Membrane nanostructure

In a series of papers, Dupuis and co-workers simulated the effect of temperature and membrane hydration on membrane nanostructure and... 

Recent results by Zawodzinski et al. [97] show that several PFSA membranes exhibit similar electroosmotic behavior, i.e., a drag coefficient of close to 1.0 H2O/H+ over a wide range of water contents for a membrane equilibrated with vapor-phase water. The lack of dependence of the drag coefficient on membrane nanostructure suggests that the drag coefficient is determined by basic elements of the proton transport process which are similar for all membranes, such as proton solvation and local water structure. 

Compared to the established membranes, nanostructured siUcoaluminophospbate (SAPO) membranes show promising properties for the separation of high CO2 concentrations from natural gas. The permeability for CO2 is improved and the SAPO membranes show a higher selectivity than the standard polymer materials. (Li et al., 2010) [9]... 

Devanathan R, Venkatnathan A, Dupuis M. Atomistic simulation of Nation membrane I. Effect of hydration on membrane nanostructure. J Phys Chem B 2007 111.28 8069-79. 

Since perfluorinated PEM, Nation, was developed by the Dupont Company in the 1960s, it has an over 50 years of history. The tremendous fundamental and applied research results built up over these decades on the membrane, which contribute to much deeper understanding of the membrane and the wider application of the membrane. In the foreseeable future, perfluorinated PEM continues to be the most widely studied and employed membrane for PEMECs due to its excellent oxidative stability and superior proton conductivity. However, there are some drawbacks for perfluorinated PEM such as poor mechanical and chemical stability and poor performance at elevated temperature, insufficient resistance to methanol crossover, and high cost. Both chemical and physical modifications on the membrane are the current and future hot points of researcher works. At the same time, a better understanding of the membrane nanostructures and their relationship to the proton transport mechanism is needed to enhance the performance of the membrane. 

A question of practical interest is the amount of electrolyte adsorbed into nanostructures and how this depends on various surface and solution parameters. The equilibrium concentration of ions inside porous structures will affect the applications, such as ion exchange resins and membranes, containment of nuclear wastes [67], and battery materials [68]. Experimental studies of electrosorption studies on a single planar electrode were reported [69]. Studies on porous structures are difficult, since most structures are ill defined with a wide distribution of pore sizes and surface charges. Only rough estimates of the average number of fixed charges and pore sizes were reported [70-73]. Molecular simulations of nonelectrolyte adsorption into nanopores were widely reported [58]. The confinement effect can lead to abnormalities of lowered critical points and compressed two-phase envelope [74]. 

Chapter 15 gives an extensive and detailed review of theoretical and practical aspects of macromolecular transport in nanostructured media. Chapter 16 examines the change in transport properties of electrolytes confmed in nanostructures, such as pores of membranes. The confinment effect is also analyzed by molecular dynamic simulation. 

Thin film nanostructures of the III-VI compound In2Se3 were obtained inside the pores (200 nm) of commercial polycarbonate membrane by automated ECALE methodology at room temperature [157], Buffered solutions with millimolar concentrations of In2(S04)3 (pH 3.0) and Se02 (pH 5.5) were used. The atomic ratio of Se/In in the deposited films was found to be 3/2. Band gaps from FTIR reflection absorption measurements were found to be 1.73 eV. AFM imaging showed that the deposits consist of 100 nm crystallites. 

Within the scope of thermoelectric nanostructures, Sima et al. [161] prepared nanorod (fibril) and microtube (tubule) arrays of PbSei. , Tej by potentiostatic electrodeposition from nitric acid solutions of Pb(N03)2, H2Se03, and Te02, using a 30 fim thick polycarbonate track-etch membrane, with pores 100-2,000 nm in diameter, as template (Cu supported). After electrodeposition the polymer membrane was dissolved in CH2CI2. Solid rods were obtained in membranes with small pores, and hollow tubes in those with large pores. The formation of microtubes rather than nanorods in the larger pores was attributed to the higher deposition current. 

Jiang J, Kucernak A. 2004. Investigations of fuel cell reactions at the composite microelectrode solid polymer electrol3de interface. I. Hydrogen oxidation at the nanostructured Pt Nafion membrane interface. J Electroanal Chem 567 123-137. 

Fuel cell applications Manganese dioxide as a new cathode catalyst in microbial fuel cells [118] OMS-2 catalysts in proton exchange membrane fuel cell applications [119] An improved cathode for alkaline fuel cells [120] Nanostructured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell [121] Carbon-supported tetragonal MnOOH catalysts for oxygen reduction reaction in alkaline media [122]... 

Micro/nanostructures generated using these and related top-down approaches are geometrically and electrically homogeneous, with layouts that can be controlled over a wide range to realize not only ribbons and wires but also bars, platelets, membranes, and other structures. The main limitations of the top-down approach are as follows (1) The composition of the fabricated objects is limited to materials that are readily available in wafer or thin-film forms, (2) the etching processes can lead to some level of roughness on the surfaces of the structures, and (3) dimensions of less than 20 nm, for other than the thickness, are difficult to obtain reliably. 

When these ID nanocrystals are deposited on a surface, typically a random direction exists for the elongating axis of each ID nanocrystal. However, if the preparation method leads to an alignment of the elongating axis in one single direction, e.g. when an ordered array is present, quasi-2E) nanostructures are present. This class of nanostructured Titania thin film may be extended to include also ordered mesoporous Titania membranes, e.g. when the pores are aligned in one single direction. 

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