MgB 2 bulks were successfully prepared by Cu-doping sintering at 575 • C for only 5 h, exhibiting an obvious decrease in the sintering time at low temperature. According to the thermal analysis, the local Mg-Cu liquid formed first during the sintering process and then provided higher transport than the solid for the diffusion of Mg atoms into B, resulting in an accelerated reaction between Mg and B. The measured critical current density (J c ) of all the doped (Mg 1.1 B 2 ) 1−x Cu x (x < 0.10) samples was 1 × 10 6 A cm −2 in zero field at 20 K and about 1 × 10 5 A cm −2 in 2 T field at 20 K, respectively. The excellent J c is mainly attributed to the grain-boundary pinning mechanism resulting from the formation of small MgB 2 grains during the low-temperature sintering. Further, we found that with increasing the amount of Cu addition in the low-temperature sintered MgB 2 samples, the predominant flux pinning mechanism of the doped sample varies from grain-boundary pinning to MgCu 2 -nanoinclusion pinning introduced by the reaction between Mg 2 Cu and residual B. This transition results in an abnormal increase of J c in the sintered (Mg 1.1 B 2 ) 0.90 Cu 0.10 sample compared to the sintered (Mg 1.1 B 2 ) 0.95 Cu 0.05 sample in which only Mg 2 Cu was found around the edge of voids.

CNTs were treated with hydrazine hydrate and diethylenetriamine, respectively. Scanning electron spectroscopy (SEM) observation showed that the doped CNTs kept the length/diameter ratio of pristine CNTs. X-ray photoelectron spectroscopy (XPS) characterized that nitrogen can be doped to CNTs. XPS analysis further indicated that C/N atomic ratio of CNTs treated by hydrazine hydrate is 95/2, four times of CNTs treated by diethylenetriamine, which is 96/0.5. The hydrophilicity for N-doped CNTs (N-CNTs) is much improved and enhanced by increasing N proportion. As electrode material of supercapacitor, nitrogen functional groups contribute pseudo-Faradic capacitance, but its cyclic performance still need to be improved. Thanks to the good hydrophilicity for N-CNTs that improves the wettability of CNTs for electrolyte; the specific capacitance of N-CNTs is still slightly higher than pristine CNTs after cycling.