Electrode proton conductivity

The standard electrode potential and its temperature coefficient are found in the literature.36 Kinetic parameter values were measured in-house for HOR,33 ORR,34 OER,35 and COR.12 22 Table 2 gives cell component materials and transport properties. The membrane and electrode proton conductivity in Table 2 are based on the measured membrane and electrode resistance,42,43 which is a strong function of relative humidity (RH). In what follows next, we will describe the... 

The concept of the reversed fuel cell, as shown schematically, consists of two parts. One is the already discussed direct oxidation fuel cell. The other consists of an electrochemical cell consisting of a membrane electrode assembly where the anode comprises Pt/C (or related) catalysts and the cathode, various metal catalysts on carbon. The membrane used is the new proton-conducting PEM-type membrane we developed, which minimizes crossover. 

Figure 9.32. Experimental set-up (a) Machinable ceramic holders and two proton conducting pellets showing the location of catalyst, counter and reference electrodes, (b) Twenty four pellet unit, (c) High-pressure reactor, gas feed and analysis unit.43 Reprinted with permission from the American Chemical Society.

But when the contents of Nafion ionomer was increased from 30 to 45 % to find out the better electrode structures, the Pt-Ru/SRaw, which had showed the lowest single cell performance, became the best electro-catalyst. By this result one can conclude that as long as the structure of the electrode can be optimized for the each of new electro-catalysts, the active metal size is a more important design parameter rather than inter-metal distances. Furthermore, when the electro-catalysts are designed, the principal parameters should be determined in the consideration of the electrode structures which affect on the electron conduction, gas permeability, proton conductivity, and so on. 

Apart from the problems of low electrocatalytic activity of the methanol electrode and poisoning of the electrocatalyst by adsorbed intermediates, an overwhelming problem is the migration of the methanol from the anode to the cathode via the proton-conducting membrane. The perfluoro-sulfonic acid membrane contains about 30% of water by weight, which is essential for achieving the desired conductivity. The proton conduction occurs by a mechanism (proton hopping process) similar to what occurs... 

A considerable decrease in platinum consumption without performance loss was attained when a certain amount (30 to 40% by mass) of the proton-conducting polymer was introduced into the catalytically active layer of the electrode. To this end a mixture of platinized carbon black and a solution of (low-equivalent-weight ionomeric ) Nafion is homogenized by ultrasonic treatment, applied to the diffusion layer, and freed of its solvent by exposure to a temperature of about 100°C. The part of the catalyst s surface area that is in contact with the electrolyte (which in the case of solid electrolytes is always quite small) increases considerably, due to the ionomer present in the active layer. 

This electrochemical decomposition requires about 1 V at the electrode surface. To drive the protons into the WO3 film, a proton-conducting electrolyte, typically... 

The main components of a PEM fuel cell are the flow channels, gas diffusion layers, catalyst layers, and the electrolyte membrane. The respective electrodes are attached on opposing sides of the electrolyte membrane. Both electrodes are covered with diffusion layers, and the flow channels/current collectors. The flow channels collect current from the electrodes while providing the fuel or oxidant with access to the electrodes. The gas diffusion layer allows gases to diffuse to the electro-catalysts and provides electrical contact throughout the catalyst layers. Within the anode catalyst layer, the fuel (typically H2) is oxidized to produce electrons and protons. The electrons travel through an external circuit to produce electricity, while the protons pass through the proton conducting electrolyte membrane. Within the cathode catalyst layer, the electrons and protons recombine with the oxidant (usually 02) to produce water. 

GDE s may be interesting for synthesis cells as depolarized electrodes (e.g. [48]). A hydrogen-consuming anode will work at a low potential that avoids undesired anodic oxidations (e.g. no chlorine evolution in presence of chlorides). In order to reject an excess of the electrolyte from the GDE structure, a proton-conducting membrane (Nafion ) between the GDE and the electrolyte can be used ( Hydrina , De Nora Spa. [49]). 

Concentrating on the operation of the so-called membrane electrode assembly (MEA), E includes irreversible voltage losses due to proton conduction in the PEM and voltage losses due to transport and activation of electrocatalytic processes involved in the oxygen reduction reaction (ORR) in the cathode catalyst layer (CCL) ... 

The first demonstration of a PEM with electrochromic properties was disclosed by SchlenofFand coworkers [66], using poly(butanylviologen)/ PSS films. While this film exhibited strong electrochromic response, it still required the use of an outer electrolyte solution. DeLongchamp and Hammond disclosed for the first time a solid-state device comprised of two electrochromic PEM-modified ITO electrodes separated by a 200-p,m thick poly(2-acrylamido-methane-2-propanesulfonic acid), proton-conducting PAMPS membrane (see Eigure 2.30) [196]. Both PEMs used in... 

Proton conductive electrolyte properties of step 2 membranes were determined at 150°C by the impedance measurement using a 13-mm circular-plate-shaped platinum electrode. Testing results are provided in Table 1. 

In earlier investigations by the authors (2,3) solid sulfonic acid resins containing polyarylether and cyano substituents, (II) and (III), respectively, were prepared and used as proton-conductive membranes, electrode electrolytes, electrode paste, and in membrane electrode assemblies. 

The ionic monomer that forms the proton exchange membrane (PEM) separating and ionically connecting the two gas diffusion electrodes can be dissolved in isobutyl alcohol or other organic solvents, such as isopropanol. This circumstance opens the way for improving the ionic contact between the catalyst particles of a gas diffusion electrode and the proton-conducting membrane and electrolyte. 

The fuel cell in Figure 13.9 can be conceptually viewed as a combination of a Nafion film-coated cathode and a Nafion film-coated anode. Hence, the fuel cell is, in essence, a combination of two chemically modified electrodes. This idea is, in fact, more than just a concept, because electrochemical investigations of Nafion film-coated electrodes have been used to obtain fundamental chemical and electrochemical information that is relevant to the operation of such devices [93]. For example, the kinetics of 02 reduction in fuel cells can be investigated at such modified electrodes the solubility and diffusion coefficient for 02 in Nafion and the proton conductivity of this membrane material can also be determined. Chemically modified electrodes have made analogous contributions to battery development. 

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