One-dimensional heterostructures of polyoxometalate-encapsulated carbon nanotubes for enhanced capacitive energy storage

Carbon nanotubes are promising electrode materials for electrochemical capacitive energy storage. Here, we report a host-guest strategy to construct one-dimensional heterostructures by encapsulating redox-active polyoxometalate molecular clusters within single-walled carbon nanotubes. The electron transfer from nanotubes to clusters loosens π−π stacking of carbon nanotubes, leading to improved dispersion and higher electrical double-layer capacity. Besides, the nanoconfinement effect of carbon nanotubes not only facilitates electron transfer for inner redox-active polyoxometalates but also protects them from chemical degradation. Typically, the hybrid redox material delivers a high specific capacity of 328.6 F g−1 at 10 mV s−1 in phosphoric acid electrolyte and a prominent rate capability with 82.1% capacity retention at 500 mV s−1. The assembled supercapacitor exhibits maximum energy density of 33.4 Wh kg−1 and long-term stability with 91.3% of the initial capacity retained over 10,000 cycles. This study underlines the potential of redox-driven encapsulation strategies in developing high-performance energy storage materials.