Porous, electrodes catalysis

But catalysis is not the only reason for using porous electrodes. 

Cylindrical Porous Electrode Model. In electrocatalysis, and in catalysis generally, there is a great interest in increasing the real surface area, especially the electrochemical active area of electrodes. In such cases, porous electrodes are used. First investigations of porous electrodes with EIS were applied by de Levie (for details see Section 2.1.6—Rough and Porous Electrodes), presenting a model describing... 

It is well known that for optimal performance of electrochemical energy storage and conversion devices, it is necessary to have a nonplanar electrode to increase reaction area. One requires a porous electrode with multiple phases that can transport the reactant and products in the electrode while also undergoing reaction [1] an analogy in heterogeneous catalysis is reaction through a catalyst particle [2], For traditional devices, porous electrodes are often comprised of an electrolyte (which can be solid or liquid) that carries the ions or ionic current and a solid phase that carries the electrons or electronic current. In addition, there may be other phases such as a gas phase (e.g., fuel cells). Schematically one can consider the porous electrode as a transmission-line model as shown in Fig. 1. 

Certainly, the same arguments apply for chemical redox catalysis , but as discussed above, thinner films may be effective in this case. Hence, it will be reasonable to work with modified electrodes having a large effective area instead of thick films, i.e. three-dimensional, porous or fibrous electrodes. The notorious problem with current/potential distribution in such electrodes may be overcome by the potential bias given by selective redox catalysts. Some approaches in this direction are described in the next section. 

Since improvements achievable with bulky electrodes are limited by the structure of the electrode itself, sintered, porous, Teflon bonded, or phosphate-bonded Ni electrodes have been proposed [386, 391, 399, 400]. A mere increase in surface area is observed without any change in Thfel slope. The same is the case with Ni wiskers in spite of their very large surface area and small particle size [401, 402], A decisive modification of the kinetic pattern is indeed obtained as Raney Ni is used [93, 403] (see Fig. 11). This form of Ni is well known also in the field of hydrogenation catalysis. As an electrocatalyst it was proposed by Justi et al. [404] long ago. Raney Ni is obtained by allowing Ni with a component (usually Al or Zn) which is then... 

Finally, the electrochemistry of porous metal oxides prepared as films from anodic treatment of metal electrodes will also be discussed. Porous metal oxide films on electrodes have applications in a variety of fields, from corrosion protection to batteries and catalysis. 

Porous materials continue to attract considerable attention because of their wide variety ot scientific and technological applications, such as catalysis, shape- and size-selective absorjition and adsorption, gas storage, and electrode materials. Roth research and applications of porous materials—via electroanalysis, electrosynthesis, sensing, fuel cells, capacitors, electro-optical devices, and other means—heavily rely on electrochemistry. 

A transition element containing an incomplete d subshell has many interesting properties and its oxides form a series of compounds with various unique electronic properties. They have a variety of applications such as catalysis, photocatalysis, sensors and electrode materials because of their catalytic, optical and electronic properties. Recently, many attempts have been made to combine these chemical and physical properties and ordered porous properties in order to create novel functional materials. In this chapter, we summarise the synthetic procedures, structural characterisation and applications of ordered porous crystalline transition metal oxides. 

Metal-organic frameworks (MOFs), as a new class of porous materials, are well-known for high specific surface areas and high porosity that have potential applications in gas storage and separation, catalysis, sensor, and drug delivery (Furukawa et al., 2010). In recent years, the exploration of MOFs as electrode materials for supercapacitors has also been... 

Support materials in electrocatalysis, as in heterogeneous catalysis, first serve as substrates for the deposition and stabihzation of the active material (in most cases metallic nanoparticles). Furthermore, the supports have to be conductive to provide electronic pathways to and from the active sites. The latter also impHes that the catalyst deposition during electrode preparation must be carried out in such a way that a conductive but highly porous network may form (see above, triple-phase boundary). 

The formation of open and porous structures with extremely large surface area is of high technological significance, because this structure type is very suitable for electrodes in many electrochemical devices, such as fuel cells, batteries and sensors [1,2], and in catalysis applications [3]. The template-directed synthesis method is most commonly used for the preparation of such electrodes. This method is based on a deposition of desired materials in interstitial spaces of disposable hard template. When interstitial spaces of template are filled by deposited material, the template is removed by combustion or etching, and then the deposited material with the replica structure of the template is obtained [4, 5]. The most often used hard templates are porous polycarbonate membranes [6, 7], anodic alumina membrane [8-10], colloidal crystals [11, 12], echinoid skeletal stractures [13], and polystyrene spheres [14, 15]. 

Porous carbon materials with high surface areas and pore volumes prepared from porous inorganic templates are of current interest for energy storage, gas separation, heterogeneous catalysis, and many other applications including water purification, catalyst support as well as electrode material... 

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