Doping crystalline electrolytes

Equation 7.45 is similar to Equation 7.40 and gives a direct relation between the charge conductivity and the ion concentration. In a crystalline electrolyte, the ion concentrations and the number of vacancy sites are controlled by doping the base material with an impurity element. 

Since boron-doped diamond electrodes are commercially available, most of these suppliers offer a wide variety of electrolysis cells. Modular electrochemical cells equipped with BDD electrodes have been reported in detail [122]. However, most of these cells were designed for waste water treatment and were not suitable for electrosynthesis in organic media. Electrolysis cells for synthetic purposes designed for a small volume made of organic-compatible materials are required. Additionally, any contact of the support with the organic electrolyte has to be strictly eliminated in order to avoid the corrosion. Most BDD electrodes are on a silicon support which causes eventual loss of the BDD electrode by the brittle nature of crystalline silicon. Consequently, the material used for sealing has to be inert but soft enough to avoid friction of the silicon support. The available BDD... 

In the above analysis, we used the concept of space charge layer, to be more precise, a depletion layer that would form in a doped, wide-gap semiconductor contacting another phase (a metal, an electrolyte solution, or vacuum). The poly crystalline diamond/metal junctions (where metal is Au, Pt, Pd, etc.) often show rectifying properties [67, 68] and their capacitance characteristics resemble those of a diamond/electrolyte solution junction. 

Germanium — (Ge, atomic number 32) is a lustrous, hard, silver-white metalloid (m.p. 938 °C), chemically similar to tin. Ge is a low-band-gap - semiconductor that, in its pure state, is crystalline (with the same crystal structure as diamond), brittle, and retains its luster in air at room temperature. Anodic dissolution of the material occurs at potentials more positive than ca. -0.2 V vs SCE. Peaks in the voltammograms of germanium in acidic electrolyte are ascribed to a back-and-forth change between hydrogenated and hydroxy-lated surfaces [i]. Studies are often conducted at p-doped and n-doped Ge electrodes [ii] or at Ge alloys (e.g., GeSe) where photoelectrochemical properties have been of considerable interest [iii]. 

Electrodes The anodes of SOFC consist of Ni cermet, a composite of metallic Ni and YSZ, Ni provides the high electrical conductivity and catalytic activity, zirconia provides the mechanical, thermal, and chemical stability. In addition, it confers to the anode the same expansion coefficient of the electrolyte and renders compatible anode and electrolyte. The electrical conductivity of such anodes is predominantly electronic. Figure 14 shows the three-phase boundary at the interface porous anode YSZ and the reactions which take place. The cathode of the SOFC consists of mixed conductive oxides with perovskite crystalline structure. Sr doped lanthanum manganite is mostly used, it is a good /7-type conductor and can contain noble metals. 

In this study, the solubilities of crystalline zirconia (monoclinic form, m-Zr02 as well as Y-stabilized cubic form, c-Zr02) and of a fresh hydroxide doped with Zr have been investigated at pH 9. All measurements were carried out Ifom undersaturation starting from pure water, with or without addition of sodium bicarbonate (5 x 10, 0.05 and 0.5 M NaHCOs). Equilibration times ranged from 1 day up to 250 days. Because the only electrolyte added was NaHCOs in different concentrations, these solubility experiments do not comply with the usual requirement for a fixed ionic strength, which varied from almost zero to 0.5 M. 

SoUdState CrystaMne and Pressed-PeOet Electrodes. There are two basic types of crystalline-based electrodes. The first is exemplified by the fluoride electrode, with a europium-doped LaFs single crystal as the sensor. The LaFg crystal is sealed into the end of a rigid, cylindrical electrode body made of plastic an internal electrolyte solution, typically NaF and NaCl, and an internal reference electrode complete the construction (Fig. 2.6). At room temperature, LaFg is a pure F"-ion conductor. 

---