Platinum-rare earth intermetallic alloys as anode electrocatalysts for borohydride oxidation

Sodium borohydride (NaBH4) is being actively investigated as an anodic fuel for direct borohydride fuel cells. Platinum (Pt) displays a rather good borohydride (BH4-) oxidation activity but its catalytic effect towards the BH4- hydrolysis leads to an overall number of exchanged electrons in the oxidation process, n, between 2 and 4. The doping of Pt with rare earth (RE) elements may decrease or increase the BH4- hydrolysis, thereby increasing or decreasing the n value. Among other factors, these changes will depend on the composition of the alloying elements as well as on the applied anodic potential range. In this paper, Pt and three Pt-RE intermetallic alloy (Pt-Ho, Pt-Sm, and Pt-Ce) electrodes are studied by cyclic voltammetry (CV) and chronopotentiometry (CP) in the temperature range 25-55 degrees C. Modelling of CV and CP data indicate that these Pt-RE electrodes do not show enhanced performance for the BH4- oxidation in comparison to the single Pt electrocatalyst. Of the Pt alloys, the Pt-Ho shows the highest catalytic activity for the BH4- oxidation reaction and the Pt-Ce the worst. Relevant kinetic parameters (n, alpha, k(s)) are also estimated

Nickel-Rare Earth (RE = Ce, Sm, Dy) Electrodes for H2O2 Reduction in Fuel Cells

The use of hydrogen peroxide (H2O2) as an oxidant is considered a good alternative to oxygen for the cathodic process in liquid fuel cells. Herein, we studied the reduction of H2O2 at nickel and at nickel-rare earth (RE = Ce, Sm, Dy) alloys containing 5 and 10 at.% of RE metal. The alloys were prepared by arc melting, starting from the stoichiometric amounts of the two parent metals, and analyzed by X-ray diffraction and scanning electron microscopy coupled with energy-dispersive spectroscopy. The electrochemical characterization was carried out by voltammetry and chronoamperometry measurements in alkaline media, in which main parameters were calculated, namely diffusion coefficients and number of exchanged electrons. Ni0.95Ce0.05 alloy exhibited the highest catalytic activity for H2O2 reduction reaction, with a number of exchanged electrons of 1.7. Additionally, activation energies were estimated according to Arrhenius equation

Nickel-rare earth electrodes for sodium borohydride electrooxidation

Binary alloys of nickel (Ni) and dysprosium (Dy) or samarium (Sm) of different composition were prepared. Their electrocatalytic activity in respect to borohydride oxidation in alkaline medium was investigated by cyclic voltammetry, chronoamperometry and chronopotentiometry. It was correlated to their morphological and structural properties examined by SEM/EDXS and XRPD. Ni0.95Dy0.05 alloy electrode showed the highest electrocatalytic activity for BOR, and Ni0.90Sm0.10 showed the lowest. The activity of the rare earth alloys was compared to other Ni- and Pt-based materials, with promising results being reported, which envisage application of these materials as electrodes in direct borohydride fuel cells