Teflon-bonded electrode

Figure 3.79 Fe K-edge XANES of FeTMPPCl BP pyrolyzed at 800°C in powder form (solid line) and following incorporation into a Teflon-bonded electrode immersed in 0.1 M H3PO4 at open circuit (about 0.6 V versus DHE, in situ, dotted line). Also shown in this figure is the ex situ XANES of an Fe foil for comparison (dashed line).

Figure 3.6. Cyclic voltammograms of Teflon-bonded electrodes (2 mg active material, 0.15 cm projected area) containing intact (panel A) and heat treated ClFeTMPP/BP (panel B) in 1 M H3PO4 (according to Figure 1 in ref. [45] reproduced with permission of the American Chemical Society).

Much of the technology relating to PEMFC systems originates from the development of PAFC and its demonstration [15]. Notable in this are the use of highly dispersed Pt metal catalysts. Teflon-bonded electrode structures, graphite bipolar... 

FIGURE 12, In situ Mossbauer spectra of a 50% w/w Fe-enriched hydrated ferric oxide precipitated on Shawinigan black high-area carbon in the form of a Teflon-bonded electrode in 4 M KOH at (a) -0.3 V and (b) -1.1 V versus Hg/HgO, OH". Inset Cyclic voltammogram of the same, although nonenriched, material as in (a) in the form of a thin porous Teflon-bonded coating electrode deposited on an ordinary pyrolytic graphite electrode, in 4 M KOH. Scan rate 10 mV s" ... 

The packaging approach utilized for tliis battery is similar to that for nickel—hydrogen single cylindrical cells as shown in Figure 23. The sdv er electrode is typically the sintered type used in rechargeable sdv er—zinc cells. The hydrogen electrode is a Teflon-bonded platinum black gas difhision electrode. 

In their earlier work, Modes et al. [53] described low polarization electrodes composed of Teflon-bonded high surface area carbon, loaded with different electrocatalysts (Pt, platinized Pt, Co, Ni). The best results were obtained by using cobalt... 

Fig. 1 shows the cyclic voltammetry of an FePc/XC-72 dispersion, heated at 280°C in an inert atmosphere, in the form a thin porous Teflon bonded coating electrode in a 1 M NaOH solution. A description of the methodology involved in the preparation of this type of electrode may be found in Ref. 3. As can be clearly seen, the voltammetry of this specimen exhibits two sharply defined peaks separated by about 330 mV. The potentials associated with these features are essentially identical to those found by other workers for the reduction and oxidation of films of iron oxy-hydroxide formed on a number of host surfaces, including iron and carbon.(5)... 

Phosphoric acid fuel cells (PAFC) use liquid phosphoric acid as an electrolyte - the acid is contained in a Teflon-bonded silicon carbide matrix - and porous carbon electrodes containing a platinum catalyst. The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types, the first to be used commercially, and features the most proven track record in terms of commercial applications with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. 

Studies by Sedlak (j6) have shown a similar response-flow relationship for liquid electrolyte cells which utilize a teflon-bonded diffusion electrode. The empirical equations and relationships derived generally apply to the SPE sensor cells. 

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... 

NiSx has been observed to behave better than CoSx and FeSx. The decrease in overpotential can be as high as 0.3 V with respect to Ni [25, 151]. NiCo2S4 (formal composition) has been found to operate at -0.1 V vs DHE, at a current density of 1 A cm-2 and has been tested successfully for several thousand hours [444,452]. At open circuit a bluish coloration of the solution indicates that some Co is leached out since it becomes anodic with respect to Ni. A small continuous cathodic protection would be necessary. Teflon-bonded NiCoSx electrodes have been found to be immune from Fe poisoning this has been attributed to the precipitation of FeSx on the electrode surface due to the presence of sulfur in solution leached out from the surface. This condition will not be realized in a continuously flowing solution. 

Chen K.Y., Shen P.K., Tseung A.C. Anodic oxidation of impure H2 teflon-bonded Pt-Ru/W03/C electrodes. J. Electrochem.Soc. (1995) 142(10) L185-L187. 

The catalysts and electrode materials used in PAFCs are also similar to those in acidic H2/air fuel cells. Carbon-supported Pt is used as the catalyst at both anode and cathode, porous carbon paper serves as the electrode substrate, and graphite carbon forms the bipolar plates. Since a liquid electrolyte is used, an efficient water removal system is extremely important. Otherwise, the liquid electrolyte is easily lost with the removed water. An electrolyte matrix is needed to support the liquid phosphoric acid. In general, a Teflon -bonded silicon carbide is used as the matrix. 

Compared with a Teflon -bonded commercial electrode, the composite electrode showed lower polarization losses at high current densities, even though the composite material did not contain Pt. The ohmic and mass transfer resistances were lower in the composite electrode than in the commercial electrode. The sintered contacts and interlocked networks formed in the composite structure permitted better electrical and physical contact between the carbon fibres and metal fibres, leading to a composite electrode with a high void volume and large macroscopic porosity, which increased the accessibility of carbon to the reactants [22],... 

Fig. 24. Current-potential curves for a Teflon-bonded Ru02 layer on a GC disk electrode in...

Mahmood et al. [117] studied the electrochemical reduction of carbon dioxide using gas diffusion electrodes. The reduction was performed on metal (lead, indium, and tin)-impregnated Teflon -bonded carbon gas diffusion electrodes in a sulfuric acid electrolyte over a 1 - 5 pH range. A schematic of the cell is shown in Fig. 24. The following reactions occurred ... 

For Teflon-bonded gas-fed electrodes prepared from carbons that have little peroxide-decomposing activity, the OERR at the highest current densities appears to be limited by converging characteristics related to carbon itself, its electrocatalytic activity for oxygen reduction to peroxide and peroxide decomposition, the gas mass transport, and the electronic conductivity. 

Gas-diffusion electrode (GDE) is a porous composite electrode developed for fuel cell technology, usually composed of Teflon bonded catalyst particles and carbon black. GDEs have been ap-... 

Electroorganic oxidation reactions were monitored on electrodes that were fully immersed in the electrolyte. The organic reactants were directly added to the electrolyte. In some of these experiments, the electrodes described above were used. In other experiments, non-Teflon-bonded catalyts were used by employing a specially constructed Teflon cell. The sample was placed in this cell between a piece of gold foil and a piece of gold screen. The gold screen served as the current collector. An outer layer of Celgard microporous film, placed over the screen, was used to prevent loss of sample into the solution. Additional experimental details may be found in reference (3). 

Hydrogen gas fuel and air (O2) are fed to anode and cathode Pt catalyst powder layers, respectively. The Pt catalysts is Teflon-bonded to porous carbon sheets to form gas-diffusion electrodes, with a catalyst loading of about 1.0 mg/cm. The Pt anode and cathode are separated by a thin inert porous matrix that is filled with concentrated phosphoric acid. The cell operates at 200°C (to improve the electrode kinetics), with a cell voltage of about 0.67 V at a current density of 0.150 A/cm. Most voltage losses occur at the air cathode. The hydrogen gas must be pure because sulfur and carbon monoxide poison the Pt anode catalyst. This type of fuel cell is commercially available today, with more than 200 systems installed all over the world in hospitals, hotels, office buildings, and utility power plants. 

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