Evaluating the Effect of WO3 on Electrochemical and Corrosion Properties of TiO2-RuO2-Coated Titanium Anodes with Low Content of RuO2

Electrochemical and Catalytic Properties of Carbon Dioxide-Activated Graphite Felt

The commercial graphite felt GFA 10 was subjected to an activation process with the use of CO₂ at 900 °C for 35 and 70 min. Pristine and heat-treated materials were characterized using various methods: low-temperature N₂ adsorption, SEM, and EDS. Voltammetric measurements of GFA samples (before and after activation) as the working electrode were carried out. Voltammograms were recorded in aqueous solutions of 4-chlorophenol and sodium sulfate as supporting electrolyte. The catalytic activity of GFA samples in the process of 4-chlorophenol oxidation with the use of H₂O₂ was also investigated. The influence of graphite felt thermal activation in the CO₂ atmosphere on its electrochemical and catalytic behavior was analyzed and discussed. Results of the investigation indicate that GFA activated in CO₂ can be applied as an electrode material or catalytic material in the removal of organic compounds from industrial wastewater. However, the corrosion resistance of GFA, which is decreasing during the activation, needs to be refined.

Mixed Oxide Electrodes Based on Ruthenium and Copper: Electrochemical Properties as a Function of the Composition and Method of Manufacture

The development of mixed oxide electrodes is being intensively investigated to reduce the high cost associated with the use of noble metals and to obtain versatile and long-lasting devices. To evaluate their use for charge storage or anodic oxidation, in this paper, thin-film electrodes coated with ruthenium (RuOx) and copper oxide (CuOx) are fabricated by thermal decomposition of organic solutions containing the precursors by drop-casting on titanium (Ti) foils. The coating consisted of four layers of metal oxide. To investigate the effect of copper (Cu) on electrochemical performances, different approaches are adopted by varying the ratios of precursors’ concentration and including a RuOx interlayer. A comparison with samples obtained by only RuOx has been also performed. The electrodes are characterized using scanning electron microscopy (SEM), cyclic (CV) and linear sweep (LSV) voltammetry, electrochemical impedance spectroscopy (EIS), and corrosion tests. The addition of Cu enhances the capacitive response of the materials and promotes electron transfer reversibility. The coatings obtained by the highest Ru:Cu ratio (95:5) exhibit a more uniform surface distribution and increased corrosion resistance. The interlayer is beneficial to further reduce the corrosion susceptibility and to promote the oxygen evolution but detrimental in the charge storage power. The results suggest the possibility to enhance the electrochemical performance of expensive RuOx through a combination with a low amount of cheaper and more abundant CuOx.

Effect of Spin Coating Parameters on the Electrochemical Properties of Ruthenium Oxide Thin Films

Ruthenium oxide (RuOx) thin films were spin coated by thermal decomposition of alcoholic solutions of RuCl3 on titanium foils and subsequently annealed at 400 °C. The effect of spin coating parameters, such as spinning speed, volume, and molar concentration of the precursor as well as the number of deposits, on the morphology and electrochemical performance of the electrodes was investigated. The films were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV) with and without chloride, and linear sweep voltammetry (LSV). The prepared materials were also compared to drop cast films and spin-coated films obtained by adopting low-temperature intermediate treatments. The results indicate that even dispersion of the oxide layer was always achieved. By tuning the spin coating parameters, it was possible to obtain different electrochemical responses. The most influential parameter is the number of deposits, while the concentration of the precursor salt and the rotation speed were less relevant, under the adopted conditions.

In Situ Wet Etching of MoS2@dWO3 Heterostructure as Ultra-Stable Highly Active Electrocatalyst for Hydrogen Evolution Reaction

Electrocatalysts featuring robust structure, excellent catalytic activity and strong stability are highly desirable, but challenging. The rapid development of two-dimensional transition metal chalcogenide (such as WO3, MoS2 and WS2) nanostructures offers a hopeful strategy to increase the active edge sites and expedite the efficiency of electronic transport for hydrogen evolution reaction. Herein, we report a distinctive strategy to construct two-dimensional MoS2@dWO3 heterostructure nanosheets by in situ wet etching. Synthesized oxygen-incorporated MoS2-was loaded on the surface of defective WO3 square nanoframes with abundant oxygen vacancies. The resulting nanocomposite exhibits a low overpotential of 191 mV at 10 mA cm−2 and a very low Tafel slope of 42 mV dec−1 toward hydrogen evolution reaction. The long-term cyclic voltammetry cycling of 5000 cycles and more than 80,000 s chronoamperometry tests promises its outstanding stability. The intimate and large interfacial contact between MoS2 and WO3, favoring the charge transfer and electron–hole separation by the synergy of defective WO3 and oxygen-incorporated MoS2, is believed the decisive factor for improving the electrocatalytic efficiency of the nanocomposite. Moreover, the defective WO3 nanoframes with plentiful oxygen vacancies could serve as an anisotropic substrate to promote charge transport and oxygen incorporation into the interface of MoS2. This work provides a unique methodology for designing and constructing excellently heterostructure electrocatalysts for hydrogen evolution reaction.

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1-xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm-2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec-1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1-xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.