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Mechanistic Insight into Sulfide-Enhanced Oxygen Reduction Reaction Activity and Stability of Commercial Pt Black: an in situ Raman Spectroscopic Study Yan-Yan Wang, Dejun Chen, and YuYe J. Tong ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00907 • Publication Date (Web): 22 Jun 2016 Downloaded from http://pubs.acs.org on June 24, 2016
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ACS Catalysis
Mechanistic Insight into Sulfide-Enhanced Oxygen Reduction Reaction Activity and Stability of Commercial Pt Black: an in situ Raman Spectroscopic Study Yan-Yan Wang, De-Jun Chen, and YuYe J. Tong* Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington, DC 20057, USA.
ABSTRACT: Adsorption of sulfur-containing species on a catalyst surface has long been treated as an un-welcoming process in catalysis because it is frequently related to poisoning of the catalyst. But we reported recently that sulfide adsorption of moderate coverage on commercial carbon-supported Pt electrocatalyst could enhance substantially oxygen reduction reaction (ORR). Herein, we not only reproduced the sulfide-adsorption-enhanced ORR on a different type of commercial Pt electrocatalyst–Pt black, but we also discovered that the sulfide adsorption enhanced the stability of the Pt black as well. In situ surface-enhanced Raman spectroscopic (SERS) studies of a roughened Pt surface in a flow cell strongly suggest that the enhanced ORR activity and stability was most likely due to that the sulfide-adsorption made the Pt surface more oxidation resistant.
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KEYWORDS: Sulfide-adsorption-enhanced stability, enhanced oxygen reduction reaction, resistance to surface oxidation, in situ SERS, platinum electrocatalyst. INTRODUCTION Overcoming the still high over-potential of ORR and inhibiting the degradation of the Ptbased electrocatalysts are currently of great fundamental and practical importance in advancing clean energy technologies.1 It was observed that the degradation in fuel cell performance can be associated with the dissolution and aggregation of Pt that can occur in acidic media either at high potentials2,3 or during potential cycles.4,5 While mechanistic details are still lacking, the current consensus is that the repetitive formation and reduction of Pt oxides, as during a laboratory accelerated durability test (ADT), plays a crucial role in the dissolution of surface Pt. On the other hand, it was observed as early as in 19676 that the ORR activity might be intimately related to Pt surface’s resistance to oxidation. Recently, the role of surface Pt oxide in ORR has drawn more attentions7,8 and the highly active ORR catalysts reported recently9,10 did show much less surface oxidation at potential beyond 0.9 V than pure Pt does. It was also reported that Pt oxide formed at the relatively high potentials (1.15~1.6 V vs. RHE) strongly inhibited the ORR but OHad or Oad generated at low potentials (E
