Rational design of metal organic framework derived hierarchical structural nitrogen doped porous carbon coated CoSe/nitrogen doped carbon nanotubes composites as a robust Pt-free electrocatalyst for dye-sensitized solar cells

A novel hierarchical structural hybrid of nitrogen-doped porous carbon (NPC) coated hollow CoSe nanoparticles anchored on nitrogen-doped carbon nanotubes (NCNTs) is enabled from the zeolitic imidazolate framework ZIF-67. In this composite, polypyrrole-derived NCNTs as a nitrogen-rich template effectively alleviates the irreversible aggregation of ZIF-67 derivatives. The hollow CoSe embedded NPC nanoparticles(CoSe@NPC) as high catalytic activity centres endow sufficiently available active sites for the reduction of triiodide, while NCNTs serve as both the bridge and the dispersant for the CoSe@NPC. Moreover, the outstanding catalytic metal-nitrogen bonds(Co-N-C) species take the role of high-speed transport pathway to facilitate transfer of electrons from the carbon skeleton to active sites. Benefiting from the above advantages, the hybrid of CoSe@NPC anchored on NCNTs shows fabulous electrocatalytic activity with an energy conversion efficiency of 7.58%, which is even higher than that of Pt counter electrode (7.27%). More remarkably, the composite also demonstrates a good long-term electrochemical stability in iodine-based electrolyte. The present work proves the rationality of the preparation of ZIFs-derived materials with special structures and their application in dye-sensitized solar cells system.