The present invention relates to a composite which, compared to a conventional pure platinum catalyst, is economical and exhibits excellent catalytic activity and notably enhanced stability. Specifically, the composite, according to the present invention, comprises: a carbon support; and a binary alloy supported on the carbon support and containing platinum (Pt) and an alkaline earth metal, wherein, in a Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS), E1 and E2, prescribed by formulas 1 and 2, respectively, below, satisfy formula 3 below. (Formula 1) E1 = E0 - E0(ref) (Formula 2) E2 = EII - EII(ref) (Formula 3) E1/E2 ≤ 0.85 In formulas 1 and 2, E0(ref) and EII(ref) respectively represent, in a Pt 4f XPS spectrum of pure platinum (Pt), the binding energy (center) of the Pt(0) peak and the binding energy (center) of the Pt(II) peak, and E0 and EII respectively represent, in the Pt 4f XPS spectrum of the binary alloy, the binding energy (center) of the Pt(0) peak and the binding energy (center) of the Pt(II) peak
