Copper doped CoSx@Co(OH)2 hierarchical mesoporous nanosheet arrays as binder-free electrodes for superior supercapacitors

Heteroatom doping is an effective route to boost the capacitance performance of metal sulfides-based electrode materials. Herein, an array of hierarchical 3D mesoporous Cu doped CoSx@Co(OH)2 nanosheets (namely Cu/CoSx@Co(OH)2) is successfully prepared on Ni foam through a metal-organic-framework (MOF) mediated approach. The combination of compositional merits and tuned electronic properties induced by copper doping leads to superior capacitance performance. The optimal Cu doped electrode (Cu/CoSx@Co(OH)2-2) displays an ultrahigh specific capacitance and outstanding rate capability, which outperforms the best values obtained on other transition metal sulfide (TMS) electrodes. And the Cu/CoSx@Co(OH)2-2//activated carbon (AC) asymmetric two-electrode supercapacitor device exhibits a favorable energy density of 39.25 Wh kg−1 and outstanding cycle life. X-ray photoelectron spectroscopy (XPS) results reveal that the greatly decreased binding energy barriers of two redox pairs (Co2+/Co3+ and Cu+/Cu2+) are beneficial to higher electrochemical performance. Density function theory (DFT) results further disclose the Cu-doping effect and the benefit of nanocomposite formation on the energy storage performance. The results provide an inspiration to the optimization of TMS-based electrodes for high performance electrochemical energy storage systems.