TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compounds: The metal salt of the second metal can be ionized into a cationic complex. The metal salt of the second metal is of formula XAmB'n (I).X= a group III-XV metal, metalloid, lanthanide metal or actinide metal, preferably platinum, ruthenium, rhodium, molybdenum, osmium, iridium, rhenium, palladium, vanadium, tungsten, cobalt, iron, selenium, nickel, bismuth, tin, chromium, titanium, gold, cerium, silver or copper;A= NH3, CH3NH2 or H2O;B'= a monovalent anion, preferably NO3-, NO2-, OH-, F-, Cl-, Br- or I-;m= 2, 4 or 6, andn= 1-7.The first metal is also defined by X and is different from the second metal.The carrier is a carbon-based material or an inorganic fine particle. The carbon-based material comprises carbon black, carbon nanotube (CNT), graphite, graphene, activated carbon, mesoporous carbon, carbon fiber or carbon nanowire. The inorganic fine particle comprises alumina, silica, titania or zirconia.The solvent includes water.The reducing agent has a standard reduction potential of -0.23 V or less and comprises sodium borohydride, hydrazine, lithium aluminum hydride and/or lithium triethylborohydride.Preferred Method: The method is effected at room temperature and without surfactant. The metal salt of the second metal is added so that the molar ratio of the first metal to the second metal in the solution is 1:1-10:1. The pH of the solution is adjusted by adding a base solution comprising sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide or lithium hydroxide.Preferred Product: The particle diameter of the core-shell particle is 80-120% of the average particle diameter of the core-shell particles, The average particle diameter is 2-300 nm. The particle diameter of the core is 1-200 nm and the thickness of the shell is 0.5-50 nm. EXAMPLE - 60 mg Vulcan (RTM: carbon black) XC 72 in which nickel particles having a size of 5-10 nm are supported was added to and dispersed in 10 ml distilled water to form a solution. The pH of the solution was adjusted to 11 by adding 0.3 ml 1 M sodium hydroxide. 50 mg Pt(NH3)4(NO3)2 as a platinum precursor dissolved in distilled water is added to the solution, and the resulting solution is stirred at room temperature for 30 minutes. The molar ratio of nickel to platinum is 3:1. Core-shell particles comprising a core including nickel and a shell including platinum are formed by adding 60 mg sodium borohydride while stirring the solution and reacting the resulting solution for 1 hour. The core-shell particles are centrifuged at 10,000 rpm for 10 minutes, the supernatant in the upper layer is discarded and the remaining precipitate is re-dispersed in 20 ml water. The centrifugation is repeated two more times to separate and wash the core-shell particles.