Electrochemical Study

Energy and environment crises motivated scientists to develop sustainable, renewable, and clean energy resources mainly based on solar hydrogen. For this purpose, one main challenge is the low cost flexible substrates for designing earth abundant efficient cocatalysts to reduce required water oxidation overpotential. Here, a systematic morphological and electrochemical study has been reported for cobalt oxide/hydroxide nanoflakes simply electrodeposited on four different commercially available substrates, titanium, copper sheet, steel mesh, and nickel foam. Remarkable dependence between the used substrate, morphology, and electrocatalytic properties of nanoflakes introduced flexible porous steel layer as the best substrate for samples with 499 mV overpotential, 5.3 Ω charge transfer resistance, and 0.03 S -1 turnover frequency. Besides, carbonaceous paste including carbon nanotubes and graphene sheets as the middle layer increased turnover frequency by 33%, effective surface interface nearly three times while it reduced 7.5% of resistance. Hence, optimizing the conductive nanostructured paste can lead to more efficient cobalt electrocatalysts exposing more active atomic surface sites.

intensive use of pesticides in modern agriculture has led to serious problems in the quality of superficial or underground water, which led to the development of diseases and destruction of fauna and flora. Water pollution by these pesticides is a reality more and more present in Morocco that requires control and elimination of these compounds in the aqueous medium. Therefore, it is important to take interest in their ability to be degraded and the degradation pathway. Pesticides are only partially degraded in the field and transformation products are formed which can also be found in groundwater or rivers. The downside of partial degradation is that transformation products are often more mobile than their parent compound, can be more persistent and even more toxic; inducing the increase of total contamination. In this study, we focused on fenamiphos as pesticide. This product belongs to the chemical family of organophosphates and it is widely used as an insecticide and nematicide o...

intensive use of pesticides in modern agriculture has led to serious problems in the quality of superficial or underground water, which led to the development of diseases and destruction of fauna and flora. Water pollution by these pesticides is a reality more and more present in Morocco that requires control and elimination of these compounds in the aqueous medium. Therefore, it is important to take interest in their ability to be degraded and the degradation pathway. Pesticides are only partially degraded in the field and transformation products are formed which can also be found in groundwater or rivers. The downside of partial degradation is that transformation products are often more mobile than their parent compound, can be more persistent and even more toxic; inducing the increase of total contamination. In this study, we focused on fenamiphos as pesticide. This product belongs to the chemical family of organophosphates and it is widely used as an insecticide and nematicide o...

Phenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl and hydroxyl radicals of the coumarin derivatives.

The electrochemical oxidation of iodide in the presence of phenol and o-cresol was investigated at a glassy carbon electrode in buffered media by cyclic voltammetry, linear sweep voltammetry and controlled-potential coulometry. The experimental results indicate that the phenol and o-cresol convert to their derivatives after participating in a halogenation coupled reaction (quasi-catalytic reaction) following the oxidation of iodide to iodine. The concentrations of phenol and o-cresol have been determined in aqueous solutions according to the linear dependence of quasi-catalytic peak currents with the concentration. The calibration graphs show two linear sections of 0.0 to 1.0×10-4 M and 2.0×10-4 to 1.0 ×10-3 M for phenol and 4.2×10-5 to 1.0×10-4 M and 2.0×10-4 to 1.0×10-3 M for o-cresol. The theoretical detection limits and the relative standard deviations for ten measurements of phenol and o-cresol are 1.125×10-5 M, 1.06% and 4.201×10-5 M, 1.44%, respectively.

Phenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl and hydroxyl radicals of the coumarin derivatives.

intensive use of pesticides in modern agriculture has led to serious problems in the quality of superficial or underground water, which led to the development of diseases and destruction of fauna and flora. Water pollution by these pesticides is a reality more and more present in Morocco that requires control and elimination of these compounds in the aqueous medium. Therefore, it is important to take interest in their ability to be degraded and the degradation pathway. Pesticides are only partially degraded in the field and transformation products are formed which can also be found in groundwater or rivers. The downside of partial degradation is that transformation products are often more mobile than their parent compound, can be more persistent and even more toxic; inducing the increase of total contamination. In this study, we focused on fenamiphos as pesticide. This product belongs to the chemical family of organophosphates and it is widely used as an insecticide and nematicide o...

intensive use of pesticides in modern agriculture has led to serious problems in the quality of superficial or underground water, which led to the development of diseases and destruction of fauna and flora. Water pollution by these pesticides is a reality more and more present in Morocco that requires control and elimination of these compounds in the aqueous medium. Therefore, it is important to take interest in their ability to be degraded and the degradation pathway. Pesticides are only partially degraded in the field and transformation products are formed which can also be found in groundwater or rivers. The downside of partial degradation is that transformation products are often more mobile than their parent compound, can be more persistent and even more toxic; inducing the increase of total contamination. In this study, we focused on fenamiphos as pesticide. This product belongs to the chemical family of organophosphates and it is widely used as an insecticide and nematicide o...

Phenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl and hydroxyl radicals of the coumarin derivatives.

Phenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl and hydroxyl radicals of the coumarin derivatives.

We report a mechanistic investigation of the electrochemical behavior of TiO 2 nanotubes (NTs) in amorphous and anatase phases during sodiation/desodiation. The local structure variations of these two host structures upon Na + uptake/release are comparatively examined by X-ray absorption near edge structure (XANES) at the Ti K and L, O K, and Na K edges. Upon Na + insertion/extraction, the surface/near surface XANES analysis at the Ti K edge suggests that the surface/near surface of TiO 2 NTs in both phases is partially reduced to metallic Ti from the unstable sodium titanate formed at the electrolyte/electrode interface, and the sodiation of amorphous NTs is more effective than anatase ones. More importantly, it further reveals that irreversible phase transformations from pure amorphous and anatase TiO 2 to amorphous sodium titanate take place on the NT surface/near surface after the first cycle of discharge/charge. The bulk XANES analysis at the Ti L edge demonstrates that irreversible phase transformation also proceeds in the bulk of these two phase structures, where, however, the formation stable amorphous sodium titanate is observed. All the findings are corroborated by energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and XANES analysis at the O K and Na K edges.

Resumen En este trabajo se establecen las condiciones operatorias adecuadas para la cuantificación de la cantidad de potasio en diferentes muestras de interés farmacéutico y clínico, mediante la utilización de diferentes técnicas electroquímicas de análisis, conductimetría, voltamperometría lineal y polarografía clásica, acoplando una reacción específica clásica del análisis químico cualitativo para K +. Se determina la concentración de potasio de manera indirecta por la precipitación del hexanitrocobaltato (III) de potasio (K 3 [Co(NO 2) 6 ]) como reactivo piloto. Se describió la construcción de una microcelda electroanalítica con un volumen menor a 1 mL utilizando tres electrodos miniaturizados. Se monitoreó el Co (III) remanente a la reacción con K + por polarografía clásica y alternativamente el Co(II) proveniente de la transformación del Co(III) remanente a pH controlado. Se establecieron las condiciones operatorias para obtener curvas de calibración mediante apoyo conductimétr...

Doping of rare-earth metal oxides into nanocrystalline titanium dioxide (NTD) films is known to improve performance for photovoltaic and photocatalytic applications, however, the reasons for this improvement are not well understood. To explore the enhancement mechanism, an electrical and electrochemical study of rare earth oxide doped NTD films was performed. Doped films were found to be 40-50 times more conductive than undoped films, with linear current-voltage characteristics and decreased light sensitivity. Cyclic voltammograms of doped samples show an enhanced scan rate dependence in the deep trap regime due to a slower charge trapping rate. Finally, electrochemical impedance measurements reveal a decrease in space charge density and a shift in the flat-band potential. Taken together, these results suggest that charge transfer from the rare earth oxide neutralizes the deep trap states in the NTD film, decreasing charge scattering, and improving the NTD performance as an electron acceptor and electron transport material.

The performance of high-rate supercapacitors requires fine morphological and electrical properties of the electrode. Polyaniline (PANI), as one of the most promising materials for energy storage, shows different behaviour on different substrates. The present study reports on the surface modification of fluorine doped tin oxide (FTO) with the sodium phytate doped PANI without any binder and its utilization as a novel current collector in symmetric supercapacitor devices. The electrochemical behaviour of the sodium phytate doped PANI thin film with and without a binder on fluorine doped tin oxide (FTO) as current collector was investigated by cyclic voltammetry (CV). The electrode without a binder showed higher electrocatalytic efficiency. A symmetrical cell configuration was therefore constructed with the binder-free electrodes. The device showed excellent electrochemical performance with high specific capacities of 550 Fg−1 at 1 Ag−1 and 355 Fg−1 at 40 Ag−1 calculated from galvanost...

