Spectroelectrochemical Investigation of the Electrocatalysis of Platinum-based Nanocatalysts for Fuel Cell Application
Atienza, Dianne O
Spectroelectrochemical measurements, namely ATR-SEIRAS (attenuated total reflection-surface enhanced IR reflection absorption spectroscopy) and EC-NMR (electrochemical-nuclear magnetic resonance), were performed to determine the molecular and electronic properties of Ru@Pt (Ru-core Pt-shell) and Au@Pt (Au-core Pt-shell) NPs, which are known efficient catalysts for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) in fuel cell, respectively. ATR-SEIRAS combined with electrochemical techniques have identified different reaction intermediates as a consequence of varying Pt coverages on Ru core. The MOR on Ru@Pt NPs was observed to undergo both direct and indirect reaction pathway. The former leads to the formation of formate and the latter to adsorbed CO. The study suggests that an efficient electrocatalyst must have surface that can favor the dehydrogenation of monodentate formate to CO2 and the inhibition of spectator species, bidentate formate. The study also identified a general correlation between the two participating weakly H- bonded H2O and the MOR pathways.The electronic properties of Ru@Pt and Au@Pt NPs were investigated using 195Pt and 13CO EC-NMR, which measured the s-like and the d-like (E<sub>f</sub>-LDOS) at the surface Pt sites on core metals, and the 5σ- and 2π*-like <italic>E</italic><sub>f</sub>-LDOS of the adsorbed CO (CO<sub>ads</sub>) generated from MOR. The observed linear correlation between the D<sub>s</sub>(<italic>E</italic><sub>f</sub>) at surface Pt atoms and the D<sub>2π*</sub>(<italic>E</italic><sub>f</sub>) at the CO<sub>ads</sub> suggested a more defined role of electron partition, i.e., 6s,p vs 5d electrons, at Pt than the previously recognized electronic changes in metal-CO bonding. The substantial reduction in D<sub>d</sub>(<italic>E</italic><sub>f</sub>) of Au@Pt NPs have rationalized the experimentally observed suppression of Pt oxidation. The electronic partition, i.e., 6s,p vs 5d electrons, at Pt on different core metals indicates the different interactions of the catalysts with -carbon and -oxygen binding species, which can then be altered to enhance the catalyst's preference to undergo a specific reaction pathway.Low-temperature ORR was performed on Pt thin film using ATR-SEIRAS. The signal to noise ratio of the IR observable peaks was significantly improved. The potential dependence of the IR observable species corresponding to the ORR on Pt suggested the applicability of the technique in investigating spectroscopically the ORR mechanism on Pt-based catalysts.
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Electrochemical Studies and In Situ Electrochemical Nuclear Magnetic Resonance Investigations on Platinum-based Bimetallic Electrocatalysts for Direct Methanol Fuel Cells Du, Bingchen (Georgetown University, 2009)Two parallel objectives of this thesis research are 1) to investigate the electrocatalytic activities of Pt-based bimetallic nanoparticles (NPs) towards methanol (MeOH) electro-oxidation reaction (MOR), carbon monoxide ...
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