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 °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, α, ks) are also estimated.

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► Pt and Pt–RE (RE = Ho, Sm, Ce) alloys show catalytic activity for BH4− oxidation.
► BH4− direct/indirect oxidation proceeds via highly irreversible processes.
► CV and CP curves indicate superior kinetics for the single Pt electrocatalyst.
► Pt–Ho favours BH4− direct oxidation and Pt–Ce favours its heterogeneous hydrolysis.
► The relative activity of each Pt–RE alloy is independent of temperature (25–55 °C).