Carbon-Free Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

A nanoporous Ag-embedded SnO₂ thin film was fabricated by anodic treatment of electrodeposited Ag–Sn alloy layers. The ordered nanoporous structure formed by anodization played a key role in enhancing the electrocatalytic performance of the Ag-embedded SnO₂ layer in several ways: (1) the roughness factor of the thin film is greatly increased from 23 in the compact layer to 145 in the nanoporous layer, creating additional active sites that are involved in oxygen electrochemical reactions; (2) a trace amount of Ag (∼1.7 at %, corresponding to a Ag loading of ∼3.8 μg cm^–2) embedded in the self-organized SnO₂ nanoporous matrix avoids the agglomeration of nanoparticles, which is a common problem leading to the electrocatalyst deactivation; (3) the fabricated nanoporous thin film is active without additional additives or porous carbon that is usually necessary to support and stabilize the electrocatalyst. More importantly, the Ag-embedded SnO₂ nanoporous thin film shows outstanding bifunctional oxygen electrochemical performance (oxygen reduction and evolution reactions) that is considered a promising candidate for use in metal-air batteries. The present technique has a wide range of applications for the preparation of other carbon-free electrocatalytic nanoporous films that could be useful for renewable energy production and storage applications.