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.