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

Abstract

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, CoFe 2 O 4 @C nanoparticles with core-shell structure are successfully prepared using the treatment of quasi-sol-gel method. The size of CoFe 2 O 4 @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 CoFe 2 O 4 @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 - /I 3 - redox couple steadily, providing more possibilities for the study of Pt-free materials about DSSCs counter electrode. Through the simple quasi sol-gel method, the carbon material with good conductivity and CoFe 2 O 4 with excellent catalytic activity are tactfully combined to form stabile CoFe 2 O 4 @C nanoparticles with core-shell structure, which are successfully applied to DSSCs counter electrodes. The photoelectric conversion performance of DSSCs is greatly improved by utilizing the sufficient specific surface area of the composite material and its stable catalytic ability to electrolyte cycle. A PCE of 7.80% is achieved literally with the further optimization of adjusting the carbon-transition metal oxide ratio and the film thickness of CoFe 2 O 4 @C-based CE, which is enhanced by 11% and 23% than that of Pt (PCE=7.05%) and pure carbon (PCE=6.36%). This attempt provides a new idea and reference for further optimization of DSSCs. • A core-shell structure CoFe 2 O 4 @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 CoFe 2 O 4 core. • A PCE of 7.80% is achieved with the optimization of the ratio of C and CoFe 2 O 4 and the thickness of CoFe 2 O 4 @C-based CE.