Atomic Evolution of Metal–Organic Frameworks into Co–N<sub>3</sub> Coupling Vacancies by Cooperative Cascade Protection Strategy for Promoting Triiodide Reduction
Hongyu Jing, Zhengyan Zhao, Jiangwei Zhang, Chao Zhu, Wei Liu, Nannan Li, Ce Hao, Yantao Shi, Dingsheng Wang
Abstract
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–N3 coupling vacancies (Co–N3-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–N3-V geometry structure has an enhanced electron-donating ability and a suitable electronic coupling with I2, which promotes rapid electron transfer and ensures highly accessible I2 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.