Synthesis of Co3O4@TiO2 catalysts for oxygen evolution and oxygen reduction reactions

The electrospinning method combined with high temperature thermal annealing was used to prepare TiO2 fibers modified with different concentrations of Co3O4. Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), desktop scanning electron microscope (TM3030)-energy spectrometer (SwiftED3000), thermal analyzer (TGA), X-ray diffractometer (XRD), X-ray photoelectron energy Spectral analyzer (XPS), Brunauer–Emmett–Teller (BET) (BET) were used to study the influence of different cobalt oxide concentrations on the morphology of mesoporous TiO2 fibers. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and continuous cycle method were used to evaluate the fiber's oxygen evolution reaction (OER) and oxygen reduction (ORR) reactivity. It was found that the fiber with a molar ratio of Co to Ti of 1:10 showed the best performance for both OER and ORR reactions in alkaline solution. The fiber showed an overpotential of 382 mV at a current density of 10 mA cm−2, a Tafel slope of 58 mV·dec−1, and a half-wave potential change of only 10 mV after 4000 CV cycles. It has an onset potential of 0.83 V (vs RHE) in the ORR reaction. The OER/ORR overpotential gap (E) of 0.85 V is significantly lower than commercial platinum/carbon and bulk TiO2 analogs. Obviously, this catalytic activity stems from the synergy between Co3O4 and TiO2 fibers. In addition, the higher specific surface area and the presence of disordered mesopores provide a higher charge carrier density during the electrocatalytic process, which improves the reaction activity.