Electrochemical oxidation in a CH₄-H₂O system at the interface of a Pt electrode and Y₂O₃-stabilized ZrO₂ electrolyte. II. The rates of electrochemical reactions taking place in parallel

The rate processes of electrochemical reactions were clarified in a CH₄-H₂O system at the interface of a porous Pt electrode/Y₂O₃-stabilized ZrO₂ electrolyte. Direct-current polarization measurements and ac impedance spectroscopy were made with gas analysis before and after the reaction at 1073 K. We proposed an analytical method to determine the rates of electrochemical reactions taking place in parallel. When the ratio p(H₂O)/p(CH₄) of the inlet gas was close to zero, the observed relationship between the polarization current and electrode potential was interpreted by the electrochemical oxidation processes of H₂, CO, C, and CH₄ in parallel using the proposed method. For example, the ratio of the oxidation rates for C/CO/CH₄/H₂ is 1/1.3×10/1.9×10²/2.8×10³ at E = -600 mV vs. air. This result was obtained under very low CH₄ concentration. The estimated oxidation rates of H₂ and CO as functions of the electrode potential were described by the model proposed by Mizusaki et al. for the reaction of H₂-H₂O and CO-CO₂.