Engineering ZnNi-LDH with improved wettability by N-direct-doping for high-performance supercapacitor

Abstract

Reforming transition metal layered double hydroxides (LDH) is an unswerving desire to enable them high-performance electrode materials for supercapacitors. In this work, an efficient strategy was proposed to boost the charge-storage performances of ZnNi-LDH grown on NF by direct-doping of N species using 2-methylimidazole as N source via one-step hydrothermal method. N-doping endowed them with ultrathin nanosheets, abundant active sites and improved wettability, which were conducive to expediting the electron/ion transport and reaction kinetics, and thus greatly enhancing the electrochemical properties. Density functional theory (DFT) calculations further verified that in-situ N-direct-doping regulated the electronic structure and reduced the OH⁻ adsorption energy, which effectively promoted the ion adsorption capability and intrinsic wettability, which made the electron/ion transport more rapid. As a result, the optimal N-doped ZnNi-LDH (N/ZnNi-LDH₍₃₎) showed a high specific charge of 1265.7 C g⁻¹ at 1 A g⁻¹, much higher than that of the pristine ZnNi-LDH (406.8 C g⁻¹ at 1 A g⁻¹). Furthermore, the hybrid supercapacitor was assembled with N/ZnNi-LDH₍₃₎ and activated carbon as the positive and negative electrodes, respectively, which delivered a satisfactory energy density of 64.6 Wh kg⁻¹ at 850 W kg⁻¹ and excellent long-term cycling lifetime. The strategy provided a feasible route for optimizing the energy storage performance.