Electrosynthesis of hydrogen peroxide via the reduction of oxygen assisted by power ultrasound

The electrosynthesis of hydrogen peroxide using the oxygen reduction reaction has been studied in the absence and presence of power ultrasound in a non-optimized sono-electrochemical flow reactor (20 cm cathodic compartment length with 6.5 cm inner diameter) with reticulated vitreous glassy carbon electrode (30 x 40 x 10 mm, 10 ppi, 7 cm2 cm-3) as the cathode. The effect of several electrochemical operational variables (pH, volumetric flow, potential) and of the sono-electrochemical parameters (ultrasound amplitude and horn-to-electrode distance) on the cumulative concentration of hydrogen peroxide and current efficiency of the electrosynthesis process have been explored. The application of power ultrasound was found to increase both the cumulative concentration of hydrogen peroxide and the current efficiency. The application of ultrasound is therefore a promising approach to the increased efficiency of production of hydrogen peroxide by electrosynthesis, even in the solutions of lower pH (<12). The results demonstrate the feasibility of at-site-of-use green synthesis of hydrogen peroxide.Ministerio de Educación y Ciencia (Spain) for the Grant (PR2004-0480) and Generalidad Valenciana (Project GV05/104)

Electrochemical synthesis of hydrogen peroxide assisted by ultrasound

Presentación realizada en el 10th Meeting of the European Society of Sonochemistry, Hamburg, June 4-8, 2006

Concentration of heavy metals and stand state of sesille oak (quercus petraea (matt.) Liebl.) On avala mountain (Serbia)

The research of heavy metals contents in soil and leaves of Sessile oak (Quercus petraea (Matt.) Liebl.). Moreover, the paper presents the analysis of the stand state on the Avala Mountain. The Avala area is high-grade protected natural resource located on the territory of Belgrade (Serbia) and its regime of exploitation and protection is clearly defined. It is assumed that the human factor is the primary cause of degradation of the protected areas of Avala. Therefore, the current inadequate stand composition and the impact of traffic pollution can be considered the decisive causes of degradation on mountain, as a natural area under special protection. Determining the degree of loading of soil and plants with heavy metals and the analysis of stand conditions of such valuable protected areas such as the area of Avala, are of great importance, based on the results obtained, to take appropriate timely precautionary measures, in order to preserve, improve nature conservation, the environment in general, and especially health conditions. The research of the contents of heavy metals (Pb, Ni, Fe, Zn i Mn) in soil showed the load of soil especially with Pb and Ni. In third locaction the concentration of Ni (amounting to 7.0 mu g/g) in the plants leaves is significantly higher which indicates the existance of chemical contamination of soil, before all, with this pollutant. The measured concentrations of all examined heavy metals (Pb, Ni, Zn, Mn and Fe) in the leaves of Sessile oak on Avala fall within the maximum allowed values in accordance with the legal regulations in Serbia

Enhanced borohydride oxidation kinetics at gold-rare earth alloys

none6Gold-rare earth (Au-RE) alloys with equiatomic compositions are prepared by arc (RE = Dy, Ho, Y) or induction (RE = Sm) melting. Morphology and phase composition is assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDXS), while X-ray powder diffraction (XRPD) is used to confirm crystal structures. The Au-RE electrodes are evaluated for borohydride oxidation reaction (BOR) in alkaline media employing cyclic voltammetry and chronoamperometry. The obtained data allows calculation of kinetic parameters that characterize the borohydride (BH4-) oxidation at Au-RE alloys, including the number of exchanged electrons, n, and the anodic charge transfer coefficient, α. n values range from 2.4 to 4.4, while α values are found to be in the 0.60–0.83 range. The BOR apparent activation energy, Eaapp, and the reaction order, β, are also determined from CV data obtained at different temperatures and different BH4- concentrations, respectively. Low Eaapp values range from 16.4 (Au-Sm) to 20.2 kJ mol−1 (Au-Y) and β values suggest that BOR at the examined alloys is a 1st order reaction with respect to BH-4 concentration. A small-scale direct borohydride-peroxide fuel cell (DBPFC) operating with Au-Y anode at 25 °C reaches a peak power density of 150 mW cm−2. The cell performance is enhanced when increasing the temperature to 45 °C, with a maximum power density of 215 mW cm−2 being attained.noneBackovic G.; Milikic J.; De Negri S.; Saccone A.; Sljukic B.; Santos D.M.F.Backovic, G.; Milikic, J.; De Negri, S.; Saccone, A.; Sljukic, B.; Santos, D. M. F

Mn2O3-MO (MO = ZrO2, V2O5, WO3) supported PtNi nanoparticles: Designing stable and efficient electrocatalysts for oxygen reduction and borohydride oxidation

