Iron Cobaltite (FeCo₂O₄) Nanocatalysts for Water-Oxidation: Effects of Annealing Temperature on Catalytic Properties

The development of efficient, stable, and non-precious metal water oxidation catalysts (WOCs) is a matter of importance for sustainable energy research. In this work, iron cobaltite (FeCo₂O₄) nanoparticles were prepared by the coprecipitation method, and we present the effect of heat treatment (250, 350, 450, 650 and 900 °C) on the catalytic properties. Catalytic activity tests of FeCo₂O₄ nanocatalysts were performed in the presence of ammonium cerium(IV) nitrate (CAN), and the formation of oxygen was followed using a Clark-type oxygen electrode. The samples were characterized by infrared (IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their surface areas were determined by the Brunauer, Emmett, and Teller (BET) method. Fourier transform infrared (FTIR) data confirm a metal-oxygen bond at the octahedral and tetrahedral sites. XRDs data were characteristic of spinel-like cubic materials. The XPS results confirmed the presence of trivalent and divalent cobalt and iron ions in the samples and showed that the non-heated sample has a greater amount of cobalt on the nanoparticles’ surface than those heated to 900 °C. The surface area decreased from 92.00 m² g^-1 for the material that was unannealed to 2.00 m² g^-1 for the sample annealed at 900 °C. The unannealed nanomaterials showed an oxygen production of 790 mmol s^-1 g^-1. This was 790 times greater than the oxygen production from nanomaterials heated to 900 °C. Although the surface structure of nanomaterials is unclear, the amount of surface cobalt appears to have implications for catalytic activity. Optimization of superficial cobalt content may be key to improving catalytic activity.

Keywords:
iron cobaltite; ferrite; water splitting; water oxidation catalysis (WOC); oxygen evolution reaction (OER)