Engineering of the Catalyst Surface and Morphology

In addition to improvements in the intrinsic electrocatalytic activity, research has been carried out to modify ( design , possibly) the catalyst surface in order to enhance the catalyst utilization efficiency and ultimately the fuel oxidation superficial current density. The latter can be expressed in terms of catalyst layer physico-chemical properties as [218]  

The local current density 4 is expressed by various electrode polarization scenarios, such as intrinsic kinetic control, or mixed control involving intrinsic electrode kinetics together with reactant mass transfer and/or ionic conductivity effects, leading to multiple apparent Tafel slopes [146]. 

in terms of Equation 4.36, modifying a , /c, and r could significantly increase the superficial current density i for a given catalyts load and electrode polarization condition (i.e., overpotential). 

Gonzalez and eo-workers provided other evidence for the catalyst morphology effect on direct fuel eell polarization behavior [223]. Their objective was to compare Pt-Ru eatalysts of the same particle size but with different morphology, imparted by the various preparation methods based on formie aeid reduetion. For a narrow partiele size range distribution (3.8-4.8 nm diameter) the eatalysts with more homogeneous Ru deposits on the surfaee gave higher power outputs for the DMFC [223]. 

The structural sensitivity of electrode reactions such as oxygen reduction and oxidation of organic molecules is well known. This is brought about by the particle size dependence of various physico-chemical factors such as heats of adsorption, Fermi level density of states, electron binding energies in the catalyst, and selective surface segregation in the case of multi-component catalysts [224-229]. 

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