To address the above challenges in the development and study of NCs, surfactant-free (SF) colloidal syntheses are promising strategies . The definition of a SF synthesis is debatable and we here consider that a synthesis is SF, if no chemical used for the synthesis other than the metal precursor has a molar mass above 100 g mol -1 , and no support is used during the synthesis to avoid support-dependent effects, discussed elsewhere . Note that in this definition, the accent is on the synthesis and not the resulting NPs, which are necessarily stabilized by electrostatic interactions and/or small molecules such as CO . Using polyol-based syntheses, we could study size and particle proximity effects of Pt NPs for the oxygen reduction reaction (ORR), showing that achieving high metal loadings with small size NPs leads to several benefits to improve mass activity (MA) and stability . Recently, we developed SF synthetic strategies in low boiling point solvents to facilitate the synthesis of the NPs .