Core-shell structured Ni6MnO8@carbon nanotube hybrid as high-performance pseudocapacitive electrode material

Binary metal oxides have been proved to possess better pseudocapacitive performance than single metal oxide analogies. Substitution of toxic and high-cost ions (Co and Mo) in binary metal oxides with low-cost and environmentally-friendly ions (Ni and Mn) is of great economic and environmental importance. In this paper, murdochite-type binary metal oxides (i.e., Ni₆MnO₈) and binary metal oxides@carbon nanotubes (i.e., Ni₆MnO₈@CNTs) core-shell structure were synthesized via a facile hydrothermal approach followed by a calcination process. Electrochemical measurement results indicated that the synthesized Ni₆MnO₈@CNT core-shell structure showed a high specific capacitance of 1213 F g⁻¹ at 1 A g⁻¹ with two times capacitance value of Ni₆MnO₈ at same current density. Even at the high current density of 20 A g⁻¹, the Ni₆MnO₈@CNT core-shell structure can still deliver a high capacitance value of 711 F g⁻¹, which value is also much higher than that of Ni₆MnO₈ at the current density of 1 A g⁻¹. With the prepared Ni₆MnO₈@CNT hybrid as positive electrode and activated-polyaniline-derived-carbon as negative electrode, an asymmetric supercapacitor cell (ASC) was successfully assembled. The assembled ASC device exhibited excellent pseudocapacitive performance with a high specific capacitance of 154 F g⁻¹ at 1 A g⁻¹ and a high energy density of 58.2 Wh kg⁻¹ at a power density of 831.4 W kg⁻¹. Even at a high power density of 16.6 kW kg⁻¹, the ASC device can still deliver a high energy density of 23.1 Wh kg⁻¹, suggesting the promising applications of Ni₆MnO₈@CNT hybrid in supercapacitors.