NOVELTY - Using ethanol as solvent and a reducing agent, silver nitrate and copper nitrate trihydrate are reduced hydrothermally into silver and copper nanoparticles. The nanoparticles are deposited on carbon particles to form a carbon-supported silver-copper binary nano-metal catalyst. The catalyst particles are chemically surface-modified using polyaniline, to obtain a carbon-silver-copper-polyaniline composite electrocatalyst.    USE - Preparation of carbon-silver-copper-polyaniline composite electrocatalyst used for oxygen-reduction reaction in fuel cells (all claimed).    ADVANTAGE - The method enables simple preparation of carbon-silver-copper-polyaniline composite electrocatalyst having stable structure and excellent electrocatalytic activity with respect to oxygen-reduction reaction. The oxygen-reduction reaction initial potential is 0.16 V (Vs standard hydrogen electrode), and the current density is 1.5 A/cm2 at -0.15 V (Vs standard hydrogen electrode). The usage amount of expensive silver is reduced.    DETAILED DESCRIPTION - Silver nitrate-ethanol solution with a concentration of 2-8 mM and copper nitrate trihydrate-ethanol solution with a concentration of 2-8 mM are placed in a hydrothermal reactor. Vulcan XC-72 (RTM: carbon black powder) is added and ultrasonically treated for 5-20 minutes. The addition amount of carbon black powder is 1.5-2 times the total content of silver and copper. While stirring, sodium hydroxide-ethanol solution with a concentration of 0.5-2M is added to the hydrothermal reactor slowly and ultrasonically treated for 5-20 minutes. The reactor is heated to 150-200 degrees C for 0.5-5 hours and then cooled to room temperature. The reaction liquid is filtered, and the obtained catalyst particles are washed with pure water and absolute ethanol to obtain a carbon-supported silver-copper binary nano-metal catalyst. The catalyst is mixed with hydrochloric acid solution of aniline and ultrasonically dispersed. Hydrochloric acid solution of ammonium sulfate is dripped at 0-5 degrees C and stirred for 6 hours. The mixture is placed for 12 hours at room temperature. Hydrochloric acid solution of aniline is obtained by dissolving aniline in hydrochloric acid with a concentration of 1 mM of aqueous solution of aniline. The aniline concentration is 2-8M. The hydrochloric acid solution of ammonium persulfate is obtained by dissolving ammonium persulfate with a concentration of 1 mM in hydrochloric acid. The concentration of ammonium persulfate is 10-20 mM. The mixture is filtered, and washed with pure water and absolute ethanol to obtain a carbon-silver-copper-polyaniline composite electrocatalyst. An INDEPENDENT CLAIM is included for usage method of carbon-silver-copper-polyaniline composite electrocatalyst, which involves mixing the electrocatalyst and anhydrous ethanol, adding 5 %mass Nafion (RTM: perfluorinated resin solution), ultrasonically processing into a paste, dripping the paste on the surface of a carbon electrode, and drying to obtain a working electrode.