Electrochemical deposition of PtRu on an uncatalyzed carbon electrode for methanol electrooxidation

This research aims to increase the utilization of platinum–ruthenium alloy (PtRu) catalysts and thus to lower the catalyst loadings in the electrode for methanol electrooxidation. The electrodeposition of PtRu was performed on a rotating disk electrode (RDE) of glassy carbon (GC), on which a layer of Nafion®-bonded carbon (Vulcan XC 72R) was dispersed in advance. First, the behavior of Pt RDE and GC RDE in an aqueous solution containing HCl, H2PtCl6 and RuCl3 was studied. It was found that the hydrogen evolution becomes a dominant reaction when the electrode potential is below −0.20 V vs. SSCE (saturated-potassium–chloride silver chloride electrode). The hydrogen evolution was strongly enhanced with the formation of nanometer-sized Pt particles on the RDE. To enrich Pt and Ru ions, present in the form of anionic complexes in solution, onto the carbon particles in the uncatalyzed carbon electrode (UCE) and, most importantly, to eliminate the hydrogen bubbles formed on the UCE during the cathodic deposition, a positive current was imposed on the UCE for a period of time prior to each step of cathodic deposition of PtRu, should multiple steps of cathodic deposition be required. Cyclic voltammograms (CVs) of electrodes in 0.5 M H2SO4 before and after deposition were used to evaluate the loading of metal catalysts based upon the profile of CV in a wide range of potentials from −0.20 to 1.1 V vs. SSCE. The catalytic activity of electrodes prepared under different conditions for methanol electrooxidation was studied by electrochemical methods. The results showed that the performance of the electrode (prepared in this study) with loadings estimated to 77 μg PtRu/cm2 is much better than that of a conventional electrode with loadings of 100 μg Pt/cm2. The role of ruthenium in methanol oxidation was also discussed in electrochemical terms.