Nanostructured Carbon Materials for Fuel Cells

Dear Colleagues,

Since the activity of a catalyst increases as the reaction surface area of the catalyst increases, the size of metal particles used as anode and cathode catalysts in low-temperature fuel cells should be reduced to increase the active surface. Thus, the catalysts are supported on a high surface area substrate. The structure and proper dispersal of these metal particles make low loading catalysts feasible for fuel cell operation. The main requirements of suitable fuel cell catalyst support are (i) a high surface area, to obtain high metal dispersion, (ii) suitable porosity, to boost gas flow, (iii) high electrical conductivity, and (iv) high stability under fuel cell operational conditions. A conventional example of such support is an amorphous microporous carbon powder, such as carbon black. It has been reported that nanostructured carbon materials with both a high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles but also facilitate electron transfer, resulting in a suitable fuel cell performance. On this basis, novel nonconventional nanocarbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example, microsphere). Examples of these nanostructured materials are graphene, carbon nanotubes, ordered mesoporous carbons, carbon aerogels, carbon nanohorns, carbon nanocoils, and carbon nanofibers.

Moreover, the high cost of platinum and its kinetic limitations for oxygen reduction pushed toward considerable research efforts aiming to develop more active and less expensive low-temperature fuel cell electrocatalysts than pure Pt, such as Pt–Co and Pt–Ni alloys. One of the major problems of these alloy catalysts is their stability in the acid environment. Pt and nonprecious metal dissolution and Pt sintering occurs during low-temperature fuel cell operation. Indeed, pure Pt presented higher electrochemical stability than the binary catalyst. A main problem of direct alcohol fuel cells is the alcohol crossover through the polymer electrolyte, affecting the conversion of the chemical energy of the fuel to electrical energy: indeed, a direct reaction between alcohol and oxygen takes place on Pt sites. The resulting mixed potential decreases the cell voltage, forms more water, and increases the required oxygen stoichiometric ratio. A way to overcome this problem is the development of electrocatalysts with a higher alcohol tolerance than Pt. Thus, the search on fuel cell cathode materials was focused on nonplatinum catalysts. Among them, heteroatom-doped nanostructured carbon materials, due to their low cost, appreciable catalytic activity, and high fuel poisoning tolerance, have aroused growing interest. These doped nanostructured carbon materials showed a good activity for oxygen reduction, particularly in alkaline media, fuel selectivity (alcohol tolerance), and electrochemical stability.

The aim of this Special Issue is to cover promising recent research and novel trends in the use of nanostructured carbons in low-temperature fuel cells either as catalysts or catalyst supports. Contributions from all areas of homogeneous and supported catalysis, based on experimental results and/or molecular modeling, would be of great interest.

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• Low-temperature fuel cells
• Supported catalysts
• Nonprecious catalysts
• Nanostructured carbons
• Heterogeneous catalysis