Proton conductor fuel cells

High-temperature fuel cells solid oxide and proton conductor fuel cells... 

Our approach is to separate the conduction paths for H+ ions and electrons through the incorporation of a ceramic second phase. This approach essentially eliminates the combined dependence of hydrogen flux on electronic and proton conductivities. The approach is to short-circuit the electron flow-paths so that the overall flux is limited only by the proton conductivity. A similar mixed conducting requirement exists for electrodes in high-temperature proton conducting fuel cells, and some work has been carried out to develop mixed conductors as electrodes [24]. 

Fuel cells based on proton conductors have clear potential advantages over oxide ion-conducting SOFCs, and perovskites constitute our best class of proton conductors. However, the difficulty of identifying stable and highly proton-conducting materials has so far limited the performance of demonstration cells of this kind, and commercialization of ceramic proton-conducting fuel cells thus still lies ahead of us. 

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 (

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

Proton, that is, H+ ion, conductors are of importance as potential electrolytes in fuel cells. There are a number of hydroxides, zeolites, and other hydrated materials that conduct hydrogen ions, but these are not usually stable at moderate temperatures, when water or hydroxyl tends to be lost, and so have only limited applicability. 

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... 

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. 

Steininger, H., Schuster, M., Kreuer, K. D., Kaltbeitzel, A., Bingol, B., Meyer, W. H., Schauff, S., Brunklaus, G., Maier, J. and Spiess, H. W. 2007. Intermediate temperature proton conductors for PEM fuel cells based on phosphonic acid as protogenic group A progress report. Physical Chemistry Chemical Physics 9 1764-1773. 

Dr. Hui has worked on various projects, including chemical sensors, solid oxide fuel cells, magnetic materials, gas separation membranes, nanostruc-tured materials, thin film fabrication, and protective coatings for metals. He has more than 80 research publications, one worldwide patent, and one U.S. patent (pending). He is currently leading and involved in several projects for the development of metal-supported solid oxide fuel cells (SOFCs), ceramic nanomaterials as catalyst supports for high-temperature PEM fuel cells, protective ceramic coatings on metallic substrates, ceramic electrode materials for batteries, and ceramic proton conductors. Dr. Hui is also an active member of the Electrochemical Society and the American Ceramic Society. 

Fitch, A. N. (1982) in Solid State Protonic Conductors (I) for Fuel Cells and Sensors, Eds. J. Jensen M. Kleitz, Odense University Press, Odense, p. 235. Geller, S. A. (1967) Science, 159, 310. 

Transport in Proton Conductors for Fuel-Cell Applications Simulations, Elementary Reactions, and Phenomenology Klaus-Dieter Kreuer, Stephen J. Paddison, Eckhard Spohr, and Michael Schuster pp 4637 - 4678 (Review) DOl 10.1021/cr020715f... 

All acidic proton conductors discussed so far in this review have relied on the presence of large amounts of water (A = 10—30) as a mobile phase for the conduction of protons. Current targets for automotive use of hydrogen/air fuel cells are 120 °C and 50% or lower relative humidity. Under these conditions, the conductivity of the membrane decreases due to low water uptake at 50% relative humidity and thus creates large resistive losses in the cell. To meet the needs of advanced fuel cell systems, membranes will have to function without large amounts of absorbed water. Organic—inorganic composites are one preferred approach. ... 

Transport in Proton Conductors for Fuel-Cell Applications Simulations, Elementary Reactions, and Phenomenology... 

---