Fe-doped calcium cobaltites as electrocatalysts for oxygen evolution reaction

The electrolysis of alkaline solutions is one of the most used strategies for producing hydrogen (H 2 ). 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 store 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, Ca 3 Co 4- x Fe x O 9 ( 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 microscope (FESEM). X-ray photoelectron spectroscopy (XPS) provided information on the surface chemical states, while Mössbauer spectroscopy indicated that Fe has a strong preference for octahedral sites in the CoO 2 layer rather than in the Ca 2 CoO 3 layer in the calcium cobaltite misfit-type structure. Linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to analyze the electrochemical performance. The results indicate that Ca 3 Co 3·2 Fe 0·8 O 9 needs the lowest overpotential of 320 mV to generate a current density of 10 mA cm −2 . • Calcium cobaltites (C349) synthesized by a proteic sol-gel method. • Fe location in the calcium cobaltite structure through Mössbauer spectroscopy. • C349–Fe0.8 sample needed a potential of 320 mV to generate a current density of 10 mA cm −2 .