Protonic conductor

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

Nevertheless there are some reactions which never change. Thus NO reduction on noble metals, a very important catalytic reaction, is in the vast majority of cases electrophilic, regardless of the type of solid electrolyte used (YSZ or P"-A1203). And practically all oxidations are electrophobic under fuel lean conditions, regardless of the type of solid electrolyte used (YSZ, p"-Al203, proton conductors, even alkaline aqueous solutions). 

M. Makri, A. Buekenhoudt, J. Luyten, and C.G. Vayenas, Non-Faradaic Electrochemical Modification of the Catalytic Activity of Pt using aCaZr09ln0 03.a Proton Conductor, Ionics 2, 282-288 (1996). 

A recent electrochemical promotion study ofNH3 synthesis43 utilized a commercial fully promoted Fe-based NH3 synthesis catalyst (BASF S6 -10RED) deposited on CaZro.9lno.i03 a, a proton conductor. 

This study is noteworthy because it was the first one showing that a proton conductor can be used for the electrochemical promotion of an oxidation reaction. It underlines that, contrary to chemisorbed H which is a... 

Proton conductors ammonia synthesis, 468 conductivity, 93 ethylene oxidation, 470 hydrogen oxidation, 457 list of electrochemically promoted reactions, 146... 

FIGURE 25.10 Conductivity of some proton conductors as a function of HT. The overlapping area between BaCeOj and SrCeOj indicates sohd solutions based on these compounds. (From Gelings and Bouwmeester, 1997, Fig. 6.17, with permission from CRC Press LLC via CCC.)... 

Bohnke, O., Applications of proton condnctors in electrochromic devices, in Proton Conductors Solids, Membranes and Gels—Materials and Devices, P. Colomban, Ed., Cambridge University Press, New York, 1992. 

Significant advances have been made in this decade in electrochemical H2 separation, mostly through the use of solid polymer electrolytes. Since the overpotentials for H2 reduction and oxidation are extremely low at properly constructed gas diffusion electrodes, very high current densities are achievable at low total polarization. Sedlak [13] plated thin layer of Pt directly on Nafion proton conductors 0.1-0.2cm in thickness, and obtained nearly 1200 mA/cm2 at less than 0.3 V. The... 

Guan, J., S.E. Dorris, U. Balachandran, and M. Liu, The effects of dopants and A B site nonstoichiometry on properties of perovskite-type proton conductors, /. Electrochem. Soc., 145,1780,1998. 

The coordination chemistry of the trichalcogenophosphonates is very undeveloped when compared to the analogous metal organophosphonates (RP032), which have been extensively studied owing to their potential and practical applications as ion exchangers, sorbents, sensors, proton conductors, nonlinear optical materials, photochemically active materials, catalysts and hosts for the intercalation of a broad spectrum of guests.145... 

The resulting phases are good proton conductors and operate up to high temperatures. 

A perovskite structure oxide such as BaZrCLt can be made into a proton conductor by doping so as to introduce ... 

Acceptor doping in perovskite oxides gives materials with a vacancy population that can act as proton conductors in moist atmospheres (Section 6.9). In addition, the doped materials are generally p-type semiconductors. This means that in moist atmospheres there is the possibility of mixed conductivity involving three charge carriers (H+, O2-, and h ) or four if electrons, e, are included. 

The resulting phases are good proton conductors. The total conductivity is due to contributions from oxygen ions, protons, and holes ... 

A number of factors must be taken into account when the diagrammatic representation of mixed proton conductivity is attempted. The behavior of the solid depends upon the temperature, the dopant concentration, the partial pressure of oxygen, and the partial pressure of hydrogen or water vapor. Schematic representation of defect concentrations in mixed proton conductors on a Brouwer diagram therefore requires a four-dimensional depiction. A three-dimensional plot can be constructed if two variables, often temperature and dopant concentration, are fixed (Fig. 8.18a). It is often clearer to use two-dimensional sections of such a plot, constructed with three variables fixed (Fig. 8.18h-8.18<7). 

Figure 8.18 Schematic representation of defect concentrations in mixed proton conductors on a Brouwer diagram (a) three-dimensional plot with two variables fixed (b)-(d) two-dimensional plots with three variables fixed.

The use of this approach can be illustrated by the perovskite structure proton conductor BaYo.2Zro.gO3 g- This material has been investigated for possible use in solid oxide fuel cells, hydrogen sensors and pumps, and as catalysts. It is similar to the BaPr03 oxide described above. The parent phase is Ba2+Zr4+03, and doping with... 

Typically, Nation ionomer is the predominant additive in the catalyst layer. However, other types of CLs with various hygroscopic or proton conductor additives have also been developed for fuel cells operafed xmder low relative humidity (RH) and/or at elevated temperatures. Many studies have reported the use of hygroscopic y-Al203 [52] and silica [53,54] in the CE to improve the water retention capacity and make such CEs viable for operation af lower relative humidity and/or elevated temperature. Alternatively, proton conducting materials such as ZrP [55] or heteropoly acid HEA [56] have also been added... 

Conductivity of Nation in comparison to some intermediate-temperature proton conductors and the oxide ion conductivity of YSZ (yttria-stabilized zirconia). (From Kreuer, K. D. et al 2004. Chemical Reviews 104 4637-4678.)... 

All of the examples of PEMs discussed within Section 3.3 unhl now have been composed of only one polymer system without any other compounds present—be they small molecules, polymers, or solid-state materials. A wide variety of different polymer blend and composite PEMs has been made. However, in this section, only a brief overview highlighting some of the more interesting examples that have been reported in the literature will be presented. Eor discussion, these types of PEMs have been divided into three categories polymer blends, ionomer-filled porous substrates and reinforced PEMs, and composite PEMs for high-temperature operation and alternative proton conductors. 

Composite PEMs for High-Temperature Operation and Alternative Proton Conductors... 

Kreuer, K. D., Paddison, S. J., Spohr, E. and Schuster, M. 2004. Transport in proton conductors for fuel-cell applications Simulations, elementary reactions, and phenomenology. Chemical Reviews 104 4637-4678. 

Schuster, M., Kreuer, K. D., Anderson, H. T. and Maier, J. 2007. Sulfonated poly(phenylene sulfone) polymers as hydrolytically and thermooxidatively stable proton conductors. Macromolecules 40 598-607. 

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