NOVELTY - A metal-air fuel cell based on a solid oxide electrolyte comprises an anode (400), a cathode (200), a solid oxide electrolyte (300) and a metal fuel (500), where the metal fuel comprises metal nanoparticles having an average particle diameter of 1 nm to 100 nm.    USE - As metal-air fuel cell based on a solid oxide electrolyte (claimed); and as electrochemical device that generates electric energy based on change in free energy of fuel caused by oxidation of the fuel. The fuel cells include phosphoric acid fuel cell, a polymer electrolyte membrane fuel cell, a molten carbonate fuel cell, a metal-air fuel cell, a solid oxide fuel cell and the like.    ADVANTAGE - The metal nanoparticles have a low melting point and provide high reactivity. Thus, the metal-air fuel cell forms a metal molten phase at a relatively low temperature thereby improving contactability and has improved reactivity to promote oxidation, thereby enabling highly efficient power generation. The solid oxide-based metal-air fuel cell not only solve the problem of the conventional metal-air fuel cell suffering from loss of the liquid electrolyte, but also allows application of inherent merits of the solid electrolyte fuel cell which promotes oxidation under high temperature operation conditions. The fuel cell exhibits improved power generation efficiency. The fuel materials have various physical chemical characteristics. The metal-air fuel cell based on a solid oxide employing a metal fuel has improved reactivity and contactability. The nanoparticles exhibit low melting point to facilitate formation of a molten phase, thereby improving contactability. With the reduced average nano-scale diameter of the metal particles, the fuel cell provides a high oxidation rate, thereby achieving further improved power generation efficiency. The fuel cell employs metal particles, which have an average particle diameter of 1 nm to 100 nm and have a lowered melting point and high oxidation reactivity, to secure high contactability using the metal nanoparticles easily melted at a relatively low temperature, thereby reducing resistance between the catalyst and the fuel while continuously producing high voltage current through rapid reaction. The fuel cell allows the metal nanoparticle fuel to be mixed with an organic solvent or other materials to have a solid, liquid, gel or powdery phase as needed, thereby enabling compatibility.    DESCRIPTION OF DRAWING(S) - The figure shows diagram of a fuel cell.    Cathode inlet (100)    Cathode catalyst (200)    Electrolyte (300)    Anode catalyst (400)    Metal fuel (500)    Anode inlet (600)    Cell sheath (700)    Anode collector (800)    Cathode collector (900)    Connecting material (1000)