Electrode lattice

Kubo et al. [122] have covered the sensing area of a gold electrode lattice with a polyimide layer which supports an atrazine selective MIP prepared with MAA and EDMA and functional monomer and cross linker, respectively. The detection limit was 50 nM (11 ppb) with a working range up to 15 pM atrazine. Other herbicides... 

As can be seen in Figure 2.8, the metal M is coupled with the platinum (Ft) electrode and the electric potential of M at the surface is measured against the SHE. Recall that this potential is the resultant of several interfacial potentials described by eq. (2.7a). The junction potentials of the Pt and M electrodes are small, equd, and apposite so that they cancel out. The liquid junction potential is also small and negligible. The ceU potential is also Imown as the inteifacial cell potential, which depends on the chemical potential of the species (ions) in solution at equilibrium and it is predicted by eq. (2.28). The electrons flow toward the cathodic electrode M, where the metal cations M+ gain these electrons and enter the electrode lattice. This is a reduction process that strongly depends on the chemical potential of the M+ cations. 

The most important rechargeable lithium batteries are those using a soHd positive electrode within which the lithium ion is capable of intercalating. These intercalation, or insertion, electrodes function by allowing the interstitial introduction of the LE ion into a host lattice (16,17). The general reaction can be represented by the equation ... 

Grounding plates or lattices made of pure copper, while displaying good current-carrying capacities, do not provide a particularly low resistance due to the depth at which they can be buried. The third alternative is to bury lengths of copper tape around the installation. The use of reinforced concrete foundations for grounding electrodes has also recently been considered. 

For simplicity a cell consisting of two identical electrodes of silver immersed in silver nitrate solution will be considered first (Fig. 1.20a), i.e. Agi/AgNOj/Ag,. On open circuit each electrode will be at equilibrium, and the rate of transfer of silver ions from the metal lattice to the solution and from the solution to the metal lattice will be equal, i.e. the electrodes will be in a state of dynamic equilibrium. The rate of charge transfer, which may be regarded as either the rate of transfer of silver cations (positive charge) in one direction, or the transfer of electrons (negative charge) in the opposite direction, in an electrochemical reaction is the current I, so that for the equilibrium at electrode I... 

If the electrode potential of iron is made sufficiently negative, positively charged iron ions will not be able to leave the metallic lattice, i.e. cathodic protection. 

Similarly, all points within a metal, which consists of an ordered rigid lattice of metal cations surrounded by a cloud of free electrons, are electrically neutral. Transport of charge through a metal under the influence of a potential difference is due to the flow of free electrons, i.e. to electronic conduction. The simultaneous transport of electrons through a metal, transport of ions through a solution and the transfer of electrons at the metal/solution interfaces constitute an electrochemical reaction, in which the electrode at which positive current flows from the solution to the electrode is the cathode (e.g. M (aq.) + ze M) and the electrode at which positive flows from it to the solution (e.g. M - M (aq.) -)- ze) is the anode. 

At each interface the interfacial potential will depend upon the chemical potentials of the species involved in the equilibrium. Thus at the Zn/Zn electrode there will be a tendency for zinc ions in the lattice to lose electrons and to pass across the interface and form hydrated ions in solution this tendency is given by the chemical potential of zinc which for pure zinc will be a constant. Similarly, there will be a tendency for hydrated Zn ions in solution to lose their hydration sheaths, to gain electrons and to enter the lattice of the metal this tendency is given by the chemical potential of the Zn ions, which is related to their activity. (See equation 20.155.) Thermodynamically... 

The concentration of the solution within the glass bulb is fixed, and hence on the inner side of the bulb an equilibrium condition leading to a constant potential is established. On the outside of the bulb, the potential developed will be dependent upon the hydrogen ion concentration of the solution in which the bulb is immersed. Within the layer of dry glass which exists between the inner and outer hydrated layers, the conductivity is due to the interstitial migration of sodium ions within the silicate lattice. For a detailed account of the theory of the glass electrode a textbook of electrochemistry should be consulted. 

The lanthanum fluoride crystal is a conductor for fluoride ions which being small can move through the crystal from one lattice defect to another, and equilibrium is established between the crystal face inside the electrode and the internal solution. Likewise, when the electrode is placed in a solution containing fluoride ions, equilibrium is established at the external surface of the crystal. In general, the fluoride ion activities at the two faces of the crystal are different and so a potential is established, and since the conditions at the internal face are constant, the resultant potential is proportional to the fluoride ion activity of the test solution. 

Reaction overpotential. Both overpotentials mentioned above are normally of higher importance than the reaction overpotential. It may happen sometimes, however, that other phenomena, which occur in the electrolyte or during electrode processes, such as adsorption and desorption, are the speed-limiting factors. Crystallization overpotential. This exists as a result of the inhibited intercalation of metal ions into their lattice. This process is of fundamental importance when secondary batteries are charged, especially during metal deposition on the negative side. 

The Raman spectroscopic work of Ja-covitz [31], Cornilsen et al. [32, 33], and Audemer et al. [34] is the most direct spectroscopic evidence that the discharge product in battery electrodes, operating of the pi ji cycle, is different from well-crystallized / -Ni(OH)2. The O-H stretching modes and the lattice modes in the Raman spectra are different from those found for well-crystallized Ni(OH)2, prepared by recrystallization from the ammonia complex, and are more similar to those... 

LaNi3 85 Co075Mn04Alt (x = 0, 0.1, 0.2, 0.3) electrodes [51] the Al-free electrode corrodes at a greatly increased rate. As illustrated in Table 7 and Fig. 16, the presence of even a small amount of A1 substantially decreases VH and n, and consequently both lattice expansion and corrosion. 

The cyclic behaviour of a series of electrodes of varying Mn content is shown in Fig. 17. It apparently increases VH (Table 8) slightly and although the correlation between lattice expansion, n, and corrosion rate is fairly strong, they are not a function of Mn content, as shown in Fig. 18. 

It is of interest to note that VH in the hydride phase is significantly less than in AB5 hydrides. Consequently, lattice expansion is also significantly reduced. However, the corrosion rate of the electrodes in Table 9 is still appreciable. Indeed, for the electrode with x - 0.25 the... 

Both factors are sensitive to alloy composition, which can be adjusted to produce electrodes having an acceptable cycle life. In AB5 alloys the effects of Ce, Co, Mn, and A1 upon cycle life in commercial AB5 -type electrodes are correlated with lattice expansion and charge capacity. Ce was shown to inhibit corrosion even though lattice expansion increases. Co and A1 also inhibit corrosion. XAS results indicate that Ce and Co inhibit corrosion though surface passivation. 

There are few systematic guidelines which can be used to predict the properties of AB2 metal hydride electrodes. Alloy formulation is primarily an empirical process where the composition is designed to provide a bulk hydride-forming phase (or phases) which form, in situ, a corrosion— resistance surface of semipassivating oxide (hydroxide) layers. Lattice expansion is usually reduced relative to the ABS hydrides because of a lower VH. Pressure-composition isotherms of complex AB2 electrode materials indicate nonideal behaviour. 

The second way in which an electroactive species such as lithium can be incorporated into the structure of an electrode is by a topotactic insertion reaction. In this case the guest species is relatively mobile and enters the crystal structure of the host phase so that no significant change in the structural configuration of the host lattice occurs. 

Ionic transport in solid electrolytes and electrodes may also be treated by the statistical process of successive jumps between the various accessible sites of the lattice. For random motion in a three-dimensional isotropic crystal, the diffusivity is related to the jump distance r and the jump frequency v by [3] ... 

---