Composite containing platinum-alkaline earth metal alloy, fuel cell and water electrolysis cell containing the composite, and method of producing the composite

A method of producing a composite, the method comprising:

• a step a) of preparing a mixed solution containing a platinum precursor, an alkaline earth metal precursor, a first reducing agent, and an aprotic organic solvent by dissolving the platinum precursor, the alkaline earth metal precursor, and the first reducing agent into the aprotic organic solvent;
• a step b) of preparing a colloid containing a synthetic product by performing a first heat treatment on the mixed solution at a temperature equal to or higher than a boiling point of the aprotic organic solvent and then naturally cooling the mixed solution;
• a step c) of obtaining the synthetic product by centrifuging the colloid;
• a step d) of mixing the synthetic product with a powdery second reducing agent, applying the synthetic product mixed with the powdery second reducing agent onto a carbon support, and then performing a second heat treatment in an inert reducing atmosphere to induce alloying between platinum and an alkaline earth metal to provide an alloyed synthetic product;
• and
• a step e) of removing impurities included in the alloyed synthetic product through an acid treatment.