Modulator Directed Synthesis of Size-Tunable Mesoporous MOFs and Their Derived Nanocarbon-Based Electrocatalysts for Oxygen Reduction

Although MOF-derived carbon materials have been widely used for electrocatalysis, it is challenging to prepare size-tunable MOF precursors through simple modulation. In this work, a series of mesoporous MOF (PCN-224) with a wide tunable particle size from micro- to nano-scale were successfully synthesized by in-situ introduction of 3-mercaptopropionic acid as the modulator. After carbonization and acid etching, the derived carbons (MA(x)-NC) inherit the mesoporous structure and exhibit uniform particles ranging from 30 to 900 nm. MA(x)-NC were used as model catalysts to explore the size effects on electrocatalysis. Considering the similar compositional and structural properties, the electrochemical activity depends on the number of accessible surface active sites. MA(3)-NC with optimized particle sizes (similar to 300 nm) would not only provide abundant surface active sites but also consist of large secondary pores between the particles for fast mass transport. Moreover, suitable Fe atom was introduced into the optimized MA(x)-NC, which shows comparable half-wave potential and better stability than commercial Pt/C for the typical oxygen reduction reaction. This work provides an efficient "modulation" strategy for preparing size-tunable mesoporous MOF cubes and their carbon derivatives, paving a new way to customize nanosized MOFs for wider applications.