Facile synthesis of efficient CoO nanostructures using the milky sap of for oxygen evolution reactions and supercapacitor applications.

The preparation of CoO nanostructures by a green method has been rapidly increasing owing to its promising aspects, such as facileness, atom economy, low cost, scale-up synthesis, environmental friendliness, and minimal use of hazardous chemicals. In this study, we report on the synthesis of CoO nanostructures using the milky sap of (CP) by a low-temperature aqueous chemical growth method. The milky sap of CP-mediated CoO nanostructures were investigated for oxygen evolution reactions (OERs) and supercapacitor applications. The structure and shape characterizations were done by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. The prepared CoO nanostructures showed a heterogeneous morphology consisting of nanoparticles and large micro clusters. A typical cubic phase and a spinel structure of CoO nanostructures were also observed. The OER result was obtained at a low overpotential of 250 mV at 10 mA cm and a low Tafel slope of 53 mV dec. In addition, the durability of 45 hours was also found at 20 mA cm. The newly prepared CoO nanostructures using the milky sap of CP were also used to demonstrate a high specific capacitance of 700 F g at a current density of 0.8 A g and a power density of 30 W h kg. The enhanced electrochemical performance of CoO nanostructures prepared using the milky sap of CP could be attributed to the surface oxygen vacancies, a relatively high amount of Co, the reduction in the optical band gap and the fast charge transfer rate. These surface, structural, and optical properties were induced by reducing, capping, and stabilizing agents from the milky sap of CP. The obtained results of OERs and supercapacitor applications strongly recommend the use of the milky sap of CP for the synthesis of diverse efficient nanostructured materials in a specific application, particularly in energy conversion and storage devices.