Solid indicator electrodes

Prepare 250 mL of 0.02 M potassium dichromate solution and an equal volume of ca 0.1 M ammonium iron(II) sulphate solution the latter must contain sufficient dilute sulphuric acid to produce a clear solution, and the exact weight of ammonium iron(II) sulphate employed should be noted. Place 25 mL of the ammonium iron(II) sulphate solution in the beaker, add 25 mL of ca 2.5M sulphuric acid and 50 mL of water. Charge the burette with the 0.02 M potassium dichromate solution, and add a capillary extension tube. Use a bright platinum electrode as indicator electrode and an S.C.E. reference electrode. Set the stirrer in motion. Proceed with the titration as directed in Experiment 1. After each addition of the dichromate solution measure the e.m.f. of the cell. Determine the end point (1) from the potential-volume curve and (2) by the derivative method. Calculate the molarity of the ammonium iron(II) sulphate solution, and compare this with the value calculated from the actual weight of solid employed in preparing the solution. 

A potentiometric electrochemical cell consisting of a reference electrode, solid-state electrolyte(s), and an indicator electrode can provide information about the partial pressure of gas in the same way as the cells utilizing ion-selective electrodes and liquid electrolytes can. The general mechanism is as follows. A sample gas, which is part of a redox couple, permeates into the solid-state structure usually through the porous metal electrode and sets up a reversible potential difference at that interface according to the reaction... 

Fig. 6.7 Variation of (a) the peak potential and (b) the peak current of the cyclic voltarrunograms with the scan rate (through the parameter Qa) at disc (solid line) and spherical (dashed line) electrodes. The value of the electrode radius is fixed fulfilling that r = rs = 0.01 cm. K = 0. The values of the peak potential and peak current for a simple fast charge transfer process at planar electrodes are indicated (dashed-dotted line). Reproduced with permission from [21]...

Figure 29. Calculated current-potential characteristics for direct (dashed lines, 0/cm ) and surface state mediated electron transfer between an -type semiconductor electrode and a simple redox system. The plots show the transition from ideal diode behavior to metallic behavior with increasing density of surface states at around the Fermi-level of the solid (indicated in the figures). This is also clear from the plots below, which show the change of the interfacial potential drop over the Helmholtz-layer (here denoted as A(Pfj) with respect tot the total change of the interfacial potential drop (here denoted as A(p). Results from D. Vanmaekelbergh, Electrochim. Acta 42, 1121 (1997).

The curves obtained by titration with n-butylamine for bulk TPA, PVA-PEG beads and TPA-PVA-PEG sample are shown in Fig. 3. A criterion for interpreting the results is that the initial electrode potential (Ei) indicates the maximum acid strength of the surface sites and the range where the plateau is reached (meq/g solid) indicates the total number of acid sites [14]. 

The metal content of the resulting solids is constant, ranging between 19.5 and 21%. The constancy of metal content, whatever the nature and geometry of the electrodes, would indicate that carbonaceous solid production, like metal volatilization are essentially surface phenomena occuring at the hydrocarbon electrodes interface. 

Eor a lot of potentiometric indicator electrodes solid-state embodiments are available widely equivalent to the electrolyte containing systems concerning the electrode performance. Because this does not apply for all measuring electrodes (e.g., for pH glass electrodes) and for reference electrodes to the full extent, there is also still a need for development in this field. 

Figure 4.25. Oscillatory phenomena dining galvanostatic oxidation of HCOOH on Pt at 0.15 mA cm in 0.9 M HCOOH - 0.5 M H2SO4 [136]. a) Pt electrode mass (indicated as fiequency change Af in quartz crystal microbalance measurements), b) Pt surface energy Af and c) electrode potential (With kind permission from Springer Science+Business Media Journal of Solid State Electrochemistry, Simultaneous oscillations of surface energy, superficial mass and electrode potential in the course of galvanostatic oxidation of formic acid, 9,2005, 347-53, Lang GG, Seo M, Heusler KE, figure 4.)...

Figure 20.15 compares flie CVs for methanol oxidation at the PtRu/MWCNT (dotted line) and Pt/MWCNT (solid line) electrodes in 0.5 M H2SO4. CVs at the PtRu/MWCNT electrode are relatively different from fliose obtained at the Pt/CNT electrode at the former eleetrode, CH3OH oxidation oeeurs at a potential more negative ( 190 mV) than that at flie Pl/MWCNT electrode (solid line), indicating that the co-existence of Ru accelerates flie eleetron-transfer kinetics for CH3OH oxidation. 

Fig. 9.3 Illustration of the electrical potential distribution calculated for the flat-plate cell with ideally symmetrical working and counter electrodes, according to [25]. Solid lines correspond to the equipotential surfaces. Possible positions of reference electrodes are indicated...

Figure C2.8.4. The solid line shows a typical semilogaritlimic polarization curve (logy against U) for an active electrode. Different stages of reaction control are shown in tlie anodic and catliodic regimes tlie linear slope according to an exponential law indicates activation control at high anodic and catliodic potentials tlie current becomes independent of applied voltage, indicating diffusion control.

The proposed model for the so-called sodium-potassium pump should be regarded as a first tentative attempt to stimulate the well-informed specialists in that field to investigate the details, i.e., the exact form of the sodium and potassium current-voltage curves at the inner and outer membrane surfaces to demonstrate the excitability (e.g. N, S or Z shaped) connected with changes in the conductance and ion fluxes with this model. To date, the latter is explained by the theory of Hodgkin and Huxley U1) which does not take into account the possibility of solid-state conduction and the fact that a fraction of Na+ in nerves is complexed as indicated by NMR-studies 124). As shown by Iljuschenko and Mirkin 106), the stationary-state approach also considers electron transfer reactions at semiconductors like those of ionselective membranes. It is hoped that this article may facilitate the translation of concepts from the domain of electrodes in corrosion research to membrane research. 

The cell notation is Zn Zn2+1 Co3+, Co2+ Pt Note that a comma separates the half-cell components that are in the same phase. The symbol Pt is used to indicate the presence of an inert platinum electrode. A single vertical line separates Pt (a solid) from the components of the half-cell, which are in the liquid phase. 

Solar energy, 6, 488 surface modified electrodes, 6, 30 Sol-Gel process fast reactor fuel, 6, 924 Solid state reactions, 1, 463-471 fraction of reaction, 1, 464 geometric, 1, 464 growth, 1, 464 nucleation, 1, 464 rate laws, 1,464 Solochrome black T metallochromic indicators, 1,555 Solubility... 

The electrical double layer has been studied at the interface of acidified (pH = 3) KCIO4 and K2SO4 solutions in contact with an Sn solid drop electrode with an additionally remelted surface (SnDER).616 The E, is independent of ctl as well as of the electrolyte. Weak specific adsorption of CIO4 at SnDER is probable around <7 = 0. This view is supported by the high value of/pz for SnDER/H20 + KCIO4 (fpz = 1 -27). A value of fpz = 0.99 for SnDER/H20 + K2S04 indicates that the surface of SnDER is geometrically smooth and free from components of pseudo-capacitance.616... 

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