The ultra-small size of the pre-cat

The ultra-small size of the pre-catalysts plays an important role in forming the core/shell structure. The force of electroreduction pulls all of the anions out of the core lattice along the short diffusion channels, while the quantum confinement of electrons—together with the higher affinity of Ru toward oxygen than chlorine— detains oxygen at the sub-lattice.29 Meanwhile, the force of electrooxidation promotes coordination between residual oxygen and subsurface Ru. Such highly strained configuration cannot be achieved with a larger precatalyst (12 nm; Figure S3).