Design and characterization of frog egg shaped CoFe2O4@C core-shell composite as a novel multi-functional counter electrode for low-cost energy devices

The electrical conductivity and catalytic activity of the electrode materials greatly affect the photoelectric conversion performance of DSSCs. However, the commonly used Pt electrodes no longer meet the needs of long-term development at present. Herein, based on the Kirkendall effect, CoFe2O4 @C nanoparticles with core-shell structure are successfully prepared using the treatment of quasi-sol-gel method. The size of CoFe2O4 @C nanoparticles is homogenized without agglomeration through adjusting the ratio of metal salt in the precursor. The composite exhibits excellent counter electrode properties in DSSCs, which attributes to the large specific surface area and superior electro-catalytic activity. With the optimized film thickness (12 µm) of CoFe2O4 @C, an excellent photoelectric conversion efficiency of 7.80% is finally achieved, significantly higher than that of pure carbon (PC) electrode (6.36%) and even Pt counter electrode (7.05%) under the same conditions. The composite can additionally catalyze the recycling of I-/I3- redox couple steadily, providing more possibilities for the study of Pt-free materials about DSSCs counter electrode. [Display omitted] •A core-shell structure CoFe2O4@C composite was prepared efficiently by quasi-sol-gel method based on the Kirkendall effect.•The composite combines the superior conductivity of the carbon shell with the good catalysis of the CoFe2O4 core.•A PCE of 7.80% is achieved with the optimization of the ratio of C and CoFe2O4 and the thickness of CoFe2O4@C-based CE.