Microfluidic Assisted Synthesis of Hybrid Au–Pd Dumbbell-like Nanostructures: Sequential Addition of Reagents and Ultrasonic Radiation

A sequential-addition microfluidic reactor and an ultrasonic integrated microfluidic reactor were designed to produce with high selectivity hybrid Au–Pd dumbbell-like nanostructures (Au–Pd DBNPs), consisting of a palladium segment tipped with gold heads. A single-stage synthesis was not able to synthesize hybrid nanostructures due to the high reactivity of gold. On the other hand, a two-step method was successful by first synthesizing Pd nanorod-like structures and subsequent growing of Au on the tips of those structures by the localized galvanic replacement reaction. The localized deposition of Au onto both tips of palladium rods was achieved by using two different microfluidic approaches: (i) by sequential injection of gold along the reaction channel at 100 °C and a 5 min residence time, and (ii) by ultrasonic radiation at room temperature and a 2 min residence time. The synthesized Au–Pd DBNPs had higher electrocatalytic activity in the ethanol oxidation reaction in alkaline media than the Pd nanorods.