Hierarchically nanoporous structures

The polymer template was removed in two different ways, by toluene extraction and by pyrolysis, which resulted in very different types of gold replicas. In the first case the nanoparticles retained their shape, which led to a hierarchical network structure with nanopores between the nanoparticles and macropores from the templating polymer spheres. When the latex was removed by calcination at 300 °C, the gold nanoparticles fused to a dense metal matrix with only macropores. 

Continuous mesoporous carbon thin films were fabricated by direct carbonization of sucrose-silica nanocomposite films and subsequent removal of the silica [236]. The mesoporous carbon film with uniform and interconnected pores had a surface area of 2603 mVg and a pore volume of 1.39 cmVg. Subsequently, nanoporous carbons with bimodal PSD centered at about 2 and 27 nm in diameter were prepared by using both the TEOS-derived silica network and the colloidal silica particles as templates [237]. Figure 2.33 illustrates the preparation pathway. The pore sizes of the carbon are determined by the sizes of the added silica particles and the silica network. As the colloidal silica particles are commercially available with different diameters (e.g., 20 to 500 nm), this dual template synthesis process provides an efficient route to preparing nanoporous carbons with a controllable hierarchical pore structure. 

Figure 4.5 Hierarchically nanoporous carbon GDE structure scanned under laser microscopy, [a], [b Pristine GDE and (c), (d) discharged GDE under argon atmosphere [exsitu].

Figure 4.6 2D microstructure of hierarchically nanoporous carbon developed as an engineered carbonaceous material for air cathode, [a] HRTEM picture showing the porous structure, [b] Pore size distribution obtained through DFT calculation. 

This chapter will cover major topics of CL research, focusing on (i) electrocatalysis of the ORR, (ii) porous electrode theory, (iii) structure and properties of nanoporous composite media, and (iv) modern aspects in understanding CL operation. Porous electrode theory is a classical subject of applied electrochemistry. It is central to all electrochemical energy conversion and storage technologies, including batteries, fuel cell, supercapacitors, electrolyzers, and photoelectrochemi-cal cells, to name a few examples. Discussions will be on generic concepts of porous electrodes and their percolation properties, hierarchical porous structure and flow phenomena, and rationalization of their impact on reaction penetration depth and effectiveness factor. 

Much attention is currently devoted to the synthesis and properties of shape-persistent macrocycles[l]. Such compounds are interesting for a variety of reasons including formation of columnar stacks potentially capable of performing as nanopores for incorporation into membranes or for the generation of nanowires[2]. Furthermore, in shape-persistent macrocycles incorporating coordination units, enc/o-cyclic metal-ion coordination may be exploited to generate nanowires[3], whereas e.ro-cyclic coordination can be used to construct large arrays of polynuclear metal complexes[4]. Shape-persistent macrocycles with reactive substituents may also be linked to other units to yield multicomponent, hierarchical structures. 

XU HJ, LI XJ. Silicon nanoporous piUar array a silicon hierarchical structure with high... 

PEM research is a multidisciplinary, hierarchical exercise that spans scales from Angstrom to meters. It needs to address challenges related to (i) to ionomer chemistry, (ii) physics of self-organization in ionomer solution, (iii) water sorption equilibria in nanoporous media, (iv) proton transport phenomena in aqueous media and at charged interfaces, (v) percolation effects in random heterogeneous media, and (vi) engineering optimization of coupled water and proton fluxes under operation. Figme 1.13 illustrates the three main levels of the hierarchical structure and phenomena in PEMs. 

Kawasaki T, Tokuhiro M., Kimizuka N., Kunitake T. Hierarchical self-assembly of chiral complementary hydrogen-bond networks in water. J. Am. Chem. Soc. 2001 123 6792-6800 Kharton V.V., Marques F.M.B. Mixed ionic-electronic conductors effects of ceramic microstructure on transport properties. Curr. Opin. Solid State Mater. Sci. 2002 6(3) 261-269 Kikkinides E.S., Stoitsas K.A., Zaspalis V.T. Correlation of structural and permeation properties in sol-gel-made nanoporous membranes. J. Colloid Interface Sci. 2003 259 322-330 Kilner J., Benson S., Lane J., Waller D. Ceramic ion conducting membranes for oxygen separation. Chem. Ind. November 1997 907-911... 

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