Cell potentials representation

Figure 17.17 Schematic representation of a single-compartment glucose/02 enzyme fuel cell built from carbon fiber electrodes modified with Os -containing polymers that incorporate glucose oxidase at the anode and bilirubin oxidase at the cathode. The inset shows power density versus cell potential curves for this fuel cell operating in a quiescent solution in air at pH 7.2, 0.14 M NaCl, 20 mM phosphate, and 15 mM glucose. Parts of this figure are reprinted with permission from Mano et al. [2003]. Copyright (2003) American Chemical Society.

You can use Table 11.1 to calculate the standard cell potential of the familiar Daniell cell. This cell has its standard potential when the solution concentrations are 1 mol/L, as shown in the shorthand representation below. 

Fig. 13.7. Graphical representation of the influence of the internal resistance of an electrochemical energy converter on the cell potential when mass-transfer polarization is negligible. The early nonlinear part of the curve represents the effect of the activation overpotential on the cell potential before ohmic polarization has become important.

The initial consideration in analyzing an existing or proposed metal/environment combination for possible corrosion is determination of the stability of the system. According to Eq 1.18, the criterion is whether the equilibrium half-cell potential for an assumed cathodic reaction, E x, is greater than the equilibrium half-cell potential for the anodic reaction, E M. A convenient representation of relative positions of equilibrium half-cell potentials of several common metals and selected possible corrodent species is given in Fig. 1.7. To the left is the scale of potentials in millivolts relative to the standard hydrogen electrode (SHE). The solid vertical lines identified by the name of the metal give... 

From the convention relating the cell reaction to the cell representation (Table 2.2), the cell potentials are written as ... 

The equilibrium electrochemistry of an element in aqueous solution can be represented graphically using coordinates of equilibrium half-cell potential, E, and pH. These graphical representations, known... 

Figure 16.7 Examples of half-cell potential maps (riding deck In the tunnel San Bernardino). Data representation colour plot (a) and equicontour line plot (fc). DF dilatation joint (every 25 m)...

A FIGURE 20.10 Graphical representation of standard cell potential of a voltaic cell. 

The current scientific method used in the modeling discipline can be schematized as the process in Fig. 3. In this process, the first and second steps consist respectively of defining the physical problem (i.e., the system which will be modeled the electrode alone the complete cell an active particle etc.), and on indentifying the observables one would intend to simulate with the model (e.g., electrode potential cell potential active area evolution ). Then, the third and fourth steps consist respectively of defining the structural model which will be used (i.e., the geometrical assumptions e.g., ID, 2D, or fuUy 3D representation of the electrode ) and the physics... 

Shorthand Notation for Electrochemical Cells Although Figure 11.5 provides a useful picture of an electrochemical cell, it does not provide a convenient representation. A more useful representation is a shorthand, or schematic, notation that uses symbols to indicate the different phases present in the electrochemical cell, as well as the composition of each phase. A vertical slash ( ) indicates a phase boundary where a potential develops, and a comma (,) separates species in the same phase, or two phases where no potential develops. Shorthand cell notations begin with the anode and continue to the cathode. The electrochemical cell in Figure 11.5, for example, is described in shorthand notation as... 

In assembling cells for making thermodynamic measurements, one should try not to combine half-cells in a manner that results in a junction potential. Figure 9.7 is a schematic representation of the Daniell cell, which is one with a junction potential. The half-cell reactions are... 

Figure 7.9. Schematic representation of the density of states N(E) in the conduction band of two transition metal electrodes (W and R) and of the definitions of work function O, chemical potential of electrons p, electrochemical potential of electrons or Fermi level p, surface potential x, Galvani (or inner) potential (p and Volta (or outer) potential for the catalyst (W) and for the reference electrode (R). The measured potential difference UWr is by definition the difference in p q>, p and p are spatially uniform O and can vary locally on the metal surfaces 21 the T terms are equal, see Fig. 5.18, for the case of fast spillover, in which case they also vanish for an overall neutral cell Reprinted with permission from The Electrochemical Society.

Figure 7.14. Schematic representation of the spatial variation of electrode potential, chemical potential of oxygen and electrochemical potential of O2 for the cell 02, M1YSZ1M, 02 (=1 atm).

