Porous protonic solids

C. Porous protonic solids Rotational dynamics of liquids at surfaces References... 

Hamakawa et al. [2.66]) utilized exactly such a concept shown schematically in Figure 2.2. Hamakawa et al. [2.66], for example, used a SrCe0.95Yb0.05O2.95 membrane as a proton, solid oxide electrolyte with two porous Ag electrodes attached to it. CH4 was passed in the one compartment of the electrochemical membrane reactor (the anode) while Ar was flown into the other cell. C2 products (C2H4 and C2H6) were detected in the anode... 

Crude oil is converted into gasoline in cracking reactions that transform large molecules into smaller ones. The catalytic reactions occur in the interiors of porous inorganic solids called zeolites. The actual catalysts are protons that exist on the interior walls of the zeolites. Titanium dioxide, a photocatalyst, is an interesting solid because it functions as a catalyst only when it is exposed to light. This is environmentally advantageous, as the... 

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. 

Here, Pc is the capillary pressure which is a function of s, permeability K, and surface tension. Equations (5.33-5.45) along with Navier-Stokes Equations and species equations constitute a fully 3-D description of a PEMFC. When the membrane is replaced by a solid, non porous electrolyte conducting oxide ions instead of protons, the above model essentially becomes a model for SOFCs. In an SOFC, of course, there is no condensation /zphase = 0 and Equations (5.43-5.45) would not be necessary. 

CP dynamics has also been very useful technique for estimation of the connectivities in the porous solids. Classic example in this case would be a clear distinction between Q2, Q3 and Q4 silicate sites in the molecular sieves on the basis of not only the chemical shift but also Tcp times which, as a result of no protons connected directly are much longer for Q4 sites (Si(OSi)4). Introduction of guest species in the pores has a dramatic effect on the CP-dynamics of the different silica sites. Thus, in the MCM-41 impregnated with the mixed metal clusters/counter-cation species, presence of embedded organic counter-cation lead to a significant reduction of Tcp and Tiph due to the presence of a different source of protons at the porous silica surface.21... 

Electroosmosis — (also called electroendosmosis and endosmosis) The movement of a polar liquid through a capillary tubing or porous solid driven by an electrical potential difference. First described by F. F. Reuss in 1809. In fuel cells, electroosmosis causes protons moving through a proton exchange membrane (PEM) to drag water molecules from one side (anode) to the other (cathode). This phenomenon is utilized for the dessica-tion of different objects, e.g., walls of buildings. 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

H, 13C and 27 A1 solid -state NMR spectra show that trapped water molecules in porous aluminium terephthalate interact with carboxylate groups via hydrogen-bonds.626 Proton NMR studies have been reported for H20 molecules confined within SWCNT (210-300 K).627... 

Japanese researchers [248] have designed an apparatus for the electrochemical reduction of carbon dioxide employing ultrasound. The apparatus comprises an electrolytic cell containing C02-dissolved electrolytic solution, a porous Pt-group metal anode, a proton-conductive solid electrolyte having a porous metal cathode used as a catalyst for the electrochemical reduction of COz on one side and a second anode on the other side facing oppositely to the cathode, and an ultrasonic vibrator. C02 can be reduced effectively for a long time. 

The well-defined porous structure of zeolitic materials makes these materials true shape-selective molecular sieves. The presence of charge-compensating cations such as alkaline and alkaline earth cations, protons, etc. within the inorganic frameworks adds ion exchange and catalytic properties. Moreover, the hydrophobic nature of pure silica zeolites or the hydrophilic nature of aluminosilicates makes these solids useful as specific adsorbents of organic molecules or water in the gas or liquid phase. 

Chemical Surface Properties While a few other porous solids can match most of the physical surface properties of carbon materials (except the very high surface areas, in excess of 2000 m /g), when it comes to surface chemistry the flexibility offered by carbons is rather unique. This is because of their unique proton-. 

---