Proton-conducting polymers

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. 

Inzelt, G., M. Pineri, 1. W. Schultze, and M. A. Vorotyntsev, Electron and proton conducting polymers recent developments and prospects, Electrochim. Acta, 45, 2403 (2000). 

PEM Proton-exchange-membrane fuel cell (Polymer-electrolyte-membrane fuel cell) Proton- conducting polymer membrane (e.g., Nafion ) H+ (proton) 50-80 mW (Laptop) 50 kW (Ballard) modular up to 200 kW 25-=45% Immediate Road vehicles, stationary electricity generation, heat and electricity co-generation, submarines, space travel... 

Direct-methanol fuel cell Proton- conducting polymer membrane H+ (proton) 80-100... 

The strategy towards CO tolerance has therefore been changed, towards the development of proton conducting polymers suitable for high-temperature operation of the PEMFC, i.e., 120 °C and higher. It is already demonstrated [68] that at this temperature, 1000 ppm CO leads to only minor loss of performance. The high temperature operation will be further addressed in the final section of this chapter. 

The blending of two or more polymers is frequently used to try to combine the separate desirable properties of each system rather than trying to develop one system with all the properties. In the case of PEMs, this has led to the blending of proton-conducting polymers with non-ionic polymers, low lEC polymers, or polymer-containing basic moieties, particularly for DMFC applications in order to decrease MeOH crossover. These different types of blends will be briefly discussed next. 

Zawodzinski, T. A., Davey, J., Valerio, J. and Gottesfeld, S. 1995. The water-con-tent dependence of electro-osmotic drag in proton-conducting polymer electrolytes. Electrochimica Acta 40 297-302. 

Asensio, J. A., Borros, S. and Gomez-Romero, P. 2002. Proton-conducting polymers based on benzimidazoles and sulfonated benzimidazoles. Journal of Polymer Science Part A Polymer Chemistry 40 3703-3710. 

Kreuer, K. D., Fuchs, A., Ise, M., Spaeth, M. and Maier, J. 1998. Imidazole and pyrazole-based proton conducting polymers and liquids. Electrochimica Acta 43 1281-1288. 

This chapter gives an overview of the state of affairs in physical theory and molecular modeling of materials for PEECs. The scope encompasses systems suitable for operation at T < 100°C that contain aqueous-based, proton-conducting polymer membranes and catalyst layers based on nanoparticles of Pt. 

M. Eikerling, A. A. Kornyshev, and E. Spohr. Proton-conducting polymer electrolyte membranes Water and structure in charge. Advances in Polymer Science 215 (2008) 15-54. 

Still higher total conductivities are achievable in a special class of hydrogen-ion (proton)-conducting polymers. These polymers are particularly useful for fuel-cell and chlor-alkaU processing applications in which the efficient transfer of protons is critical. These polymers are of produced in membrane form and are therefore referred to as proton-exchange membranes (PEM). 

The proton conductivity of Nafion is orders of magnitudes higher than most other proton-conducting polymers (see Table 6.11). The conductivity, however, is... 

For the preparation of proton-conducting polymers, aminoalkyl-substituted siloxanes made by sol-gel processing of (MeO)3Si(CH2)3NR2 [for example, NR2 = NH2, NH(CH2)2NH2, NH(CH2)2NH(CH2)2NH2] were doped with CF3SO3H129. 

IRRADIATION EFFECT OF GAMMA-RAY ON THE PROTON-CONDUCTING POLYMER... 

In polyelectrolyte gels the variation of pH or salt concentration (cs) causes a swelling or shrinkage. Therefore, in this case chemical energy is transformed to mechanical work (artificial muscles). An increase of cs (or a decrease of temperature) makes the gel shrink. Usually, the shrinking process occurs smoothly, but under certain conditions a tiny addition of salt leads to the collapse of the gel [iii, iv]. Hydration of macroions also plays an important role, e.g., in the case of proton-conductive polymers, such as -> Nafion, which are applied in -rfuel cells, -> chlor-alkali electrolysis, effluent treatment, etc. [v]. Polyelectrolytes have to be distinguished from the solid polymer electrolytes [vi] (- polymer electrolytes) inasmuch as the latter usually contain an undissociable polymer and dissolved small electrolytes. 

Andreaus B, Scherer GG (2004) Proton-conducting polymer membranes in fuel cells— humidification aspects. Sohd State Ionics 168(3—4) 311—20... 

Using proton-conducting ceramics as an electrolyte for a steam electrolyzer involves the same reactions as for a low-temperature proton-conducting polymer membrane ... 

Nam, K. et al., Acid-Base Proton Conducting Polymer Blend Membrane, U.S. Patent Application 2003/0219640, November 27, 2003. 

Kreuer, K.D., On the development of proton conducting polymer membranes for hydrogen and methanol fuel cells, J. Membr. Sci., 185, 29, 2001. 

Advances in fuel cells were later accelerated by space and defense programs. Fuel cells found initial practical application with the Gemini (1962-1966) and the Apollo (1968-1972) spacecraft missions, and are still used to provide water and electricity for the Space Shuttle. The upgrade in fuel cell performance over the last four decades has been based on the development of new proton-conducting polymers, like Nafion and Gore-tex , ceramics and catalysts, as well as on greater insights into... 

Among the proton-conducting membranes Nation or Nafion-like sulfonated perfluorinated polymers should also be mentioned. These materials are used for polymer electrolyte membrane (PEM) fuel cells, and in addition to being chemically very stable, they exhibit high proton conductivity at temperatures lower than 100°C. It is believed that permeability and thermal stability may be increased if tailor-made lamellar nanoparticles are added to a proton conducting polymer. 

FIGURE 27.20 Structure of Nation. The characteristic value of proton-conducting polymer membranes is the EW, which is defined as the weight of polymer that will neutralize one equivalent of base, and is inversely proportional to the lEC. The values n, m, n can he varied to produce materials with different equivalent weights. 

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