Bilayered NiZn(CO3)(OH)2–Ni2(CO3)(OH)2 nanocomposites as positive electrode for supercapacitors

Highlights: • A composite stacked in a unique two-layer structure was fabricated. • This two-layer electrode provide the large surface area for the redox reaction. • As the cycles increased, the electrode became damaged and the capacity deteriorated. • The optimized two-layer electrode improved the retention results after cycle test. Open architecture and porous NiZn(CO₃)(OH)₂–Ni₂(CO₃)(OH)₂ bilayers were fabricated on a nickel foam substrate through a two-step processing of Ni and Zn salts under hydrothermal conditions. The initial layer of NiZn(CO₃)(OH)₂ nanosheets, obtained by alkaline hydrolysis of nickel and zinc salts, was cladded with a top layer consisting of Ni₂(CO₃)(OH)₂ nanowire arrays. This double-decker arrangement offered a higher mechanical stability and enhanced electrochemical performance in NiZn(CO₃)(OH)₂–Ni₂(CO₃)(OH)₂ electrodes, which showed an excellent maximum specific capacitance of 1168.8 F g⁻¹ at 3 A g⁻¹ and superior cycling stability with a capacity retention of ~85.7% after 5000 cycles. Moreover, the asymmetric two-layered NiZn(CO₃)(OH)₂–Ni₂(CO₃)(OH)₂//graphene electrodes provided sufficient capacitive energy to turn on a LED light. This superior electrochemical performance is attributed to the hierarchical architecture and large surface area of the composite electrodes that render them in view of facile and scalable synthesis and greater cycling safety as promising candidates for practical applications.