Mechanisms of the Oxidation of Carbon Monoxide and Small Organic Molecules at Metal Electrodes - Fuel Cell Catalysis: A Surface Science Approach - page 179

Figure 6.14 Oxidation of 0.01 M H 12 COOH in 0.5 M H 2 SO 4 on a polycrystalline electrode
pre-covered with 13 CO. (a) Voltammetric currents. (b) Mass signals for 12 CO 2 (m/e ¼ 44) and
13 CO 2 (m/e ¼ 45). (Reproduced from Willsau and Heitbaum [1986].)
the total current is less that 5% in a wide range of temperatures [Chen et al., 2006b].
Therefore, the reaction through the poisoning intermediate can be written as
HCOOH þ ! CO ads þ H 2 O ! CO 2 þ 2H þ þ 2e þ
As can be seen, the first part of the reaction is chemical decomposition of the formic
acid to yield CO and water, and the second part is the classical reaction for adsorbed
CO, which has been reviewed extensively in the previous section. We shall focus on
the first part of the reaction.
As shown in the reaction Scheme (6.16), the reaction that yields the poisoning
intermediate is a chemical reaction, and no electrons are implied in the process.
Additionally, the reaction takes place at open circuit, i.e., without potential control.
This property has been used to measure the total amount of poisoning intermediate
that can be accumulated on the surface. The amount and fraction of the surface blocked