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Titanium dioxide Nanowires (NWs) are particularly interesting because of their very high surface/volume ratio and their photocatalytic activity allows them to be used in a myriad of applications. This manuscript presents a study of nanowires grown on a conductive substrate making use of a seed-assisted thermal oxidation process. To obtain doped NWs, before the oxidation, metallic titanium was doped with Fe (or Cr) by ion implantation technology. Analyses showed good quality Rutile phase and light absorption in the visible range. Transport properties of the NWs/electrolyte junction were investigated by using linear sweep voltammetry and electrochemical impedance spectroscopy. They allowed us to measure the photovoltage and the barrier height of the junction. We also evaluated the density of hole trap states at the interface during illumination. Electrical results indicate that the formation of deep levels, induced by doping, influences the electron concentration in the TiO2 and the transport properties. [ABSTRACT FROM AUTHOR]

Green hydrogen production by water splitting holds great potential as a clean and renewable source of energy for sustainable energy solutions. However, the efficiency of this process is hampered by the sluggish oxygen evolution reaction (OER). Overcoming these kinetic hurdles requires the development of highly efficient electrocatalysts. This study explores the effect of transition metal doping on the electrocatalytic properties of Ni(OH)2 microflowers towards alkaline OER. Transition metal‐doped Ni(OH)2 microflowers, with highly porous structures due to interconnected nanosheets, are synthesized by a facile, cheap, and scalable chemical bath deposition (CBD), and combined with graphene paper (GP) substrates to fabricate electrodes. Through a systematic exploration of the relationship between the transition metal dopant element type (Mn, Fe, Co, Zn) or concentration and the consequent electrochemical properties, Co‐doping demonstrates improvement in the overpotential at a current density of 10 mA cm−2 (329 mV), Tafel slope (45 mV dec−1), and other key performance indicators of Ni(OH)2 microflowers for OER. These results are attributed to the high number of active sites and their enhanced electrocatalytic activity benefiting from the presence of the transition metal dopant. The proposed strategy paves the way for the development of cost‐effective and highly efficient electrocatalysts for water splitting technologies. [ABSTRACT FROM AUTHOR]

Electrochemical energy storage devices are one of the main protagonists in the ongoing technological advances in the energy field, whereby the development of efficient, sustainable, and durable storage systems aroused a great interest in the scientific community. Batteries, electrical double layer capacitors (EDLC), and pseudocapacitors are characterized in depth in the literature as the most powerful energy storage devices for practical applications. Pseudocapacitors bridge the gap between batteries and EDLCs, thus supplying both high energy and power densities, and transition metal oxide (TMO)-based nanostructures are used for their realization. Among them, WO3 nanostructures inspired the scientific community, thanks to WO3's excellent electrochemical stability, low cost, and abundance in nature. This review analyzes the morphological and electrochemical properties of WO3 nanostructures and their most used synthesis techniques. Moreover, a brief description of the electrochemical characterization methods of electrodes for energy storage, such as Cyclic Voltammetry (CV), Galvanostatic Charge–Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) are reported, to better understand the recent advances in WO3-based nanostructures, such as pore WO3 nanostructures, WO3/carbon nanocomposites, and metal-doped WO3 nanostructure-based electrodes for pseudocapacitor applications. This analysis is reported in terms of specific capacitance calculated as a function of current density and scan rate. Then we move to the recent progress made for the design and fabrication of WO3-based symmetric and asymmetric supercapacitors (SSCs and ASCs), thus studying a comparative Ragone plot of the state-of-the-art research. [ABSTRACT FROM AUTHOR]

The electrochemical hydrogen evolution reaction (HER) is one of the most promising green methods for the efficient production of renewable and sustainable H2, for which platinum possesses the highest catalytic activity. Cost-effective alternatives can be obtained by reducing the Pt amount and still preserving its activity. The Pt nanoparticle decoration of suitable current collectors can be effectively realized by using transition metal oxide (TMO) nanostructures. Among them, WO3 nanorods are the most eligible option, thanks to their high stability in acidic environments, and large availability. Herein, a simple and affordable hydrothermal route is used for the synthesis of hexagonal WO3 nanorods (average length and diameter of 400 and 50 nm, respectively), whose crystal structure is modified after annealing at 400 °C for 60 min, to obtain a mixed hexagonal/monoclinic crystal structure. These nanostructures were investigated as support for the ultra-low-Pt nanoparticles (0.2–1.13 μg/cm2): decoration occurs by drop casting some drops of a Pt nanoparticle aqueous solution and the electrodes were tested for the HER in acidic environment. Pt-decorated WO3 nanorods were characterized by performing scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Rutherford backscattering spectrometry (RBS), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry. HER catalytic activity is studied as a function of the total Pt nanoparticle loading, thus obtaining an outstanding overpotential of 32 mV at 10 mA/cm2, a Tafel slope of 31 mV/dec, a turn-over frequency of 5 Hz at −15 mV, and a mass activity of 9 A/mg at 10 mA/cm2 for the sample decorated with the highest Pt amount (1.13 μg/cm2). These data show that WO3 nanorods act as excellent supports for the development of an ultra-low-Pt-amount-based cathode for efficient and low-cost electrochemical HER. [ABSTRACT FROM AUTHOR]

Transition metal oxide nanostructures are promising materials for energy storage devices, exploiting electrochemical reactions at nanometer solid–liquid interface. Herein, WO3 nanorods and hierarchical urchin-like nanostructures were obtained by hydrothermal method and calcination processes. The morphology and crystal phase of WO3 nanostructures were investigated by scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD), while energy storage performances of WO3 nanostructures-based electrodes were evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests. Promising values of specific capacitance (632 F/g at 5 mV/s and 466 F/g at 0.5 A/g) are obtained when pure hexagonal crystal phase WO3 hierarchical urchin-like nanostructures are used. A detailed modeling is given of surface and diffusion-controlled mechanisms in the energy storage process. An asymmetric supercapacitor has also been realized by using WO3 urchin-like nanostructures and a graphene paper electrode, revealing the highest energy density (90 W × h/kg) at a power density of 90 W × kg−1 and the highest power density (9000 W/kg) at an energy density of 18 W × h/kg. The presented correlation among physical features and electrochemical performances of WO3 nanostructures provides a solid base for further developing energy storage devices based on transition metal oxides. [ABSTRACT FROM AUTHOR]

In this work we describe the Square Wave Anodic Stripping Voltammetry (SWASV) electrochemical technique for the determination of lead (Pb2+) and cadmium (Cd2+) metal ions at concentration of sub-part per billion (ppb) in aqueous solution. Moreover, simple and low-cost procedures for the fabrication of high performance working nano-electrode are reported. The electrode structure consists of a graphene paper (GP) $240~\mu \text{m}$ thick with the function of electrical conductor and substrate, a layer of nafion 0.5- $0.7~\mu \text{m}$ thick onto the graphene paper and bismuth nanoparticles embedded in the nafion thin layer. The bismuth nanoparticles were fabricated by electrodeposition starting from Bi(III) ions, employing a key step of hydrogen ions of nafion $\text{H}^{\mathbf {+}}$ exchange with bismuth ions Bi(III). This procedure is aimed to improve the bismuth nanoparticles concentration. The SWASV applied to the low-cost nanoelectrode allows detecting Pb2+ and Cd2+ at concentration as low as 0.1 ppb. [ABSTRACT FROM AUTHOR]