Abstract
The role played by the surface properties of carbon blacks used as electrocatalyst supports in fuel cell electrodes is crucial in determining the performance and durability characteristics of the final membrane electrode assembly. These key surface properties include the polar character arising from the presence of heteroatoms, and the proportion of the surface area that corresponds to graphitic carbon sites. We have used flow calorimetry to characterise the surface properties of a family of carbon blacks having the same BET surface area (400±10 m2/g), but different pore size characteristics and different properties in terms of polar and graphitic surface sites. The preferential heat of adsorption of n-dotriacontane and n-butanol for basal plane sites and polar sites respectively has been determined for the carbon sites immersed in n-heptane1. The overall hydrophobic character of the carbon surface was evaluated by measuring the heat of adsorption of n-butanol from its aqueous solution2. Platinum nanoparticles prepared by a microwave-assisted polyol method2 were deposited on each of the carbons, and the electrochemical surface area, the mass and specific activity of the Pt/C samples were determined. Membrane-electrode assemblies were prepared using the electrocatalysts at the cathode and they were tested in fuel cell over a range of temperatures and relative humidities, when the observed performance could be related to the relative hydrophobic/hydrophilic properties of the carbons. Further, the stability of the carbons to electrochemical corrosion was assessed by submitting them to high voltage (1.4 V/RHE) and determining the corrosion current and the corresponding mass loss, and the results related to the graphitic character of the carbons determined from flow microcalorimetry and Raman spectroscopy. This understanding will be beneficial in the tuned design of PEMFC electrocatalyst supports for the targeted operation conditions. This work demonstrates the importance of calorimetric methods in characterising carbons for electrochemical applications.
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