Metal-organic framework (MOF)-derived carbon materials have been widely used as catalysts for a variety of electrochemical energy applications, and thermally carbonized zinc-2-methylimidazole (ZIF-8) has shown particularly high performance owing to its microporous structure with a large surface area. However, in the presence of bulky chemical species, such as triiodide, in mesoscopic dye-sensitized solar cells (DSCs), the small pore size of carbonized ZIF-8 causes a significant limitation in mass transfer and consequentially results in a poor performance. To resolve this problem, we herein report a simple strategy to enlarge the pore sizes of ZIF-8-derived carbon by increasing the dwelling time of Zn in ZIF-8 during the thermal carbonization process. A thin and uniform polydopamine shell introduced on the surface of ZIF-8, with the aim of retarding the escape of vaporized Zn species, leads to a dramatic increase in pore sizes, from the micropore to mesopore range. The porosity-tailored carbonized ZIF-8 manifests an excellent electrocatalytic performance in triiodide reduction, and when it was applied as the counter electrode of DSCs, an energy conversion efficiency of up to 9.03% is achievable, which is not only superior to that of the Pt-based counterpart but also among the highest performances of DSCs employing carbonaceous electrocatalysts.
Bibliographical noteFunding Information:
This work was supported by the Institute for Basic Science (IBS) in Republic of Korea (Project Code: IBS-R006-A2). This work was also nancially supported by the Technology Innovation Program (10082572) funded by the Ministry of Trade, Industry & Energy (MOTIE) in Republic of Korea and the Global Frontier R&D Program on Center for Multiscale Energy System (2016M3A6A7945505) funded by the National Research Foundation (NRF) in Republic of Korea.
© 2018 The Royal Society of Chemistry.