Preparation and electrocatalytic activity of rhodium modified pitch-based carbon fiber electrodes

Rh-modified carbon electrodes are prepared through cation-exchange of Rh3+ with the H+ ions of the acidic surface groups of the electrooxidized (by double pulse application) Pitch-based carbon fibers, followed by electrochemical reduction of the exchanged quantity of Rh3+ to Rh-0. Systems obtained by 1 and 5 subsequent cation-exchange-reduction procedures are studied. The electrocatalytic activity of the above systems is investigated for the hydrogen evolution reaction by impedance spectroscopic measurements and for hydrazine electrooxidation by cyclic voltammetric measurements. The amount of rhodium deposited on the carbon fibers was determined by electrothermic atom adsorption spectroscopy and was found 6% w/w for electrodes modified by 1 Ph-layer and 20% w/w for electrodes modified by 5 Rh-layers. The strong electrocatalytic properties of the Rh-modified carbon fibers::art mainly due to the high distribution of small Ph crystals on the carbon substrate observed in the corresponding SEM micrographs and EDAX mapping. These figures are more characteristic for carbon fibers modified by 5 Ph-layers. The electrocatalytic efficiency of the Rh-modified carbon fibers is much more pronounced in comparison to a Ph-wire-electrode of the same surface area. (C) 1998 Elsevier Science Ltd. All rights reserved.