Assembling 2D ultrathin nanosheets into vertical heterostructures offers significant potential for advanced energy storage due to enhanced active sites, improved ion diffusion, and increased electrical conductivity, leading to superior ion/electron transport, higher energy density, and improved rate performance. However, breaking crystal symmetry and fostering the anisotropy in crystal growth is critical in non-layered materials. In case of transition metal hydroxides, to overcome with challenges such as random assembly, complex synthesis, instability, and poor interfacial contact is critical. This study synthesizes large area, ultrathin, 2D Nickel/Cobalt hydroxide vertical heterostructures achieving 32% higher areal charge storage compared to cobalt/nickel hydroxide vertical heterostructures and 57% and 330% better than individual Ni(OH)2 and Co(OH)2. The synergistic interaction between nickel and cobalt hydroxides contributes to a high volumetric capacity (710 mAh cm-3) and energy density (285 mWh cm-3) in symmetric devices. The flexible micro-supercapacitor retains 75% capacitance after 15,000 cycles and demonstrates stability under bending up to 135°, with a volumetric capacity of 393 mAh cm-3. DFT simulations complement experiments, revealing interaction energy and electronic state redistribution near the Fermi level. This integrated approach serves as a guide for enhancing electrochemical properties in 2D heterostructures, aiding in the development of next-generation, high-performance energy storage materials.
Keywords: ultrathin, 2d nanomaterials, vertical heterostructure, flexible device, micro-supercapacitor.
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