Performance of CNT- and CNF-Based Catalysts

Owing to the advantageous properties of CNTs and CNFs as supports, several studies have been carried out on different catalytic reactions. In particular, much attention has been dedicated to liquid-phase reactions with MCWNT- and CNF-supported catalysts indeed, their high external surface and their mesoporos-ity would result in a significant decrease in mass-transfer limitations compared with activated carbon. It is worth noting that as for fullerenes [28], few studies on SWCNT-supported catalytic systems have been reported, due either to their microporosity or to the fact that it is still very difficult to obtain the large amounts of pure material required to conduct catalytic studies. In this section we present the results obtained for each type of reaction and, when possible, we will try to rationalize these results by comparison with other carbonaceous supports. 

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A key advantage of CNTs and CNFs is the possibility to functionalize or dope their surface with various elements to improve the dispersion of the inorganic active phase or introduce new organic active sites for performing subsequent catalytic reactions. Chemical functionalization of CNTs and/or CNFs is critically important for developing new, highly efficient, carbon-based materials for downstream catalytic applications. It is expected that doped CNTs could represent an important class of new metal-free catalysts with better catalytic performance and improved resistance toward deactivation compared with traditional supported transition metals and oxides. 

Many studies have examined various aspects of PEM fuel cell performance as a function of operating conditions [180-182]. Gottesfeld wrote an excellent review of PEM fuel cells components and operation [183]. In addition to experimental characterization, much research has focused on first-principles-based modeling of the PEM fuel cells [184, 185]. Polarization occurs during operation of PEM fuel cells and it dramatically influences both the performance and the commercialization of the technology. In order to systematically improve the efficiency of the fuel cell, a better understanding of the reactions and mass transport in the cell is essential. In this section, the improvement of the MEA performance based on CNTs and CNFs catalysts will be discussed. 

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