Correlations of Calcination Temperature with the Catalytic Properties of CuFe₂O₄ for the Synthesis of Green Fuels

Spinel oxides are promising multifunctional electrocatalysts based on earth‐abundant elements. While NiFe 2 O 4 and CoFe 2 O 4 have been widely studied for the oxygen evolution reaction (OER), CuFe 2 O 4 has been less investigated. Herein, cubic CuFe 2 O 4 nanoparticles are synthetic using a microwave‐assisted approach. The effect of post‐synthetic calcination on particle morphology, crystal structure, and inherent properties such as optical bandgap, magnetic moment, or degree of inversion is investigated. The influence of the post‐synthetic treatment on the electrochemical performance is then evaluated. It is found that higher calcination temperatures are beneficial for the OER, the hydrogen evolution reaction, and the oxygen reduction reaction (ORR), which can be explained by an improved crystallinity, removal of organic surface residues and changes in the dominant crystal phase—and relatedly the conductivity. Especially for the ORR activity, an increase in the electrochemical active surface area and a decrease in the charge transfer resistance upon calcination are important prerequisites. The activity of CuFe 2 O 4 for the reduction of CO 2 to CO, in contrast, is mainly determined by the local environment of Cu 2+ and is best at a comparatively high degree of inversion and low amounts of organic residues and for particles with a cubic structure.