N-doped ZnCo-LDH ultrathin nanosheet array on nickel foam for high performance supercapacitors

Abstract

Layered double hydroxides (LDH) are regarded as promising electrode materials for supercapacitors due to their abundance, multiple oxidation states, and high theoretical capacitance. However, the limited active sites and dull reaction kinetics restrict their commercialization. In this work, the 3D hierarchical N-doping ZnCo-LDH array on nickel foam (NF) as an electrode material (N-ZnCo-LDH) was designed and directly fabricated via a hydrothermal method using 2-Methylimidazole as a nitrogen source. Consequently, the N-doping confined the growth of the N-ZnCo-LDH to form ultrathin nanosheets, which exposed more redox reaction active sites and facilitated the charge transfer, resulting in the enhancement in charge storage capacity. As a result, the optimal N(0.5)-ZnCo-LDH achieved a high specific charge of 942.6 C g−1 at 1.0 A g−1, excellent charge-discharge rate property (68.9% retention) and long durability (84.1% after 5 000 cycles). Also, the hybrid supercapacitor (N-ZnCo-LDH//AC) was fabricated employing N(0.5)-ZnCo-LDH as anode and activated carbon (AC) as cathode, which achieved an energy density of 29.2 Wh kg−1 at a power density of 750.0 W kg−1, and excellent cycling stability (84.0% retention after 10,000 cycles), which highlighted the potential of the N(0.5)-ZnCo-LDH electrode material towards practical application of supercapacitors.