Effect of Temperature on Platinum Dissolution from PEFC Catalysts

Abstract

The durability of polymer electrolyte fuel cells (PEFCs) is a big concern for its applications like FCVs to be commercialized on a large scale. In particular, the instability of Pt-based cathode catalyst has been discussed intensively. Platinum (Pt) dissolution is recognized as one of the degradation mechanisms for carbon supported Pt catalysts (Pt/C) in PEFCs. It has been found that repeated potential cycles accelerate Pt dissolution.[1-3] Fundamental studies in aqueous media revealed preliminary behaviors of Pt dissolution during one potential cycle. The up-to-date data were mostly obtained near room temperature, and a dominant cathodic dissolution during reduction of Pt oxide was understood. As reported by Fuller et al.,[4] however, degradation of Pt/Cs at an elevated temperature near 60 to 80 °C, whereat a PEFC normally operates, was severer than that at room temperatures. Thus, it is necessary to evaluate Pt dissolution from Pt/Cs at such temperatures. In prior studies,[5-6] we compared Pt dissolution at 25 °C and 65 °C by inductively coupled plasma mass spectrometry (ICP-MS) and a channel flow double electrode (CFDE). The experiments had some difficulties, but the results showed a ca. 5-time enhancement from 25 to 65 °C. The cathodic dissolution was enhanced because larger amount of Pt oxide was formed at 65 °C. The effect of temperature on the anodic dissolutions and the place exchange process remains unclear yet. In this study, we evaluate Pt dissolution under temperatures ranging from 20 to 80 °C. We test a series of commercial Pt/C catalysts produced by TKK that have Pt loadings from 20 to 70 wt% and average Pt particle size from ca. 1.5 to 5 nm. We limited the potential region between 0.6 and 1.4 V, which is closely related to the operation region of a PEFC cathode. We use ICP-MS to evaluate to overall dissolutions and a CFDE to analyze the dissolution behavior in one potential cycle. The attached Figure showed a typical CFDE data presenting the current on a working electrode loading a 30wt% Pt/C (TEC10E30A) under potential cycling (I WE) and the current recorded on a collector electrode (I CE) at 80 °C in 0.5 M H2SO4. The I CE helps to understand the dissolution of Pt4+ and Pt2+ complex during one potential cycle. Similar analysis will be discussed at other temperatures like 20, 40, and 80 °C in the presentation. Reference Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161, F380 (2014).A.A. Topalov, S. Cherevko, A.R. Zeradjanin, J.C. Meier, I. Katsounaros, and K.J.J. Mayrhofer, Chem. Sci., 5, 631 (2014).P. Jovanovič, A. Pavlišič, V.S. Šelih, M. Šala, N. Hodnik, M. Bele, S. Hočevar, and M. Gaberšček, ChemCatChem, 6, 449 (2014).W. Bi and T.F. Fuller, J. Electrochem. Soc., 155, B215 (2008).Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 163, F1-F3 (2016).Z. Wang, E. Tada, and A. Nishikata, ECS Trans., 69, 255 (2015). Figure 1