Rational Design of Hierarchical Structural CoSe@NPC/CoSe@CNT Nanocomposites Derived from Metal-Organic Frameworks as a Robust Pt-free Electrocatalyst for Dye-Sensitized Solar Cells.

Transition-metal compounds/carbon hybrids with high electrocatalytic capability possess attractive potential as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). However, the simple structure and agglomeration always result in poor performance. Herein, cobalt selenides confined in hollow N-doped porous carbon interconnected by carbon nanotubes (CNTs) with cobalt selenides encapsulated inside (denoted as CoSe@NPC/CoSe@CNTs) are formed through pyrolysis and selenization process. In this strategy, ZIF-67 is used as the precursor, structure inducer, and carbon source for the orientated growth of CNTs. Such a rational architecture provides a stable interconnected conductive network and a hierarchically porous structure, with more available active sites and a shortened pathway for charge transport, synergistically enhancing the electrocatalytic activity. Specifically, the DSSCs based on CoSe@NPC/CoSe@CNTs demonstrate a high efficiency of 7.36%, even superior to that of Pt (7.16%). Furthermore, the CoSe@NPC/CoSe@CNT CE also demonstrates a good long-term stability in the iodine-based electrolyte.