INFLUENCE OF WATER VAPOR ON ELECTROCHEMICAL OXIDATION OF HYDROGEN AT THE Ni/ZIRCONIA INTERFACE

摘要

The influence of water vapor on the kinetics of the H_2-H_2O, Ni/YSZ electrode was investigated varying temperature, hydrogen and water partial pressures, P_(H_2) and P_(H_2O). A three-electrode cell was used with a point shaped working electrode. The electrode surrounding gas is a mixture of hydrogen, water vapor and argon. Measurements were carried out between 700 and 1000℃. The electrode was first studied at equilibrium using impedance spectroscopy. Activation energy of the polarizationrnconductivity σ_p is equal to 1.6 eV. At 975℃ and fixed P_(H_2O). the variation of σ_p versusrnP_(H_2) shows a minimum. At 975℃ and fixed P_(H_2) . a linear variation of σ_p versus P_(H_2O) is observed with a slope of 1/2. Anodic polarization results may be represented by a Butler-Volmer-type relation which cannot be associated to a pure charge transfer mechanism. Finally, the electrocatalytic effect of water vapor on the kinetics of hydrogen oxidation was shown at equilibrium and under polarization, and the H_2O electrochemically produced at the anode enhances this effect.