Chemically Derived Graphene: Functionalization, Properties and Applications
CHAPTER 3: Functionalization of Chemically Derived Graphene as Electrode Materials for Fuel Cells
Published:10 May 2018
In this chapter, functionalization of chemically derived graphene is discussed with a focus on its use as active electrode materials in proton-exchange membrane fuel cells (PEMFCs). More specifically, we feature fuel cells employing hydrogen gas or direct methanol as the fuel, which represent two major sub-areas of development in PEMFCs, with the latter being singled-out as direct methanol fuel cells (DMFCs) for their great potential. A wide range of composites with graphene or chemically derived graphene (heteroatom-doped graphene or graphene alloys) as the support to nanoparticles of either platinum-group metals or transitional metal-based compounds are screened with respect to their electrochemical performance, such as their catalytic activity toward the hydrogen oxidation reaction at the anode and the oxygen reduction reaction (ORR) at the cathode of hydrogen-based PEMFCs, or toward the methanol oxidation reaction at the anode and the ORR at the cathode of DMFCs, as well as their durability as catalysts. Clearly, graphene-type carbon materials greatly improve the performance of the resultant catalysts compared to their counterparts with non-graphene carbon of low crystallinity as the support. Emphasis is placed on the cost-reduction of the catalysts used in these fuel cells. A typical concept consists in reducing the use of platinum or even replacing it in the catalysts. Nevertheless, the number of reported competitive catalysts (vs. Pt/C) toward the ORR are largely only useful in alkaline electrolytes. Fortunately, a few scattered successes have been demonstrated very recently. These inspiring findings suggest that a combination of such catalysts in the cathode and Pt/graphene-type catalysts in the anode may likely afford commercially viable fuel cells in the near future.