Electrocatalysis for the Direct Alcohol Fuel Cell - Fuel Cell Catalysis: A Surface Science Approach - page 346

Figure 11.4 Tafel plots for methanol oxidation on Pt þ Ru/C colloid catalysts with different
atomic compositions; at T ¼ 298K: (a) 1.0 M MeOH; (b) 0.1 M MeOH (0.5 M H 2 SO 4 ; sweep
rate 1 mV s 21 ).

activation (30 kJ mol 21 ). Electrochemical NMR studies [Tong et al., 2002] have
shown that CO diffusion at a pure Pt surface was slow compared with that near
Pt/Ru islands. Then, the slow diffusion of adsorbed CO from Pt sites away from Ru
to Pt sites close to Ru where the oxygenated species on Ru oxidize the CO species
can be proposed as the rate-determining step [Gasteiger et al., 1994]. Finally, the
intermediate value obtained with the Pt catalyst (45 kJ mol 21 ) may be attributed
to the oxidation of CO ads to CO 2 , which is the rate-determining step, according to
the reaction

CO ads þ OH ads ! CO 2 þ H þ þ e (11 : 12)