Electrochemical crystal platinum

In this chapter, we overview first some recent examples of interfacial electrochemical ET of composite metalloproteins where molecular mechanistic detail has in some way been achieved. We discuss next some theoretical issues regarding in situ STM of large molecules, where resonance or environmentally activated tunnel channels are opened by the redox metal centre. This is followed by an overview of some recent achievements in the area of in situ STM/AFM of the single-metal proteins cytochrome c and azurin on polycrystalline and single-crystal platinum and gold surfaces. Such an integrated approach offers new perspectives for experimental and theoretical characterization of metalloproteins at solid surfaces in contact with the natural aqueous medium for metalloprotein function. 

A number of electro-oxidation studies on ruthenium-modified, platinum singlecrystal surfaces have recently appeared. Ruthenium has most commonly been deposited from solution on single-crystal platinum surfaces through spontaneous deposition or under electrochemical control [80-82,88-93]. In some cases MVD... 

Clavilier J, Parsons R, Durand Ret al (1981) Formic acid oxidation rai single crystal platinum electrodes. Comparison with polycrystalline platinum. J Electroanal Chtan Inttafacial Electrochem 124 321-326... 

The electrochemical oxidation of glucose has been reviewed (49 refs.). Special attention was given to the effect of the electrode material on the process, and to the adsorption of glucose and its oxidation products on the electrode surface. The oxidation of glucose with single-crystal platinum electrodes in different orientations has been studied. Pronounced stmctural sensitivity of the reaction was discovered, the Pt(lll) and its vicinal surfaces being the most active. ... 

The mechanism of the oxidation of D-glucose in alkaline solution on single crystal platinum electrodes has been investigated. A process for the preparation of d-arabinose from sodium D-gluconate in an electrochemical reactor with a fluidized bed electrode has been developed. ... 

An uncommon, rather new technique where temperature affects electrochemical processes is DBMS (differential electrochemical mass spectrometry) [100, 177-180]. In this method, tiny amounts of organic substances, e.g., in adsorption films, are desorbed and/or oxidised and the volatile reaction products are determined by mass spectrometry. This technique is useful to detect organic substances adsorbed at the metal-electrolyte interface. In a thin-layer cell, adsorbed molecules are desorbed by potential variation. The desorbed material diffuses through a porous PTFE membrane and is detected by mass spectrometry. Besides potential, also temperature variation influences the desorption process. This way, temperature dependence of adsorption at single crystal platinum surfaces has been studied [178]. Other DBMS experiments have been done imder pressure in autoclave cells [179, 180]. 

Fig. VIII-2. Scanning tunneling microscopy images illustrating the capabilities of the technique (a) a 10-nm-square scan of a silicon(lll) crystal showing defects and terraces from Ref. 21 (b) the surface of an Ag-Au alloy electrode being electrochemically roughened at 0.2 V and 2 and 42 min after reaching 0.70 V (from Ref. 22) (c) an island of CO molecules on a platinum surface formed by sliding the molecules along the surface with the STM tip (from Ref. 41).

CO adsorption on electrochemically facetted (Clavilier), 135 Hamm etal, 134 surfaces (Hamm etal), 134 Platinum group metals in aqueous solutions, 132 and Frumkin s work on the potential of zero charge thereon, 129 Iwasita and Xia, 133 and non-aqueous solutions, 137 potentials of zero charge, 132, 137 preparation of platinum single crystals (Iwasita and Xia), 133 Platinum-DMSO interfaces, double layer structure, 141 Polarization time, 328 Polarons, 310... 

Electrochemical nuclear magnetic resonance (NMR) is a relatively new technique that has recently been reviewed (Babu et al., 2003). NMR has low sensitivity, and a typical high-held NMR instrument needs 10 to 10 NMR active atoms (e.g., spins), to collect good data in a reasonable time period. Since 1 cm of a single-crystal metal contains about 10 atoms, at least 1 m of surface area is needed to meet the NMR sensitivity requirement. This can be met by working with carbon-supported platinum... 

Jerkiewicz G, Vatankhah G, Lessard J, Soriaga MP, Park YS. 2004. Surface-oxide growth at platinum electrodes in aqueous H2SO4 Reexamination of its mecharusm through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements. Electrochim Acta 49 1451-1459. 

Angelucci CA, Nart FC, Heirero E, Feliu JM. 2007a. Anion re-adsorption and displacement at platinum single crystal electrodes in CO-containing solutions. Electrochem Commun 9 1113-1119. 

Clavilier J, Sun SG. 1986. Electrochemical study of the chemisorbed species formed from formic acid dissociation at platinum single crystal electrodes. J Electroanal Chem 199 ... 

Climent V, Gomez R, Orts JM, Aldaz A, Fehu JM. 1997. The potential of zero total charge of single-crystal electrodes of platinum group metals. In Korzeniewski C, Conway BE, eds. The Electrochemical Society Proceedings (Electrochemical Double Layer). Pennington, NJ The Electrochemical Society, pp. 222-237. 

Dam VAT, de Bmijn FA. 2007. The stability of PEMFC electrodes—Platinum dissolution vs. potential and temperature investigated by quartz crystal microbalance. J Electrochem Soc 154 B494-B499. 

Chrzanowski W, Wieckowski A. 1997. Ultrathin films of ruthenium on low index platinum single crystal surfaces An electrochemical study. Langmuir 13 5974-5978. 

Climent V, Garcia-Araez N, Henero E, Feliu JM. 2006. Potential of zero total charge of platinum single crystals A local approach to stepped surfaces vicinal to Pt(lll). Russ J Electrochem 42 1145-1160. 

El Kadiri F, Fame R, Dmand R. 1991. Electrochemical reduction of molecular-oxygen on platinum single-crystals. J Electroanal Chem 301 177-188. 

Park S, Wasileski SA, Weaver MJ. 2001. Electrochemical infrared characterization of carbon-supported platinum nanoparticles A benchmark structural comparison with single-crystal electrodes and high-nuclearity carbonyl clusters. J Phys Chem B 105 9719 -9725. 

Platinum electrodes are made usually from poly crystalline metal the crystal planes at the surface include both the (111) and (100) faces in approximately equal proportions. The electrochemical properties of Pt(lll) and Pt(100) faces are not identical. (Generally, the physical properties of individual metal crystal faces, such as work function, catalytic activity, etc., are different.)... 

The kinetics of CO oxidation from HClOi, solutions on the (100), (111) and (311) single crystal planes of platinum has been investigated. Electrochemical oxidation of CO involves a surface reaction between adsorbed CO molecules and a surface oxide of Pt. To determine the rate of this reaction the electrode was first covered by a monolayer of CO and subsequently exposed to anodic potentials at which Pt oxide is formed. Under these conditions the rate of CO oxidation is controlled by the rate of nucleation and growth of the oxide islands in the CO monolayer. By combination of the single and double potential step techniques the rates of the nucleation and the island growth have been determined independently. The results show that the rate of the two processes significantly depend on the crystallography of the Pt surfaces. 

The electrochemical oxidation of polyhydric alcohols, viz. ethylene glycol, glycerol, meso-erythritol, xilitol, on a platinum electrode show high reactivity in alkaline solutions of KOH and K2C03 [53]. This electro-oxidation shows structural effects, Pt(lll) being the most active orientation. This results from different adsorption interactions of glycerol with the crystal planes [59]. 

---