Hierarchical 3D structured nanoporous Co9S8@Nix:Moy–Se core–shell nanowire array electrodes for high-performance asymmetric supercapacitors

The rational design of free-standing hierarchic core–shell nanoporous architectures is a good strategy for fabricating next-generation electrode materials for application to electrochemical energy conversion/storage systems. Herein, hierarchical core–shell 3D Co9S8@Nix:Moy–Se nanowire arrays (NWAs) are constructed by a low-cost, straightforward two-step hydrothermal method and an effective electrodeposition process. The optimal 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode displays the excellent specific capacity of 460.81 mAh g-1 with a corresponding areal capacity of 0.93 mA h cm-2 at 1.5 mA cm-2. It also demonstrates superb rate capability (~68.4 % capacity retention at 20 mA cm-2) and remarkable cyclic stability (~ 94.3 % capacity retention after 10,000 charge and discharge cycles). Additionally, an asymmetric supercapacitor (ASC) is assembled using the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs as the positive electrode, and the as-obtained Fe2O3@PANNFs/N-rGO aerogel as the negative electrode. The assembled Co9S8@Ni0.5Mo0.5–Se//Fe2O3@PANNFs/N-rGO ASC shows a larger operating voltage range of 1.7 V, a high electrochemical energy storage capability (96.90 W h kg−1 at 1,158 W kg−1), and excellent cyclic stability (capacity remained ~ 94.47 % of the original capacity before 10,000 cycles). The all-solid-state ASC device that is also fabricated exhibits a high export working potential window of ~1.8 V, and an outstanding energy density of ~ 102.94 W h kg−1 at ~1,534 W kg−1, demonstrating that the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode materials are potential candidates for the high-performance energy storage device.