Effect of the calcination temperature on the characteristics of Ni/Fe-oxide electrocatalysts for application in anion exchange membrane electrolysers

Abstract

Nickel–iron-oxide catalysts were synthesized by a liquid-phase method, through the oxalate route, and used, as anodes, in an anion exchange membrane electrolyzer. The effect of the heating treatments (performed at 350 °C, 450 °C, and 550 °C) on the structure, composition, particle size, and catalytic activity was analyzed. The morphological features were investigated by transmission electron microscopy (TEM), showing an increased particle size for the catalysts treated at higher temperatures (from ≈4 nm at 350 °C to ≈10 nm at 550 °C). The structure and surface composition were evaluated by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The electrochemical characterization was performed in a 5 cm² single-cell setup. The highest performance was obtained with the sample treated at 450 °C, reaching current density values equal to 3.25 A cm⁻² at 2.2 V. The catalysts' behavior was also compared, under the same conditions, with NiO and IrO₂ commercial catalysts, demonstrating a higher activity of this class of compounds. The time-stability test of ca. 100 h showed a more constant behavior for the catalyst treated at 350 °C.

Keywords: Electrolyser; Nickel–iron oxides; Anion exchange membrane; Oxygen evolution reaction; Calcination temperature.