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)
- 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)
- 박희영; 최인수; 정영훈; 유성종; 김형준; 조은애; 헨켄스마이어디억; 남석우; 장종현
- High temperature-polymer electrolyte membrane fuel cell; Phsohporic acid; Pt/C; X-ray absorption spectroscopy
- Issue Date
- 17th Solid State Protonic Conductors
- 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 . 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.
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