Platinum Nanostructure Tailoring for Fuel Cell Applications Using Levitated Water Droplets as Green Chemical Reactors

Tailoring of nanostructured materials with well-controlled morphologies and their integration into valuable applications in a facile, cheap, and green way remain a key challenge. Herein, platinum nanoparticles as well as Pt–polymer nanocomposites with unique shapes, including flower-, needle-, porous-, and worm-like structures, were synthesized and simultaneously deposited on a three-dimensional carbon substrate and carbon nanofibers in one step using a levitated, overheated water drop as a green, rotating chemical reactor. Sprinkling of a metal aqueous solution on a hot surface results in its sudden evaporation and creates an overheated zone along with the water self-ionization (i.e., charge separation) at the hot interface. These generated Leidenfrost conditions are believed to induce a series of chemical reactions involving the used solvent and counterions, resulting in the nanoparticles formation. Besides, the in situ generated basic conditions in the vicinity of the liquid–vapor interface due to the loss of hydronium ions into the vapor layer could also play a role in the mechanism of the nanoparticles formation, e.g., by discharging. The as-prepared Pt nanostructures exhibited a superior catalytic activity and stability toward the desired direct formic acid oxidation (essential anodic reaction in fuel cells) into CO2 without generating CO poisoning intermediates compared to the state-of-the-art commercial PtC electrode. The addressed nanotailoring technique is believed to be a promising, inexpensive, and scalable way for the sustainable manufacture of well-designed nanomaterials for future applications.