Continuous and controllable synthesis of MnO2/PPy composites with core–shell structures for supercapacitors

Abstract A slug-based microreactor system was constructed to integrate the redox reaction between KMnO4 and MnSO4 with the chemical oxidative polymerization of pyrrole for the preparation of MnO2/PPy composite with a typical core–shell structure. MnO2 was formed as the core while PPy acted as the shell. The size distribution variation of MnO2 particles was elaborated by the crystallization theory and the comparison between the micromixing time and the nucleation induction time. It was found that the morphology of the MnO2/PPy composite was significantly affected by the molar ratio among KMnO4, MnSO4 and pyrrole and the residence time due to the competition between the pyrrole polymerization and the MnO2 crystallization. A probable mechanism for the formation of the PPy/MnO2 composite was proposed. The electrochemical performance of the MnO2/PPy composite with core–shell was better than that of MnO2. The enhanced performance demonstrated the synergistic effect between MnO2 and PPy for the fabrication of the core–shell structure. This work developed the design of particles with core–shell structures from the droplet-based microreactor to the slug-based microreactor with a relatively higher flux. The size of the prepared material decreased from microscale in the droplet-based microreactor to nanoscale in this slug-based microreactor. Such a novel strategy can be applied for efficiently preparing functional materials with controllable structures and properties.