Manganese doped Co ₃ O ₄ mesoporous nanoneedle array for long cycle-stable supercapacitors

Long–term cycling stability is an important criterion and big challenge for pseudocapacitive materials. Ultra-stable manganese doped Co ₃ O ₄ mesoporous nanoneedles were synthesized via one-step hydrothermal reaction followed by annealing grown on nickel foam (noted as Mn _x Co _y O/NF, x + y = 2.25) for supercapacitors. The Mn doping in Co ₃ O ₄ was confirmed by several techniques. Among various Mn _x Co _y O/NF electrodes, the Mn _1.5 Co _0.75 O/NF demonstrated the superior electrochemical performance, with an excellent cycling stability of 104% capacitance retention after 10 000 charge–discharge cycles at 6 A g ⁻¹ , as well as a good capability (668.4 F g ⁻¹ at 1 A g ⁻¹ compared to that of undoped Co ₃ O ₄ which is 201.3 F g ⁻¹ ). Moreover, the assembled asymmetric supercapacitor based on Mn _1.5 Co _0.75 O/NF//graphene performs a high energy density of 25.88 Wh kg ⁻¹ (at 359.5 W kg ⁻¹ ) and a high power density of 14.7 kW kg ⁻¹ (at 10.63 Wh kg ⁻¹ ). The improved electrochemical properties are mainly owing to the enhanced intrinsic conductivity and electrochemical activity of Co ₃ O ₄ after doped with appropriate Mn concentration. The three-dimensional nanostructure of mesoporous nanoneedle array grown on NF also provides short ion diffusion path and large active surface areas, contributing to the high rate performance and high energy density. This study may offer a new approach to fabricate the unique 3D nanostructured electrode materials based on doped metal oxides for supercapacitors with long-term cycling stability and high energy density.