KINETIC-STUDIES OF THE EFFECTS OF H2S IMPURITY ON HYDROGEN OXIDATION IN MOLTEN (LI+K)CO3

The effect of hydrogen sulfide on the electrode kinetics of hydrogen o xidation in (62 + 38)mol% (Li + K)CO3 melt at 650-degrees-C was invest igated at Au, Cu and Ni electrodes using cyclic voltammetry, electroch emical impedance spectroscopy and chronocoulometry. Kinetic parameters such as j0, alpha and the stoichiometric number nu, which were obtain ed with and without 90 ppm H2S in a simulated fuel gas (P(H-2)/P(CO2) =0.7/0.3), were compared with each other to study the poisoning effect of H2S on the electrode kinetics. X-ray diffraction studies on the el ectrode surfaces exposed to the melt with H2S proved that the electrod e materials used in this work stayed in the metallic state around the open-circuit potential (OCP). Cyclic voltammograms for Cu and Ni elect rodes showed the formation of metal sulfides at potentials more positi ve (approximately 100 mV) than the OCP. However, they were re-reduced to metallic states around the OCP. The poisoning effect due to sulfide formation was not observable in the kinetic study carried out around the OCP, and another poisoning effect on electrocatalysis, supposedly due to the molecular level adsorption of sulfide ions on the electrode surface, is extremely weak, not exerting any serious retardating effe ct on the rate of hydrogen oxidation.