Charge transport, evaluation

The DNS model can be deployed subsequently on the liquid water blocked CL structure pertaining to a saturation level for the evaluation of the hindered oxygen transport. In brief, the DNS model is a top-down numerical approach based on a fine-scale CFD framework which solves point-wise accurate conservation equations for species and charge transport in the CL with appropriate source terms due to the oxygen reduction reaction (ORR) directly on the CL microstructures.25-27 67 The conservation equations for proton, oxygen and water vapor transport, respectively, are given by 25-27 68... 

In order to evaluate the effect of pore volume blockage in the presence of liquid water causing hindered oxygen transport to the active reaction sites, the direct numerical simulation (DNS) model, mentioned earlier and detailed in our work,25-27 68 is deployed for the pore-scale description of species and charge transport through the reconstructed CL microstructure. 

With the evaluated site coverage and pore blockage correlations for the effective ECA and oxygen diffusivity, respectively, and the intrinsic active area available from the reconstructed CL microstructure, the electrochemistry coupled species and charge transport equations can be solved with different liquid water saturation levels within the 1-D macrohomogeneous modeling framework,25,27 and the cathode overpotential, q can be estimated. 

The spiro compound 61 has been prepared and evaluated as a new charge transport material <07AM4049>. It has also been demonstrated that several 3-boryl-2,2 -bithiophene systems, for instance 62, may have potential as full-color emissive materials <07AG(E)4273>. The donor-acceptor system 5-diphenylamino-5 -... 

In short, there are some encouraging results, particularly the adjustable optical absorption edge and some discouraging results such as the low photoconductivity. The charge transport mechanism Is still poorly understood. An evaluation of the suitability of PAN as a photovoltaic material requires better data on charge transport, doping and junction formation. 

Sampled current voltammetry (SC V) involves applying a potential-step wave form of increasing amplitude, covering a potential window where initially no redox reaction occurs, to one where the current response is diffusion-controlled. The current decay from the exciting pulses is then recorded instantaneously at several different times. In the work under discussion, plots of /nm versus were linear in accordance with the Cottrell equation. Charge transport rates evaluated using this technique were essentially the same, within experimental error, as those evaluated using chronamperometry. 

Abstract Polymeric materials confining functional molecules are one of the most promising materials for designing nanodevices for energy conversion, e.g., solar cells, fuel cells, and artificial photosynthetic devices that are expected to provide a renewable energy resource. Charge transport (CT) and catalysis by redox molecules in polymeric solid materials are reviewed with a focus on a polyanion film, typically Nafion and other polymeric materials, containing excess water. CT in a polyanion film is evaluated based on the... 

As discussed earlier, electrochemical rate constant measurements provide one platform upon which to evaluate charge transport across molecules. However, the electrochemical system contains a lot of complexity, including the presence of ions (i.e., the impact of the electrical double layer cannot be ignored), and relies on electron transfer reactions that may or may not be straightforward to probe the... 

Penner, R. M., and Martin, C. R., Electrochemical investigations of electronically conductive polymers. 2. Evaluation of charge-transport rates in polypyrrole using an alternating current impedance method, J. Phys. Chem., 93, 984-989 (1989). 

Because large amplitude electrochemical methods have proven useful for evaluations of charge-transport rates in redox polymers(19-24), analogous... 

Third, unlike conventional methods for evaluating charge transport in pol3nmer films on electrode surfaces (19-24), there is no current flow during the data acquisition period. Thus, effects of migration and uncompensated film resistance are minimized or completely eliminated. Fourth, the theoretical model for obtaining D pp is applicable to both the semi-infinite and finite diffusion cases. Thus, unlike many other methods (19-24), it is not necessary to adjust the experimental conditions such that the semi-infinite case is obtained. 

The interesting point to note here is that from knowledge of both the slope and the intercept, we can evaluate both the charge transport diffusion coefficient Dcr and the total redox center concentration in the layer. This is done using the following expressions ... 

In a recent communication, Fenner, Van Dyke, and Martin report a variant of the chronopotentiometric current pulse technique, which involves examining the time variation of the open-circuit electrode potential. The open-circuit potential recorded after applying a current pulse varied in a linear manner with The charge transport diffusion coefficient is evaluated by comparing simulated and experimental oc transients. Martin and coworkers show that the concentration of diffusing species at any distance x in the film at any time t after terminating the current pulse is given by... 

The apparent charge transport diffusion coeflScient D r can readily be evaluated using this type of analysis. Aoki and coworkers propose that the peak current/sweep rate variation be expressed by the following expression ... 

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