Layered Manganese Dioxide Thin Films Intercalated with Ag⁺ Ions Reduceable In Situ for Oxygen Reduction Reaction

The purpose of this study is to propose a new strategy based on electrodeposition to create binder-free composites of metallic silver supported on MnO₂. The process involves in situ reduction of the Ag⁺ ions incorporated in the interlayer spaces of layered MnO₂ in an alkaline electrolyte without Ag⁺ ions. The reduction process of the incorporated Ag⁺ was monitored in situ based on the characteristic surface plasmon resonance in the visible region, and the resulting metallic Ag was identified by X-ray photoelectron spectroscopy. Because the formation of metallic Ag is only possible via electron injection into the Ag⁺ ions between MnO₂ layers, the growth of Ag metals was inevitably limited, although the reduced Ag did not remain immobilized in the interlayers of MnO₂. The thus-formed Ag in the MnO₂ composite functioned as an electrocatalyst for the oxygen reduction reaction in a gas diffusion electrode system, showing a much better mass activity compared to Ag particles electrodeposited from an aqueous solution containing AgNO₃.