NOVELTY - A supported metal-containing powder is made by forming a dispersion of a particulate support in a solution comprising a solvent and a dissolved metal; removing heat from the dispersion to precipitate the dissolved metal onto the support and to freeze the solution, where the heat is removed from the dispersion by contacting a container containing the dispersion with a cryogenic liquid; and separating the support from the solution by freeze drying.    USE - For forming a supported metal-containing powder, for use as an electrocatalyst in fuel cells.    ADVANTAGE - The novel method results in improvements in the efficiency of preparing supported metal electrocatalyst powders and improvements to the powders themselves. It allows for control of the stoichiometry of the deposits, since the suspension is preferably kept within a single container, the solution is not physically separated from the supports (e.g. by filtration), and freezing results in all of the solute precipitating on the supports. Additionally, it allows for the deposition of compounds that may not be deposited by other conventional methods. The deposits formed are isolated, small, and uniformly dispersed over the surface of the supports, and tend to increase the electro-catalytic activity. Since filtering is not necessary, extremely fine particles are not lost and the supported metal powders produced tend to have a greater surface area and activity. Further, the act of depositing the metal species on the supports is fast, e.g. immersing a container of the dispersion/suspension in a cryogenic liquid can solidify the dispersion/suspension in 3-4 minutes.    DETAILED DESCRIPTION - Formation of a supported metal-containing powder includes forming a dispersion of a particulate support in a solution comprising a solvent and a dissolved metal; removing heat from the dispersion to precipitate the dissolved metal from the solution onto the particulate support and to freeze the solution, where the heat is removed from the dispersion by contacting a container containing the dispersion with a cryogenic liquid; and then, separating the particulate support from the solution by freeze drying to yield the supported metal-containing powder comprising the particulate support and a precipitated metal.    An INDEPENDENT CLAIM is also included for a method of forming a carbon-supported platinum alloy, by forming a dispersion of a carbon-supported platinum in a solution comprising a solvent and a dissolved non-platinum metal, where the carbon-supported platinum comprises a particulate carbon support and platinum in its metallic oxidation state; removing heat from the dispersion to precipitate the dissolved non-platinum metal from the solution onto the carbon supported platinum and to freeze the solution, where the heat is removed from the dispersion by contacting a container containing the dispersion with a cryogenic liquid; separating the frozen solution and the carbon-supported platinum by freeze drying; and then forming an alloy on the particulate carbon support to yield the carbon-supported platinum alloy. The carbon-supported platinum alloy comprises the particulate carbon support, the platinum, and the non-platinum metal derived from the precipitated non-platinum metal.