Cobalt thin films as water-recombination electrocatalysts

• Published in: Surface & coatings technology 2020-12, Vol.404, p.126643, Article 126643
• Main Authors: Linder, Clara, Rao, Smita Gangaprasad, le Febvrier, Arnaud, Greczynski, Grzegorz, Sjövall, Rune, Munktell, Sara, Eklund, Per, Björk, Emma M.
• Format: Article
• Language: English
• Subjects: Alkaline solutions; Anodization; Catalyst activity; Characterization of the films; Cobalt compounds; Cobalt oxide; Cobalt thin film; Cyclic voltammetry; Cyclic voltammograms; Electrocatalyst; Electrocatalysts; Electrocatalytic performance; Electrochemical modification; Electrolysis; Electrolytes; Electrolytic reduction; Energy productions; Functionalized surfaces; Low alloyed steels; Oxide films; Oxygen; Oxygen reduction reaction; Potassium hydroxide; Thin films; Water recombination
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126643

Catalysts and electrocatalysts are crucial for energy production and storage. To develop cost-efficient systems taking advantage of functionalized surfaces, the catalysts can be synthesized as nanomaterials or thin films. In this work, cobalt thin films were deposited on low-alloyed steel using magnetron sputtering. The films are uniform with a smooth surface and a thickness of ~400 nm. The films were electrochemically oxidized via anodization to a mix of cobalt oxides, one of them being Co3O4, at room temperature in an alkaline solution. The electrocatalytic performances of the anodized films were evaluated in 1 M KOH electrolyte saturated with oxygen. Cathodic currents in −0.5 mA/cm2 range, corresponding to oxygen reduction reaction (ORR) activity, were measured with cyclic voltammetry. The catalytic activity of the films was evaluated as a function of time. The anodized Co coating exhibited three times higher activity than the steel substrate. The kinetics for the ORR were evaluated through Tafel plots and a slope of 226 mV/decade was found. Post-ORR characterization of the films revealed hexagonal plate-like oxide particles on the surface. After 50 cyclic voltammograms, the film was further oxidized, indicating that the ORR activity also affects the overall surface state of the film. This study demonstrates that thin films, after electrochemical modification, can be electrocatalysts for the oxygen reduction reaction and potentially used for applications in energy production and storage. •Co thin films can be modified by anodization to become catalysts for ORR.•Electrochemical anodization of Co films yields growth of Co3O4 nanoparticles.•The formed Co3O4 nanoparticles are the catalytically active sites.•Anodized film has three times higher ORR current response than the steel substrate.•Cycling potential over the film promotes further oxidation and particle growth.