a membrane - electrode assembly includes a catalyst layer formed on both sides of a polymer electrolyte membrane , a platinum - metal alloy catalyst included in the catalyst layer , wherein the alloy catalyst shows a diffraction peak in a 110 plane at a degree of 2q = 30 − 35 in the measurement of x - ray diffraction . the alloy catalyst has an excellent stability due to the compact crystal lattice structure of the catalyst , and it incurs low production costs and has sensitive reactivity .