1D compound [Zn(Im)(HIm) 2 (OAc)] was used as a single precursor of metal and imidazole to prepare several 3-dimensional (3D) Zn(Im) 2 frameworks by solution-mediated transformation. Specifically, three known topologies, zni, coi and crb (BCT) were obtained using a solution-mediated transformation with CH 3 OH, DMF and DMA as solvent, respectively. Structural studies by 13 C MAS NMR spectroscopy and TG imply that in the transformation process from 1D compound to coi-[Zn(Im) 2 ]•(DMF) x and crb-[Zn(Im) 2 ]•(DMA) x (ZIF-1), DMF and DMA solvent molecules acted as structure-directing agent and, therefore, were occluded inside the framework, respectively. In contrast, in the formation of zni-[Zn(Im) 2 ], no solvent molecules were present in the frameworks; therefore the transformation from 1D compound to zni was induced by temperature. Thus, solution-mediated transformation of a single precursor (1D compound) approach was established for the synthesis of ZIFs.
Aprotic lithium–oxygen (Li–O2) batteries with an ultrahigh theoretical energy density have great potential in rechargeable power supply, while their application still faces several challenges, especially poor cycle stability. To solve the problems, one of the effective strategies is to inhibit the generation of the LiO2 intermediate produced via a surface-mediated oxygen reduction reaction (ORR) pathway, which is an important species inducing byproduct generation and low cell cyclic stability. Herein, a series of quinones and solid materials serve as the solution-mediated and surface-mediated ORR catalysts, and it was found that the generation of LiO2 and byproducts from solid catalysts was inhibited by quinones. Among the studied quinones, benzo[1,2-b:4,5-b′]dithiophene-4,8-dione, a quinone molecule with the advantage of a highly symmetrical planar and conjugated structure and without α-H, exhibits high redox potential, diffusion coefficient, and electrochemical stability, and consequently the best ORR activities and the capability to inhibit byproduct generation. It indicated that the increase of the solution-mediated ORR pathway plays an important role in restraining the discharging side reaction, substantially improving cell cycle stability and capacity. This study provides the theoretical and experimental basis for better understanding the ORR process of Li–O2 batteries.
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