Construction of mesoporous Cu-doped Co9S8 rectangular nanotube arrays for high energy density all-solid-state asymmetric supercapacitors

Heteroatom doping has been regarded as an effective route to tune the electronic structure of electrode materials to achieve enhanced electrical conductivity as well as more electroactive sites and boost the devices' capacitive performance and cycling stability. Herein, novel high-performance all-solid-state asymmetric supercapacitors (ASCs) based on mesoporous Cu-doped Co9S8 rectangular nanotube arrays (Cu-Co9S8 NTAs) are successfully fabricated. Using Cu-Co(CO3)(0.5)(OH) nanowire arrays as the precursor and 1,3,5-benzenetricarboxylic acid (H3BTC) as the ligand, intermediate CuCo-MOF nanorod arrays are first obtained and then converted into Cu-Co9S8 rectangular NTAs via a facile sulfidation reaction. Interestingly, the intermediate CuCo-MOF nanorods play a determinant role in forming the hollow nanostructures of the final products. Due to the arrays of the unique hollow nanostructures and novel electronic properties induced by Cu doping, a battery-type electrode based on the Cu-Co9S8 NTAs exhibits a high specific capacity of 366 mA h g(-1) (2636 F g(-1)) at 2 A g(-1) and excellent cycling stability (94.0% capacity retention after 5000 cycles). Furthermore, all-solid-state ASCs assembled using the Cu-Co9S8 NTAs as the positive electrode and active carbon as the negative electrode demonstrate a high energy density of 71.93 W h kg(-1) at a power density of 750 W kg(-1) and outstanding cycling stability (96.2% retention after 5000 cycles). The ASC device exhibits enhanced energy density compared with reported state-of-the-art supercapacitors as well as excellent flexibility under different bending conditions.