Smartly tailored Co(OH)2-Ni(OH)2 heterostucture on nickel foam as binder-free electrode for high-energy hybrid capacitors

Heterostructured materials composed of nickel and cobalt hydroxides exhibit impressive prospect in aqueous-based supercapacitors owing to their unique layered frameworks. Herein, a series of Co(OH)₂-Ni(OH)₂ heterostructures are prepared on nickel foam as binder-free electrodes (denoted as NCN-x) via a simple two-step electrodeposition method, where Co(OH)₂ serves as the interlayer and Ni(OH)₂ serves as the out layer. By tuning the deposition charge quantities of these two kinds of hydroxides, different electrode architectures with various mass ratios of α-Ni(OH)₂ to β-Co(OH)₂ are obtained. Among these electrodes, the smartly tailored NCN-3 electrode representing 1.0 C and 0.75 C deposition charges separately for Co(OH)₂ and Ni(OH)₂ exhibits particular core-shell nanosheet-like microstructure, possessing large surface area and short ion/electron transportation pathways. As a result, it delivers good cycling performance of ∼75.8% capacitance retention after 1000 cycles at 5 A g⁻¹. Moreover, the hybrid capacitor consists of NCN-3 cathode and AC anode realizes high energy and power densities (32.6 Wh kg⁻¹ at 465.7 W kg⁻¹ and 25.5 Wh kg⁻¹ at 7061.5 W kg⁻¹). This work can serve as a guide for designing other heterostructured electrodes by electrochemical method.