Ni-foam supported Ni(OH)2 sheets decorated by MXene quantum dots for high performance supercapacitors

The MXene quantum dots (MQDs) were prepared by microwave-sonication exfoliation, and further loaded on Ni (OH)2 sheets using Ni form as substrate by one-pot solvothermal synthesis. Three different exfoliation mediums (ethanol-EtOH, N,N-dimethylformamide-DMF, dimethyl sulfoxide-DMSO) were changed to investigate their influences on the structure of MQDs and MQDs-Ni(OH)2 composites. The DMF medium is better than the other two due to its good reducibility and small polarity, and the obtained MDQf from DMF exfoliation has less oxidation and higher quantum yield, while the prepared MQDf-Ni(OH)2 composites possessed large Ni(OH)2 sheet, high Ni3+ ratio and high N doping content. All these material changes caused by DMF can promote the chargedischarge process during the supercapacitor application, resulting in the best electrochemical performance of 1660 F/g at 1 A/g using MQDf-Ni(OH)2 composites as electrodes. Moreover, the asymmetric supercapacitors using MQDf-Ni(OH)2 composites and active carbon as electrodes possessed a maximum specific capacitance of 98 F/g, and a maximum energy density of 30.6 Wh/kg (with a power density of 750 W/kg).