Hierarchical Co₃O₄/Co(OH)₂ Nanoflakes as a Supercapacitor Electrode: Experimental and Semi-Empirical Model

In this research, facile and low cost synthesis methods, electrodeposition at constant current density and anodization at various applied voltages, were used to produce hierarchical cobalt oxide/hydroxide nanoflakes on top of porous anodized cobalt layer. The maximum electrochemical capacitance of 601 mF cm(-2) at scan rate of 2 mV s(-1) was achieved for 30 V optimized anodization applied voltage with high stability. Morphology and surface chemical composition were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The size, thickness, and density of nanoflakes, as well as length of the porous anodized Co layer were measured about 460±45 nm, 52±5 nm, 22±3 μm(-2), and 3.4±0.3 μm for the optimized anodization voltage, respectively. Moreover, the effect of anodization voltage on the resulting supercapacitance was modeled by using the Butler-Volmer formalism. The behavior of the modeled capacitance in different anodization voltages was in good agreement with the measured experimental data, and it was found that the role and contribution of the porous morphology was more decisive than structure of nanoflakes in the supercapacitance application.