Nafion proton conducting, structure

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. 

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]). 

Studies on morphology and conclusions about observed levels of proton conductivity have also been carried out on PEMs other than Nafion and sulfonated poly(ether ketone). These include studies in which phenomenological examinations of relationships between conductivity and observed microstructure were carried out upon polymer systems where acid content was varied but the basic chemical structure was kept constant. In addition, other systems allowed... 

The highest level, at structural scales >10 nm, is that over which long-range transport takes place and diffusion depends on the degree of connectivity of the water pockets, which involves the concept of percolation. The observed decrease in water permeation with decreasing water volume fraction is more pronounced in sulfonated poly(ether ketone) than in Nafion, owing to differences in the state of percolation. Proton conductivity decreases in the same order, as well. 

In a H2/air fuel cell, the protons produced at the anode side need to be transferred to the cathode side to react with 02. This requires a proton transport electrolyte. Nafion membranes, composed of a perfluorosulfonated polymer, are the most commonly used polymer electrolyte membranes to conduct protons. The structure of the Nafion membrane is shown in Figure 1.5. Nafion can take on a... 

The degree of hydration of hydronium has relevance to structural diffusion as it requires the presence of Eigen ion (HsO + 3 H2O), which is discussed in detail in Section III. Figure 14 supports the experimental observation of low proton conductivity at low water contents due in part to the reduction of stractural diffusion because the probability of finding HsO surrounded by sufficient H2O molecules is lower. Figure 14 shows that at intermediate water contents, the probabilities for hydronium ions hydrated with three or more H2O molecules are higher in Nafion than in... 

Dupont de Nemours) or analogous perfluorosulphonic acid membranes have been the dominating choice. The structure of the repeat structure of the polymer fluorocarbon backbone and a side chain with sulphonic acid ends upon which Nafion is based is shown in Fig. 3.42 (the commercial product is sold with various thicknesses and dimensions denoted by a number code such as "Nafion-117", related to non-SI units). The membranes should have high protonic conductivity, low gas permeability and, of course, a suitable mechanical strength and low temperature sensitivity. 

A newly-designed photoelectrocatalytic (PEC) reactor for CO2 reduction, which combines photocatalysis by Ti02 and electrocatalysis by carbon nanotubes (CNT), has recently been proposed (Fig. 7) [152]. A proton-conductive Nafion membrane connects the Ti02 and CNT. Irradiation of the combined system of nano-structured Ti02 deposited on a metal Ti electrode with Pt modified CNT deposited on carbon sheet caused water splitting to H2 and O2. A half-cell for the cathodic electrode, i.e., Pt or Fe modified CNT electrode, produces various organic molecules such as 2-propanol due to electrocatalytic reduction of CO2 on the electrode. The proposed PEC reactor is incomplete in its present state. However, these systems are expected to couple water splitting and CO2 reduction, and thus it may establish a new artificial photosynthetic system. 

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