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We newly developed a rotating disk electrode-online electrochemical mass spectrometry (RDE-OLEMS) to investigate potentialdependent molecular behaviors in electrode surface vicinity under mass transport-controlled conditions of reacting molecules. The potential-dependent molecular behaviors were investigated by using a quadrupole mass spectrometer (Q-mass) where the molecules are collected through a gas-sampling tip located in near the electrode surface. For the oxygen reduction reaction (ORR) on the polycrystalline Pt electrode, the potential-dependent Q-mass ion signal intensities of O2 (m/z = 32) that are ascribable to the dissolved oxygen molecules increased linearly with the disk electrode rotation rates without substantial interference from the collection tip, clearly showing that the dissolved O2 for ORR can be monitored by the RDE-OLEMS. For electrochemical carbon dioxide reduction (ECR) on the polycrystalline Au electrode, the potential-dependent Q-mass ion signal intensities of CO (m/z = 28) generated by the ECR increased with increasing disk rotation rates from 0 (without disk rotation) to 300 rpm in the potential region from -0.4 to -1.4 V vs. the reversible hydrogen electrode. The results demonstrate that the RDE-OLEMS enables us to evaluate the potential-dependent behaviors of reactant and product molecules present near the electrode surface under the mass transport-controlled condition. [ABSTRACT FROM AUTHOR]

We investigated electrochemical properties for the Pt-Au bimetallic surfaces prepared by 0.3-nm-thick Pt depositions on Au(111), (110), and (100) substrates (Pt0.3nm/Au(hkl)) by molecular beam epitaxy. The Pt0.3nm/Au(111) surface prepared at the substrate temperature of 300 K (300K-Pt0.3nm/Au(111)) showed a corrugated Pt(111) epitaxial surface on which 3-5 nm size monoatomic height Pt islands are located. Oxygen reduction reaction (ORR) activity of the surface was enhanced by a factor of ca. 2 relative to that of the clean Pt( 1 I 1 ) surface. In contrast, the topmost surfaces of 473K-Pt0.3nm/Au(111), 300K-Pt0.3nm/Au(100), and 300K- Pt0.3nm/Au(110) were composed of both Pt and Au atoms, and the ORR activities were lower than those for corresponding clean surfaces. The specific ORR activities for the Pt0.3nm/Au(111) and Pt0.3nm/Au(100) surfaces estimated after recording CV curves of 0.05-1.7 V were enhanced relative to the as-prepared samples, although the activity of the Pt0.3nm/Au(110) surface was slightly decreased by the wide region CV recording. These results suggest that atomic arrangements of surface Pt atoms, particularly the most dense plane of Pt(111), determine the ORR activity enhancement for Pt-Au bimetallic surfaces. [ABSTRACT FROM AUTHOR]