In situ growth of Co9S8 nanocrystals on reduced graphene oxide for the enhanced catalytic performance of dye-sensitized solar cell

Abstract

The counter electrode material of dye-sensitized solar cells (DSSCs) with excellent catalytic activity and fast electron transfer ability could effectively improve the overall photoelectrical conversion efficiency (PCE). In this work, monodispersed Co9S8 nanocrystals (NCs) were in situ grown on the surface of the reduced graphene oxide (RGO) through a simple hot-injection method. Due to the confinement of organic ligand oleylamine, the Co9S8 NCs with the size of ca. 8 nm were mainly dispersed on the surface of RGO (Co9S8/RGO). The Co9S8/RGO composite with the optimal contents (RGO contents of 44.4 wt%) was prepared by controlling the amount of graphene oxide (GO) added, which possessed the optimal catalytic active site numbers and electron transfer ability as it showed a higher PCE of 7.31%. It was higher than that of the solo Co9S8 NCs and comparable to that of the Pt (7.72%). The electrochemical characteristics (cyclic voltammetry, Tafel polarization curve, and electrochemical impedance spectroscopy) confirmed their excellent electrocatalytic activity towards I3−/I− redox reduction. Furthermore, the calculations based on the density functional theory (DFT) revealed that the absorption energy of I3− on the Co site at the interface of Co9S8/RGO composite was −1.881 eV, which was higher than that of solo Co9S8 NCs (−1.078 eV). So, Co atoms in the Co9S8/RGO interface was the predominant catalytic active center for the I3− reduction. This in situ growth strategy provided a new strategy for the preparation of electrocatalytic materials.