Electrochemical characterization of degradation of oxygen evolution anode for seawater electrolysis

Abstract

The electrolysis at a high current density, such as 2000 A m−2 for hydrogen production in 0.5M NaCl of pH 1 using the oxygen evolution anode consisting of three layers of Mn0.929Mo0.067Sn0.004O2.067/Ir0.84Sn0.16O2/Ti led to a gradual increase in the cell voltage due to the oxide growth on the titanium substrate of the anode. The potential decay curves of the anode measured every 0.1μsec and 0.4 msec after the interruption of a high polarization current density differentiated discharges of the oxide condenser and the electrochemical double layer. The potential measured by galvanostatic polarization was the sum of the potential drop based on the solution resistance, the overpotential for the electrochemical reaction, the equilibrium potential of the reaction and the potential drop based on the oxide resistance. The potential difference, ΔEj, at individual current density, j, between galvanostatic polarization curves of an anode after and before electrolysis showed a linear increase beginning from the origin of the coordinate axes with current density, j, the gradient, ∂ΔEj/∂j, of which corresponded to the difference in the oxide resistance after and before electrolysis at the high current density. The linear increase of the potential difference after and before electrolysis with current density of galvanostatic polarization and the gradient increase with time of electrolysis indicated the electric resistance increase by electrolysis at the high current density without change in the electrochemical properties of the anode surface. The oxide resistance for the anode examined became about 0.8 mΩ m2 after oxygen evolution for 430h at 2000 A m−2.