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

Abstract

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.[1] O. Savadogo, K. Lee, K. Oishi, S. Mitsushima, N. Kamiya, K.-I. Ota, Electrochem. Commun. 6 (2004) 105[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) 3AcknowledgementsThis 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.