Electrolytes catalyst-free

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

Pt/XC-72R catalyst mixture that was sprayed directly onto one of the graphite separator plates that came with the high-flow rate single-cell electrolysis cell. We have found that the copper(I) oxidation reaction does not require a catalyst (see below). Thus, a catalyst-free graphite separator plate was used as the anode. Nafion membranes were used as the electrolyte for H+ conduction. 

The exchange current, ij corresponds to the rate-determining step for copper deposition on surface sites j and a factor of two is used to account for the overall two-electron Cu2+/Cu process. The values of iPEG and the transfer coefficient aPEG are readily determined from T -i and i-t experiments performed in a catalyst-free PEG-Cl electrolyte. Evaluation of igPS and asps is more difficult. It involves... 

One additional function of catalyst support material is to enhance the platinum utilization in the electrode. This leads to an enlarged three phase reaction zone in the MEA and higher electrochemical active catalyst areas at the same catalyst loading of the electrode. For this reason, support materials with adequate surface area and porosity have to be chosen. Antolini [9] shows the benefits of using meso porous stractured carriers with pore sizes between 2 and 50 nm. Here, free pore volume is available for the electrolyte which enables an additional rise of three phase boundary zone and an increased interaction between catalyst and electrolyte [5, 6, 9-15]. 

The experimental setup is shown in Figure 9.23. The Pt-black catalyst film also served as the working electrode in a Nafion 117 solid polymer electrolyte cell. The Pt-covered side of the Nafion 117 membrane was exposed to the flowing H2-02 mixture and the other side was in contact with a 0.1 M KOH aqueous solution with an immersed Pt counterelectrode. The Pt catalyst-working electrode potential, Urhe (=Uwr)> was measured with respect to a reversible reference H2 electrode (RHE) via a Luggin capillary in contact with the Pt-free side of the Nafion membrane. 

In order to obtain a definite breakthrough of current across an electrode, a potential in excess of its equilibrium potential must be applied any such excess potential is called an overpotential. If it concerns an ideal polarizable electrode, i.e., an electrode whose surface acts as an ideal catalyst in the electrolytic process, then the overpotential can be considered merely as a diffusion overpotential (nD) and yields (cf., Section 3.1) a real diffusion current. Often, however, the electrode surface is not ideal, which means that the purely chemical reaction concerned has a free enthalpy barrier especially at low current density, where the ion diffusion control of the electrolytic conversion becomes less pronounced, the thermal activation energy (AG°) plays an appreciable role, so that, once the activated complex is reached at the maximum of the enthalpy barrier, only a fraction a (the transfer coefficient) of the electrical energy difference nF(E ml - E ) = nFtjt is used for conversion. 

Perfluoro-l,3,2-dithiazolidine 1,1,3,3-tetraoxide (73) is a useful fluorinating agent <87JAP8726264). Compound (72) (free or in salt form) is proposed for use as a polymerization catalyst <82EUP57327>, the salts are suggested as ingredients in battery electrolytes <88FRP2606217>. A- ec-Alkyl substituted... 

In another non-electrolytic process, arylacetic acids are converted to vic-diaryl compounds 2ArCR2COOH — ArCR2CR2Ar by treatment with sodium persulfate Na2S2Og and a catalytic amount of AgN03.436 Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2ArCOCI — ArAr) by treatment with a disilane R3SiSiR3 and a palladium catalyst.437 OS III, 401 V, 445, 463 VII, 181. 

Agglomeration of Pt crystallites due to Brownian motion can really be observed and it can also be shown that, indeed, the interaction between the Pt particles and the supporting soot in the presence of the electrolyte, phosphoric acid, is weak enough to allow for relatively free movement of the Pt particles. This fast process obviously is also the reason for the nonobservability of slower surface diffusion-induced Ostwald ripening. Fortunately alloy catalysts composed of platinum and nonnoble metals seem to show a reduced tendency to agglomeration as their deterioration and activity loss is much slower than that of the pure platinum catalyst. 

Before getting into the subject, classifying in accordance with their process and mechanism the electrolytic initiation reactions which have appeared in the literature will afford the reader a better understanding. The reactions are classified firstly into two types cathodic and anodic. For the cathodic reaction, generation of free-radical and radical-anion, and formation of unstable monomer and active catalyst are visualized from the corresponding references. 

Fig. 11.7 Parallel voltammetric screening of 64 Pt thin film catalysts for the electroreduction of oxygen in acidic solution. In the kinetically controlled region, the activity of all 64 catalysts shows good reproducibility. Conditions 0.5 M H2S04, oxygen saturated 20 mV s 1 anodic scan rate, 60°C, electrolyte stirring, potentials are plotted on the mercury/mercury sulfate electrode scale. Inset voltammogram of 64 Pt thin film catalysts in oxygen-free sulfuric acid, 20 mV s-1, prior to oxygen screening.

---