Synergistic\nEffects of ZnO@NiM′-Layered Double\nHydroxide (M′ = Mn, Co, and Fe) Composites on Supercapacitor\nPerformance: A Comparative Evaluation

The development of\nsupercapacitors is pivotal for sustainable energy\nstorage solutions, necessitating the advancement of innovative electrode\nmaterials to supplant fossil-fuel-based energy sources. Zinc oxide\n(ZnO) is widely studied for use in supercapacitor electrodes because\nof its beneficial physicochemical properties, including excellent\nchemical and thermal stability, semiconducting characteristics, low\ncost, and environmentally friendly nature. In this study, ZnO nanorods\nwere synthesized using a simple hydrothermal method and then combined\nwith various Ni-based layered double hydroxides (LDHs) [NiM′-LDHs\n(M′ = Mn, Co, and Fe)] to improve the electrochemical performance\nof the ZnO nanorods. These LDHs are well-known for their outstanding\nelectrochemical and electronic properties, high specific capacitance,\nand efficient dispersion of cations within host nanolayers. The synthesized\ncomposites ZnO@NiMn-LDH, ZnO@NiCo-LDH, and ZnO@NiFe-LDH exhibit enhanced\nspecific capacitances of 569.3, 284.6, and 133.0 F/g, respectively,\nat a current rate of 1 A/g, outperforming bare ZnO (98.4 F/g). Notably,\nZnO@NiMn-LDH demonstrates superior electrochemical performance along\nwith a capacitance retention of 76%, compared to ZnO@NiCo-LDH (58%),\nZnO@NiFe-LDH (49%), and bare ZnO (23%) over 5000 cycles. Furthermore,\nan asymmetric supercapacitor (ASC) was developed by using ZnO@NiMn-LDH\nas the positive electrode and activated carbon (AC) as the negative\nelectrode to assess its practical applicability. The fabricated ASC\n(ZnO@NiMn-LDH//AC) demonstrated a specific capacitance of 45.22 F/g\nat a current rate of 1 A/g, an energy density of 16.08 W h/kg at a\npower density of 798.8 W/kg, and a capacitance retention of 75% over\n5000 cycles. These findings underscore the potential of the composite\nformation of ZnO with Ni-based LDHs in advancing the efficiency and\ndurability of supercapacitors.