An innovative nanostructure, namely the core–ring structure, is reported in this paper. It occurs in NiCo2O4 nanoplatelets, synthesized by the coprecipitation decomposition method using sodium hydroxide as the precipitant. The yield of core–ring hexagonal NiCo2O4 nanoplatelets is greater than 80% at 200 °C. A high-resolution transmission electron microscopy and energy dispersive spectroscopy investigation reveals the typical core–ring nanostructure, which shows a strong enrichment of Co in the core with a Co content higher than 80%. A mechanism for the core–ring structure formation is proposed. The core–ring NiCo2O4 can be used as an electrocatalyst for an oxygen evolution reaction (OER) in alkaline water electrolysis. Compared with the electrodes of ordinary NiCo2O4 and Co3O4, or other NiCo2O4 electrodes prepared by alternate methods, the electrode coated by core-ring NiCo2O4 nanoplatelets exhibits the greatest electrocatalytic properties, with an over-potential of 0.315 V at a current density of 100 mA cm−2.