Modulating CoFeO_X Nanosheets Towards Enhanced CO₂ Photoreduction to Syngas: Effect of Calcination Temperature and Mixed-Valence Multi-Metals

CoFeO_X nanosheets were synthesized by a facile coprecipitation and calcination method. The effect of calcination temperature on the crystal texture, morphology and surface areas of CoFeO_X were fully explored. CoFeO_X sample calcined at 600 °C (CoFeO_X-600) showed superior catalytic performance for the reduction of CO₂ under visible light. Compared with the pure Ru(bpy)₃²⁺-sensitized CO₂ reduction system, the CoFeO_X-added system achieved 19-fold enhancement of CO production (45.7 μmol/h). The mixed valence state and nanosheet-like structure of CoFeO_X cocatalyst support its ultra-high charge transfer and abundant CO₂ active adsorption sites exposure, which promote the separation of photogenerated charges, and thus improve the photocatalytic CO₂ reduction activity. Carbon source of CO from CO₂ was verified by ¹³CO₂ isotopic labelling experiment. Repeated activity experiments confirmed the good stability of CoFeO_X in the CO₂ photoreduction system. This work would provide prospective insights into developing novel cost-effective, efficient, and durable non-precious metal cocatalysts to improve the efficiency of photocatalytic reduction of CO₂.