Electrodeposited Co Crystalline Islands Shelled with Facile Spontaneously Deposited Pt for Improved Oxygen Reduction

The cobalt crystalline islands (Cocryst) were electrochemically deposited onto a glassy carbon (GC) support and then modified by a facile spontaneous deposition of platinum. The electrocatalytic activity of the resulting Cocryst-Pt core-shell catalyst was evaluated for the oxygen reduction reaction (ORR) in an alkaline medium. The XRD characterization of the Cocryst-Pt islands revealed that the cobalt core had a hexagonal close-packed (hcp) crystalline structure, and that the platinum shell exhibited a crystalline structure with a preferential (111) orientation. SEM images showed that the average lateral size of the Cocryst islands was 1.17 μm, which increased to 1.32 μm after adding platinum. The XPS analysis indicated that the outer layer of the bulk metallic Cocryst islands was fully oxidized. During the spontaneous deposition of platinum, the outer Co(OH)2 layer was dissolved, leaving the cobalt core in a metallic state, while the platinum shell remained only partially oxidized. The high electrochemically active surface area of the Cocryst-Pt/GC electrode, along with a suitable crystalline structure of the Cocryst-Pt islands, contributes to enhancing its ORR activity by providing a greater number of surface active sites for oxygen adsorption and subsequent reduction. The ORR on the Cocryst-Pt catalyst occurs via a four-electron reaction pathway, with onset and half-wave potentials of 1.07 V and 0.87 V, respectively, which exceed those of polycrystalline platinum and a commercial benchmark Pt/C.