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. (C) 2011 Elsevier B.V. All rights reserved.