Improving the Activity and Stability of PdSn Catalyst for Oxygen Reduction by Heat Treatment

The search for new efficient and inexpensive ORR electrocatalysts for cathodes of PEMFCs has been a fast-growing area of research over the past 10 years.

One of the most promising cathode systems are the Pd-based alloys, such as PdCo, PdCr, PdNi [1,2], PdFe [3] and PdP [4] that compete with platinum in terms of electrocatalytic activity.

A very important concern in the development of fuel cells is the electrochemical stability of the catalyst, which can affect the fuel cell lifetime. A few publications have described the ORR activity of PdSn alloys in acid media [5,6]. However, to the best of our knowledge, the effect of heat treatment on PdSn electrocatalyst activity and stability has not been yet investigated.

In this work, PdSn/C electrocatalysts for ORR have been synthesized by the sodium borohydride method with sensitizing (Sn²⁺/SnO₂ or Sn⁴⁺) and activating pretreatment (Pd²⁺/Pd) of the carbon support Vulcan XC72. The electrocatalysts have been then heat treated at 300 ºC in a reducing atmosphere (3% hydrogen in nitrogen). The morphology, structure and composition of the catalysts as-prepared and subject to thermal treatment have been characterized by XRD, SEM/EDS and TEM. The activity of PdSn/C catalysts for ORR in acid media has been studied using a rotating disc electrode (RDE) and electrochemical impedance spectroscopy (EIS). Specific activity-time curves measured at a fixed potential have been used to study the long-term catalyst performance for more than 2 days. The PdSn/C catalysts prepared with heat treatment exhibited an enhanced activity and stability as compared to those synthesized without treatment.

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[2] K. Lee, O. Savadogo, A. Ishihara, S. Mitsushima, N. Kamiya, K.-i Ota, J. Electrochem. Soc. 153 (2006) A20

[3] M.-H. Shao, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 128 (2006) 3526

[4] R. Rego, A. M. Ferraria, A.M. Botelho do Rego, M. Cristina Oliveira, Electrochimica Acta 87 (2013) 73

[5] Md. R. Miah, J. Masud, T. Ohsaka, Electrochimica Acta 56 (2010) 285

[6] J. Salvador-Pascual, J. A. Chávez-Carvayar, O. Solorza-Feria, ECS Transactions 15 (2008) 3

Acknowledgements

This work was supported by Fundação para a Ciência e a Tecnologia (FCT) and FEDER (contracts PTDC/QUI-QUI/110855/2009, PEst-OE/QUI/UI0616/2014) and COST Action MP1202 "Rational design of hybrid organic-inorganic interfaces". R. Rego acknowledges FCT for grant SFRH/BSAB/1337/2013.