Effect on the Ligand of Triruthenium Unit for Hydrogen Evolution Reaction

Abstract

At present, various energy problems occur on the earth. In order to solve the problems utilization of hydrogen is a candidate. Because hydrogen is a clean and highly efficient energy that does not produce sulfur oxides and nitrogen oxides and is attracting attention as a substitute for primary energy such as petroleum and natural gas. In this study, we focused on the ruthenium cluster unit (1-mer) forming a cyclic structure having three ruthenium ions in a mixed-valence state. Here, we examined a catalytic function of hydrogen evolution reaction (HER) at the 1-mer modified highly oriented pyrolytic graphite (HOPG) electrode. In addition, we have studied effects of alcohol as ligands for 1-mer. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used for electrochemical measurements. HOPG was modified by drop casting of 0.5 μM 1-mer dichloromethane or methanol solution and used as a working electrode. A Ag/AgCl (KCl sat.) or a reversible hydrogen electrode (RHE) was used as a reference electrode, and a platinum plate was used as a counter electrode. LSV and CV were carried out in 0.1 M HClO4 in the presence of various alcohols such as methanol and ethanol. Figure 1 shows the LSVs of 0.1 M HClO4 at the 1-mer modified HOPG. The surface concentration of 1-mer was cocurated to be 18 nmol cm-2. At the 1-mer modified HOPG electrode, the starting potential of HER was slightly shifted to positive as compared with that of bare HOPG electrode. This means that the 1-mer modified HOPG has a little catalytic activity for HER. On the other hand, addition of alcohol to the system changes drastically the catalytic activity of the HER. Onset potential of HER was shifted to positive by the addition of alcohol. Comparing the current densities in the presence of each alcohol at –0.80 V, the HER current was influenced by the kinds of alcohol. Especially, when methanol was added to the system, the current density of 0.02 A cm-2 at –0.80 V. Although the reason why the catalytic current for HER depends on the type of alcohol is not clear, it may be considered that the THF ligands of 1-mer are substituted by the alcohol used. We have been are studying the effect of surface concentration and nanoscale structure of 1-mer, and the anion of the electrolyte. Figure 1