This chapter discusses the radiotracer methods in in-situ techniques that use a radioactive label to monitor molecules of interest adsorbed at the electrode-solution interface. By pressing the electrode down against the scintillator, the detector responds to radioactive species adsorbed onto the electrode surface. Two main measuring principles are currently used for the radiotracer study of adsorption events at electrodes. Correspondingly, two different types of radiochemical-electrochemical cells are in operation. Both methods have been used for study of reversibly adsorbed and strongly chemisorbed systems. There are two major limitations in using thin-foil electrodes, namely, the restriction of the radiotracer work to polycrystalline electrodes and the need for electrode roughening, especially for weakly adsorbing species at low coverages. The smaller values of this ratio for higher concentrations show explicitly the advantage of the thin-gap method over the thin-film technique, making the latter one the most appropriate for studies of electrode adsorption on smooth surfaces.

Recent advances in vibrational broadband sum-frequency generation (SFG) have allowed us to address electrochemical adsorption and electrocatalytic reactions in unprecedented detail. SFG, as an inherently surface-specific technique, provides a direct observation of only those molecular species that are adsorbed to single crystalline or polycrystalline electrodes without spectral interference from molecular species in the bulk electrolyte. Our data thus offer unique insights into the chemical identity of surface-adsorbed intermediates on single crystals. In this article we will review recent developments in the field of spectro-electrochemistry with sum-frequency generation (SFG) and discuss adsorption of (bi)sulfate as a model system for broadband SFG. Advancing SFG for in situ studies of anion specific adsorption has provided the basis for further studies on formic acid oxidation. Here, rapid acquisitions of broadband SFG spectra synchronized with voltammetric scans have allowed us to perform the first SFG study on the formation of surface adsorbed formate HCOO∗ on a well-ordered Pt(111) single crystal. Our information from broadband SFG may provide useful information on possible reaction mechanism of formic acid oxidation on Pt(111) and thus for future theoretical investigations of this intriguing interface.

In this report, we discuss some of the advances in surface science and theory that have enabled a more detailed understanding of the mechanisms that govern the electrocatalysis. More specifically, we examine in detail the electrooxidation of C1 and C2 alcohol molecules in both acidic and basic media. A combination of detailed in situ spectroscopic measurements along with density functional theory calculations have helped to establish the mechanisms that control the reaction paths and the influence of acidic and alkaline media. We discuss some of the synergies and differences between electrocatalysis and aqueous phase heterogeneous catalysis. Such analyses begin to establish a common language and framework by which to compare as well as advance both fields.

We co-deposited cobalt porphyrins (Cop) and transition metal oxides on gold and carbon/graphene electrodes as catalysts for the oxygen reduction reaction (ORR). Porphyrins were adsorbed spontaneously, and the transition metal oxides (CoOx and NiOx) were deposited using spontaneous deposition tactics or an electrochemical deposition method. The electrodes were characterized in acidic media by cyclic voltammetry (CV), by broad-band sum frequency generation (BB-SFG) and - in vacuum - by the Auger electron spectroscopy (AES). The ORR activity data indicate that the activity of cobalt porphyrin towards ORR is enhanced by co-deposited transition metal oxides. The detailed reasons for this behavior are being interrogated. (C) 2013 Elsevier B.V. All rights reserved.

Preface to the Wiley Series on Electrocatalysis and Electrochemistry vii Foreword ix by Masatoshi Osawa Preface xi Contributors xiii Part One Nonlinear Vibrational Spectroscopy 1. Water Hydrogen Bonding Dynamics at Charged Interfaces Observed with Ultrafast Nonlinear Vibrational Spectroscopy 3 Emily E. Fenn and Michael D. Fayer 2. SFG Studies of Oxide Water Interfaces: Protonation States, Water Polar Orientations, and Comparison with Structure Results from X-Ray Scattering 48 Y. Ron Shen and Glenn A. Waychunas 3. Vibrational Sum Frequency Generation Spectroscopy of Interfacial Dynamics 85 Christopher M. Berg and Dana D. Dlott 4. Spectroscopy of Electrifi ed Interfaces with Broadband Sum Frequency Generation: From Electrocatalysis to Protein Foams 120 Bjorn Braunschweig, Prabuddha Mukherjee, Robert B. Kutz, Armin Rumpel, Kathrin Engelhardt, Wolfgang Peukert, Dana D. Dlott, and Andrzej Wieckowski Part Two Raman Spectroscopy 5. Surface-Enhanced Resonance Raman Scattering (SERRS) Studies of Electron-Transfer Redox-Active Protein Attached to Thiol-Modified Metal: Case of Cytochrome c 153 Agata Krolikowska 6. Depolarization of Surface-Enhanced Raman Scattering Photons from a Small Number of Molecules on Metal Surfaces 220 Fumika Nagasawa, Mai Takase, Hideki Nabika, and Kei Murakoshi Part Three IRRAS Spectroscopy (Including PM IRRAS) 7. DFT and In Situ Infrared Studies on Adsorption and Oxidation of Glycine, l-Alanine, and l-Serine on Gold Electrodes 241 Andrea P. Sandoval, Jose Manuel Orts, Antonio Rodes, and Juan M. Feliu 8. Composition, Structure, and Reaction Dynamics at Electrode Electrolyte Interfaces Using Infrared Spectroscopy 266 Angel Cuesta 9. Vibrational Stark Effect at Halide Precovered Cu(100) Electrodes 307 Melanie Roefzaad, Duc Thanh Pham, and Klaus Wandelt 10. Vibrational Spectroscopy of the Ionomer Catalyst Interface 327 Ian Kendrick, Jonathan Doan, and Eugene S. Smotkin 11. In Situ PM IRRAS Studies of Biomimetic Membranes Supported at Gold Electrode Surfaces 345 Annia H. Kycia, ZhangFei Su, Christa L. Brosseau, and Jacek Lipkowski Index 418

Electrooxidation of formate on high-surface Pt black in alkaline media has been studied at varying temperature by means of cyclic voltammetry and stripping voltammetry. In the positive-going scans from 0.10 to 1.2V vs RHE, the formate oxidation produces three oxidation current peaks: (i) peak I (at potentials where the coverages of both surface hydrogen and oxygen-species are very low), (ii) peak II (exhibiting obvious potential shift from 0.66 to 0.51V upon increasing temperature from 20 to 80°C), and (iii) peak III (at higher potentials where a considerable formation of surface oxygen species commences). Both peaks I and II are closely correlated but they are independent of peak III. Among the three peaks, the temperature dependence of peak II is well in agreement with that of the stripping peak of a CO adlayer. These results suggest a triple-path reaction mechanism. Adsorption of formate onto Pt surfaces may result in formation of precursor adsorbates with different reactivity. Analogous to the reported dual-path mechanism, active precursor adsorbate is responsible for (i) a direct path involving the formate oxidation to CO2 (leading to peak I), and (ii) an indirect path involving the formation of surface CO and its further oxidation to CO2 (leading to peak II). An independent third path via oxidation of less-active precursor adsorbate to CO2 with adsorbed HCOO as the most likely intermediate accounts for peak III. All the oxidation reactions involved in the triple paths are accelerated by increasing reaction temperature with different apparent activation energies. At elevated temperature, diffusion-limited oxidation currents are attained. It is suggested that both the activities of surface OH and precursor adsorbates play a major role in mediating the reaction mechanism as well as participating in the formate oxidation.