In-Situ X-ray Absorption Spectroscopy (XAS) Analysis of the Phosphoric Adsorption on Pt Nanocatalysts for Polybenzimidazol-based High-Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC)

Title
In-Situ X-ray Absorption Spectroscopy (XAS) Analysis of the Phosphoric Adsorption on Pt Nanocatalysts for Polybenzimidazol-based High-Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC)
Authors
박희영최인수정영훈유성종김형준조은애헨켄스마이어디억남석우장종현
Keywords
High temperature-polymer electrolyte membrane fuel cell; Phsohporic acid; Pt/C; X-ray absorption spectroscopy
Issue Date
2014-09
Publisher
17th Solid State Protonic Conductors
Abstract
As a polymer electrolyte for high temperature proton exchange membrane fuel cells (HT-PEMFCs), polybenzimidazol (PBI) membranes doped with phosphoric acid have been widely utilized due to its high proton conductivity (ca. 0.1 S cm-1) and stability under operating temperature (160 oC ~ 200 oC). However, it has been reported that, as the surface Pt atoms can be strongly adsorbed by phosphoric acids, the Pt nanocatalysts in the anodes and cathodes of HT-PEMFCs are significantly deactivated. Thus, it is highly required to understand the phosphate adsorption mechanism and develop proper strategies to alleviate the Pt poisoning. Previously, there have been several reports to characterize the phosphate adsorption on bulk Pt surfaces by various techniques, such as FT-IR and radio tracer method. However, the carbon-supported Pt nanocatalysts (Pt/C), which are widely utilized for HT-PEMFCs, cannot be directly analysed by those conventional techniques. For the surface and structure characterizations of nanocatalysts, X-ray absorption spectroscopy (XAS) has been widely utilized. Recently, the X-ray absorption near edge structure (XANES) analysis was carried out for Pt/C and PtNi/C nanocatalysts, but the fraction of PA-adsorbed Pt surface could not be determined quantitatively [1]. In this study, extended X-ray absorption fine structure (EXAFS) analysis was performed in order to measure the amount of PA adsorption on Pt/C. The experimental EXAFS spectra were fitted based on bulk models, and resultant bulk-based coordination number (CN*) was determined at various electrode potential. Then, utilizing the charge of electrochemical PA adsorption in cyclic voltammetry, the fraction of PA-adsorbed Pt/C was determined as a function of electrode potential.
URI
http://pubs.kist.re.kr/handle/201004/48207
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KIST Publication > Conference Paper
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