Attachment of Cobalt “Picket Fence” Porphyrin to the Surface of Gold Electrodes Coated with 1-(10-Mercaptodecyl)imidazole

Self-assembled monolayers of 1-(10-mercaptodecyl)imidazole on Au electrodes were used to bind cobalt “picket fence” porphyrin (cobalt 5,10,15,20-tetrakis(α,α,α,α-2-pivalamidophenyl)porphyrin) to the electrode surface. The binding involved coordination of the cobalt center of the porphyrin to the pendant imidazole groups in the monolayer coating. Attempts to coordinate the Co(II) oxidation state of the porphyrin to the coatings were not successful. However, with the Co(III) oxidation state, substantial binding was achieved which persisted even when the Co(III) was reduced to Co(II). Absorption spectra of the attached porphyrin were obtained for both oxidation states of the cobalt center. The remaining axial coordination site on the attached cobalt porphyrin is accessible to ligands, for example, imidazole, in aqueous solution

Adsorption and Electrooxidation of Carbon Monoxide on Platinum Surfaces Modified with Sulfur

吸附硫通常被认为是表面化学反应毒物. 然而，少量的硫能够增强铂的一氧化碳（CO）电氧化活性。本文利用常规电化学手段及表面增强拉曼光谱研究了CO在硫修饰的铂表面的电氧化. 对于溶液中的CO，其在硫修饰铂电极上的起始氧化电位最多可以比非修饰电极负移超过300 mV，而且在硫覆盖度低于0.6的条件下电位负移量随覆盖度增加而增大. 这一电催化活性的增强也受溶液pH值的影响. 在低硫覆盖度（小于0.3）下，吸附态的CO电氧化峰值电位比非修饰铂电极负移约40 mV. 然而，在高硫覆盖度下，其峰值电位比非修饰铂电极正移近30 mV. 表面增强拉曼光谱显示共吸附硫使Pt-CO振动频率显著红移. 作者认为这些结果是由于吸附硫弱化Pt-CO键及阻化CO在铂表面的移动引起的.Adsorbed sulfur is commonly considered as a reaction poison. However, small amounts of sulfur on platinum significantly increase the surface reactivity toward carbon monoxide (CO) electrooxidation. For the solution CO oxidation, the onset potential was shifted up to over 300 mV negative to that on S-free surface, and the extent of the negative potential shift increases with the sulfur coverage (Xs) up to about 0.6. The enhanced CO oxidation also depends on the solution pH. For the adsorbed CO, at low sulfur coverages (Xs < 0.3), the oxidation peak potential is about 40 mV negative to that of the corresponding clean Pt. However, at higher coverages, the peak potential is about 30 mV more positive. Surface-enhanced Raman spectra show that the adsorption of sulfur significantly redshifts the Pt-CO stretching frequency. These observations are explained by the weakening of the Pt-CO bond and the hindrance of CO diffusion by Sads.This work was supported by Miami University startup fundsThis work was supported by Miami University startup funds作者联系地址：迈阿密大学牛津分校化学&生物化学系，美国 俄亥俄州 45056，Author's Address: Department of Chemistry & Biochemistry, Miami University, Oxford, OH 45056, USA通讯作者E-mail：[email protected]

Microscopic characterization of electrochemical interfaces

Surface-enhanced Raman spectroscopy (SERS) and infrared reflection-absorption spectroscopy (IRAS) have been employed for in-situ probing molecular interaction and structure at electrochemical interfaces. The first technique was applied to Pt-group transition metal surfaces by an “overlayer” SERS strategy involving electrodeposition as ultrathin films on SERS-active gold, thereby entirely chemically modifying the substrate yet largely retaining the giant Raman enhancement. A new deposition procedure utilizing constant-current, rather than constant-potential, deposition was developed, yielding pinhole-free films. This improvement opens up important opportunities for studying interfacial chemistry on transition-metal surfaces. Rich SER spectra for chemisorbed benzene and monosubstituted benzenes, specifically toluene and benzonitrile, were observed in aqueous solutions. The spectral fingerprints indicate that benzene and toluene adsorb “flat”, while benzonitrile binds via the nitrile group with the benzene ring pendant. Significant Raman enhancement was also found on these transition-metal films deposited on SERS-inactive substrates, including carbon and unroughened gold, utilizing either green or red excitation, indicating transition metals can also support SERS. The overlayer-SERS strategy was also utilized for characterizing lattice vibrations (phonons) for cadmium chalcogenide ultrathin films and superlattices formed by electrochemical atomic-layer epitaxy. The band broadening and frequency redshifts with decreasing film thickness for these semiconductor films signal the occurrence of quantum confinement effects. The large phonon softening observed for CdS in CdS/CdSe superlattices provides strong evidence for tensile strain in the CdS layers. Intermolecular interactions at ordered electrochemical interfaces were investigated by means of IRAS, utilizing carbon monoxide and nitric oxide adsorbed on Pt-group, single crystal electrodes as model systems. Detailed comparison of the vibrational fingerprints with corresponding data obtained in ultrahigh vacuum shed light on the influence of the double-layer solvation on the adlayer structure

Electrooxidation of Carbon Monoxide on Pd Thin Film-Coated Au Electrodes:Film Thickness Dependence

采用扫描循环伏安法及表面增强拉曼散射光谱研究了一氧化碳(CO)在钯修饰金电极上的吸附与氧化.结果表明CO氧化电位随钯膜厚度增加而正移,同时C—O伸缩振动频率红移.本文利用d能带理论解释观察现象.应力效应使CO吸附变强,难以氧化;但配体效应使CO吸附变弱,易于氧化.在薄膜中配体效应强于应力效应.The adsorption and electrooxidation of CO on Pd-coated Au electrodes were studied by cyclic voltammetry and surface-enhanced Raman spectroscopy (SERS) . It is found that CO oxidation activity is film thickness dependent. Cyclic voltammograms (CVs) showed that CO oxidation peak potential shifted positively with the increase of the Pd thickness. SERS showed a redshift of the C—O stretching frequency with increasing Pd film thickness. These observations were explained by the dband theory. The strain effect strengthens CO adsorption and stabilizes adsorbed CO,while the ligand effect weakens CO adsorption and eases its oxidation. The ligand effect overpowers the strain effect.作者联系地址：美国迈阿密大学化学与生化系;Author's Address: Department of Chemistry and Biochemistry,Miami University,Oxford,OH 45056,US

Recent Advances on Electro-Oxidation of Ethanol on Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials

The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Since EOR is a complex multiple-electron process involving various intermediates and products, the mechanistic investigation as well as the rational design of electrocatalysts are challenging yet essential for the desired complete oxidation to CO2. This mini review is aimed at presenting an overview of the advances in the study of reaction mechanisms and electrocatalytic materials for EOR over the past two decades with a focus on Pt- and Pd-based catalysts. We start with discussion on the mechanistic understanding of EOR on Pt and Pd surfaces using selected publications as examples. Consensuses from the mechanistic studies are that sufficient active surface sites to facilitate the cleavage of the C–C bond and the adsorption of water or its residue are critical for obtaining a higher electro-oxidation activity. We then show how this understanding has been applied to achieve improved performance on various Pt- and Pd-based catalysts through optimizing electronic and bifunctional effects, as well as by tuning their surface composition and structure. Finally we point out the remaining key problems in the development of anode electrocatalysts for EOR