Single-crystal Cr₂O₃ nanoplates with differing crystalinities, derived from trinuclear complexes and embedded in a carbon matrix, as an electrode material for supercapacitors

As one kind of important p-type semiconductors, Cr₂O₃ has been widely used for optical and electronic devices due to its high electrical conductivity and special optoelectronic characteristics, as well as high chemical and thermal stability. In this paper, single-crystalline Cr₂O₃ nanoplates embedded in carbon matrix were successfully synthesized through direct thermal decomposition of a trinuclear cluster complex of [Cr₃O(CH₃CO₂)₆(H₂O)₃]NO₃·CH₃COOH ([Cr₃O]) in Ar atmosphere. The synergetic effect of the plate-like structure and embedding in carbon matrix contributes to the enhanced electrochemical performance of the Cr₂O₃-C nanoplates. Owing to different crystallinity and composition, the obtained products at 400, 500, 600, and 700 °C with different carbon content of 12.52, 8.26, 5.35 and 3.27% exhibited enhanced battery-type electrode materials in three-electrode system with high specific capacitance (823.11, 781.65, 720.72, and 696.73 F g⁻¹ at 1 A g⁻¹) and remarkable cycling stability (about 0.3, 2.7, 4.5 and 5.6% loss of its initial capacitance after 5000 charge-discharge cycles at a current density of 5 A g⁻¹). Furthermore, an assembled asymmetric device (Cr₂O₃-C nanoplates (positive electrode)//activated carbon (AC, negative one)) with an extended operating voltage window of 1.8 V achieves a specific capacitance of 58.06 F g⁻¹ at the current density of 1 A g⁻¹ and an energy density of 26.125 W h kg⁻¹ at power density of 0.9 kW kg⁻¹, as well as superior cycling stability with 91.4% capacitance retention after 10,000 cycles. The results indicate that the Cr₂O₃ nanoplates embedded in carbon matrix show promising potential to construct high-performance energy storage devices.