H. Baroody, S. Rinaldo (Simon Fraser University), and M. Eikerling (Simon Fraser University, Department of Chemistry)
The formation and reduction of surface oxide species determine both the electrocatalytic activity of Pt towards the oxygen reduction reaction as well as the rate of corrosive Pt dissolution [1]. We perform theory and modeling work to rationalize the various stages of oxide formation and reduction at Pt. Our mechanistic models establish relations between metal phase potential and surface oxidation state that govern the transient current response of the electrode, as probed for instance in cyclic voltammetry. In the first part, we will discuss a recently developed kinetic model for oxide formation and reduction at Pt in the voltage range of 0.65–1.15 V [2]. The model is evaluated against electrochemical [3], spectroscopic [4] and computational studies [5]. In the second part, we will present a kinetic model of oxide growth on platinum in the high voltage regime, above 1.15 V. The governing equations of the oxide growth model account for mass and charge conservation, species migration, and electric field effects. As the outcome, we will obtain a generalized oxide growth law of platinum. The results will be compared to experimental cyclic voltammetry data to extract rates of kinetic and transport processes. Moreover, the model incorporates a mechanism of platinum dissolution. Using this model, we strive to explain the dramatically enhanced rate of Pt dissolution at extended surfaces and in nanoparticle systems, observed in experimental studies that involved voltage cycling through the high voltage regime [6,7,8]. Knowledge of the mechanisms of growth and reduction of oxides on platinum will allow us to refine our theory of platinum dissolution in polymer electrolyte fuel cells [9].
References
[1] A. Seyeux, V. Maurice, and P. Marcus, J. Electrochem. Soc. 160, C189 (2013).
[2] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Electrocatalysis 5, 262 (2014).
[3] A.M. Gómez-Marín, J. Clavilier, J.M. Feliu, J. Electroanal. Chem. 688, 360 (2013)
[4] M. Wakisaka, H. Suzuki, S. Mitsui, H. Uchida, M. Watanabe, Langmuir 25, 1897 (2009)
[5] L. Wang, A. Roudgar, M. Eikerling, J. Phys. Chem. C 113, 17989 (2009)
[6] S. G. Rinaldo, P. Urchaga, J. Hu, W. Lee, J. Stumper, C. Rice, and M. Eikerling, Phys. Chem. Chem. Phys., submitted.
[7] A. A. Topalov, S. Cherevko, A. R. Zeradjanin, J. C. Meier, I. Katsounaros, and K. J. J. Mayrhofer, Chemical Science 5, 631 (2014).
[8] L. Xing, M. A. Hossain, M. Tian, D. Beauchemin, K. T. Adjemian, and G. Jerkiewicz, Electrocatalysis 5, 96 (2014).
[9] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Physical Review E 86, 041601 (2012).
