Interface molecule-electrode

Yokota, K., Taniguchi, M. and Kawai, T. (2007) Control of the Electrode-Molecule Interface for Molecular Devices. Journal of the American Chemical Society, 129, 5818-5819. 

Vladimiro Mujica (Central University of Venezuela). Electronic Correlation Effects on Transport at Electrode-Molecule Interfaces... 

The basic components of the SOFC are the anode, the cathode and the electrolyte, as shown in Fig. 10.1. They are together referred to as the membrane electrode assembly (MEA). Fuel (hydrogen) is supplied to the anode side and air is supplied to the cathode side. At the cathode-electrolyte interface, oxygen molecules accept electrons coming from the external circuit to form oxide ions. The solid electrolyte allows only oxide ions to pass through. At the anode-electrolyte interface, hydrogen molecules present in the fuel react with oxide ions to form steam, and electrons get released. As a result of the potential difference set up between anode and cathode... 

Voltammetry combines extraordinary determination sensitivity with inherently high accuracy, i.e. small tendency for systematic errors, and good precision. These important properties are connected with the fact, that this electroanalytical approach is based on the Faraday law according to which 1 mole of a substance undergoing an electrode process is equivalent to the transfer of the enormous electrical charge of n x 96500 C through the interface electrode/solution. The quantity n is the number of electrons transferred in the elementary step per ion or molecule and for trace metals corresponds frequently to 2,... 

Injection of positive charge carriers at a semiconductor electrode in contact with a hydrocarbon can be achieved with the participation of solute molecules with a low ionization potential. Fositive charge carriers and electrons are produced in a semiconductor layer by illumination. The holes are driven to the semiconductor/liquid interface. Solute molecules adjacent to the semiconductor surface react with the holes by electron transfer and become ionized. The mechanism is depicted schematically in Figure 11. Reinis and Cressman (1979) used tertiary alkylamines in dodecane. Under the influence of an electric field of 10 V/cm positive amine ions were injected, the mobility of which could be measured by a time-of-flight experiment. 

The performance of the PP-interfaced electrode was controllable as far as the applied potential was in the range from 0.1 V to 0.6 V without any deterioration of the enzyme. Since PP is doped state in this potential range, the y-conjugated polymer works as a molecular interface which carries electron between a protein molecule and an electrode. 

Electrode processes are a class of heterogeneous chemical reaction that involves the transfer of charge across the interface between a solid and an adjacent solution phase, either in equilibrium or under partial or total kinetic control. A simple type of electrode reaction involves electron transfer between an inert metal electrode and an ion or molecule in solution. Oxidation of an electroactive species corresponds to the transfer of electrons from the solution phase to the electrode (anodic), whereas electron transfer in the opposite direction results in the reduction of the species (cathodic). Electron transfer is only possible when the electroactive material is within molecular distances of the electrode surface thus for a simple electrode reaction involving solution species of the fonn... 

Eigure 3 schematically depicts the stmcture of the electrode—solution interface. The inner Helmholtz plane (IHP) refers to the distance of closest approach of specifically adsorbed ions, generally anions to the electrode surface. In aqueous systems, water molecules adsorb onto the electrode surface. 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

The electrical double layer at Hg, Tl(Ga), In(Ga), and Ga/aliphatic alcohol (MeOH, EtOH) interfaces has been studied by impedance and streaming electrode methods.360,361 In both solvents the value ofis, was independent of cei (0.01 < cucio4 <0.25 M)and v. The Parsons-Zobel plots were linear, with /pz very close to unity. The differential capacity at metal nature, but at a = 0,C,-rises in the order Tl(Ga) < In(Ga) < Ga. Thus, as for other solvents,120 343 the interaction energy of MeOH and EtOH molecules with the surface increases in the given order of metals. The distance of closest approach of solvent molecules and other fundamental characteristics of Ga, In(Ga), Tl(Ga)/MeOH interfaces have been obtained by Emets etal.m... 

According to Vitanov et a/.,61,151 C,- varies in the order Ag(100) < Ag(lll), i.e., in the reverse order with respect to that of Valette and Hamelin.24 63 67 150 383-390 The order of electrolytically grown planes clashes with the results of quantum-chemical calculations,436 439 as well as with the results of the jellium/hard sphere model for the metal/electro-lyte interface.428 429 435 A comparison of C, values for quasi-perfect Ag planes with the data of real Ag planes shows that for quasi-perfect Ag planes, the values of Cf 0 are remarkably higher than those for real Ag planes. A definite difference between real and quasi-perfect Ag electrodes may be the higher number of defects expected for a real Ag crystal. 15 32 i25 401407 10-416-422 since the defects seem to be the sites of stronger adsorption, one would expect that quasi-perfect surfaces would have a smaller surface activity toward H20 molecules and so lower Cf"0 values. The influence of the surface defects on H20 adsorption at Ag from a gas phase has been demonstrated by Klaua and Madey.445... 

As discussed in Section I.3(i), AX indicates the variation in the work function of a metal as an interface is created by bringing a solid and a liquid in contact. In principle, it should be possible to compare AX values with A values measured directly in gas phase experiments. This is the aim of UHV synthesis of the electrochemical double layer868 in which the electrode interface is created molecule by molecule, starting with the bare metal surface. It is thus possible to obtain evidence of ion-water interactions that can be envisaged from electrochemical measurements but that are not directly demonstrable. Wagner55 has given a recent comprehensive review of electrochemical UHV experiments. 

Many organic electrode processes require the adsorption of the electroactive species at the electrode surface before the electron transfer can occur. This adsorption may take the form of physical or reversible chemical adsorption, as has been commonly observed at a mercury/water interface, or it may take the form of irreversible, dissociative chemical adsorption where bond fracture occurs during the adsorption process and often leads to the complete destruction of the molecule. This latter t q)e of adsorption is particularly prevalent at metals in the platinum group and accounts for their activity as heterogeneous catalysts and as... 

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