NOVELTY - A synthetic reaction solution having a composition comprising precursors, capping materials and/or reducing agent is prepared. At least one of the precursors contained in the solution is thermally decomposed and chemically reduced, such that core-shell platinum-vanadium-iron nanoparticles are precipitated from the reaction solution.    USE - Used for forming carbon-supported alloy core-shell platinum-vanadium-iron nanoparticles used as an electrocatalyst (claimed) for a fuel cell.    ADVANTAGE - The process provides core-shell platinum-vanadium-iron nanoparticles having controlled size and high size monodispersity. The nanoparticle catalyst has high monodispersity, a controlled composition, and uniform distribution. The catalyst has high oxygen reduction reaction activity.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) assembling a nanoparticle platinum-vanadium-iron catalyst, involving synthesizing platinum-vanadium-iron nanoparticles having a size of 1-10 nm, and assembling the obtained nanoparticles onto a carbon support, and thermally treating the obtained assembled nanoparticles;    (2) the formation of a carbon-supported core-shell platinum-vanadium-iron nanoparticles catalyst, in which a synthetic reaction solution containing platinum acetylacetonate (Pt(II)(acac)2), vanadyl acetylacetonate (V(V)O(acac)2) and iron pentacarbonyl (Fe(CO)5), is prepared, the precursors in the reaction solution is thermally decomposed and chemically reduced, int he presence of 1,2-hexadecanediol as reducing agent, the nanoparticles are precipitated from the thermally decomposed and reduced precursors in the reaction solution, the nanoparticles are assembled onto a carbon support, by pre-treating, particle loading, sonication and/or stirring and the assembled nanoparticles are thermally treated to form a nanoparticles catalyst;    (3) the formation of core-supported platinum-containing ternary metal nanoparticles, involving decomposing and chemically reducing precursors contained in the reaction solution, and precipitating nanoparticles from the reaction solution;    (4) assembling a ternary metal nanoparticle platinum-containing catalyst, involving forming platinum-containing nanoparticles having a size of 1-10 nm, assembling platinum-containing nanoparticles onto a support, and thermally treating the assembled nanoparticles; and    (5) the formation of a carbon-support core-shell platinum-containing ternary metal nanoparticle catalyst, where a synthetic reaction solution containing platinum acetylacetonate (Pt(II)(acac)2), is prepared, the precursors in the reaction solution are thermally decomposed and chemically reduced, in the presence of 1,2-hexadecanediol as reducing agent, the nanoparticles are precipitated from precursors in the reaction solution, and assembled onto a carbon support and the assembled nanoparticles are thermally treated to form a nanoparticles catalyst.    DESCRIPTION OF DRAWING(S) - The figures show a pictorial schematic representation of a single platinum-vanadium-iron nanoparticle, and an enlarged view of a portion of the surface of the nanoparticle.