Electrode development, catalytic

Catalytic electrode development has involved the identification of a ternary oxygen evolution catalyst which offer both reduced cost and improved performance in comparison to the current state-of-the-art for aerospace systems. 

The air gas-diffusion electrode developed in this laboratory [5] is a double-layer tablet (thickness ca.1.5 mm), which separates the electrolyte in the cell from the surrounding air. The electrode comprises two layers a porous, from highly hydrophobic, electrically conductive gas layer (from the side of the air) and a catalytic layer (from the side of the electrolyte). The gas layer consists of a carbon-based hydrophobic material produced from acetylene black and PTFE by a special technology [6], The high porosity of the gas layer ensures effective oxygen supply into the reaction zone of the electrode simultaneously the leakage of the electrolyte through the electrode... 

Electrochemical Adsorption at Catalytic Electrodes. A classification of adsorption processes at catalytic electrodes, such as platinum or rhodium, first proposed by Horanyi (24) and further developed by Wieckowski (21,25,26), categorizes adsorption processes into three fundamental groups ... 

The first methanol-fed PEM EC working with an AEM was conceived by Hunger in 1960 [15,45]. This system contained an AEM with porous catalytic electrodes pressed on both sides and led to relatively poor electrical performance (1 mA cm at 0.25 Vat room temperature with methanol and air as the reactants). Since this first attempt, many studies have been carried out to develop alkaline membranes. 

In a fuel cell, the oxidation and reduction steps take place in separate compartments, unlike in conventional combustion.The fuel in this particular cell is hydrogen, but methanol or any other fuel can also be used. Developing suitably active and permanent catalytic electrode surfaces is the principal engineering problem. 

Fast-scan cyclic voltammetry (10 mVs-1 to 106 Vs-1) was used to measure the rate constants of C—X cleavage, which are extremely fast. The technique was applied to measure rate constants of the order of submicrosecond half-lives. For example, the radical anions generated at the electrode surface were determined to have a half-life ranging from less than 100 ns in the case ofp-bromoacetophenone to 70 ms for m-nitrobenzyl chloride189. The method complements the redox catalytic method developed by Saveant and co workers190. 

The nucleus or development center in physical development can be described as a dual electrode on which the reduction of silver ion to silver and the oxidation of developing agent take place simultaneously. Electrochemical measurements of silver physical development in a hydroquinone/Phenidone physical developer with silver ion complexed with thiocyanate proceed as a catalytic electrode process [39]. 

The use of various electrode materials to explore chemical reactions in an electric field dates back to the beginning of the nineteenth century. Although the catalytic nature of some electrodes was only appreciated much later. Grove (7) recognized their chemical or catalytic action and the need for a notable surface action in early fuel cells, just a few years after the dawn of the notion of catalysis (2). When the term electrocatalysis was deliberately introduced by Grubb in 1963 (5), it did not reflect an unnecessary complication in nomenclature, but a real need to identify and comprehend the unique and characteristic features of catalytic electrode processes. How has this need been fulfilled to date Where does the field of electrocatalysis stand compared to the development of conventional catalytic and electrochemical processes What are the new directions and goals of this discipline ... 

The auxiliary electrodes intended to facilitate the reduction of oxygen comprise of, for example, carhon—teflon porous mass catalyzed with silver [6,7] or phthalocyanine [8]. Ruetschi and Ockermann have established that both hydrogen oxidation and oxygen reduction can proceed on the same auxiliary electrode [9]. In our institute, we developed auxiliary catalytic electrodes with tungsten carbide (WC) or a mixture of WC and active carbon as catalyst [10—12], Figure 14.4 presents the volt-ampere curves of the hydrogen and oxygen reactions on partially immersed auxiliary electrodes with different catalysts WC alone, or WC plus active carbon (WC-I-C), or platinum (Pt) [10-12]. 

Most metals are stable in operation as cathodes but unstable as anodes. Satisfactory stability is at least 1,000 hours of continuous operation and preferably 10,000 hours for commercial operations. Of the many categories of electrodes developed, four merit special attention for use in electrosynthesis in different media chemically modified electrodes (CMEs), dimensionally stable anodes (DSAs), conducting polymers, and catalytic cathodes (especially of Raney nickel). 

The analytical application of particle-dispersed-modified electrodes to the selective detection of a single analyte is limited because of broad catalytic activities thus their use as electrochemical detectors following chromatographic separation of carbohydrates is often suggested. Similar nonspecific catalytic PMEs consisting of electrocatalytic RUO2 particles and Ru(OH2)6 in Nafion have been shown to catalyze the oxidation of catechol and of alcohols, respectively these could presumably be used in place of the carbon paste Ru02-modified electrode developed for postseparation detection of carbohydrates and alcohols. Other electrocatalytic particle electrodes were prepared from lead dioxide in polypyrrole and CoPc entrapped behind a permselective cellulose acetate film. ... 

Unsupported materials sueh as metal blaeks were initially used as catalytic electrodes, but they were rapidly disregarded due to the need of using high loadings of expensive noble metals. This led to the development of supported systems, in which the fine dispersion of the catalyst in the very porous support allows increasing the active surface where the electrochemical reaction takes place. 

The role of an AEM is to conduct hydroxyl ions from cathode to anode at match-able rates to the foreign current, as well as the separation of fuels and oxidants. In addition, its integration with the catalytic electrodes forms the heart, MEA, of the AEM fuel cell system. The basic requirements for an AEM are summarized in Section 11.2. To evaluate the performance of a developed AEM material, the fundamental physicochemical properties, including lEC, water absorbing and dimensional swelling, mechanical and thermal properties, membrane morphology, and methanol permeability, are usually investigated. The physical properties of some selected aromatic AEMs are summarized in Table 11.1. 

To circumvent high overvoltage and fouling problems encountered with the direct oxidation of NADH at conventional electrode (equation 6-11), much work has been devoted to the development of modified electrodes with catalytic properties for... 

O.A. Mar ina, V.A. Sobyanin, V.D. Belyaev, and V.N. Parmon, The effect of electrochemical pumping of oxygen on catalytic behaviour of metal electrodes in methane oxidation, in New Aspects of Spillover Effect in Catalysis for Development of Highly Active Catalysts, Stud. Surf. Sci. Catal. 77 (T. Inui, K. Fujimoto, T. Uchijima,... 

Recent research development of hydrodynamics and heat and mass transfer in inverse and circulating three-phase fluidized beds for waste water treatment is summarized. The three-phase (gas-liquid-solid) fluidized bed can be utilized for catalytic and photo-catalytic gas-liquid reactions such as chemical, biochemical, biofilm and electrode reactions. For the more effective treatment of wastewater, recently, new processing modes such as the inverse and circulation fluidization have been developed and adopted to circumvent the conventional three-phase fluidized bed reactors [1-6]. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

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