Sustainable synthesis of Co NPs@Graphited carbon microspheres as an efficient electrocatalyst for the oxygen-evolution reaction

•Excellent microsphere structure is succeeded from a green precursor of starch.•A new strategy to avoid the dissolution and collapse of starch microspheres.•The Co NPs were well enwrapped by porous graphited carbon nanofilms.•A relatively high degree of graphitization for GCMs is achieved at 900 °C.

A temperature-controlled water-swelling and catalytic graphitization associated strategy has been demonstrated for the sustainable synthesis of perfect Co nanoparticles-wrapped graphited carbon microspheres (Co@GCMs) from a green precursor of corn starch at a relatively low temperature. This strategy results in a relatively high degree of graphitization for GCMs at 900 °C and excellent microsphere structure succeeded from the precursor. The Co nanoparticles were well enwrapped by porous graphited carbon nanofilms which have been grown on the surface of GCMs. Such a unique Co@GCMs hybrid architecture could afford a very high catalytic activity as well as a desirable electrochemical stability for the oxygen evolution reaction (OER). The Co@GCMs sample sintered at 900 °C shows an ideal onset potentials of 1.36 V and a very high catalytic current density of 6.43 A g−1 at 1.60 V potential, which demonstrates a positive application prospect of this hybrid material.