Ceria　has　been　widely　used　as　support　in　electrocatalysis　for　its　high　degree　of　oxygen　storage,　fast　oxygen　mobility,　and　reduction　and　oxidation　properties　at　mild　conditions.　However,　it　is　unclear　what　are　the　underlying　principles　and　the　nature　of　surface　involved.　By　controlling　the　growth　of　various　morphologies　of　ceria　nanoparticles,　it　is　demonstrated　that　the　cubic-form　of　ceria,　predominantly　covered　with　higher　energy　polar　surface　(100),　as　support　for　Pd　gives　much　higher　activity　in　the　electrocatalytic　oxidation　of　formic　acid　than　ceria　of　other　morphologies　(rods　and　spheres)　with　low-indexed　facets　((110)　and　(111)).　High-resolution　transmission　electron　spectroscopy　confirms　the　alternating　layer-to-layer　of　cations　and　anions　in　(100)　surface,　and　the　electrostatic　repulsion　of　oxygen　anions　within　the　same　layers　gives　intrinsically　higher　oxygen　vacancies　on　this　redox　active　surface　in　order　to　reduce　surface　polarity.　Density　functional　theory　calculations　suggest　that　the　properties　of　fast　oxygen　mobility　to　reoxidize　the　CO-poisoned　Pd　may　arise　from　the　overdosed　oxygens　on　these　ceria　surface　layers　during　electro-oxidation　hence　sustaining　higher　activity.