Metal monolayers, electrochemical cells

The first structural study of a UPD layer involved the formation of a series of Agl monolayers on Pt(lll) single crystals [132, 133], Pt is the quintessential catalytic metal, and thus reacts with almost any organic compound, other than simple alkanes [134], in other words, it is easily contaminated. In the early days of UHV-EC studies, contamination during transfer of Pt single crystals from the analysis chamber to the electrochemical cell and back was the chief stumbling block to well-defined studies of... 

Adsorptive accumulation can also be used in chronopotentiometric stripping as the preconcentration step allowing a large number of organic compoimds to be determined. It is assumed that the adsorption kinetics is sufficiently rapid for the process to be mass transport controlled. During the preconcentration step, the solution is normally stirred in order to enhance the mass transport of the analyte to the electrode smface, thereby reducing the time required for preconcentration. For nonelectrolytic or adsorptive accumulation, tacc has an upper limit governed by the time required for the electrode to be saturated with a monolayer of adsorbate. This is determined experimentally and will depend on the mass transport conditions that exist in the electrochemical cell. For example, the amount of adsorbed metal ion complex would be... 

The presence of a liquid metal phase makes it difficult for one to study and utilize the effect of liquid metal embrittlement because of the need to employ high temperatures, the difficulties in ensuring good wetting conditions, and especially the need to remove the residual films and traces of the active component. A principally new approach to overcoming these issues was the use of liquid metal embrittlement in the absence of a liquid metal phase. This is achieved in an electrochemical cell by the cathode reduction of ions of the selected surface-active metal directly at the sample surface. The amount of metal formed can be controlled and fine-tuned down to the formation of monolayers. It is also possible for one to conduct these studies at room temperature [59,107,108] (Figures 7.51 and 7.52). 

The method has been applied, for example, in electrochemical investigations (110) and also for surface catalytic reactions in the presence of a gas phase 111). When PM-IRRAS is used with a thin-layer cell, as depicted in Fig. 37, the contribution from dissolved molecules in the liquid phase can be minimized. Still, the layer thickness has to be small to prevent complete absorption of the IR radiation by the solvent. The combination of polarization modulation and ATR for metal films was demonstrated recently and applied in an investigation of self-assembled octadecylmercaptan monolayers on thin gold films 112). This combination could emerge as a valuable technique for the investigation of model catalysts. 

E25.17 Electrocatalysts are compounds that are capable of reducing the kinetic barrier for electrochemical reactions (barrier known as overpotential). While platinum is the most efficient electrocatalyst for accelerating oxygen reduction at the fuel cell cathode, it is expensive (recall Section 25.18 Electrocatalysis). Current research is focused on the efficiency of a platinum monolayer by placing it on a stable metal or alloy clusters your book mentions the use of the alloy PtsN. An example would be a platinum monolayer fuel-cell anode electrocatalyst, which consists of ruthenium nanoparticles with a sub-monolayer of platinum. Other areas of research include using tethered metalloporphyrin complexes for oxygen activation and subsequent reduction. 

The electrochemical active surface area (EASA) of fuel cell Pt-based catalysts could be measured by the electrochemical hydrogen adsorption/desorption method. For carbon supported Pt, Pt alloy, and other noble metals catalysts, the real surface area can be measured by the cyclic voltammetry method [55-59], which is based on the formation of a hydrogen monolayer electrochemically adsorbed on the catalyst s surface. Generally, the electrode for measurement is prepared by dropping catalyst ink on the surface of smooth platinum or glassy carbon substrate (e.g, a glassy carbon disk electrode or platinum disk electrode), followed by drying to form a catalyst film on the substrate. The catalyst ink is composed of catalyst powder, adhesive material (e.g., Nafion solution), and solvent. 

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