PtNi nanoparticles (NPs) are synthesised by microwave irradiation technique and anchored onto three binary metal oxide (BMO) supports, namely Mn2O3-ZrO2, Mn2O3-V2O5 and Mn2O3-WO3, prepared by solid-state dispersion method. The BMO supports are characterised using SEM, FTIR, N-2-sorption and electrical conductivity measurements. XRD, XPS and TEM analysis confirm the formation of PtNi NPs on the BMO supports. Pt and Ni content over the support materials is set to 10 wt.% for each element. These electrocatalysts activity for oxygen reduction (ORR) and borohydride oxidation (BOR) reaction in alkaline media is assessed for the first time using voltammetric and chronoamperometric techniques. All three PtNi electrocatalysts revealed activity for ORR and BOR, with PtNi/(Mn2O3- ZrO2) exhibiting the highest current densities. The ORR onset potentials were observed to range from 0.84 to 0.97 V vs. RHE, with Tafel slopes ranging from 0.101 to 0.230 V dec(-1). BOR activation energies were found to range from 27 to 30 kJ mol(-1). Obtained results point out PtNi/(Mn2O3- ZrO2) as suitable electrocatalyst for fuel cell applications, particularly for BOR, with lower catalyst price due to partial replacement of the noble metal by a transition metal and improved stability achieved by introducing a binary metal oxide support

Tailoring metal-oxide-supported PtNi as bifunctional catalysts of superior activity and stability for unitised regenerative fuel cell applications

Three different metal oxides based on Mn2O3 with TiO2 or NiO were synthesised. Pt or PtNi nanoparticles were anchored on each support, creating a set of nine samples that were tested for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). PtNi/Mn2O3-NiO showed the most promising results for ORR as evidenced by the lowest Tafel slope, the highest diffusion-limited current density and number of electrons exchanged, along with the highest stability. The best performance of PtNi/Mn2O3-NiO reflects its highest electrochemical surface area and the lowest charge-transfer resistance. Furthermore, this catalyst showed high activity for the OER as evidenced by the low Tafel slope and high current density at an overpotential of 400 mV. The present study indicated different active sites for the two reactions, i.e., PtNi NPs for the ORR and NiO for the OER

A Pt/MnV2O6 nanocomposite for the borohydride oxidation reaction

Problems associated with carbon support corrosion under operating fuel cell conditions require the identification of alternative supports for platinum-based nanosized electrocatalysts. Platinum supported on manganese vanadate (Pt/MnV2O6 ) was prepared by microwave irradiation method and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy. The borohydride oxidation reaction (BOR) on Pt/MnV2O6 was studied in highly alkaline media using voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. BOR electrocatalytic activity of Pt/MnV2O6 was also compared with that of commercial Pt/C (46 wt% Pt) electrocatalyst. The apparent activation energy of BOR at Pt/MnV2O6 was estimated to be 32 kJ mol(-1) and the order of reaction to be 0.51, indicating that borohydride hydrolysis proceeds in parallel with its oxidation. Long-term stability of Pt/MnV2O6 under BOR typical conditions was observed. A laboratory-scale direct borohydride fuel cell assembled with a Pt/MnV2O6 anode reached a specific power of 274 W g(-1). Experimental results on Pt/MnV2O6 were complemented by DFT calculations, which indicated good adherence of Pt to MnV2O6, beneficial for electrocatalyst stability. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved

Benzimidazole Schiff base copper(II) complexes as catalysts for environmental and energy applications: VOC oxidation, oxygen reduction and water splitting reactions

The new copper(II) complexes [Cu(mu-1 kappa O:2 kappa ONN'-HL1)(mu-1 kappa O:2 kappa O'-NO3)](2)center dot[Cu(mu-1 kappa O:2 kappa ONN'-HL1)(CH3OH)](2)(NO3)(2) (1) and [Cu(kappa ONN'-HL2)(mu-1 kappa OO':2 kappa O'-NO3)](n) (2), derived from the new pro-ligands H(2)L1 = 2-(5,6-dihydroindolo[1,2-c]quinazolin-6-yl)-5-methylphenol and H(2)L2 = 2-(5,6-dihydroindolo[1,2-c]quinazolin-6-yl)-4-nitrophenol, were synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and their structural features were unveiled by single-crystal X-ray diffraction analysis. This discloses a dimeric structure for 1 and a polymeric infinite 1D metal-organic chain for 2. The complexes were evaluated as catalysts for the oxidation of toluene, a volatile organic compound (VOC), and for oxygen reduction and water splitting reactions. 1 exhibits a higher activity for the peroxidative conversion of toluene to oxygenated products (total yields up to 38%), whereas 2 demonstrates a superior performance for electrochemical energy conversion applications, i.e., for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline medium in terms of higher ORR current densities, lower Tafel slope (73 mV dec(-1)) and higher number of electrons exchanged (3.9), comparable to that of commercial Pt/C. Complex 2 also shows a better performance with lower onset potential and higher current densities for both OER and HER when studied as electrocatalyst for water splitting.info:eu-repo/semantics/publishedVersio