Cobalt-based ferrites as efficient redox materials for thermochemical two-step CO2-splitting: enhanced performance due to cation diffusion

Abstract

Thermochemical two-step CO₂ splitting under concentrated solar energy has received significant attention, and ferrites are promising materials for such a redox reaction. However, their application is still challenged by the sintering problem due to the inevitably high operating temperature. Herein, we report non-stoichiometric cobalt-based ferrites, with no thermostable supports employed, as efficient redox materials for thermochemical two-step CO₂ splitting. In comparison with ZrO₂- and Al₂O₃-added CoFe₂O₄, CoO-added CoFe₂O₄ (CoFe₂O₄/CoO) shows a CO productivity of 8.5 mL g⁻¹, which is 1.5 and 3.2 times higher than that of CoFe₂O₄/ZrO₂ (5.4 mL g⁻¹) and CoFe₂O₄/Al₂O₃ (2.6 mL g⁻¹), respectively. Based on the morphological and crystal structure characterization by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and Fourier transform infrared spectroscopy (FT-IR), the ferrites were thoroughly analyzed and thereby bulk cation diffusion for CoFe₂O₄/CoO over the reaction is kinetically demonstrated to play an important role in enhancing the performance.