Incorporation of Fe in mixed CoCu-alkoxide hollow sphere for enhancing the electrochemical water oxidation performance

Abstract

The promotion of water electrolysis performance heavily relies on the development of affordable and efficient electrocatalytic materials for the oxygen evolution reaction (OER). In this study, ternary Fe-substituted CoCu-glycerate microspheres (CoCuFe(X)-Gly) with cobalt (Co):copper (Cu):iron (Fe) atomic ratio of 2:1-X:X (X = 0.15, 0.3, 0.5, 0.8) have been prepared through facile template-free solvothermal method to examine their performance as alkaline OER catalyst. The results suggested that Fe incorporation could enhance the OER activity, and all Fe-modified samples showed lower overpotential with faster kinetic, as revealed by their Tafel slope and electrochemical impedance spectroscopy (EIS) analysis. Among the fabricated samples, CoCuFe(0.5)-Gly possessed the smallest overpotential of 317 mV at 10 mA/cm2 with 3.58-fold higher current density than that of Fe-free CoCu-Gly at the overpotential of 350 mV. Cyclic voltammetry (CV) disclosed that Fe incorporation imposed strong electronic interactions that facilitate the transformation of metal-glycerate surface into active oxyhydroxide species under anodic condition prevalent before oxygen evolution reaction. Using various characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method of surface area analysis, and thermogravimetric analysis (TGA), the physiochemical traits of samples have been carefully elucidated to determine the changes applied upon Fe substitution. Also, through Fe introduction, owing to the outward diffusion of ions to replace 2-propanol with glycerol, the solid microspheres partly become hollow which results in higher BET surface area and increase in accessible active sites. However, the evaluation of current density normalized by electrochemical active surface area (ECSA) indicates that the promotional effect of Fe was not solely related to the higher surface area but also because the intrinsic activity of Fe-modified samples has also been enhanced. The durability of optimal CoCuFe(0.5)-Gly catalyst has been examined using chronopotentiometry, chronoamperometry and potential cycling methods the findings of which suggest the good short-term and long-term stability of catalyst.