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.