Sandwich-like octahedral cobalt disulfide/reduced graphene oxide as an efficient Pt-free electrocatalyst for high-performance dye-sensitized solar cells

A novel sandwich-like hierarchical structure composed of reduced graphene oxide (RGO) and uniform cobalt disulfide (CoS₂) octahedrons is successfully prepared by a simple one-step solvothermal process, in which Co²⁺ cations attracted into graphene framework by the electrostatic adsorption induce the growth of octahedral CoS₂ nanoparticles between the layers of graphene. The fascinating sandwich-like structured CoS₂/RGO hybrid inherits excellent electrical conductivity of graphene skeletons. Meanwhile, CoS₂ octahedrons intercalated between the layers of graphene provide both rich inner active sites for the reduction of triiodide and abundant mesoporous structure for effective electrolyte diffusion. Benefit from the synergistic effects of CoS₂ octahedrons and RGO, the dye-sensitized solar cell (DSSC) assembled with this CoS₂/RGO counter electrode (CE) manifests excellent photoelectric conversion efficiency (7.69%), even higher than that of DSSC with conventional noble metal Pt CE (7.38%). Furthermore, CoS₂/RGO composite displays outstanding electrochemical stability in I₃⁻/I⁻ redox electrolyte. Overall, this design provides a new strategy for the development of alternative Pt-free counter electrode materials in a DSSC system.