Electrochemical reduction ruthenium centers

This is considerably different from the recombination reaction with, for example, typical ruthenium dyes. This slow re-reduction of the dyad is explained by the low redox potential of the osmium center, the value of 0.66 V (vs. SCE) observed, points to a small driving force for the redox process. This observation is important for the design of dyes for solar cell applications. Osmium compounds have very attractive absorption features, which cover a large part of the solar spectrum. However, their much less positive metal-based oxidation potentials will result in a less effective re-reduction of the dyes based on that metal and this will seriously affect the efficiency of solar cells. In addition, for many ruthenium-based dyes, the presence of low energy absorptions, desirable for spectral coverage, is often connected with low metal-based redox potentials. This intrinsically hinders the search for dyes which have a more complete coverage of the solar spectrum. Since electronic and electrochemical properties are very much related, a lowering of the LUMO-HOMO distance also leads to a less positive oxidation potential. 

The ruthenium(II) bipyridyl moiety is also capable of functionally sensing the presence of bound anion. Electrochemical anion recognition experiments showed substantial anion induced cathodic perturbation of the ligand centered amide substituted 2,2 -bipyridine (bpy) reduction redox couple. These perturbations were in agreement with stability constant values, with 134 sensing H2PO4- in the presence of 10-fold excess of HS04 and Cl . Fluorescence emis-... 

The cyclic voltammograms (CV) of the bipyridine nitrosyl ruthenium complexes may reveal multiple couples resulting from redox processes centered at the metal, the nitrosyl ligand, and the bpy ligands. Two couples are evident in the CV electrochemical potential range of +1.0 to —1.0 V vs. Ag/AgCl of a 5/ira s-[Ru(bpy)2L(NO)] complexes in organic solvent or aqueous solution. The reduction peak at the more positive value is chemically reversible, whereas the second reduction peak is practically irreversible in the CV time scale such peaks correspond to the NO "° and pro-... 

The electrochemical signature in acid medium of ruthenium nanoparticles supported onto carbon shown in Fig. 14.11a resembles that of ruthenium s well-defined surface (0001) [80]. Indeed, surface oxide formation starts at ca. 0.2 V/RHE. The cathodic scan shows a broad peak between 0.2 and 0.4 V attributed to the surface oxide reduction. The irreversibility of this peak is enhanced when a more positive anodic potential is explored. In the alkaline counterpart (pH 13) (Fig. 14.11c), this material clearly shows a well-resolved hydrogen desorption peak centered at 0.1 V. Here, one can observe the interaction of OH species with the ruthenium surface atoms in the region of 0.3 V/RHE. The reverse scan also reveals the reduction of the ruthenium oxide species centered at ca. 0.4 V. Hence, the signature of Ru nanoparticles looks similar in both media. However, comparison of parts (a) and... 

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