Thin Film Coating of Mg-Intercalated Layered MnO2 to Suppress Chlorine Evolution at an IrO2 Anode in Cathodic Protection

Titanium-supported electrocatalysts composed of novel metal oxides have exclusively been utilized as anodes in the cathodic protection (CP) of steel structures. These types of anodes have a small overpotential toward the chlorine evolution reaction (CER) in impressed-current cathodic protection (ICCP) systems and vigorously evolve chlorine (Cl-2) in electrolytes containing Cl-, such as seawater. Cl-2 has a negative impact on the ecosystem because of its intrinsic toxicity and corrosivity. We present herein a thin film coating that can effectively suppress the CER without prevention of the oxygen evolution reaction (OER) at the underlying iridium oxide (IrO2) layer coated on a titanium substrate in 0.5M NaCl solution. The thin film consists of buserite-type layered manganese dioxide (MnO2), the interlayer of which accommodates Mg2+ cations and two layers of H2O molecules, and is uniformly deposited via an electrochemical route and subsequent ion-exchange. The CER efficiency of the electrode modified with the Mg-buserite layer was as small as 11% at +1.7V vs. Ag/AgCl.