Porous conductivity

Both questions have been recently addressed via a surface diffusion-reaction model developed and solved to describe the effect of electrochemical promotion on porous conductive catalyst films supported on solid electrolyte supports.23 The model accounts for the migration (backspillover) of promoting anionic, O5, species from the solid electrolyte onto the catalyst surface. The... 

Herein, we consider the case when a porous conducting matrix with inclusion of active solid reagents represents the electrode. It is supposed, that both the reagent and the product are nonconductive. The conversion of the solid reagents is assumed to proceed via a liquid-phase mechanism in the following way dissolution - electrochemical reaction - crystallization. Figure 1 shows the structure of the electrode and its model. The model has been developed on the bases of several assumptions. 

As a main feature, the usage of a conducting matrix can be expected to help to decrease the resistance and to increase the mean life of the generated electrons. Also, a porous conducting electrode enables a more intimate contact between the electrode and the semiconductor. Despite the prelimi-... 

To sum up the results the deviation of the surface capacitance is a meaningful supplementation in characterizing the microstructure of porous conducting materials. Beyond that by dividing the total capacitance by the surface capacitance the determination of the surface area of samples with known pore size distribution is possible. This enables especially the characterization of ultra thin carbon films which can not be analyzed by-adsorption measurements because of their low mass. 

Different electrode designs were developed. Porous conductive electrodes having at least two zones can be used either as reversed dual porosity electrode or as electrode assembly with conductive, noncompressible porous carbon matrices [92]. 

E. Ekanayake, D.M.G. Preethichandra, and K. Kaneto, An amperometric glucose biosensor with enhanced measurement stability and sensitivity using an artificially porous conducting polymer, IEEE Tran. Instrument. Meas., 57(8), 1621-1626 (2008). 

Novel conductive composite films have been developed by Kaplin and Qutubuddin [101] using a two-step process microemulsion polymerization to form a porous conductive coating on an electrode followed by electropolymerization of an electroactive monomer such as pyrrole. The porous matrix was prepared by polymerizing an SDS microemulsion containing two monomers, acrylamide and styrene [102], The electropolymerization of pyrrole was performed in an aqueous perchlorate or toluenesulfonate solution. The effects of polymerization potential on the electropolymerization, morphology, and electrochemical properties were reported [101]. The copolymer matrix improves the mechanical behavior of the polypyrrole composite film. 

As mentioned, Go can be determined separately performing the same step experiment in pure supporting electrolyte. It is of importance to note that adsorption usually influences the interfacial capacitance thus if R or O is adsorbed, the capacitive components determined in the absence or presence of the adsorbing species, respectively, will differ from each other. For films - especially in the case of porous conducting polymer - Cd evaluated for metal/electrolyte and metal/film/electrolyte systems, respectively, may differ by orders of magnitude. 

Wang J., Naguib H. E., and Bazylak A., Electrospun porous conductive polymer membrane., Proc. SPIE 8342 83420F-1 Behavior and mechanics of multifunctional materials and composites 2012, Goulbourne N. C., and Ounaies Z. [Eds.], Proc. SPIE 8342, 83420F 2012 SPIE, DOI 10.1117/12.923599. 

Sujith K., Asha A. M., Anjali R, Sivakumar N., Subramanian K. R. V., Nair S. V., and Baiakrishnan A, Fabrication of highly porous conducting PANI-C composite fiber mats via eiectrospinning. Mater. Lett, 2012, 67,376-378. 

These cells operate only with hydrogen as the anode fuel and, moreover, the hydrogen must be pure since sulphur compounds and carbon monoxide adversely affect the performance of the Pt catalyst. Each cell consists of two teflon-bonded gas diffusion electrodes on a porous conducting support (see Fig. 10.21). At both anode and cathode the catalyst is platinum particles dispersed on carbon and a recent success has been a reduction in Pt loading from 10 mg cm to 0.75 mg cm ". The electrolyte is concentrated phosphoric acid absorbed onto a solid matrix and the cell operates at 200°C to improve the electrode kinetics. The cells are then mounted in stacks to increase the power output. 

A number of biomolecules have been physically immobilised on conducting polymers [66,112, 116-119]. This is the simplest method of enzyme immobilisation. Since the binding forces involved are hydrogen bonds, van der Waals forces, etc., porous conducting polymer surfaces are most commonly used. The pre-adsorption of an enzyme monolayer prior to the electrodeposition of the polymer, [120] and two-step enzyme adsorption on the bare electrode surface and then on PPy film [121] have also been investigated. 

Other templates have also been used. Polypyrrole nanowires have been produced by growing the polymer in porous alumina. Highly porous conducting polymers have also been produced using the inverse opal method [38], in which the polymer is deposited around a matrix of tightly packed spheres, which form the synthetic opal. When the spheres are removed, a highly porous film is left with... 

Due to the excellent redox properties and high conductivity of the conducting polymer nanocomposites, researchers have been extensively investigating them as electrode materials for batteries and supercapacitors [29,30]. Further, the soft porous conductive polymer matrix can efficiently buffer the severe volume changes of active electrode material during the ion intercalation and extraction process, hence improving cyclability of the electrode material and also acts as a conductive binder, decreasing the contact resistance between particles of active material [31]. In this section... 

Cosnier and coworkers coupled the polymer entrapment strategy with the use of CNTs as porous conductive support [28]. Methyl viologen as a redox mediator covalently bound to the polymer ensured a high indirect electron transfer from D. jructosovorans hydrogenase to the CNTs. Again, a 10-fold increase in... 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

These cells operate only with hydrogen as the anode fuel and, moreover, the hydrogen must be pure since sulphur compounds and carbon monoxide adversely alTect the performance of the Ft catalyst. Each cell consists of two Teflon>bonded gas difTusion electrodes on a porous conducting support (Fig. 

Metallic, porous, conductive and water retaining cathode current collector... 

The electro-catalyst layers, which are porous, conduct both ions and electrons to facilitate oxidation and reduction reactions. For example, the electrocatalyst layers in most PEMFCs are 5-30 pm thick. The ion conductivity of these layers varies from 1 to 5 S/m and hence electro-catalyst layer area specific resistance values vary from 0.01 Q cm to 0.03 Q cm (or 10-300 mQ cm ). The Nafion electrolyte in PEMFC has a conductivity of 10 S/m when hydrated. Hence, for electrolyte thickness of 50-200 pm, the area specific resistance varies from 50 mil cm to 200 mil cm. Thus, it can be seen that the electro-catalyst layer contribution to ohmic resistance is significant. In Table 5.3, typical thickness and area-specific resistance values for selected fuel components are listed. 

The molten carbonate fuel cell (MCFC) operates at high temperature, which is about 600-700 °C. It consists of two porous conductive electrodes in contact with an electrolyte of molten carbonate. This type of cell allows the internal reform. The main advantage of the MCFC is its high efficiency (50-60%) without external reformer and metal catalyst, due to the high operating temperature (Farooque Maru, 2001). This cell is intolerant to sulfur and its launching is slow, these are its main disadvantages. 

Especially for supercapacitor electrode, combination of metal oxides with highly conductive carbon nanofiber has been studied intensively. Figure 7.6 shows the illustration for preparing hybrid carbon/metal oxides nanofiber. In these composite electrodes, the carbon substrate acts as a highly porous conducting network that enables a good access of ions and electrons to the metal oxides. 

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