Core-shell nanoparticles and methods of fabricating core-shell nanoparticles are provided. A core-shell nanoparticle can include an inner core(1) surrounded by an outer shell(2). The core(1) can include one or more platinum group metal, noble metal, oxidized platinum group metal, and/or oxidized noble metal. The shell(2) can be platinum or platinum alloy. The platinum alloy can be a mixture of platinum and transition metals. The core(1) can be an oxidized ruthenium core, and the shell(2) can be a platinum- nickel alloy. A carbon source can also be included to act as a support for the core-shell nanoparticles.