Fuel cells, which are attracting attention as an eco-friendly energy source, obtain electricity and heat simultaneously through the reverse reaction of water electrolysis. Therefore, the catalyst that enhances the reaction efficiency is directly connected to the performance of the fuel cell. To this, a POSTECH-UNIST joint research team has taken a step closer to developing high-performance catalysts by uncovering the ex-solution and phase transition phenomena at the atomic level for the first time.