Atomic Evolution of Metal-Organic Frameworks into Co-N3 Coupling Vacancies by Cooperative Cascade Protection Strategy for Promoting Triiodide Reduction

Precisely controlled synthesis is one of the key issues for single-atom catalysts (SACs) due to isolated atoms have high surface-free-energy toward aggregation. Here, we propose a facile cooperative cascade protection strategy that can transform zeolitic imidazolate frameworks-67 (ZIF-67) to SACs with assistance of readily available salts and glucose. By precisely controlling the proportions of ZIF-67 and glucose precursors in a molten salt medium, the Co atoms in the ZIF-67 were transformed to Co-N-3 coupling vacancies (Co-N-3-V) upon pyrolysis (labeled as SGZ-800). Benefiting from the unique composition and structure properties, the SGZ-800 counter electrode (CE) catalysts for triiodine reduction reaction (TRR) in dye-sensitized solar cells (DSCs) exhibit excellent photovoltaic performance with a power conversion efficiency of 7.89% compared to that of Pt counterpart (7.76%). Density functional theory (DFT) calculations elucidate that the Co-N-3-V geometry structure has an enhanced electron-donating ability and a suitable electronic coupling with I-2, which promotes rapid electron transfer and ensures highly accessible I-2 adsorption. This cascade protection strategy for controlling conversion of ZIF-67 to SACs not only provides new avenue to the construction of metal-organic framework (MOF) derived carbon-supported SACs with tailor compositions but also broaden the way to energy-related electrical conversion devices.