present simulated electrode/aqueous interfaces based on DFT calculations are conducted in this work. The calculated results indicate that the alloying of Au with the transition metals Ni, Pd, Pt, Ru and Ta can facilitate the activation of N₂ molecules in the presence of the electrode/aqueous interface, which may be derived from the kinetic overpotential of the outer Helmholtz plane. The N₂ reduction pathway may be adsorption strength-dependent on N₂, in which the incorporation of transition metals with a strong chemical affinity for N₂ molecules may lead to a dissociative mechanism via the initial NN bond cleavage pathway, whereas the incorporation of transition metals with medium N₂ binding strength may make N₂ reduction proceed by the associative mechanism via the initial N₂H formation pathway. The barriers of the initial N₂ electroreduction into N₂H species can be notably decreased after alloying Au with Ni, Pd, Pt, Ru and Ta compared with that on the Au electrode and the lowest N₂H formation barriers can be obtained in these bimetallic Au-based alloy surfaces with an atomic ratio of 1 : 1, suggesting the strongest electrocatalytic activity. Further changing the atomic ratio leads to a notably increased formation barrier of N₂H species, which can be explained by the Sabatier principle. It is concluded that the incorporation of Ni, Pd, Pt and Ru into Au can remarkably enhance the electrocatalytic activity since the HER barriers are notably higher than those of N₂H formation, whereas the alloying of Au with Ta may not be able to effectively improve the N₂ reduction performance due to the uninhibited HER. The present theoretical evaluations provide a promising method to design efficient bimetallic alloy electrocatalysts for N₂ electroreduction into NH₃ products.