Topochemical Reaction of Exfoliated Layered Cobalt(II) Hydroxide for the Synthesis of Ultrapure Co3O4 as an Oxygen Reduction Catalyst

Abstract

The liquid exfoliation of hydrotalcite‐like α‐Co(OH)2 in formamide produced a new pink β‐form of Co(OH)2 nanosheets [Ex‐NS‐Co(OH)2] with unique nanoscopic properties: a larger surface area of active hydroxides and a much narrower oxidation–reduction potential for the Co2+ ions in the hydroxide layer than those of the bulk α‐Co(OH)2. These unprecedented properties of Ex‐NS‐Co(OH)2 were applied to the topochemical synthesis of crystalline Co3O4 nanocubes (NCs) with clear edges and no impurity phases from an aqueous solution of Co2+ ions at 70 °C. A Co3O4 NC/C catalyst exhibited good catalytic activity for the oxygen reduction reaction (ORR) and higher stability under a continuous electrochemical operation than that of commercial Pt/C.