Catalysts nanostructured membrane

Catalyst layer ink can be deposited on gas diffusion layers to form a CCGDL, as discussed in the previous section. Alternatively, the catalyst ink can be applied directly onto the proton exchange membrane to form a catalyst-coated membrane (CCM). The most obvious advantage of the CCM is better contact between the CL and the membrane, which can improve the ionic connection and produce a nonporous substrate, resulting in less isolated catalysts. The CCM can be classified simply as a conventional CCM or as a nanostructured thin-film CCM. 

The nanostructured thin-film electrode was first developed at 3M Company by Debe et al. [40] and Debe [41], who prepared thin films of oriented crystalline organic whiskers on which Ft had been deposited. The film was then transferred to the membrane surface using a decal method, and a nanostructured thin-film catalyst-coated membrane was formed as shown in Figure 2.10. Interestingly, both the nanostructured thin-film (NSTF) catalyst and the CL are nonconventional. The latter contains no carbon or additional ionomer and is 20-30 times thinner than the conventional dispersed Pt/ carbon-based CL. In addition, the CL was more durable than conventional CCMs made from Pt/C and Nation ionomer [40]. 

The Jet Propulsion Laboratory (JPL) has researched the stated objectives by investigating sputter-deposition (SD) of designed anode and cathode nanostructures of Pt-alloys, and electronic structures and microstructures of sputter-deposited catalyst layers. JPL has used the information derived from these investigations to develop novel catalysts and membrane electrode assemblies (MEAs) that... 

PGMs such as Pt and Pd (Figs 11.5 and 11.6). The membranes developed have been tested with various reactions, such as in proton exchange membrane (PEM) fuel cells and in hydrocarbon hydrogenation (e.g., Halonen et al, 2010 Job et al., 2009 Stair et al., 2006). The nanostructured membrane AAO framework studied by Stair et al. (2006) is presented in Fig. 11.6. A similar type of a framework has been used also with the CNT support framework (Kordas et al, 2006). This kind of a structure provides more uniform contact time and controlled reagent flow, as well as decreased sintering phenomena (Stair et al, 2006). By designing new catalyst systems by... 

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]... 

A. M. Kannan, V. P. Veedu, L. Munukutla, and M. N. Ghasemi-Nejhad. Nanostructured gas diffusion and catalyst layers for proton exchange membrane fuel cells. Electrochemical and Solid State Letters 10 (2007) B47-B50. 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

The free radicals ( OH, OOH,. ..) from H2O2 decomposition are a primary cause of membrane and ionomer chemical degradation. The H202-related membrane degradation mechanism will be discussed in more detail in section 12.3.1. The remainder of section 12.2 is divided into four subtopics anode, cathode, catalyst support, and engineered nanostructured electrodes. 

Recently, boron carbide nanostructures have attracted much attention as they have certain advantages over their bulk counterparts [147]. Nanoscale ceramic fibers, nanocylinders and nanoporous structures - as do their well-known carbon counterparts - have a tremendous number of potential applications, including uses as quantum electronic materials, structural reinforcements, and ceramic membranes for use as catalyst supports or in gas separations [148]. 

Some applications nonrelated to the properties of the nanoporous materials but to their porous structures are their use as filtration membranes, battery separators (hindering the diffusion of ions in the narrow channels), and catalyst supports (due to their high surface area) as well as gas capture and storage or light harvesting [72]. However, the common factor of all of these applications is the requirement of an open nanoporous structure not only inside the sample but also connected to the exterior of the sample. However, the CO2 foaming process from nanostructured polymers still has not allowed obtaining nanoporous samples with all of these features. Pinto et al. [102] proposed that 25/75 PMMA/MAM nanoporous foams present appropriate inner porous structures for these kinds of applications (bicontinuous nanoporous structures with tunable pore size), but further studies are required to connect effectively this inner porous structure with the exterior of the sample. 

---