Electrocatalytic Nitrogen Reduction to Ammonia by Graphene-Supported Au4Cu2 and Au2Ag2 Nanoclusters

Abstract

Understanding the impact of size dependence and doping effects in small metal cluster catalysis is crucial for the rational design and development of new catalysts. We synthesized Au2Ag2(PPh3)2(PhC≡C)4 and Au4Cu2(PPh3)4(PhC≡C)6 nanoclusters (NCs), and assessed their efficiency in the electrocatalytic nitrogen reduction reactions (ENRR). Our findings demonstrate that graphene-supported Au4Cu2 NCs exhibit remarkable ENRR efficiency, achieving an ammonia yield of 4.14 μg.h-1cm-2 and a Faradaic efficiency (FE) up to 49.60% at -0.8 V relative to the reversible hydrogen electrode (RHE). The Au2Ag2 NCs possess a similar metal core as Au4Cu2 NCs but lack two supplementary Au(PPh3)(PhC≡C) moieties, resulting in a smaller ammonia yield and FE value. The ENRR activity of graphene-supported Au4Cu2 NCs surpasses that of other supported or unsupported systems, highlighting the significance of gold catalysis, copper doping, and the major influence of graphene as a support. These findings offer critical insights into the design of highly efficient and selective electrocatalysts for improving ammonia production.