Electrocatalytic nitrogen reduction to ammonia by graphene-supported Au4Cu2 and Au2Ag2 nanoclusters

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 reaction (ENRR). Our findings demonstrate that graphene-supported Au₄Cu₂ NCs exhibit remarkable ENRR efficiency, achieving an ammonia yield of 4.14 μg h^-1 cm^-2 and a faradaic efficiency (FE) of up to 49.60% at -0.8 V relative to the reversible hydrogen electrode (RHE). The Au₂Ag₂ NCs possess a similar metal core to 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.