Electrochemical activity of rhodium complexes supported on fibrous-carbon material

The redox properties of heterogenized Rh^I, Rh^II, and Rh^III complexes with different, particularly organophosphorus, ligands were studied by cyclic voltammetry (CVA). The support is a carbon-paste electrode based on a fibrous-carbon material and activated carbon. The electrochemical reduction of Rh^III produces Rh metal, which further catalyzes hydrogen evolution. After the reduction of water-soluble binuclear Rh^II complexes, the CVA curves exhibit peaks of electrocatalytic hydrogen evolution and irreversible Rh^I→Rh^II oxidation. The Rh^II complexes with organophosphorus ligands are characterized only by the peak of Rh^I→Rh^II oxidation. After reduction, the Rh^I complexes behave as a pseudo-reverse Rh⁰/Rh^I pair. The electron-donating properties of the ligand determine the reversibility of the system. The degree of structurization of the carbon matrix and the presence of phosphorus(v) atoms in it affect the electrochemical activity of the Rh^II and Rh^I complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 908–914, May, 1999.