Hierarchical wreath-like Au-Co(OH)2 microclusters for water oxidation at neutral pH.

Hierarchical Au-Co(OH)2 microclusters have been synthesized by a facile ethanol-assisted hydrothermal method on FTO glass substrates. The as-fabricated Au-Co(OH)2 forms a typical wreath-shaped structure on a nanosheet with an urchin-like Au-Co(OH)2 structure located in the centre surrounded by densely grown Co(OH)2 nanoarrays. Morphological evolution of the Au-Co(OH)2 microclusters through intermediate steps could be identified by varying the reaction time. The incorporated electronegative Au may be responsible for the decrease of binding energy of Au-Co(OH)2 compared to Co(OH)2. The Au-Co(OH)2 electrode was found to be a promising catalyst for the oxygen evolution reaction (OER) in neutral pH solutions, with a larger roughness factor, lower OER onset and much higher current density than a Co(OH)2 electrode. The improvement of the OER activity of Au-Co(OH)2 microclusters may be due to their large surface area provided by the 3D network of microclusters, and the incorporation of Au as an electron sink to facilitate the oxidation of Co(II) and Co(III) to Co(IV).