Platinum Dissolution from Carbon Supported Nanoparticles

Tuesday, October 13, 2015: 08:40
211-A (Phoenix Convention Center)
Z. Wang, E. Tada (Tokyo Institute of Technology), and A. Nishikata (Tokyo Institute of Technology)
Platinum (Pt) dissolution concerns the instability of Pt-based cathode catalysts for polymer electrolyte fuel cells (PEFCs). Studies on unsupported Pt, polycrystalline plates or electroplated films, suggest that Pt dissolution relates to Pt oxide formation and reduction. Pt dissolution from the carbon supported nanoparticles, however, is rarely discussed. In this study, we investigated Pt dissolution using commercial carbon supported nanoparticles (Pt/C). We prepared Nafion-free inks by mixing Pt/C samples with H2O and isopropyl alcohol (IPA). We evaluated the amount of Pt dissolution over potential cycling tests using inductively-coupled plasma-mass spectrometry (ICP-MS). We also scrutinized the Pt dissolution behaviors from the Pt/C in a single cycle using a channel flow double electrode (CFDE)1.

The Pt/C samples we used were produced by Tanaka Kikinzoku Kogyo (TKK); the Pt particle size distributions before test were characterized by TEM. For each Pt/C sample, we mixed about 10 ~ 15 mg Pt/C with 3.8 ml H2O and 1.2 ml IPA, and sonicated the mixture in an ice bath for 60 mins. We loaded an appropriate amount of ink on a glassy carbon (GC) substrate. The Pt/C electrode was then dried under an ambient atmosphere for 120 mins. The Pt/C electrode was cycled 30 or more times between 0.05 and 1.4 V (vs. SHE) in 0.5 M H2SO4 to remove organic adsorbents and to obtain a reproducible electrochemical surface area (ECSA). The ECSA was used for normalization of Pt dissolution.

First, we conducted 300 cycles of potentials cycling in 0.5 M H2SO4 in a stationary cell. The geometric surface area of the GC was ca. 0.25 cm2 and we loaded about 2 µl ink on it. Two upper potential limits (EU) of 1.0 and 1.4 V were used with a same lower potential limit (EL) of 0.4 V. The testing solutions were analyzed by ICP-MS.

Second, we tested Pt dissolution from the Pt/Cs using a CFDE in argon-deaerated 0.5 M H2SO4. The CFDE consisted of a GC working electrode (WE) and a gold (Au) collector electrode (CE). The geometric surface area of the GC was ca. 0.05 cm2 and we loaded about 0.6 µl ink on it. The CV of a 46wt% Pt/C obtained in the CFDE at 25oC shows that the Pt/C is relatively stable without Nafion. Pt dissolution from the Pt/C-WE was monitored by the CE. The CE collected 30% of dissolved Ptn+. We set the CE at 1.4 V for detecting Pt2+, and at 0.7 V for Pt4+. We also set the CE at 0.3 V for collection of both Pt species.

The ICP-MS data evaluate the overall amount of Pt dissolution and CFDE data provide details of the dissolution behaviors against potential. Using both data, we discuss the mechanism of Pt dissolutions from the Pt/Cs with respect to temperature, EU, and Pt particle size.


1. Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161 (4), F380 (2014).