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Platinum multipods are attractive for catalytic and electrocatalytic applications owing to their highly open, branched structure and thus high specific surface area. A number of methods have been reported for the synthesis of Pt multipods, but they are all limited in terms of throughput due to the use of batch reactors. Here we report the use of a fluidic device for the continuous and scalable synthesis of Pt multipods with sizes controlled in the ranges of 3–5 nm and 2–3 nm for the length and width, respectively, of the branched arms. The facile protocol involves the use ofas a precursor to Pt and oleylamine as a solvent, surfactant, and temperature‐dependent reductant. When a solution of these two components is pumped into the polytetrafluoroethylene tube immersed in an oil bath and held at 180 °C, Pt multipods are formed through fast autocatalytic surface growth and small particles attachment. Compared with the batch‐based synthesis, the throughput of the production in the flow system can readily be increased to 17 mg of Pt per hour while retaining a tight control over the quality of the products. When supported on carbon, the Pt multipods exhibit enhanced activity toward oxygen reduction relative to the commercial Pt/C catalyst.

This paper describes a simple and robust method for the continuous production of water‐soluble nanocrystals using anti‐solvent precipitation under diffusion control in a fluidic device. We use sodium chloride (NaCl) as an example to demonstrate the concept. In a typical process, aqueous NaCl and ethanol (the anti‐solvent) serve as the focused and focusing phases, respectively, for the generation of a coaxial‐flow system. Upon contact with each other, the rapid diffusion between water and ethanol leads to the formation of NaCl nanocrystals at the interface while a gradient in NaCl concentration is created along the flow direction. The nucleation and growth of NaCl nanocrystals can be readily tuned by varying the hydrodynamic parameters such as the ratio between the flow rates of the two phases and the total volumetric rate. By optimizing these parameters, we are able to produce NaCl nanocubes and nanospheres as small as 20 nm and 6 nm, respectively, while attaining a narrow distribution in size. We have also successfully generated KCl nanocrystals with similar controls, demonstrating the generality of this method for the production of water‐soluble nanocrystals.