Doping mechanism, self-doped

The electron transport mechanism in mesoporous Ti02 film is modeled mainly by using diffusion theory, except in the report by Augustinski et al.,45) who proposed the explanation that the initial film charging by dye-sensitization, in terms of the self-doping, causes an insulator-metal (Mott) transition in a donor band of Ti02, accompanied by a sharp rise in conductivity of the nanoparticles. 

The necessary porosity for thicker layers was introduced by appropriate current densities [321-323], by co-deposition of composites with carbon black [28, 324] (cf. Fig. 27), by electrodeposition into carbon felt [28], and by fabrication of pellets from chemically synthesized PPy powders with added carbon black [325]. Practical capacities of 90-100 Ah/kg could be achieved in this way even for thicker layers. Self-discharge of PPy was low, as mentioned. However, in lithium cells with solid polymer electrolytes (PEO), high values were reported also [326]. This was attributed to reduction products at the negative electrode to yield a shuttle transport to the positive electrode. The kinetics of the doping/undoping process based on Eq. (59) is normally fast, but complications due to the combined insertion/release of both ions [327-330] or the presence of a large and a small anion [331] may arise. Techniques such as QMB/CV(Quartz Micro Balance/Cyclic Voltammetry) [331] or resistometry [332] have been employed to elucidate the various mechanisms. 

The mechanism for the SPAN layer changing the emission properties of the PPy VPV polymer is attributed to the formation of new emissive species due to protonation of the pyridyl units by SPAN. These species was identified by both absorption and PL experiments. Figure 9.15 shows the absorbance spectra of a PPy VPV layer, a SPAN layer, and a bilayer of PPy VPV/SPAN. SPAN is a self-doped, water-soluble conducting polymer with a room-temperature conductivity of 10-2 S/cm.18 It has a wide optical window from green to near infrared PPy VPV... 

Gao et al. [60] reported the CV and electrochemical impedance spectroscopy of self-assembled, stainless steel supported s-BLMs, using a three-electrode system. The membrane resistance and capacitance calculated from the whole impedance spectrum rather than at certain frequencies were close to the conventional BLMs. The time course of impedance under certain applied frequencies was investigated. The results showed that the membrane capacitance of s-BLM fluctuated under low frequency and gradually reached a constant value with the increase in applied frequency. Fullerene-doped s-BLMs were demonstrated to intensify this fluctuation behavior of membrane capacitance. A possible mechanism of this peculiar property of s-BLMs under low frequencies is discussed in Ref. 43. 

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