Continuous and Scalable Production of Platinum Nanocubes with Uniform and Controllable Sizes in Air-Free Droplet Reactors

Platinum (Pt) nanocrystals hold the key to a variety of catalytic applications, and those with a cubic shape are attractive as a reference catalyst due to their well-defined {100} facets on the surface. Here we demonstrate the use of droplet reactors as a viable platform for the continuous and scalable production of Pt nanocubes with uniform and controllable sizes. The synthesis was found to be sensitive to the O2 from air because of the oxidative etching associated with the O2/Br- pair. As such, either silicone oil or an inert gas had to be employed as the carrier phase to keep the droplets isolated from air. By controlling the amounts of the precursor and halide ions, the edge length of the Pt nanocubes could be tuned from 5-7 nm. In the setting of a millifluidic device, the droplet reactors could be used to achieve a production rate as high as 31.8 mg min-1, about 10-100 times greater than what has been reported in the literature. We also evaluated the electrocatalytic properties of the as-obtained Pt nanocubes toward the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). For the Pt nanocubes of 6 nm in edge length, they showed a specific activity of 0.27 mA cm-2 toward ORR at 0.9 V and a specific activity of 0.96 mA cm-2 toward MOR at the anodic potential.