Low-Cost, High-Yield Zinc Oxide-Based Nanostars for Alkaline Overall Water Splitting.

The investigation of high-efficiency and sustainable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is critical for renewable energy technologies. Here, we report a low-cost and high-yield method to obtain ZnOHF-ZnO-based 2D nanostars (NSs) by means of chemical bath deposition (CBD). The obtained NSs, cast onto graphene paper substrates, were used as active materials for the development of a full water splitting cell. For the HER, NSs were decorated with an ultralow amount of Pt nanoparticles (11.2 µg cm-2), demonstrating an overpotential of 181 mV at a current density of 10 mA cm-2. The intrinsic activity of Pt was optimized, thanks to the ZnO supporting nanostructures, as outlined by the mass activity of Pt (0.9 mA mgPt-1) and its turnover frequency (0.27 s-1 for a Pt loading of 11.2 µg cm-2). For the OER, bare NSs showed a remarkable result of 355 mV at 10 mA cm-2 in alkaline media. Pt-decorated and bare NSs were used as the cathode and anode, respectively, for alkaline electrochemical water splitting, assessing a stable overpotential of 1.7 V at a current density of 10 mA cm-2. The reported data pave the way toward large-scale production of low-cost electrocatalysts for green hydrogen production.

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

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.

TiO2-Based Nanocomposites Thin Film Having Boosted Photocatalytic Activity for Xenobiotics Water Pollution Remediation.

Photocatalytic remediation represents a potential sustainable solution to the abatement of xenobiotic pollutants released within the water environment. Aeroxide® P25 titanium dioxide nanoparticles (TiO2 NPs) are well-known as one of the most efficient photocatalysts in several applications, and have also been investigated in water remediation as suspended powder. Recently, their application in the form of thin films has been revealed as a potential alternative to avoid time-consuming filtration processes. Polymers represent suitable substrates to immobilize TiO2 NPs, allowing further production of thin films that can be exploited as a photoactive coating for environmental remediation. Nevertheless, the methods adopted to immobilize TiO2 NPs on polymer matrix involve time-consuming procedures and the use of several reactants. Here, titanium dioxide-based nanocomposites (NCx) were obtained through a new approach based on Methyl Methacrylate in situ bulk polymerization and were compared with a blended mixture (BL). Their morphology and chemical-physical properties were investigated through Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), UV-Vis, and Raman spectroscopies. It was revealed that the in situ approach deeply influences the chemical-physical interactions between the polymer matrix and TiO2 NPs. Photocatalytic experiments revealed the boosted photodegradation activity of NCx thin films, induced by the in situ approach. The photodegradation of paraquat and acetaminophen was also ascertained.