Physical characterization of electrocatalysts

Abstract

In recent years, fuel cells have attracted considerable attention due to their high energy efficiency with zero emissions [1]. Electrocatalysts are some of the key materials used in low-temperature fuel cells such as the polymer electrolyte membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC). Creating high-performance catalysts is widely recognized as a key step for the further development and commercialization of low-temperature fuel cells. The physical characterization of electrocatalysts is very important for several areas of research: (1) preparing new types of electrocatalysts with high activity and high selectivity, (2) recognizing electrocatalyst structures, and (3) investigating the mechanisms of catalysts and certain additives. Electrocatalysts for application in low-temperature fuel cells (including PEMFCs and DMFCs) constitute a special type of heterogeneous catalyst. The most important difference between an electrocatalyst and a normal heterogeneous catalyst is that the former should have good conductivity, whereas most typical heterogeneous catalysts are insulators; therefore, most characterization techniques for electrocatalysts are the same as for regular heterogeneous catalysts, but some special techniques are required for electrocatalysts because of their conductivity. For most PEM fuel cell catalysts, carbon black and other order carbon materials (such as carbon nanotubes) are usually used as support materials. These supports can give catalysts good electron conductivity, a very important feature in a fuel cell catalyst. Platinum and its alloys are popular active components, generally highly dispersed on the surface of support materials as micro-and nano-particles. Catalyst performance is related not only to the conductivity and supporting amounts of noble metals, but also, and more importantly, to the dispersion and composition of the active components. Because the hydrogen molecule is small and easily diffused in catalysts, in general the catalyst pore structure is not more important than the surface area. Physical characterization of PEMFC catalysts includes measurement of the surface area, the electrochemical active surface area, the phase and composition of active components, the particle size and size distribution of active components, the morphology and crystal planes, and other features. © 2008 Springer-Verlag.