Symmetric batteries, in which the same active material is used for the positive and the negative electrode, simplifying the manufacture process and reducing the fabrication cost, have attracted extensive interest for large-scale stationary energy storage. In this paper, we propose a symmetric battery based on titanium hexacyanoferrate (TiHCF) with two well-separated redox peaks of Fe3+/Fe2+ and Ti4+/Ti3+ and tested it in aqueous Na-ion/ K-ion/Mg-ion electrolytes. The result shows that all the symmetric batteries exhibit a voltage plateau centered at around 0.6 V, with discharge capacity around 30 mAhg−1 at C/5. Compared to a Mg-ion electrolyte, the TiHCF symmetric batteries in Na-ion and K-ion electrolytes have better stability. The calculated diffusion coefficient of Na+, K+, and Mg2+ are in the same order of magnitude, which indicates that the three-dimensional ionic channels and interstices in the lattice of TiHCF are large enough for an efficient Na+, K+ and Mg2+ insertion and e...

TiO 2 nanoparticles are prepared via sol-gel method using titanium tetraisopropoxide (TTIP) as a precursor under refluxing and controlled pH. It is found that pure anatase phase is obtained with pH 10. Further characterization studies are carried out on pure nanoparticle anatase phase by XRD, SEM, and transmission electron microscope (TEM). Their electrochemical performances as anode material in lithium-ion batteries are investigated by cyclic voltammetry, galvanostatic cycling, and rate capability measurements. A high discharge capacity of 321 mAh/g (vs. 335 mAh/g theoretical) is achieved at 1C rate. After the first galvanostatic charge/discharge cycle, voltage profiles show plateaus at 1.75 and 1.95 V versus Li at discharge and charge, respectively. High Coulombic efficiency (>99%) is maintained after 300 cycles, which makes anatase TiO 2 nanoparticles prepared by sol-gel method, a very promising material for anode application in lithium rechargeable batteries.

TiO 2 nanoparticles are prepared via sol-gel method using titanium tetraisopropoxide (TTIP) as a precursor under refluxing and controlled pH. It is found that pure anatase phase is obtained with pH 10. Further characterization studies are carried out on pure nanoparticle anatase phase by XRD, SEM, and transmission electron microscope (TEM). Their electrochemical performances as anode material in lithium-ion batteries are investigated by cyclic voltammetry, galvanostatic cycling, and rate capability measurements. A high discharge capacity of 321 mAh/g (vs. 335 mAh/g theoretical) is achieved at 1C rate. After the first galvanostatic charge/discharge cycle, voltage profiles show plateaus at 1.75 and 1.95 V versus Li at discharge and charge, respectively. High Coulombic efficiency (>99%) is maintained after 300 cycles, which makes anatase TiO 2 nanoparticles prepared by sol-gel method, a very promising material for anode application in lithium rechargeable batteries.

The electrochemical oxidation of iodide in the presence of phenol and o-cresol was investigated at a glassy carbon electrode in buffered media by cyclic voltammetry, linear sweep voltammetry and controlled-potential coulometry. The experimental results indicate that the phenol and o-cresol convert to their derivatives after participating in a halogenation coupled reaction (quasi-catalytic reaction) following the oxidation of iodide to iodine. The concentrations of phenol and o-cresol have been determined in aqueous solutions according to the linear dependence of quasi-catalytic peak currents with the concentration. The calibration graphs show two linear sections of 0.0 to 1.0×10 -4 M and 2.0×10 -4 to 1.0 ×10 -3 M for phenol and 4.2×10 -5 to 1.0×10 -4 M and 2.0×10 -4 to 1.0×10 -3 M for o-cresol. The theoretical detection limits and the relative standard deviations for ten measurements of phenol and o-cresol are 1.125×10 -5 M, 1.06% and 4.201×10 -5 M, 1.44%, respectively.

Aurora de J. Garza, Lidia R. Naccha, Lorenzo Heyer, Noemí Waksman y Norma C. Cavazos Departamento de Química Analítica. Facultad de Medicina. Universidad Autónoma de Nuevo León (Monterrey, NL, México) E-mail: nocavazos@yahoo.com ... El avance tecnológico ...

In this paper, a basic electro-analytical study on the behavior of anatase TiO 2 in aqueous NaOH has been presented using cyclic voltammetry technique (CV). The study has explored the possibility of using TiO 2 as anode material for ARSBs in presence of 5 M NaOH aqueous electrolyte. CV profiles show that anatase TiO 2 exhibits reversible sodium ion insertion/de-insertion reactions. CV studies of TiO 2 anode in aqueous sodium electrolytes at different scan rate shows that the Na + ion insertion reaction at the electrode is diffusion controlled with a resistive behavior. Proton insertion from aqueous sodium electrolytes into TiO 2 cannot be ruled out. To confirm the ion inserted and de-inserted, CV studies are done at different concentration of NaOH and it is found that at lower concentrations of NaOH, proton insertion process competes with Na + ion insertion process and as the concentration increases, the Na + ion insertion process becomes the predominant electrode reaction making it suitable anode materials for aqueous sodium batteries in 5 M NaOH.