Sol-Gel Synthesis of Copper Ferrite Spinel Oxide and Its Use as Catalyst for the H2 Evolution and CO2 to Acetate Reduction Reactions

Transition metal oxides are promising catalysts for water electrolysis and CO₂ reduction. Herein, we report on the synthesis of copper ferrite spinel oxide (Cu_xFe_3-xO₄ with 0 < x < 3, by a sol-gel method followed by calcination at 500–800 °C. The evolution of chemical composition and crystal structure of resultant products in function of Cu²⁺/Fe³⁺ molar ratio and calcination temperature was investigated employing SEM-EDX, TEM, XRD, Raman, FTIR and XPS analyses. It was found that x = 1 produced the highest concentration of CuFe₂O₄ phase. At low calcination temperatures, the CuFe₂O₄ cubic phase was produced which was then completely transformed into the CuFe₂O₄ tetragonal phase at 800 °C. The use of the Cu_xFe_3-xO₄ nanoparticles as catalysts for the H₂ evolution reaction and the CO₂ reduction reactions was examined. The best one, being pure tetragonal CuFe₂O₄ with minor m-CuO impurity phase, showed a CO₂-to-acetate reduction selectivity of ∼4.5% at −0.6 V vs RHE in a 0.1 M NaHCO₃ electrolyte solution. Characterization of these Cu_xFe_3-xO₄ catalysts after being used for the catalysis was done using SEM, XRD, and Raman spectroscopic analyses revealing a critical change of these catalysts.