Platinum-Dysprosium Alloys for Oxygen Reduction in Alkaline Media

Oxygen reduction reaction (ORR) has become one of the most studied electrochemical reactions due to its fundamental complexity and great importance in practical applications [1]. Specifically, different renewable energy technologies, including metal-air batteries and fuel cells (FCs) [2], are based on this reaction. Direct borohydride fuel cells use alkaline sodium borohydride solution as fuel and oxygen as the oxidant.

The mechanism of the ORR is primarily determined by the electrode material and electrolyte solution. Recently, bimetallic alloys of Pt or Pd with rare earth (RE) metals scandium (Sc) or yttrium (Y) were suggested as novel electrocatalysts for the ORR based on density functional theory calculations [3]. Electrochemical measurements have confirmed improved activity of polycrystalline Pt₃Sc and Pt₃Y electrodes in comparison with pure Pt by a factor of 1.5 - 1.8 and 6 - 10, respectively, in the range 0.9 - 0.87 V.

Herein, platinum-dysprosium (Pt-Dy) alloys, with different amounts of RE metal (50 to 60 at.%) were prepared by arc-melting starting from the stoichiometric amounts of the two metals and their composition and structure were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Subsequently, electrocatalytic activity for the ORR of Pt-Dy alloy electrodes was studied in alkaline solution by cyclic voltammetry (CV) and chronoamperometry (CA). Main kinetic parameters, namely charge transfer coefficient and number of electrons exchanged, were evaluated for temperatures ranging from 25 to 65 ºC.

Furthermore, electrocatalytic activity for the ORR was studied in the presence of sodium borohydride in the supporting electrolyte in order to simulate conditions in direct borohydride fuel cells where borohydride crossover is possible to occur.

References

[1] Lee, J.; Jeong, B.; Ocon, J. D. Oxygen Elecrocatalysis in Chemical Energy Conversion and Storage Technologies. Current Applied Physics 2013, 13, 309.

[2] Mulder, G. Fuel Cells – Alkaline Fuel Cells | Overview. Encyclopedia of Electrochemical Power Sources 2009, 321.

[3] Greeley, J.; Stephens, I. E. L.; Bondarenko, A. S.; Johansson, T. P.; Hansen, H. A.; Jaramillo, T. F.; Rossmeisl, J.; Chorkendorff, I.; Nørskov, J. K. Alloys of Platinum and Early Transition Metals as Oxygen Reduction Electrocatalysts. Nature Chemistry 2009, 1, 552.