The Role of Oxidation of Silver in Bimetallic Gold-Silver Nanocages on Electrocatalytic Activity of Nitrogen Reduction Reaction.

Abstract

Electrochemical ammonia synthesis from nitrogen and water provides an alternative route to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way if electricity is generated from renewable sources. We have previously demonstrated the use of bimetallic hollow Au-Ag nanocages as an effective electrocatalyst for electrosynthesis of ammonia in an aqueous solution. The stability of the electrocatalyst during electrochemical nitrogen reduction reaction (NRR) is of paramount importance when considering the feasibility of electrochemical NRR for industrial applications. Here, the role of oxidation of silver in bimetallic Au-Ag nanocages with various localized surface plasmon resonance (LSPR) peak positions on electrocatalytic activity of NRR is studied by oxygen treatment of Ag through the simple oxidation process to form Ag2O-Au nanocages. Electrocatalytic NRR activity with an NH3 yield rate of 2.14 µg cm-2 h-1 and Faradaic efficiency of 23.4% has been achieved at -0.4V vs. RHE using Ag2O-Au-719. This electrochemical performance is a substantial reduction to our previously reported NRR activity using Ag-Au-715 nanocages (3.74 µg cm-2 h-1 and 35.9% at -0.4V vs. RHE). This work highlights the importance of an O2-free environment in electrochemical NRR for the stable N2 electrolysis operation and discerns the role of Ag on the selectivity and activity of bimetallic Au-Ag nanocages toward NRR.