Synergistic Effects of ZnO@NiM′-Layered Double Hydroxide (M′ = Mn, Co, and Fe) Composites on Supercapacitor Performance: A Comparative Evaluation

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