▎ 摘　　要

A novel hierarchical structural hybrid of two-dimensional CoS1.097 sheets assembled and decorated on reduced graphene oxide sheets (CoS1.097/RGO) with an intriguing sandwich-like structure are evaluated as electrocatalyst for the reduction of triiodide. In this composite, RGO worked as high speed electronical conductive platforms facilitates transfer of electrons, while CoS1.097 nanosheets as high-catalytically active centers provide abundant active sites for the reduction of triiodide. In addition, the unique three-dimensional structure can also efficiently accelerate the permeation of electrolyte and thereby elevate the accessibility of inner active sites to redox species. As a consequence, CoS1.097/RGO exhibits excellent electrocatalytic activity towards triiodide reduction accompanying with a high energy conversion efficiency of 6.85%, which reaches as high as ca. 95.7% to that of Pt CE (7.14%). Furthermore, CoS1.097/RGO also demonstrates a good long-term stability in I-/I-3(-) electrolyte. The present work provides a rational design strategy to develop the low-cost and high-performance Pt-free alternatives to noble Pt in a DSSC system. (C) 2017 Elsevier Ltd. All rights reserved.