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

Abstract

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 CoS x @Co(OH) 2 nanosheets (namely Cu/CoS x @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/CoS x @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/CoS x @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 (Co 2+ /Co 3+ and Cu + /Cu 2+ ) 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. • MOF-engaged strategy is employed to prepare Cu doped CoS x @Co(OH) 2 nanosheets. • Improved conductivity and facilitated reaction kinetics are induced by doping • Greatly decreased energy barrier between Cu + /Cu 2+ and Co 2+ /Co 3+ redox pairs. • DFT calculations disclose the doping effect and the superior capacitance. • Ultrahigh capacitance, outstanding stability and high energy density are obtained.