Tailoring Morphology and Elemental Distribution of Cu-In Nanocrystals via Galvanic Replacement.

The compositional and structural diversity of bimetallic nanocrystals (NCs) provides a superior tunability of their physico-chemical properties, making them attractive for a variety of applications, including sensing and catalysis. Nevertheless, the manipulation of the properties-determining features of bimetallic NCs still remains a challenge, especially when moving away from noble metals. In this work, we explore the galvanic replacement reaction (GRR) of In NCs and a copper molecular precursor to obtain Cu-In bimetallic NCs with an unprecedented variety of morphologies and distribution of the two metals. We obtain spherical Cu 11 In 9 intermetallic and patchy phase-segregated Cu-In NCs, as well as dimer-like Cu-Cu 11 In 9 and Cu-In NCs. In particular, we find that segregation of the two metals occurs as the GRR progresses with time or with a higher copper precursor concentration. We discover size-dependent reaction kinetics, with the smaller In NCs undergoing a slower transition across the different Cu-In configurations. We compare the obtained results with the bulk Cu-In phase diagram and, interestingly, find that the bigger In NCs stabilize the bulk-like Cu-Cu 11 In 9 configuration before their complete segregation into Cu-In NCs. Finally, we also prove the utility of the new family of Cu-In NCs as model catalysts to elucidate the impact of the metal elemental distribution on the selectivity of these bimetallics toward the electrochemical CO 2 reduction reaction. Generally, we demonstrate that the GRR is a powerful synthetic approach beyond noble metal-containing bimetallic structures, yet that the current knowledge on this reaction is challenged when oxophilic and poorly miscible metal pairs are used.