Support and Particle Size Effects in Electrocatalysis - Fuel Cell Catalysis: A Surface Science Approach - page 569

Figure 16.5 Schematic of the electrochemical array cell. CE, counter-electrode compartment;
WE, working electrode compartment; RE, reference electrode compartment; GS, glass sinter;
GS/GI, gas inlet with glass sinter.
the C/Au arrays in the previously described cell [Guerin et al., 2006b]. The new cell
had a counter-electrode (CE) compartment (CE Au gauze, Alfa Aeser 99.99%),
separated from the working electrode (WE) compartment by a glass sinter. The refer-
ence electrode (RE) was mounted in a Luggin capillary whose tip was placed a few
millimeters from the array. A specifically designed socket allowed precise positioning
of the array to ensure electrical contact. The array was sealed with a Viton gasket to the
WE compartment of the glass cell. The glass cell was cleaned by repeated boiling in
ultrapure water, followed by a concentrated HClO 4 rinse, and was finally washed with
ultrapure water.
16.4 CHARACTERIZATION OF SUPPORTED PARTICLES
Au was evaporated and particles nucleated on TiO x and carbon on substrates. For
particle size characterization, depositions on transmission electron microscope
(TEM) grids were performed under identical conditions to those used for other sub-
strates (support materials were deposited for shorter times to ensure passage of the
electron beam of the microscope). As an example of this approach, Fig. 16.6 shows
TEM images for five deposition times (50, 300, 600, 900, and 1200 s), corresponding
respectively to nominal thicknesses of 0.13, 0.8, 1.6, 2.3, and 3.2 nm of Au on TiO x
estimated from the known rate of Au deposition. The light field image clearly allows
identification of the Au particles. The particles appear round at the base and randomly
distributed at low coverages, and they coalesce at higher coverages.
From the TEM micrographs, particle sizes and the number of particles per unit area
could be estimated. Figure 16.6 provides a quantitative analysis of the particle sizes as
a function of deposition time. It is evident from the particle size distributions that at
low nominal Au thickness (0.13 nm), mean particle diameters are about 1.4 nm and
fall in a narrow range of sizes. As the nominal thickness becomes higher, the particle