Local electrochemical

Despite its electrode potential (p. 98), very pure zinc has little or no reaction with dilute acids. If impurities are present, local electrochemical cells are set up (cf the rusting of iron. p. 398) and the zinc reacts readily evolving hydrogen. Amalgamation of zinc with mercury reduces the reactivity by giving uniformity to the surface. Very pure zinc reacts readily with dilute acids if previously coated with copper by adding copper(II) sulphate ... 

Table 6.2. Local Electrochemical Promotion Rules (Langmuir-Hinshelwood mechanisms)...

FIGURE 36.1 Schematic illustration of some electrochemical techniques employed for surface nanostructuring (a) tip-induced local metal deposition (b) defect nanostructuring (c) localized electrochemical nucleation and growth d) electronic contact nanostructuring. 

FIGURE 36.5 Model calculation employed to study the dependence of the cluster diameter on the distance between the STM and the substrate surface for localized electrochemical nucle-ation and growth. The lower part of the figure shows the profile of the Nemst potential for the Co /Co potential as a function of the distance from the tip center. The fines indicate a constant Co concentration. (From Schindler et al., 2000, with permission from the American Institute of Physics.)... 

The electrochemical series table provides important clues as regards the chemical reaction. The evolution of hydrogen by the reaction of zinc and dilute sulfuric acid is facilitated by the impurity of copper or graphite in zinc. Copper and zinc form a local electrochemical... 

In the paper from V. Matveyev of the Ukrainian State University of Chemical Engineering, an examination of the role of conductive carbon additives in a composite porous electrode is conducted. A model for calculation of the local electrochemical characteristics of an electrode is presented. A comparison on the polarization of the electrode as a function of the redox state of the electroactive species is emphasized in the model. The electrochemical reaction of chloranil (tetrachlorobenzoquinone) was measured and results compare favorably to calculations derived from the model. 

The model for calculation of the local electrochemical characteristics of an electrode is presented below. 

Figure 5.23 Electrochemical Cu deposition onto a SAM of MBP12 on Au. (a) Patterning scheme involving patterning by electron irradiation through a mask and subsequent localized electrochemical metal deposition, (b) optical micrographs (right) and SEM image (left) of...

STM tip-induced local electrochemical dissolution of silver has been studied in the systems Ag(lll)/Ag+, C104 and Ag(lll)/Ag+, SO42- [384]... 

At the microscopic scale, mechanical stress can also develop due to the property-mismatch of the electrode and the membrane. The porous electrode is typically much weaker than the membrane and has lower hygrothermal expansion coefficient than the membrane hence it can develop mud-cracks and delaminates from the membrane after RH cycling. This will perturb the local electrochemical processes and results in non-uniform decay of membranes. 

Subcell Approach Stumper et al.135 presented the subcell approach to measure localized currents and localized electrochemical activity in a fuel cell. In this method a number of subcells were situated in different locations along the cell s active area and each subcell was electrically isolated from each other and from the main cell. Separate load banks controlled each subcell. Figure 8 shows the subcells in both the cathode and anode flow field plates (the MEA also had such subcells). The current-voltage characteristics for the... 

Each tube is a sequence of cells electrically connected in series and this justifies the hypothesis that the current is the same for all the cells. Since the fuel flows in series through the various cells of the tube, fuel compositions vary from one cell to the next. As a consequence, cell voltage also varies from cell to cell, and this can be evaluated through a detailed evaluation of the local electrochemical kinetics of the reactor, as described in Section 6.2 of this work. When the model of the electrochemical kinetics is included into the overall model of the tube, an additional type of resistance is taken into consideration, i.e. the contact resistance (an approach... 

In addition to the local electrochemical kinetics, the model of the tube includes the following mass and energy balances (for more details about mass and energy balances in SOFCs see Chapter 3) ... 

In bimetallic catalysts prepared by catalytic reduction of copper by hydrogen, copper is deposited as three-dimensional agglomerates which are located, at low copper loadings, on the edges, corners, and rims of the parent metallic particles. The mechanism of deposition can be transferred from that proposed in corrosion and involving a local electrochemical cell ... 

C. Local Electrochemical Sites Pits, Precipitates, or Inclusions... 

---