Oxidation of the borohydride Ion at silver nanoparticles on a glassy carbon electrode (GCE) using pulsed potential techniques

Direct oxidation borohydride fuel cells are very attractive energy conversion devices. Silver has been reported as one of the few materials which can catalyze an 8-electron oxidation. Potential step amperometric pulse techniques to synthesize nanostructured silver material on flat glassy carbon electrodes is reported and significant differences with bulk silver deposit have been observed. The oxidation of borohydride ion on the silver particles occurs at -0.025 V vs. SCE and the potential decreases towards negative values at longer cycle times. The oxidation current also decreases with the number of cycles, suggesting that the silver active sites become partially blocked by oxidation products of borohydride. The electroactive area per unit electrode area of silver was relatively low for particles deposited using potential step amperometric techniques on glassy carbon (0.002 cm2 per cm-2) compared with the area found at a polycrystalline silver electrode (0.103 cm2 per cm-2

Electrocatalytic urea mineralization in aqueous alkaline medium using NiIIcyclam-modified nanoparticulate TiO2 anodes and its relationship with the simultaneous electrogeneration of H2 on Pt counterelectrodes

NiIIcyclam-modified nanoparticulate TiO2-coated ITO electrodes (ITO/TiO2//NiIIcyclam) were prepared by electropolymerization of NiIIcyclam monomers to TiO2-coated ITO electrodes (ITO/TiO2) to improve electrocatalytic urea CO(NH2)2 oxidation in alkaline aqueous solutions. A high value adding secondary effect was the collection of electrons at Pt cathodes, to simultaneously generate H2 from water reduction. NiIIcyclam-modified ITO electrodes (ITO//NiIIcyclam) were also prepared by electropolymerization of NiIIcyclam monomers to bare ITO electrodes (ITO) for comparison purposes. In the presence of the TiO2 nanoparticles, the urea mineralization on NiIIcyclam coatings was doubled (23.95% – organic carbon removal at 120 min of electrolysis) compared to those without TiO2 nanoparticles (13.02% – organic carbon removal at 120 min of electrolysis). In agreement, the faradaic efficiency for H2 generation at the Pt cathode, electrically connected to an anode having TiO2 nanoparticles (0.99 at 120 min of electrolysis), was also twice as effective than that observed when the same Pt cathode was electrically connected to an anode without TiO2 nanoparticles (0.46 at 120 min of electrolysis). The experimental results indicated that the poisoning of NiII centers (which is caused by an excessive production of CO intermediates during the urea oxidation on both NiIIcyclam-modified anodes) was strongly inhibited in the presence of the nanoparticulate TiO2|NiIIcyclam junction. A final comparison between our results and those reported in selected publications revealed that the NiIIcyclam-modified nanoparticulate TiO2-coated ITO anodes here developed, constitutes a promising electrocatalytic system for performing direct urea mineralization at a relative short electrolysis time. Furthermore, the combination of the following phenomena: (a) effective charge separation on the semiconducting ITO|nanoparticulate TiO2 junctions, (b) remarkable capabilities of the nanoporous TiO2 films for tuning the load of OH� anions demanded by the urea oxidation and, (c) outstanding capabilities of the TiO2 nanoparticles for capturing CO intermediates (at Ti3+ donor sites), successfully promoted the enhancement of the electron external transport to Pt cathodes, and consequently improved the faradaic efficiency associated to the cathodic generation of H2

Electrocatalysis of the reduction of organic halide derivatives at modified electrodes coated by cobalt and iron macrocyclic complex-based films: application to the electrochemical determination of pollutants

In this study, we go into the examination of the possible use of chemically modified electrodes by Hemin embedded in surfactant film of didodecyldimethylammonium bromide or by electropolymerized cobalt porphyrin and Salen films, as potential materials for the effective electrochemical detection of several organic halides (trichloroacetic acid, ethylene dibromide, tetrachloroethylene, trichloroethylene, dichloroacetic acid, 2,4,6-trichlorophenol, 2,4-dichlorophenoxy acetic acid, methoxychloride, etc.), in aqueous and organic solutions. The reported results show an important catalytic effect induced by the modification of the electrode surface by the metal complexes which is materialized by 1.0 V decrease in the reduction potential of the examined organic halide derivatives and a large increase in their reduction current (2 to 500 times). Our descriptive results of the electrocatalytic behaviour of the examined electrodes constitute a first important step in the investigation of the evaluation of a strategy materializing the use of these modified electrodes for the detection of various significant organohalide derivatives

Electrochemical study of Co(II)/Co(III) on different electrode materials for energy storage in redox flow cells

The development of redox flow cells has been carried out through the use of several redox couples which oxidize and reduce to store electrical energy. Some problems encountered in redox cells include: low solubility of redox couples, slow kinetics, low stability of electrode materials and high toxicity of electroactive species. In this paper, Co(III)/Co(II) has been investigated as a possible electroactive material because of its high oxidizing power and the relatively low toxicity of Co(III). The electrochemical study of Co(III)/Co(II) was carried out on different electrode materials such as glassy carbon, Au, Pt, Pb and stainless steel. Results show that the high oxidizing power of Co(III) does not enable to observe its reduction reaction in the aforementioned electrode materials possibly due to electrode surface corrosion and/or water oxidation. However, the electrolysis of Co(III) with a Pb electrode shows that the system is reversible and forms PbO2 on the electrode surfac

Aguamiel syrup as a technological diversification product: Composition, bioactivity and present panorama

Mexico has a rich history of using aguamiel extracted from Agave spp to make pulque, a fermented beverage popular in Mesoamerica. However, pulque has been overtaken by more commercially produced and distilled liquors such as tequila and mezcal. As a result, alternative uses for aguamiel have been explored, including aguamiel syrup. This syrup is made by thermally concentrating aguamiel from various Agave species and has gained popularity in the health-conscious, organic, and functional food markets due to its nutraceutical properties. Two important bioactive compounds found in aguamiel and aguamiel syrup are saponins, which have anticancer, adjuvant, immunostimulant, anti-inflammatory, antimicrobial, hypocholesterolemic, and antioxidant properties, and agavin-type functional oligosaccharides, which have prebiotic activity and can help reduce energy intake in humans. However, the traditional artisanal process used to create aguamiel syrup has made it difficult to standardize its composition and increase its commercial value. This review focuses on the characteristics of aguamiel as a raw material for producing aguamiel syrup, exploring its physicochemical composition and nutraceutical properties. A proposed semi-industrial process based on the evidence from consulted references could help modernize the production of aguamiel syrup