Low-Cost, High-Yield ZnO Nanostars Synthesis for Pseudocapacitor Applications

Abstract

Energy storage devices based on earth-abundant materials are key steps towards portable and sustainable technologies used in daily life. Pseudocapacitive devices, combining high power and high energy density features, are widely required, and transition metal oxides represent promising building materials owing to their excellent stability, abundance, and ease of synthesis. Here, we report an original ZnO-based nanostructure, named nanostars (NSs), obtained at high yields by chemical bath deposition (CBD) and applied as pseudocapacitors. The ZnO NSs appeared as bundles of crystalline ZnO nanostrips (30 nm thin and up to 12 µm long) with a six-point star shape, self-assembled onto a plane. X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) were used to confirm the crystal structure, shape, and defect-mediated radiation. The ZnO NSs, dispersed onto graphene paper, were tested for energy storage by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analyses, showing a clear pseudocapacitor behavior. The energy storage mechanism was analyzed and related to oxygen vacancy defects at the surface. A proper evaluation of the charge stored on the ZnO NSs and the substrate allowed us to investigate the storage efficiency, measuring a maximum specific capacitance of 94 F g−1 due to ZnO nanostars alone, with a marked diffusion-limited behavior. The obtained results demonstrate the promising efficacy of ZnO-based NSs as sustainable materials for pseudocapacitors.

Antibacterial and Anti-Inflammatory Properties of ZnO Nanoparticles Synthesized by a Green Method Using Sargassum Extracts

“…These and other properties can be improved when ZnO is at the nanometric scale. In this sense, the synthesis of nanoparticles (NPs) [ 4 ], nanowires [ 5 ], nanostars [ 6 ], and nanoflowers [ 7 ] have been reported. ZnO nanoparticles have been widely studied due to their catalytic [ 8 ], antibacterial [ 9 ], and antiviral [ 10 ] properties, which largely depend on their size and morphology.…”

Synthesis of ZnO/C Nanocomposites via Liquid-Assisted Laser Ablation in an Applied Electric Field for Supercapacitor Applications

“…Usually, the deviations from a rectangular shape of the CV curve indicate a pseudocapacitive behavior of the active material of the electrode, which is associated with Faradaic reactions initiated at the interface of metal oxide structures and electrolyte. , Generally, the mechanisms of charge storage in ZnO nanocomposites can be attributed to three main processes: (i) Faradaic contribution due to ion intercalation, (ii) pseudocapacitance component as a Faradaic contribution resulting from charge transfer processes with surface atoms, and (iii) electric double-layer effect as a non-Faradaic contribution. , According to ref , where the mechanisms of the charge storage process in ZnO nanostructures were investigated, the capacitive process predominated in ZnO with some pseudocapacitive contribution. Furthermore, the large surface area increases both electric double-layer and pseudocapacitance charging effects, making them substantial at nanoscale dimensions of the active material.…”

“…In addition, in the case of ZnO, the surface defects may have a significant role in the surface charge-transfer processes. 42 It should be noted that a bare carbon cloth substrate is also slightly active in the charge storage process with currentpotential characteristics typical of an electric double-layer capacitor. However, the substrate mass is several orders of magnitude higher than the mass of ZnO/C nanostructures (3.7 mg); therefore, the substrate contribution is insufficient.…”

“…When the substrate was covered with as-grown ZnO/C nanostructures, a larger CV area was recorded (Figure 8c), highlighting a significant pseudocapacitive storage mechanism attributable to ZnO/C nanostructures. 42 From the CV curves, the capacitance of the electrode can be calculated based on the estimation of the stored charge Q:…”

Engineering of Nanostructured WO3 Powders for Asymmetric Supercapacitors

“…Pseudocapacitors are typically obtained by using highly porous transition metal oxide-based electrodes [ 8 , 9 ] and carbon-based materials. Di Mari et al [ 11 ] synthesized ZnO nanostars which exhibit a specific capacity of 94 F/g at 5 mV/s without any substrate contributions. Nazir et al [ 12 ] synthesized porous carbonaceous materials from banana peel waste and decorated them with nitrogen and sulfur and the obtained powder exhibited a specific capacitance of 220 F/g at 0.5 A/g.…”