Fig. 1.—Diagrammatic Representation of the Three Steps in the Taste-cell Transduction. Step 1, interaction of stimulus (S) with membrane-bound receptor (R) to form stimulus-receptor complex (SR) step 2, conformational change (SR) to (SR), brought about by interaction of S with R (this change initiates a change in plasma-membrane conformation of taste cells, probably below the level of the tight junction) and step 3, conformational changes of the membrane result in lowered membrane resistance, and the consequential influx on intracellular ionic species, probably Na. This influx generates the receptor potential which induces synaptic vesicular release to the innervating, sensory nerve, leading to the generator potential.

Figure 21-4 shows a schematic representation of an electrolysis cell for aluminum production. An external electrical potential drives electrons into a graphite cathode, where Al ions are reduced to A1 metal ... 

Figure 4.15 Representation of the disposable slide for the measurement of potassium by the Vitros Chemistry System. The difference in potential between the two half-cells, one receiving the sample and the other a reference solution of known potassium ion concentration, is mathematically converted to give the concentration of potassium ions in the sample.

Figure 6.1 Schematic representation of a cell used for voltammetry, in which the potential of the WE is measured with respect to the RE and the current through the WE is determined with respect to the CE. Wherever possible, the spatial separation between the WE and RE is minimized.

Figure 9.2. Mechanisms of aminoglycoside toxicity. This schematic representation summarizes the principles of aminoglycoside toxicity discussed in the text. Treatment with the drugs leads to the formation of reactive oxygen species through a redox-active complex with iron and unsaturated fatty acid or by triggering superoxide production by way of NADPH oxidase. An excess of reactive oxygen species, not balanced by intracellular antioxidant systems, will cause an oxidative imbalance potentially severe enough to initiate cell death pathways. Augmenting cellular defenses by antioxidant therapy can reverse the imbalance and restore homeostasis to protect the cell.

Ionic mobility refers to the velocity of an ion moving toward an oppositely charged electrode when a 1-volt potential is applied across a 1-centimeter electrochemical cell, strongly hydrated molecular cluster, such as [H-(OH2)4], is probably a more realistic representation (M. Eigen (1964) Angew. Chem. (Int. Eng. Edn.) 3, 1). 

Fig. 10 Simulated solar cell electrical behavior in the dark dotted traces) and under illumination (solid traces) comparing the effect of the saturation current parameter 7 on Foe- The black traces represent a device with /g x 10 that of the device represented by the red traces. The sharp inflection points in the semilog plots (upper panel) are the points where the current switches from positive to negative. Also illustrated in the linear representation (lower panel) are the short circuit current density, J c, and the maximum output power, Fmax. given by the product of current and voltage. The blue arrows represent the point at which the dark current and the current under illumination are equal in magnitude. The corresponding potential marked in blue on the voltage axis is Foe for the black trace...

Schematic representation of the heart and normal cardiac electrical activity (intracellular recordings from areas indicated and ECG). Sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje cells display pacemaker activity (phase 4 depolarization). The ECG is the body surface manifestation of the depolarization and repolarization waves of the heart. The P wave is generated by atrial depolarization, the QRS by ventricular muscle depolarization, and the T wave by ventricular repolarization. Thus, the PR interval is a measure of conduction time from atrium to ventricle, and the QRS duration indicates the time required for all of the ventricular cells to be activated (ie, the intraventricular conduction time). The QT interval reflects the duration of the ventricular action potential.

Figure 6.2 Schematic representation of potential gradients in a two-electrode cell.

Figure 6.5 Schematic representation of potential gradients in a three-electrode cell (a) i = 0 (b) i 0.

In the second case the standard hydrogen electrode is placed on the right-hand side of the representation of the cell, and the other electrode would be placed on the left-hand side. The emf of the cell would then be written as = i a — ij/c. The value of if/f is defined to be zero and the potential of the electrode on the left, t a, is the emf of the cell. The symbol ip is called the oxidation potential. When all of the reacting substances of the electrode are in their standard states, then // would become ip° and would be called the standard oxidation potential. This terminology is that of Latimer and emphasizes the nature of the reaction taking place at the electrode. We present it here for completeness, knowing that reduction potentials are now the standard convention, but that some of the older literature used oxidation potentials. 

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