Enhanced borohydride oxidation kinetics at gold-rare earth alloys

Gold-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, alpha. n values range from 2.4 to 4.4, while alpha values are found to be in the 0.60-0.83 range. The BOR apparent activation energy, E-a(app), and the reaction order, beta, are also determined from CV data obtained at different temperatures and different BH4- concentrations, respectively. Low E-a(app) values range from 16.4 (Au-Sm) to 20.2 kJ mol(-1) (Au-Y) and beta values suggest that BOR at the examined alloys is a 1st order reaction with respect to BH4- concentration. A small-scale direct borohydride-peroxide fuel cell (DBPFC) operating with Au-Y anode at 25 degrees C reaches a peak power density of 150 mW cm(-1). The cell performance is enhanced when increasing the temperature to 45 degrees C, with a maximum power density of 215 mW cm(-2) being attained. (C) 2020 Elsevier B.V. All rights reserved.