This paper presents an in situ chemical vapor reaction in a molten salt (KOH–NaOH, MS) for the synthesis of Pt nanosheets. Unlike conventional solution phase synthesis of nanoparticles in organic and aqueous solutions, no organic surfactant or capping agent was used. The surfactant-free Pt nanosheets were used directly to prepare oxygen reduction electrocatalysts without carbon supports and showed little loss of electrochemical surface area in the accelerated durability test. As the MS has a low vapor pressure under ambient pressure, this approach should also have environmental benefits because of reduced risk for releasing toxic gases from volatile organic solvents (VOCs).