Cobaltitas de cálcio dopadas com Fe como eletrocatalisadores para a reação de evolução de oxigênio

Abstract

The electrolysis of alkaline solutions is one of the most used strategies for producing hydrogen (H2). This process distinguishes itself by breaking the water molecule (water splitting) through two semi-reactions: Hydrogen Evolution Reaction (HER, cathodic reaction) and Oxygen Evolution Reaction (OER, anodic reaction). The OER is fundamental for several electrochemical technologies related to generate and storage energy. New research for developing low-cost electrocatalysts with a good electrochemical activity using more earth abundant elements has intensified in recent years. The current work aims to study the effect of Fe doping on the OER of calcium cobaltites, Ca3Co4-xFexO9 (x = 0, 0.1, 0.4, and 0.8). Powders were obtained by a proteic sol-gel method using gelatin with calcination at 900 °C for 2 h. The resultant samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). X-ray photoelectron spectroscopy (XPS) provided information on the chemical states of the surface, while Mössbauer spectroscopy confirmed the presence of Fe+2, Fe+3 and Fe+4 ions. The Fe+2 ions replace the Co ions in the Ca2CoO3 layer and the Fe+4 ions are located in the CoO2 layer. While the Fe+3 ions are present in the secondary phase Ca2Fe2O5 found in the samples. Fe has a strong preference for occupying octahedral sites in the CoO2 layer over the Ca2CoO3 layer in the calcium cobaltite maladjusted type structure. Linear scanning voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to analyze the electrochemical performance. The results indicated that Ca3Co3.2Fe0.8O9 needed the smallest overpotential of 320 mV to generate a current density of 10 mA cm-2.