Electroanalytical Sensing of Bromides Using Radiolytically Synthesized Silver Nanoparticle Electrocatalysts

Monitoring bromides (Br-) is of crucial importance since bromates, potential human carcinogens, are formed during ozonation of water containing bromides in concentrations GT 100 mu gL(-1). Within this study, silver (Ag) and four carbon-supported Ag catalysts were synthesized by the gamma-radiation method and their morphology and structure examined using transmission electron microscopy, X-ray diffraction, and UV-Vis analysis. The nanocatalysts were tested for Br- sensing in aqueous media using cyclic voltammetry. All five Ag materials exhibited electroactivity for sensing of Br- ions, with pure Ag catalyst giving the best response to Br- ions presence in terms of the lowest limit of detection. Sensing of bromides was also explored in tap water after addition of bromides suggesting that herein prepared catalysts could be used for bromides detection in real samples. Furthermore, sensing of other halogen ions, namely, chlorides and iodides, was examined, and response due to chloride presence was recorded

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

Radiolitically synthesized nano Ag/C catalysts for oxygen reduction and borohydride oxidation reactions in alkaline media, for potential applications in fuel cells

Carbon-supported silver nanoparticles (Ag:NPs/C) were synthesized by gamma irradiation-induced reduction method using the poly(vinyl alcohol) or poly(vinyl alcohol)/chitosan polymer as stabilizer. Prepared samples were characterized using transmission electron microscopy and X-ray diffractometry. Subsequently, Ag:NPs/C were studied using rotating disc and rotating ring disc method as electrocatalysts for ORR (oxygen reduction reaction) and BOR (borohydride oxidation reaction) for potential application in alkaline fuel cells. The synthesis method used herein offers simple and fast approach for catalytic ink preparation, since the ink is prepared in one-step radiation process, simultaneously with Ag+ ions reduction. Very high and stable catalytic efficiency toward ORR via 4e(-) path was evidenced during 4000 square pulse polarization cycles. BOR, accompanied with the simultaneous borohydride ion hydrolysis, was found to proceed at the oxidized Ag surface. (C) 2016 Elsevier Ltd. All rights reserved