Green synthesis of Co3O4 nanoparticles using psyllium husk (Plantago Ovata) and application as electrocatalyst for oxygen evolution reaction

The continuous supply of hydrogen from renewable sources through water electrolysis technology is a key issue for the development of humanity. To meet this purpose, catalysts based on transition metals (Ni, Fe and Co) are promising candidates for the hydrogen and oxygen evolution reactions. Therefore, in this work, nanocrystalline Co3O4 with a spinel-like cubic structure was prepared by a proteic sol–gel synthesis using psyllium husk as a polymerizing agent, and later tested as an electrocatalyst for the oxygen evolution reaction (OER). The purity of the Co3O4 phase was confirmed by several characterization techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The size of crystallites and particles obtained from Rietveld refinement of X-ray diffraction patterns ranged from 16.5 nm to 25.3 nm for powders calcinated at 400 °C and 600 °C, respectively, confirming nanometric Co3O4 powders. Scanning electron microscopy shows nanostructures with predominantly spherical morphology. From the electrocatalytic point of view, it was observed that the larger particle size impairs the oxygen evolution reaction. The Co3O4 calcined at 400 °C showed superior electrocatalytic performance, with an overpotential of 328 mV at 10 mA cm−2, Tafel slope of 71 mV dec-1, CDL of 5.46 mF cm−2, ECSA of 91 cm2, specific activity of 4.73 mA cm−2 and mass activity of 718 A g−1.