Adsorption of CO on Ru and Pt blacks and catalysts and the possibility of its utilization for the determination of the ruthenium-free surface

Electrochemical voltammetric curves on Ru and Pt blacks of a different surface area were measured in potential intervals 0.05–1.05 V in pure 0.5 M H₂SO₄ and after CO adsorption. It was proved that after the CO adsorption, the outset of ruthenium oxidation is shifted by about 150 mV towards the positive potentials, e.g. to the region of oxidation of adsorbed CO. This fact made possible the determination of a double-layer charging current of Ru electrodes and, subsequently, also the determination of the amount of adsorbed hydrogen on the Ru surface. An evaluation of the amount of CO and hydrogen adsorption showed that the ratio of adsorbed CO:H on the Pt surface was about 1:1, while on Ru electrodes this ratio was around twice as large. The amount of hydrogen adsorbed on Ru blacks depends on the preliminary preparation of the electrodes. The CO adsorption could also be employed in the determination of a charging current of electrode double-layers during voltammetric oxidation of adsorbed hydrogen on ruthenium supported on Al₂O₃, SiO₂, or TiO₂ carriers. However, a similar determination of hydrogen adsorbed on the tin-modified Ru catalysts is not very reliable.