Hydrogen oxidation kinetics at Ni – Zr0.9Sc0.1O1.95 anode: Influence of the difference of potential in the dense part of the double electric layer

The electrochemical behavior of Ni – Zr0.9Sc0.1O1.95 anode in contact with the YSZ electrolyte was studied in H2 + H2O + Ar mixtures at 900°С by means of impedance spectroscopy. The analysis of the impedance spectra performed by the distribution of relaxation times and non-linear least square methods demonstrated that the electrode process is limited by several rate-determining steps. High-frequency resistance at equilibrium potential does not depend on the gas mixture composition, whereas low-frequency resistance has the 0.5 reaction order and depends on the water partial pressure. The distribution of relaxation times dependencies under polarization demonstrated that the frequency range of the high-frequency step does not depend on the electrode potential and the contribution of the low-frequency step decreases as the cathode polarization increases. An anomalous behavior of the hydrogen oxidation and water reduction rates in the point of zero charge was observed. The abnormal behavior of polarization curves is for the first time explained by the influence of the difference of potential in the dense part of the double electric layer.