Electrochimica Acta, Vol.274, 224-232, 2018
Iron and cobalt hydroxides: Describing the oxygen evolution reaction activity trend with the amount of electrocatalyst
Although the amount of oxygen evolution electrocatalyst is a factor determining its efficiency, its fundamental correlation with activity remains unclear. To address this issue, we take advantage of a urea-based chemical bath deposition method (CBD) that enables to control the amount of electrocatalyst (Fe(OH)(2) and alpha-Co(OH)(2)) deposited on conducting glass. The thickness of the resulting films, whose use in electrocatalysis is unprecedented, is tuned by controlling the deposition time. The turnover frequency (TOF) for O-2 generation decreases drastically as the electrocatalyst amount increases from equivalent coverages of 3.5 monolayers (ML) for Fe(OH)(2) and of 0.06 ML for alpha-Co(OH)(2) electrodes. The contrasting behavior of both hydroxides comes from the different structure of the incipient deposits, formed by small acicular nanoparticles in the case of Fe(OH)(2) and larger flat microparticles in the case of alpha-Co(OH)(2). The former structure allows a large fraction of the Fe sites to be in direct contact with solution, while such a fraction rapidly diminishes with loading for alpha-Co(OH)(2). In addition, the resulting Co(OH)(2) electrodes show TOFs similar or higher than those of electrodes prepared by more complex routes. The optimum ultrathin films are remarkably stable in alkaline media, showing that the preparation of efficient electrocatalysts for oxygen evolution with an extremely small amount of metal through a novel, facile and scalable CBD is possible. (c) 2018 Elsevier Ltd. All rights reserved.