Finely tuning cobalt valence in Co3O4 lattice through chromium substitution: Regulating the charge transfer and oxygen vacancies for oxygen evolution and methanol oxidation reaction

Abstract

In this intriguing study, our central focus revolves around efficiency of the Oxygen Evolution Reaction (OER) and methanol oxidation Reaction (MOR) through a captivating approach: harnessing the power of cobalt valence modulation in Cobaltite (Co3O4), achieved by the enchanting substitution of chromium (Cr). By seamlessly integrating chromium atoms into the crystal lattice of Co3O4, our ultimate aim is to orchestrate a remarkable transformation in the potential-determining step of the OER, resulting in a symphony of improved catalytic performance. This substitution is done by utilizing simple sol-gel method at low temperatures. This gentle adjustment of cation valence states creates oxygen vacancies on the spinel surface, achieving an ideal ion ratio of Co2+/Co3+. The formation of spinel oxides has been confirmed by a comprehensive range of precise physicochemical techniques including, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HRTEM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) technique and Raman spectroscopy. The presence of oxygen vacancy has been verified with Electron Paramagnetic Resonance (EPR) spectroscopy. The spinel oxide, Cr1.5Co1.5O4 displays superior activity for OER with current density of 100 mA/cm2 at the overpotential of only 413 mV. Our findings highlight the significance of cobalt valence control in promoting OER/MOR activity, paving the way for advanced electrocatalytic systems with enhanced energy conversion capabilities.