Synthesis and Electrochemical Properties of Carbon Dots/Manganese Dioxide (CQDs/MnO₂) Nanoflowers for Supercapacitor Applications

Flower-like carbon dots/manganese dioxide (CQDs/MnO 2 ) nanocomposites were successfully synthesized and investigated as novel electrode materials for supercapacitors. CQDs were uniformly distributed on the transparent petal of δ-MnO 2 and a high specific surface area of 168.8 m 2 g −1 was achieved for the CQDs/MnO 2 sample with 10 wt% CQDs (CQDs/MnO 2 -10). Furthermore, the CQDs/MnO 2 -10 nanoflower electrode exhibited outstanding pseudocapacitance performance, including a high specific capacitance, good rate capability (210 F g −1 at 20 A g −1 ), and excellent charge-discharge stability (90.3% retention rate after 10,000 cycles). In addition, capacitances of 345, 333, 318, 306, and 296 F g 1 can be acquired at rates of 0.5, 1, 2, 3, and 4 A g −1 , respectively, which is much higher than the specific capacitances of most reported carbon coated MnO 2 . These excellent electrochemical properties indicate that the CQDs/MnO 2 nanoflowers were efficient active materials and have a highly promising prospect for future high-performance electrochemical energy storage systems.